add > custom-class-loader

lihengming · lihengming · commit ec90ae1823b4 · 2017-06-09T14:56:56.000+08:00
diff --git a/jvm/src/main/java/classloader/CustomClassLoader.java b/jvm/src/main/java/classloader/CustomClassLoader.java
@@ -0,0 +1,44 @@
+package classloader;
+
+import java.io.BufferedInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.FileInputStream;
+import java.io.IOException;
+
+/**
+ * Created by 李恒名 on 2017/6/8.
+ */
+public class CustomClassLoader extends ClassLoader {
+    private final String classesDir;
+
+    public CustomClassLoader(String classesDir) {
+        this.classesDir = classesDir;
+    }
+
+    @Override
+    protected Class<?> findClass(String name) throws ClassNotFoundException {
+        String fileName = name;
+        if (fileName.indexOf('.') > 0) {
+            fileName.replaceAll(".", "\\");
+        }
+        fileName = fileName + ".class";
+
+        try {
+            try (BufferedInputStream bin = new BufferedInputStream(new FileInputStream(classesDir + fileName))) {
+                try (ByteArrayOutputStream out = new ByteArrayOutputStream()) {
+                    byte[] buffer = new byte[1024];
+                    int len = 0;
+                    while ((len = bin.read(buffer)) != -1) {
+                        out.write(buffer,0,len);
+                    }
+                    byte[] data = out.toByteArray();
+                    return defineClass(name, data, 0, data.length);
+                }
+            }
+
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+        return super.findClass(name);
+    }
+}
diff --git a/jvm/src/main/java/classloader/Test.java b/jvm/src/main/java/classloader/Test.java
@@ -0,0 +1,11 @@
+package classloader;
+
+/**
+ * Created by 李恒名 on 2017/6/8.
+ */
+public class Test {
+
+    public void say (){
+        System.out.println("Hello");
+    }
+}
diff --git a/jvm/src/main/java/classloader/Tester.java b/jvm/src/main/java/classloader/Tester.java
@@ -0,0 +1,20 @@
+package classloader;
+
+import java.lang.reflect.Method;
+
+/**
+ * Created by 李恒名 on 2017/6/8.
+ */
+public class Tester {
+
+    public static void main(String[] args) throws Exception{
+        //1. 将Test.java 编译为Test.class 后复制到 E:\classes 下，当然也可以选择其他目录。
+        //2. 加载
+        ClassLoader classLoader = new CustomClassLoader("E:\\classes\\");
+        Class<?> clazz = classLoader.loadClass("Test");
+        //3. 通过反射调用say()方法
+        Object instance = clazz.newInstance();
+        Method method = clazz.getMethod("say", null);
+        method.invoke(instance);//Hello
+    }
+}
