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class="vp-sidebar-heading clickable active" type="button"><!----><span class="vp-sidebar-title">二、Java基础</span><span class="vp-arrow down"></span></button><ul class="vp-sidebar-links"><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.1 Java概述及环境配置</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.2 Java语法基础</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.3 数组&字符串</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.4 面向对象编程</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.5 集合框架（容器）</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable active" type="button"><!----><span class="vp-sidebar-title">2.6 Java IO</span><span class="vp-arrow down"></span></button><ul class="vp-sidebar-links"><li><!--[--><a class="vp-link nav-link vp-sidebar-link vp-sidebar-page" href="/io/shangtou.html"><!---->IO 分类<!----></a><ul class="vp-sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a class="vp-link nav-link vp-sidebar-link vp-sidebar-page" href="/io/file-path.html"><!---->文件流<!----></a><ul class="vp-sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a class="vp-link nav-link vp-sidebar-link vp-sidebar-page" href="/io/stream.html"><!---->字节流<!----></a><ul class="vp-sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a class="vp-link nav-link vp-sidebar-link vp-sidebar-page" href="/io/reader-writer.html"><!---->字符流<!----></a><ul class="vp-sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a class="vp-link nav-link active vp-sidebar-link vp-sidebar-page active" href="/io/buffer.html"><!---->缓冲流<!----></a><ul class="vp-sidebar-sub-headers"><li class="vp-sidebar-sub-header"><a class="vp-link nav-link vp-sidebar-link vp-heading" href="/io/buffer.html#_01、字节缓冲流"><!---->01、字节缓冲流<!----></a><ul class="vp-sidebar-sub-headers"></ul></li><li class="vp-sidebar-sub-header"><a class="vp-link nav-link vp-sidebar-link vp-heading" href="/io/buffer.html#_02、字符缓冲流"><!---->02、字符缓冲流<!----></a><ul class="vp-sidebar-sub-headers"></ul></li><li class="vp-sidebar-sub-header"><a class="vp-link nav-link vp-sidebar-link vp-heading" href="/io/buffer.html#_03、字符缓冲流练习"><!---->03、字符缓冲流练习<!----></a><ul class="vp-sidebar-sub-headers"></ul></li></ul><!--]--></li><li><!--[--><a class="vp-link nav-link vp-sidebar-link vp-sidebar-page" href="/io/char-byte.html"><!---->转换流<!----></a><ul class="vp-sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a class="vp-link nav-link vp-sidebar-link vp-sidebar-page" href="/io/serialize.html"><!---->序列流(序列化和反序列化)<!----></a><ul class="vp-sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a class="vp-link nav-link vp-sidebar-link vp-sidebar-page" href="/io/Serializbale.html"><!---->序列接口Serializable<!----></a><ul class="vp-sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a class="vp-link nav-link vp-sidebar-link vp-sidebar-page" href="/io/transient.html"><!---->transient关键字<!----></a><ul class="vp-sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a class="vp-link nav-link vp-sidebar-link vp-sidebar-page" href="/io/print.html"><!---->打印流<!----></a><ul class="vp-sidebar-sub-headers"></ul><!--]--></li></ul></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.7 异常处理</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.8 常用工具类</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.9 Java新特性</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.10 网络编程</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.11 NIO</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.12 Java重要知识点</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.13 并发编程</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.14 JVM</span><span class="vp-arrow end"></span></button><!----></section></li></ul></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">三、Java进阶</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">四、MySQL</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">五、Redis</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">六、计算机基础</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">七、求职面试</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">八、学习建议</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">九、知识库搭建</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">十、联系作者</span><span class="vp-arrow end"></span></button><!----></section></li></ul><!--[--><!----><!--]--></aside><!--[--><main id="main-content" class="vp-page"><!--[--><!----><!----><nav class="vp-breadcrumb disable"></nav><div class="vp-page-title"><h1><!---->Java 缓冲流：Java IO 的读写效率有了质的飞升</h1><div class="page-info"><span class="page-author-info" aria-label="作者🖊" data-balloon-pos="down"><svg xmlns="http://www.w3.org/2000/svg" class="icon author-icon" viewBox="0 0 1024 1024" fill="currentColor" aria-label="author icon"><path d="M649.6 633.6c86.4-48 147.2-144 147.2-249.6 0-160-128-288-288-288s-288 128-288 288c0 108.8 57.6 201.6 147.2 249.6-121.6 48-214.4 153.6-240 288-3.2 9.6 0 19.2 6.4 25.6 3.2 9.6 12.8 12.8 22.4 12.8h704c9.6 0 19.2-3.2 25.6-12.8 6.4-6.4 9.6-16 6.4-25.6-25.6-134.4-121.6-240-243.2-288z"></path></svg><span><a class="page-author-item" href="/about-the-author/" target="_blank" rel="noopener noreferrer">沉默王二</a></span><span property="author" content="沉默王二"></span></span><!