注解apt工具示例程序

  今天按照《Thinking in Java》中使用apt处理注解一节，将书中代码写了一遍，但运行过程中出现了一个问题让我很纳闷，下面先把代码呈上，问题稍后再说。

  程序功能很简单，就是从被注解的类中提取出public方法，然后使用注解处理器生成一个包含这些public方法的接口文件。

具体介绍可以参考原书。

 

ExtractInterface.java——注解定义

 /**
  *
  */
 package net.lazydoggy.annotations.aptdemo;

 import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;

 /**
  * @author hanzhaozhan
  *
  */
 @Target(ElementType.TYPE)
 @Retention(RetentionPolicy.SOURCE)
 public @interface ExtractInterface {
     String value();
 }

 

Multiplier.java——使用了注解的目标类

 /**
  *
  */
 package net.lazydoggy.annotations.aptdemo;

 /**
  * @author hanzhaozhan
  *
  */
 @ExtractInterface("Imultiplier")
 public class Multiplier {
     public int multiply(int x, int y) {
         int total = 0;
         for (int i = 0; i < x; i++) {
             total = add(total, y);
         }

         return total;
     }

     private static int add(int x, int y) {
         return x + y;
     }

     public static void main(String[] args) {
         Multiplier m = new Multiplier();
         System.out.println("11 * 16 = " + m.multiply(11, 16));
     }
 }

 

InterfaceExtractorProcessor.java——注解处理器类

 package net.lazydoggy.annotations.aptdemo;

 import java.io.IOException;
 import java.io.PrintWriter;
 import java.util.ArrayList;

 import com.sun.mirror.apt.AnnotationProcessor;
 import com.sun.mirror.apt.AnnotationProcessorEnvironment;
 import com.sun.mirror.declaration.MethodDeclaration;
 import com.sun.mirror.declaration.ParameterDeclaration;
 import com.sun.mirror.declaration.TypeDeclaration;

 public class InterfaceExtractorProcessor implements AnnotationProcessor {
     private final AnnotationProcessorEnvironment env;
     private ArrayList<MethodDeclaration> interfaceMethods = new ArrayList<MethodDeclaration>();

     public InterfaceExtractorProcessor(AnnotationProcessorEnvironment env) {
         this.env = env;
     }

     @Override
     public void process() {
         for (TypeDeclaration typeDel : env.getSpecifiedTypeDeclarations()) {
             ExtractInterface annot = typeDel
                     .getAnnotation(ExtractInterface.class);
             if (annot == null) {
                 break;
             }
             for (MethodDeclaration m : typeDel.getMethods()) {
                 if (m.getModifiers().toString().contains("public")
                         && !(m.getModifiers().toString().contains("static"))) {
                     interfaceMethods.add(m);
                 }
             }
             if (interfaceMethods.size() > 0) {
                 try {
                     PrintWriter writer = env.getFiler().createSourceFile(
                             annot.value());
                     writer.println("package "
                             + typeDel.getPackage().getQualifiedName() + ";");
                     writer.println("public interface " + annot.value() + " {");
                     for (MethodDeclaration m : interfaceMethods) {
                         writer.print("\tpublic ");
                         writer.print(m.getReturnType() + " ");
                         writer.print(m.getSimpleName() + "(");
                         int i = 0;
                         for (ParameterDeclaration param : m.getParameters()) {
                             writer.print(param.getType() + " "
                                     + param.getSimpleName());
                             if (++i < m.getParameters().size()) {
                                 writer.print(",");
                             }
                         }
                         writer.println(");");
                     }
                     writer.println("}");
                     writer.close();
                 } catch (IOException e) {
                     e.printStackTrace();
                 }

             }
         }
     }

 }

 

InterfaceExtractorProcessorFactory.java——处理器工厂类

 /**
  *
  */
 package net.lazydoggy.annotations.aptdemo;

 import java.util.Collection;
 import java.util.Collections;
 import java.util.Set;

 import com.sun.mirror.apt.AnnotationProcessor;
 import com.sun.mirror.apt.AnnotationProcessorEnvironment;
 import com.sun.mirror.apt.AnnotationProcessorFactory;
 import com.sun.mirror.declaration.AnnotationTypeDeclaration;

 /**
  * @author hanzhaozhan
  *
  */
 public class InterfaceExtractorProcessorFactory implements
         AnnotationProcessorFactory {

     /*
      * (non-Javadoc)
      *
      * @see
      * com.sun.mirror.apt.AnnotationProcessorFactory#getProcessorFor(java.util
      * .Set, com.sun.mirror.apt.AnnotationProcessorEnvironment)
      */
     @Override
     public AnnotationProcessor getProcessorFor(
             Set<AnnotationTypeDeclaration> atds,
             AnnotationProcessorEnvironment env) {
         return new InterfaceExtractorProcessor(env);
     }

     /*
      * (non-Javadoc)
      *
      * @see
      * com.sun.mirror.apt.AnnotationProcessorFactory#supportedAnnotationTypes()
      */
     @Override
     public Collection<String> supportedAnnotationTypes() {
         return Collections
                 .singleton("net.lazydoggy.annotations.aptdemo.ExtractInterface");
     }

     /*
      * (non-Javadoc)
      *
      * @see com.sun.mirror.apt.AnnotationProcessorFactory#supportedOptions()
      */
     @Override
     public Collection<String> supportedOptions() {
         return Collections.emptySet();
     }

 }

 

使用下面命令：

apt -s . -nocompile -factory net.lazydoggy.annotations.aptdemo.InterfaceExtractorProcessorFactory .\net\lazydoggy\annotations\aptdemo\Multiplier.java

就会在当前执行目录下生成一个Imultiplier .java文件，里面定义了我们在处理器中写入的接口。

 

上面的程序运行时没有问题的，因为其中的一行代码被我改动过，如下：

 for (MethodDeclaration m : typeDel.getMethods()) {
     if (m.getModifiers().toString().contains("public")
             && !(m.getModifiers().toString().contains("static"))) {
         interfaceMethods.add(m);
     }
 }

书中的代码是这样的：

 for (MethodDeclaration m : typeDel.getMethods()) {
     if (m.getModifiers().contains(Modifier.PUBLIC)
             && !(m.getModifiers().contains(Modifier.STATIC))) {
         interfaceMethods.add(m);
     }
 }

 如果使用书中的代码是无法得到预期结果的，我使用JDK1.6，不知道JDK1.5是否可以。在JDK1.6中，getModifiers()返回Collection<Modifier>类型，而Modifier类中的静态常量（PUBLIC、STATIC等）是int类型，因此书中代码总会返回false。

上面是我的一个方法，应该有更好的方法，希望大家可以分享。