ASM 改写方法

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Generator.java

import java.io.File;
import java.io.FileOutputStream;

import org.objectweb.asm.ClassAdapter;
import org.objectweb.asm.ClassReader;
import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.Opcodes;

public class Generator extends ClassLoader implements Opcodes {

/**
* @param args
*/
public static void main(String[] args) throws Exception {
   ClassReader cr = new ClassReader("MyBeanHello");
   ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS);
   ClassAdapter classAdapter = new MyClassAdapter(cw);
   cr.accept(classAdapter, ClassReader.SKIP_DEBUG);
   byte[] code = cw.toByteArray();
   Generator loader = new Generator();
   Class<?> exampleClass = loader.defineClass("MyBeanHello", code, 0, code.length);
   exampleClass.getMethods()[3].invoke(exampleClass.newInstance(), new   Object[]{ "Jack "} );
   byte[] data = cw.toByteArray();
   File file = new File("/devTool/MyBeanHello.class");
   FileOutputStream fout = new FileOutputStream(file);
   fout.write(data);
   fout.close();

}

}

MyBeanHello.java

public class MyBeanHello {

   private String name;
   private int age;
   public String getName() {
       return name;
   }
   public void setName(String name) {
       System.out.println(" run "+name);
   }
   public int getAge() {
       return age;
   }
   public void setAge(int age) {
       this.age = age;
   }

   public String toString(){
       return "name:"+name+";age:"+age;
   }
   /**
   * @param args
   */
   public static void main(String[] args) {
       System.out.println("run main ");
       System.out.println( new MyBeanHello().toString());
}

}

MyClassAdapter.java

import org.objectweb.asm.ClassAdapter;
import org.objectweb.asm.ClassVisitor;
import org.objectweb.asm.MethodVisitor;

public class MyClassAdapter extends ClassAdapter {

   public MyClassAdapter(ClassVisitor cv) {
       super(cv);
   }

   public MethodVisitor visitMethod(int access, String name, String desc,String signature, String[] exceptions) {

       MethodVisitor mv = cv.visitMethod(access, name, desc, signature,exceptions);
       MethodVisitor wrappedMv = mv;
       if (mv != null) {

           if (name.equals("setName")) {
               // 使用自定义 MethodVisitor，实际改写方法内容
               wrappedMv = new MyMethodAdapter(mv);
           } else {
           }
       }
       return wrappedMv;

   }

}

MyMethodAdapter.java

import org.objectweb.asm.Label;
import org.objectweb.asm.MethodAdapter;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;

public class MyMethodAdapter extends MethodAdapter {

   public MyMethodAdapter(MethodVisitor mv) {
       super(mv);
       mv.visitCode();
       Label l0 = new Label();
       mv.visitLabel(l0);
       mv.visitLineNumber(4, l0);
       mv.visitFieldInsn(Opcodes.GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;");
       mv.visitLdcInsn(" MyMethodAdapter Code add By ASM Eclipse ");
       mv.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V");
       Label l1 = new Label();
       mv.visitLabel(l1);
       mv.visitLineNumber(5, l1);
//       mv.visitInsn(Opcodes.RETURN);
   }
}

用jad反编译后的MyBeanHello.java

// Decompiled by Jad v1.5.8e. Copyright 2001 Pavel Kouznetsov.
// Jad home page: http://www.geocities.com/kpdus/jad.html
// Decompiler options: packimports(3)

import java.io.PrintStream;

public class MyBeanHello
{

    public MyBeanHello()
    {
    }

    public String getName()
    {
        return name;
    }

    public void setName(String s)
    {
        System.out.println(" MyMethodAdapter Code add By ASM Eclipse ");
        System.out.println((new StringBuilder(" run ")).append(s).toString());
    }

    public int getAge()
    {
        return age;
    }

    public void setAge(int i)
    {
        age = i;
    }

    public String toString()
    {
        return (new StringBuilder("name:")).append(name).append(";age:").append(age).toString();
    }

    public static void main(String args[])
    {
        System.out.println("run main ");
        System.out.println((new MyBeanHello()).toString());
    }

    private String name;
    private int age;
}