----><span class="page-date-info" aria-label="写作日期📅" data-balloon-pos="down"><svg xmlns="http://www.w3.org/2000/svg" class="icon calendar-icon" viewBox="0 0 1024 1024" fill="currentColor" aria-label="calendar icon"><path d="M716.4 110.137c0-18.753-14.72-33.473-33.472-33.473-18.753 0-33.473 14.72-33.473 33.473v33.473h66.993v-33.473zm-334.87 0c0-18.753-14.72-33.473-33.473-33.473s-33.52 14.72-33.52 33.473v33.473h66.993v-33.473zm468.81 33.52H716.4v100.465c0 18.753-14.72 33.473-33.472 33.473a33.145 33.145 0 01-33.473-33.473V143.657H381.53v100.465c0 18.753-14.72 33.473-33.473 33.473a33.145 33.145 0 01-33.473-33.473V143.657H180.6A134.314 134.314 0 0046.66 277.595v535.756A134.314 134.314 0 00180.6 947.289h669.74a134.36 134.36 0 00133.94-133.938V277.595a134.314 134.314 0 00-133.94-133.938zm33.473 267.877H147.126a33.145 33.145 0 01-33.473-33.473c0-18.752 14.72-33.473 33.473-33.473h736.687c18.752 0 33.472 14.72 33.472 33.473a33.145 33.145 0 01-33.472 33.473z"></path></svg><span><!----></span><meta property="datePublished" content="2022-08-23T08:10:06.000Z"></span><span class="page-category-info" aria-label="分类🌈" data-balloon-pos="down"><svg xmlns="http://www.w3.org/2000/svg" class="icon category-icon" viewBox="0 0 1024 1024" fill="currentColor" aria-label="category icon"><path d="M148.41 106.992h282.176c22.263 0 40.31 18.048 40.31 40.31V429.48c0 22.263-18.047 40.31-40.31 40.31H148.41c-22.263 0-40.311-18.047-40.311-40.31V147.302c0-22.263 18.048-40.31 40.311-40.31zM147.556 553.478H429.73c22.263 0 40.311 18.048 40.311 40.31v282.176c0 22.263-18.048 40.312-40.31 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class="icon tag-icon" viewBox="0 0 1024 1024" fill="currentColor" aria-label="tag icon"><path d="M939.902 458.563L910.17 144.567c-1.507-16.272-14.465-29.13-30.737-30.737L565.438 84.098h-.402c-3.215 0-5.726 1.005-7.634 2.913l-470.39 470.39a10.004 10.004 0 000 14.164l365.423 365.424c1.909 1.908 4.42 2.913 7.132 2.913s5.223-1.005 7.132-2.913l470.39-470.39c2.01-2.11 3.014-5.023 2.813-8.036zm-240.067-72.121c-35.458 0-64.286-28.828-64.286-64.286s28.828-64.285 64.286-64.285 64.286 28.828 64.286 64.285-28.829 64.286-64.286 64.286z"></path></svg><!--[--><span class="page-tag-item tag1 clickable" role="navigation">Java IO</span><!--]--><meta property="keywords" content="Java IO"></span><span class="page-word-info" aria-label="字数🔠" data-balloon-pos="down"><svg xmlns="http://www.w3.org/2000/svg" class="icon word-icon" viewBox="0 0 1024 1024" fill="currentColor" aria-label="word icon"><path d="M518.217 432.64V73.143A73.143 73.143 0 01603.43 1.097a512 512 0 01419.474 419.474 73.143 73.143 0 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450.445v352.632c117.674 1.553 211.787 40.778 211.787 88.676H304.097c0-48.286 95.149-87.382 213.728-88.676V450.445c-93.077-3.107-167.901-81.297-167.901-177.093 0-8.803 6.99-15.793 15.793-15.793 8.803 0 15.794 6.99 15.794 15.793 0 80.261 63.69 145.635 142.01 145.635s142.011-65.374 142.011-145.635c0-8.803 6.99-15.793 15.794-15.793s15.793 6.99 15.793 15.793c0 95.019-73.789 172.82-165.96 177.093z"></path></svg><span>大约 14 分钟</span><meta property="timeRequired" content="PT14M"></span></div><hr></div><div class="toc-place-holder"><aside id="toc"><!--[--><!----><!--]--><div class="toc-header">此页内容<button type="button" class="print-button" title="打印"><svg xmlns="http://www.w3.org/2000/svg" class="icon print-icon" viewBox="0 0 1024 1024" fill="currentColor" aria-label="print icon"><path d="M819.2 364.8h-44.8V128c0-17.067-14.933-32-32-32H281.6c-17.067 0-32 14.933-32 32v236.8h-44.8C145.067 364.8 96 413.867 96 473.6v192c0 59.733 49.067 108.8 108.8 108.8h44.8V896c0 17.067 14.933 32 32 32h460.8c17.067 0 32-14.933 32-32V774.4h44.8c59.733 0 108.8-49.067 108.8-108.8v-192c0-59.733-49.067-108.8-108.8-108.8zM313.6 160h396.8v204.8H313.6V160zm396.8 704H313.6V620.8h396.8V864zM864 665.6c0 25.6-19.2 44.8-44.8 44.8h-44.8V588.8c0-17.067-14.933-32-32-32H281.6c-17.067 0-32 14.933-32 32v121.6h-44.8c-25.6 0-44.8-19.2-44.8-44.8v-192c0-25.6 19.2-44.8 44.8-44.8h614.4c25.6 0 44.8 19.2 44.8 44.8v192z"></path></svg></button></div><div class="toc-wrapper"><ul class="toc-list"><!--[--><li class="toc-item"><a class="vp-link toc-link level3" href="/#_01、字节缓冲流">01、字节缓冲流</a></li><!----><!--]--><!--[--><li class="toc-item"><a class="vp-link toc-link level3" href="/#_02、字符缓冲流">02、字符缓冲流</a></li><!----><!--]--><!--[--><li class="toc-item"><a class="vp-link toc-link level3" href="/#_03、字符缓冲流练习">03、字符缓冲流练习</a></li><!----><!--]--></ul><div class="toc-marker" style="top:-1.7rem;"></div></div><!--[--><!----><!--]--></aside></div><!----><div class="theme-hope-content"><h1 id="_7-5-缓冲流" tabindex="-1"><a class="header-anchor" href="#_7-5-缓冲流" aria-hidden="true">#</a> 7.5 缓冲流</h1><p>Java 的缓冲流是对字节流和字符流的一种封装，通过在内存中开辟缓冲区来提高 I/O 操作的效率。Java 通过 BufferedInputStream 和 BufferedOutputStream 来实现字节流的缓冲，通过 BufferedReader 和 BufferedWriter 来实现字符流的缓冲。</p><p>缓冲流的工作原理是将数据先写入缓冲区中，当缓冲区满时再一次性写入文件或输出流，或者当缓冲区为空时一次性从文件或输入流中读取一定量的数据。这样可以减少系统的 I/O 操作次数，提高系统的 I/O 效率，从而提高程序的运行效率。</p><h3 id="_01、字节缓冲流" tabindex="-1"><a class="header-anchor" href="#_01、字节缓冲流" aria-hidden="true">#</a> 01、字节缓冲流</h3><p>BufferedInputStream 和 BufferedOutputStream 属于字节缓冲流，强化了字节流 InputStream 和 OutputStream，关于字节流，我们前面已经详细地讲过了，可以<a href="https://javabetter.cn/io/stream.html" target="_blank" rel="noopener noreferrer">戳这个链接<span><svg class="external-link-icon" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path><polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg><span class="external-link-icon-sr-only">open in new window</span></span></a>去温习。</p><h4 id="_1-构造方法" tabindex="-1"><a class="header-anchor" href="#_1-构造方法" aria-hidden="true">#</a> 1）构造方法</h4><ul><li><code>BufferedInputStream(InputStream in)</code> ：创建一个新的缓冲输入流，注意参数类型为<strong>InputStream</strong>。</li><li><code>BufferedOutputStream(OutputStream out)</code>： 创建一个新的缓冲输出流，注意参数类型为<strong>OutputStream</strong>。</li></ul><p>代码示例如下：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token comment">// 创建字节缓冲输入流，先声明字节流</span>
