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完成APT 编译时注解的例子
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‎src/main/java/cn/byhieg/annotationstutorial/APTAnnotation.java‎

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package cn.byhieg.annotationstutorial;
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import java.lang.annotation.ElementType;
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import java.lang.annotation.Retention;
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import java.lang.annotation.RetentionPolicy;
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import java.lang.annotation.Target;
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/**
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* Created by byhieg on 17/2/14.
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* Mail to byhieg@gmail.com
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*/
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@Target({ElementType.FIELD,ElementType.TYPE,ElementType.METHOD})
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@Retention(RetentionPolicy.SOURCE)
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public @interface APTAnnotation {
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String author() default "byhieg";
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String date();
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String version() default "1";
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}

‎src/main/java/cn/byhieg/annotationstutorial/APTProcessor.java‎

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package cn.byhieg.annotationstutorial;
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import javax.annotation.processing.AbstractProcessor;
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import javax.annotation.processing.Messager;
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import javax.annotation.processing.ProcessingEnvironment;
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import javax.annotation.processing.RoundEnvironment;
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import javax.lang.model.SourceVersion;
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import javax.lang.model.element.Element;
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import javax.lang.model.element.PackageElement;
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import javax.lang.model.element.TypeElement;
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import javax.tools.Diagnostic;
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import javax.tools.JavaFileObject;
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import java.io.IOException;
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import java.io.PrintWriter;
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import java.io.Writer;
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import java.util.Set;
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/**
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* Created by byhieg on 17/2/14.
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* Mail to byhieg@gmail.com
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*/
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public class APTProcessor extends AbstractProcessor{
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//类名的前缀、后缀
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public static final String SUFFIX = "AutoGenerate";
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public static final String PREFIX = "byhieg_";
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@Override
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public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
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for (TypeElement typeElement : annotations) {
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for (Element e : roundEnv.getElementsAnnotatedWith(typeElement)) {
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//打印消息
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Messager messager = processingEnv.getMessager();
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messager.printMessage(Diagnostic.Kind.NOTE, "Printing:" + e.toString());
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messager.printMessage(Diagnostic.Kind.NOTE, "Printing:" + e.getSimpleName());
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messager.printMessage(Diagnostic.Kind.NOTE, "Printing:" + e.getEnclosedElements().toString());
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//获取注解
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APTAnnotation aptAnnotation = e.getAnnotation(APTAnnotation.class);
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//获取元素名并将其首字母大写
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String name = e.getSimpleName().toString();
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char c = Character.toUpperCase(name.charAt(0));
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name = String.valueOf(c + name.substring(1));
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//包裹注解元素的元素, 也就是其父元素, 比如注解了成员变量或者成员函数, 其上层就是该类
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Element enclosingElement = e.getEnclosingElement();
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String enclosingQualifiedname;
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if (enclosingElement instanceof PackageElement) {
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enclosingQualifiedname = ((PackageElement) enclosingElement).getQualifiedName().toString();
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} else {
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enclosingQualifiedname = ((TypeElement) enclosingElement).getQualifiedName().toString();
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}
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try {
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//生成包名
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String generatePackageName = enclosingQualifiedname.substring(0, enclosingQualifiedname.lastIndexOf("."));
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// 生成的类名
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String genarateClassName = PREFIX + enclosingElement.getSimpleName() + SUFFIX;
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//创建Java 文件
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JavaFileObject f = processingEnv.getFiler().createSourceFile(genarateClassName);
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// 在控制台输出文件路径
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messager.printMessage(Diagnostic.Kind.NOTE, "Printing: " + f.toUri());
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Writer w = f.openWriter();
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try {
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PrintWriter pw = new PrintWriter(w);
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pw.println("package " + generatePackageName + ";");
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pw.println("\npublic class " + genarateClassName + " { ");
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pw.println("\n /** 打印值 */");
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pw.println(" public static void print" + name + "() {");
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pw.println(" // 注解的父元素: " + enclosingElement.toString());
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pw.println(" System.out.println(\"代码生成的路径: " + f.toUri() + "\");");
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pw.println(" System.out.println(\"注解的元素: " + e.toString() + "\");");
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pw.println(" System.out.println(\"注解的版本: " + aptAnnotation.version() + "\");");
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pw.println(" System.out.println(\"注解的作者: " + aptAnnotation.author() + "\");");
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pw.println(" System.out.println(\"注解的日期: " + aptAnnotation.date() + "\");");
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pw.println(" }");
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pw.println("}");
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pw.flush();
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} finally {
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w.close();
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}
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} catch (IOException e1) {
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processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR, e1.toString());
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}
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}
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}
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return true;
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}
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@Override
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public Set<String> getSupportedAnnotationTypes() {
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return super.getSupportedAnnotationTypes();
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}
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@Override
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public SourceVersion getSupportedSourceVersion() {
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return SourceVersion.latestSupported();
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}
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@Override
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public synchronized void init(ProcessingEnvironment processingEnv) {
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super.init(processingEnv);
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}
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}

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