<span class="token class-name">FileInputStream</span> fps <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">FileInputStream</span><span class="token punctuation">(</span>b<span class="token punctuation">.</span>txt<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">BufferedInputStream</span> bis <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">BufferedInputStream</span><span class="token punctuation">(</span>fps<span class="token punctuation">)</span>
<span class="token comment">// 创建字节缓冲输入流（一步到位）</span>
<span class="token class-name">BufferedInputStream</span> bis <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">BufferedInputStream</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">FileInputStream</span><span class="token punctuation">(</span><span class="token string">"b.txt"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 创建字节缓冲输出流（一步到位）</span>
<span class="token class-name">BufferedOutputStream</span> bos <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">BufferedOutputStream</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">FileOutputStream</span><span class="token punctuation">(</span><span class="token string">"b.txt"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><h4 id="_2-缓冲流的高效" tabindex="-1"><a class="header-anchor" href="#_2-缓冲流的高效" aria-hidden="true">#</a> 2）缓冲流的高效</h4><p>我们通过复制一个 370M+ 的大文件，来测试缓冲流的效率。为了做对比，我们先用基本流来实现一下，代码如下：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token comment">// 记录开始时间</span>
<span class="token keyword">long</span> start <span class="token operator">=</span> <span class="token class-name">System</span><span class="token punctuation">.</span><span class="token function">currentTimeMillis</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 创建流对象</span>
<span class="token keyword">try</span> <span class="token punctuation">(</span><span class="token class-name">FileInputStream</span> fis <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">FileInputStream</span><span class="token punctuation">(</span><span class="token string">"py.mp4"</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//exe文件够大</span>
<span class="token class-name">FileOutputStream</span> fos <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">FileOutputStream</span><span class="token punctuation">(</span><span class="token string">"copyPy.mp4"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token comment">// 读写数据</span>
<span class="token keyword">int</span> b<span class="token punctuation">;</span>
<span class="token keyword">while</span> <span class="token punctuation">(</span><span class="token punctuation">(</span>b <span class="token operator">=</span> fis<span class="token punctuation">.</span><span class="token function">read</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token operator">!=</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
fos<span class="token punctuation">.</span><span class="token function">write</span><span class="token punctuation">(</span>b<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token comment">// 记录结束时间</span>
<span class="token keyword">long</span> end <span class="token operator">=</span> <span class="token class-name">System</span><span class="token punctuation">.</span><span class="token function">currentTimeMillis</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"普通流复制时间:"</span><span class="token operator">+</span><span class="token punctuation">(</span>end <span class="token operator">-</span> start<span class="token punctuation">)</span><span class="token operator">+</span><span class="token string">" 毫秒"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>不好意思，我本机比较菜，10 分钟还在复制中。切换到缓冲流试一下，代码如下：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token comment">// 记录开始时间</span>
<span class="token keyword">long</span> start <span class="token operator">=</span> <span class="token class-name">System</span><span class="token punctuation">.</span><span class="token function">currentTimeMillis</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 创建流对象</span>
<span class="token keyword">try</span> <span class="token punctuation">(</span><span class="token class-name">BufferedInputStream</span> bis <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">BufferedInputStream</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">FileInputStream</span><span class="token punctuation">(</span><span class="token string">"py.mp4"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">BufferedOutputStream</span> bos <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">BufferedOutputStream</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">FileOutputStream</span><span class="token punctuation">(</span><span class="token string">"copyPy.mp4"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token comment">// 读写数据</span>
<span class="token keyword">int</span> b<span class="token punctuation">;</span>
<span class="token keyword">while</span> <span class="token punctuation">(</span><span class="token punctuation">(</span>b <span class="token operator">=</span> bis<span class="token punctuation">.</span><span class="token function">read</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token operator">!=</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
bos<span class="token punctuation">.</span><span class="token function">write</span><span class="token punctuation">(</span>b<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token comment">// 记录结束时间</span>
<span class="token keyword">long</span> end <span class="token operator">=</span> <span class="token class-name">System</span><span class="token punctuation">.</span><span class="token function">currentTimeMillis</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"缓冲流复制时间:"</span><span class="token operator">+</span><span class="token punctuation">(</span>end <span class="token operator">-</span> start<span class="token punctuation">)</span><span class="token operator">+</span><span class="token string">" 毫秒"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>只需要 8016 毫秒，如何更快呢？</p><p>可以换数组的方式来读写，这个我们前面也有讲到，代码如下：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token comment">// 记录开始时间</span>
<span class="token keyword">long</span> start <span class="token operator">=</span> <span class="token class-name">System</span><span class="token punctuation">.</span><span class="token function">currentTimeMillis</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 创建流对象</span>
<span class="token keyword">try</span> <span class="token punctuation">(</span><span class="token class-name">BufferedInputStream</span> bis <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">BufferedInputStream</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">FileInputStream</span><span class="token punctuation">(</span><span class="token string">"py.mp4"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">BufferedOutputStream</span> bos <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">BufferedOutputStream</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">FileOutputStream</span><span class="token punctuation">(</span><span class="token string">"copyPy.mp4"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token comment">// 读写数据</span>
<span class="token keyword">int</span> len<span class="token punctuation">;</span>
<span class="token keyword">byte</span><span class="token punctuation">[</span><span class="token punctuation">]</span> bytes <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token keyword">byte</span><span class="token punctuation">[</span><span class="token number">8</span><span class="token operator">*</span><span class="token number">1024</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token keyword">while</span> <span class="token punctuation">(</span><span class="token punctuation">(</span>len <span class="token operator">=</span> bis<span class="token punctuation">.</span><span class="token function">read</span><span class="token punctuation">(</span>bytes<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token operator">!=</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
bos<span class="token punctuation">.</span><span class="token function">write</span><span class="token punctuation">(</span>bytes<span class="token punctuation">,</span> <span class="token number">0</span> <span class="token punctuation">,</span> len<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token comment">// 记录结束时间</span>
<span class="token keyword">long</span> end <span class="token operator">=</span> <span class="token class-name">System</span><span class="token punctuation">.</span><span class="token function">currentTimeMillis</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"缓冲流使用数组复制时间:"</span><span class="token operator">+</span><span class="token punctuation">(</span>end <span class="token operator">-</span> start<span class="token punctuation">)</span><span class="token operator">+</span><span class="token string">" 毫秒"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>这下就更快了，只需要 521 毫秒。</p><h4 id="_3-为什么字节缓冲流会这么快" tabindex="-1"><a class="header-anchor" href="#_3-为什么字节缓冲流会这么快" aria-hidden="true">#</a> 3）为什么字节缓冲流会这么快？</h4><p>传统的 Java IO 是阻塞模式的，它的工作状态就是“读/写，等待，读/写，等待。。。。。。”</p><p>字节缓冲流解决的就是这个问题：<strong>一次多读点多写点，减少读写的频率，用空间换时间</strong>。</p><ul><li>减少系统调用次数：在使用字节缓冲流时，数据不是立即写入磁盘或输出流，而是先写入缓冲区，当缓冲区满时再一次性写入磁盘或输出流。这样可以减少系统调用的次数，从而提高 I/O 操作的效率。</li><li>减少磁盘读写次数：在使用字节缓冲流时，当需要读取数据时，缓冲流会先从缓冲区中读取数据，如果缓冲区中没有足够的数据，则会一次性从磁盘或输入流中读取一定量的数据。同样地，当需要写入数据时，缓冲流会先将数据写入缓冲区，如果缓冲区满了，则会一次性将缓冲区中的数据写入磁盘或输出流。这样可以减少磁盘读写的次数，从而提高 I/O 操作的效率。</li><li>提高数据传输效率：在使用字节缓冲流时，由于数据是以块的形式进行传输，因此可以减少数据传输的次数，从而提高数据传输的效率。</li></ul><p>我们来看 BufferedInputStream 的 read 方法：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token keyword">synchronized</span> <span class="token keyword">int</span> <span class="token function">read</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">IOException</span> <span class="token punctuation">{</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>pos <span class="token operator">>=</span> count<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token comment">// 如果当前位置已经到达缓冲区末尾</span>
<span class="token function">fill</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 填充缓冲区</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>pos <span class="token operator">>=</span> count<span class="token punctuation">)</span> <span class="token comment">// 如果填充后仍然到达缓冲区末尾，说明已经读取完毕</span>
<span class="token keyword">return</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">;</span> <span class="token comment">// 返回 -1 表示已经读取完毕</span>
<span class="token punctuation">}</span>
<span class="token keyword">return</span> <span class="token function">getBufIfOpen</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">[</span>pos<span class="token operator">++</span><span class="token punctuation">]</span> <span class="token operator">&</span> <span class="token number">0xff</span><span class="token punctuation">;</span> <span class="token comment">// 返回当前位置的字节，并将位置加 1</span>
<span class="token punctuation">}</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>这段代码主要有两部分：</p><ul><li><code>fill()</code>：该方法会将缓冲 buf 填满。</li><li><code>getBufIfOpen()[pos++] & 0xff</code>：返回当前读取位置 pos 处的字节（<code>getBufIfOpen()</code>返回的是 buffer 数组，是 byte 类型），并将其与 0xff 进行位与运算。这里的目的是将读取到的字节 b 当做无符号的字节处理，因为 Java 的 byte 类型是有符号的，而将 b 与 0xff 进行位与运算，就可以将其转换为无符号的字节，其范围为 0 到 255。</li></ul><blockquote><p>byte & 0xFF 我们一会再细讲。</p></blockquote><p>再来看 FileInputStream 的 read 方法：</p><figure><img src="https://cdn.tobebetterjavaer.com/stutymore/buffer-20230321154534.png" alt="" tabindex="0" loading="lazy"><figcaption></figcaption></figure><p>在这段代码中，<code>read0()</code> 方法是一个<a href="https://javabetter.cn/oo/native-method.html" target="_blank" rel="noopener noreferrer">本地方法<span><svg class="external-link-icon" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path><polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg><span class="external-link-icon-sr-only">open in new window</span></span></a>，它的实现是由底层操作系统提供的，并不是 Java 语言实现的。在不同的操作系统上，<code>read0()</code> 方法的实现可能会有所不同，但是它们的功能都是相同的，都是用于<strong>读取一个字节</strong>。</p><p>再来看一下 BufferedOutputStream 的 <code>write(byte b[], int off, int len)</code> 方法：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token keyword">synchronized</span> <span class="token keyword">void</span> <span class="token function">write</span><span class="token punctuation">(</span><span class="token keyword">byte</span> b<span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">,</span> <span class="token keyword">int</span> off<span class="token punctuation">,</span> <span class="token keyword">int</span> len<span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">IOException</span> <span class="token punctuation">{</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>len <span class="token operator">>=</span> buf<span class="token punctuation">.</span>length<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token comment">// 如果写入的字节数大于等于缓冲区长度</span>
<span class="token comment">/* 如果请求的长度超过了输出缓冲区的大小，
先刷新缓冲区，然后直接将数据写入。
这样可以避免缓冲流级联时的问题。*/</span>
<span class="token function">flushBuffer</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 先刷新缓冲区</span>
out<span class="token punctuation">.</span><span class="token function">write</span><span class="token punctuation">(</span>b<span class="token punctuation">,</span> off<span class="token punctuation">,</span> len<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 直接将数据写入输出流</span>
<span class="token keyword">return</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>len <span class="token operator">></span> buf<span class="token punctuation">.</span>length <span class="token operator">-</span> count<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token comment">// 如果写入的字节数大于空余空间</span>
<span class="token function">flushBuffer</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 先刷新缓冲区</span>
<span class="token punctuation">}</span>
<span class="token class-name">System</span><span class="token punctuation">.</span><span class="token function">arraycopy</span><span class="token punctuation">(</span>b<span class="token punctuation">,</span> off<span class="token punctuation">,</span> buf<span class="token punctuation">,</span> count<span class="token punctuation">,</span> len<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 将数据拷贝到缓冲区中</span>
count <span class="token operator">+=</span> len<span class="token punctuation">;</span> <span class="token comment">// 更新计数器</span>
<span class="token punctuation">}</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>首先，该方法会检查写入的字节数是否大于等于缓冲区长度，如果是，则先将缓冲区中的数据刷新到磁盘中，然后直接将数据写入输出流。这样做是为了避免缓冲流级联时的问题，即缓冲区的大小不足以容纳写入的数据时，可能会引发级联刷新，导致效率降低。</p><blockquote><p>级联问题（Cascade Problem）是指在一组缓冲流（Buffered Stream）中，由于缓冲区的大小不足以容纳要写入的数据，导致数据被分割成多个部分，并分别写入到不同的缓冲区中，最终需要逐个刷新缓冲区，从而导致性能下降的问题。</p></blockquote><p>其次，如果写入的字节数小于缓冲区长度，则检查缓冲区中剩余的空间是否足够容纳要写入的字节数，如果不够，则先将缓冲区中的数据刷新到磁盘中。然后，使用 <code>System.arraycopy()</code> 方法将要写入的数据拷贝到缓冲区中，并更新计数器 count。</p><p>最后，如果写入的字节数小于缓冲区长度且缓冲区中还有剩余空间，则直接将要写入的数据拷贝到缓冲区中，并更新计数器 count。</p><p>也就是说，只有当 buf 写满了，才会 flush，将数据刷到磁盘，默认一次刷 8192 个字节。</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token class-name">BufferedOutputStream</span><span class="token punctuation">(</span><span class="token class-name">OutputStream</span> out<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">this</span><span class="token punctuation">(</span>out<span class="token punctuation">,</span> <span class="token number">8192</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>如果 buf 没有写满，会继续写 buf。</p><p>对比一下 FileOutputStream 的 write 方法，同样是本地方法，一次只能写入一个字节。</p><figure><img src="https://cdn.tobebetterjavaer.com/stutymore/buffer-20230321162808.png" alt="" tabindex="0" loading="lazy"><figcaption></figcaption></figure><p>当把 BufferedOutputStream 和 BufferedInputStream 配合起来使用后，就减少了大量的读写次数，尤其是 <code>byte[] bytes = new byte[8*1024]</code>，就相当于缓冲区的空间有 8 个 1024 字节，那读写效率就会大大提高。</p><h4 id="_4-byte-0xff" tabindex="-1"><a class="header-anchor" href="#_4-byte-0xff" aria-hidden="true">#</a> 4）<code>byte & 0xFF</code></h4><p>byte 类型通常被用于存储二进制数据，例如读取和写入文件、网络传输等场景。在这些场景下，byte 类型的变量可以用来存储数据流中的每个字节，从而进行读取和写入操作。</p><p>byte 类型是有符号的，即其取值范围为 -128 到 127。如果我们希望得到的是一个无符号的 byte 值，就需要使用 <code>byte & 0xFF</code> 来进行转换。</p><p>这是因为 0xFF 是一个无符号的整数，它的二进制表示为 11111111。当一个 byte 类型的值与 0xFF 进行位与运算时，会将 byte 类型的值转换为一个无符号的整数，其范围为 0 到 255。</p><p>0xff 是一个十六进制的数，相当于二进制的 11111111，& 运算符的意思是：如果两个操作数的对应位为 1，则输出 1，否则为 0；由于 0xff 有 8 个 1，单个 byte 转成 int 其实就是将 byte 和 int 类型的 255 进行(&)与运算。</p><p>例如，如果我们有一个 byte 类型的变量 b，其值为 -1，那么 b & 0xFF 的结果就是 255。这样就可以将一个有符号的 byte 类型的值转换为一个无符号的整数。</p><p>& 运算是一种二进制数据的计算方式, 两个操作位都为1，结果才为1，否则结果为0. 在上面的 <code>getBufIfOpen()[pos++] & 0xff</code> 计算过程中, byte 有 8bit, OXFF 是16进制的255, 表示的是 int 类型, int 有 32bit.</p><p>如果 <code>getBufIfOpen()[pos++]</code> 为 -118, 那么其原码表示为</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>00000000 00000000 00000000 10001010
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>反码为</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>11111111 11111111 11111111 11110101
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>补码为</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>11111111 11111111 11111111 11110110
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>0XFF 表示16进制的数据255, 原码, 反码, 补码都是一样的, 其二进制数据为</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>00000000 00000000 00000000 11111111
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>0XFF 和 -118 进行&运算后结果为</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>00000000 00000000 00000000 11110110
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>还原为原码后为</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>00000000 00000000 00000000 10001010
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>其表示的 int 值为 138，可见将 byte 类型的 -118 与 0XFF 进行与运算后值由 -118 变成了 int 类型的 138，其中低8位和byte的-118完全一致。</p><p>顺带聊一下 原码、反码和补码。</p><p>①、原码</p><p>原码就是符号位加上真值的绝对值，即用第一位表示符号，其余位表示值。比如如果是8位二进制:</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>[+1]原 = 0000 0001
[-1]原 = 1000 0001
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>第一位是符号位。因为第一位是符号位，所以8位二进制数的取值范围就是：</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>[1111 1111 , 0111 1111]
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>即</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>[-127 , 127]
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>②、反码</p><p>反码的表示方法是：</p><ul><li>正数的反码是其本身</li><li>负数的反码是在其原码的基础上，符号位不变，其余各个位取反。</li></ul><p>例如：</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>[+1] = [00000001]原 = [00000001]反
[-1] = [10000001]原 = [11111110]反
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>可见如果一个反码表示的是负数，人脑无法直观的看出来它的数值。通常要将其转换成原码再计算。</p><p>③、补码</p><p>补码的表示方法是：</p><ul><li>正数的补码就是其本身</li><li>负数的补码是在其原码的基础上，符号位不变，其余各位取反，最后+1。(即在反码的基础上+1)</li></ul><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>[+1] = [00000001]原 = [00000001]反 = [00000001]补
[-1] = [10000001]原 = [11111110]反 = [11111111]补
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>对于负数，补码表示方式也是人脑无法直观看出其数值的。通常也需要转换成原码在计算其数值。</p><p>从上面可以看到：</p><ul><li>对于正数：原码，反码，补码都是一样的</li><li>对于负数：原码，反码，补码都是不一样的</li></ul><h3 id="_02、字符缓冲流" tabindex="-1"><a class="header-anchor" href="#_02、字符缓冲流" aria-hidden="true">#</a> 02、字符缓冲流</h3><p>BufferedReader 类继承自 Reader 类，提供了一些便捷的方法，例如 <code>readLine()</code> 方法可以一次读取一行数据，而不是一个字符一个字符地读取。</p><p>BufferedWriter 类继承自 Writer 类，提供了一些便捷的方法，例如 <code>newLine()</code> 方法可以写入一个系统特定的行分隔符。</p><h4 id="_1-构造方法-1" tabindex="-1"><a class="header-anchor" href="#_1-构造方法-1" aria-hidden="true">#</a> 1）构造方法</h4><ul><li><code>BufferedReader(Reader in)</code> ：创建一个新的缓冲输入流，注意参数类型为<strong>Reader</strong>。</li><li><code>BufferedWriter(Writer out)</code>： 创建一个新的缓冲输出流，注意参数类型为<strong>Writer</strong>。</li></ul><p>代码示例如下：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token comment">// 创建字符缓冲输入流</span>
<span class="token class-name">BufferedReader</span> br <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">BufferedReader</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">FileReader</span><span class="token punctuation">(</span><span class="token string">"b.txt"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 创建字符缓冲输出流</span>
<span class="token class-name">BufferedWriter</span> bw <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">BufferedWriter</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">FileWriter</span><span class="token punctuation">(</span><span class="token string">"b.txt"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><h4 id="_2-字符缓冲流特有方法" tabindex="-1"><a class="header-anchor" href="#_2-字符缓冲流特有方法" aria-hidden="true">#</a> 2）字符缓冲流特有方法</h4><p>字符缓冲流的基本方法与<a href="https://javabetter.cn/io/reader-writer.html" target="_blank" rel="noopener noreferrer">普通字符流<span><svg class="external-link-icon" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path><polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg><span class="external-link-icon-sr-only">open in new window</span></span></a>调用方式一致，这里不再赘述，我们来看字符缓冲流<strong>特有</strong>的方法。</p><ul><li>BufferedReader：<code>String readLine()</code>: <strong>读一行数据</strong>，读取到最后返回 null</li><li>BufferedWriter：<code>newLine()</code>: <strong>换行</strong>，由系统定义换行符。</li></ul><p>来看 <code>readLine()</code>方法的代码示例：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token comment">// 创建流对象</span>
<span class="token class-name">BufferedReader</span> br <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">BufferedReader</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">FileReader</span><span class="token punctuation">(</span><span class="token string">"a.txt"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 定义字符串,保存读取的一行文字</span>
<span class="token class-name">String</span> line <span class="token operator">=</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
<span class="token comment">// 循环读取,读取到最后返回null</span>
<span class="token keyword">while</span> <span class="token punctuation">(</span><span class="token punctuation">(</span>line <span class="token operator">=</span> br<span class="token punctuation">.</span><span class="token function">readLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token operator">!=</span><span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">print</span><span class="token punctuation">(</span>line<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"------"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token comment">// 释放资源</span>
br<span class="token punctuation">.</span><span class="token function">close</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>再来看 <code>newLine()</code> 方法的代码示例：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token comment">// 创建流对象</span>
<span class="token class-name">BfferedWriter</span> bw <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">BufferedWriter</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">FileWriter</span><span class="token punctuation">(</span><span class="token string">"b.txt"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 写出数据</span>
bw<span class="token punctuation">.</span><span class="token function">write</span><span class="token punctuation">(</span><span class="token string">"沉"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 写出换行</span>
bw<span class="token punctuation">.</span><span class="token function">newLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
bw<span class="token punctuation">.</span><span class="token function">write</span><span class="token punctuation">(</span><span class="token string">"默"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
bw<span class="token punctuation">.</span><span class="token function">newLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
bw<span class="token punctuation">.</span><span class="token function">write</span><span class="token punctuation">(</span><span class="token string">"王"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
bw<span class="token punctuation">.</span><span class="token function">newLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
bw<span class="token punctuation">.</span><span class="token function">write</span><span class="token punctuation">(</span><span class="token string">"二"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
bw<span class="token punctuation">.</span><span class="token function">newLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 释放资源</span>
bw<span class="token punctuation">.</span><span class="token function">close</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><h3 id="_03、字符缓冲流练习" tabindex="-1"><a class="header-anchor" href="#_03、字符缓冲流练习" aria-hidden="true">#</a> 03、字符缓冲流练习</h3><p>来欣赏一下我写的这篇诗：</p><blockquote><p>6.岑夫子，丹丘生，将进酒，杯莫停。</p><p>1.君不见黄河之水天上来，奔流到海不复回。</p><p>8.钟鼓馔玉不足贵，但愿长醉不愿醒。</p><p>3.人生得意须尽欢，莫使金樽空对月。</p><p>5.烹羊宰牛且为乐，会须一饮三百杯。</p><p>2.君不见高堂明镜悲白发，朝如青丝暮成雪。</p><p>7.与君歌一曲，请君为我倾耳听。</p><p>4.天生我材必有用，千金散尽还复来。</p></blockquote><p>欣赏完了没？</p><p>估计你也看出来了，这是李白写的《将进酒》，不是我王二写的。😝</p><p>不过，顺序是乱的，还好，我都编了号。那如何才能按照正确的顺序来呢？</p><p>来看代码实现：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token comment">// 创建map集合,保存文本数据,键为序号,值为文字</span>
<span class="token class-name">HashMap</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">,</span> <span class="token class-name">String</span><span class="token punctuation">></span></span> lineMap <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">HashMap</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 创建流对象 源</span>
<span class="token class-name">BufferedReader</span> br <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">BufferedReader</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">FileReader</span><span class="token punctuation">(</span><span class="token string">"logs/test.log"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//目标</span>
<span class="token class-name">BufferedWriter</span> bw <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">BufferedWriter</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">FileWriter</span><span class="token punctuation">(</span><span class="token string">"logs/test1.txt"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 读取数据</span>
<span class="token class-name">String</span> line<span class="token punctuation">;</span>
<span class="token keyword">while</span> <span class="token punctuation">(</span><span class="token punctuation">(</span>line <span class="token operator">=</span> br<span class="token punctuation">.</span><span class="token function">readLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token operator">!=</span><span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token comment">// 解析文本</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>line<span class="token punctuation">.</span><span class="token function">isEmpty</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">continue</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> split <span class="token operator">=</span> line<span class="token punctuation">.</span><span class="token function">split</span><span class="token punctuation">(</span><span class="token class-name">Pattern</span><span class="token punctuation">.</span><span class="token function">quote</span><span class="token punctuation">(</span><span class="token string">"."</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 保存到集合</span>
lineMap<span class="token punctuation">.</span><span class="token function">put</span><span class="token punctuation">(</span>split<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">,</span> split<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token comment">// 释放资源</span>
br<span class="token punctuation">.</span><span class="token function">close</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 遍历map集合</span>
<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">int</span> i <span class="token operator">=</span> <span class="token number">1</span><span class="token punctuation">;</span> i <span class="token operator"><=</span> lineMap<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">String</span> key <span class="token operator">=</span> <span class="token class-name">String</span><span class="token punctuation">.</span><span class="token function">valueOf</span><span class="token punctuation">(</span>i<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 获取map中文本</span>
<span class="token class-name">String</span> value <span class="token operator">=</span> lineMap<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span>key<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 写出拼接文本</span>
bw<span class="token punctuation">.</span><span class="token function">write</span><span class="token punctuation">(</span>key<span class="token operator">+</span><span class="token string">"."</span><span class="token operator">+</span>value<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 写出换行</span>
bw<span class="token punctuation">.</span><span class="token function">newLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token comment">// 释放资源</span>
bw<span class="token punctuation">.</span><span class="token function">close</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>这里面用到的知识都是我们前面学过的，比如说 <a href="https://javabetter.cn/collection/hashmap.html" target="_blank" rel="noopener noreferrer">HashMap<span><svg class="external-link-icon" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path><polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg><span class="external-link-icon-sr-only">open in new window</span></span></a>，<a href="https://javabetter.cn/string/split.html" target="_blank" rel="noopener noreferrer">字符串分割<span><svg class="external-link-icon" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path><polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg><span class="external-link-icon-sr-only">open in new window</span></span></a>，包括刚刚学习的字符缓冲流。</p><p>来看输出结果</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>1.君不见黄河之水天上来，奔流到海不复回。
2.君不见高堂明镜悲白发，朝如青丝暮成雪。
3.人生得意须尽欢，莫使金樽空对月。
4.天生我材必有用，千金散尽还复来。
5.烹羊宰牛且为乐，会须一饮三百杯。
6.岑夫子，丹丘生，将进酒，杯莫停。
7.与君歌一曲，请君为我倾耳听。
8.钟鼓馔玉不足贵，但愿长醉不愿醒。
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><hr><p>GitHub 上标星 9300+ 的开源知识库《<a href="https://github.com/itwanger/toBeBetterJavaer" target="_blank" rel="noopener noreferrer">二哥的 Java 进阶之路<span><svg class="external-link-icon" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path><polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg><span class="external-link-icon-sr-only">open in new 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