javaassist 的使用

1
查看版本号:

F:\bisoft\ext\javassist-3.11.GA\javassist-3.11.0>java -jar javassist.jar
Javassist version 3.11.0.GA
Copyright (C) 1999-2009 Shigeru Chiba. All Rights Reserved.

F:\bisoft\ext\javassist-3.11.GA\javassist-3.11.0>

2
Dump CLASS

package cn.bisoft.java.util.test;

import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.PrintWriter;

import javassist.bytecode.ClassFile;
import javassist.bytecode.ClassFileWriter;

public class ClassDumpUtil
{
	public static void dump(String classFilePath) throws Exception
	{
		DataInputStream in = new DataInputStream(new FileInputStream(classFilePath));
		ClassFile w = new ClassFile(in);
		PrintWriter out = new PrintWriter(System.out, true);
		out.println("*** constant pool ***");
		w.getConstPool().print(out);
		out.println();
		out.println("*** members ***");
		ClassFileWriter.print(w, out);
	}
	
	public static void main(String[] args) throws Exception {

		ClassDumpUtil.dump("E:/bisoft/code/workspace/bisoft/build/classes/cn/bisoft/java/core/F.class");
	}
}

3
javassist.jar 依赖 JDK/LIB/tools.jar

导入示例:
src -/
      example +

4
示例1:
Test.java

增加一个不存在的方法到类g()中.

package sample;

import javassist.*;

public class Test
{
	public int f(int i)
	{
		return i + 1;
	}

	public static void main(String[] args) throws Exception
	{
		ClassPool pool = ClassPool.getDefault();

		CtClass cc = pool.get("sample.Test");
		try
		{
			cc.getDeclaredMethod("g");
			System.out.println("g() is already defined in sample.Test.");
		}
		catch (NotFoundException e)
		{
			/*
			 * getDeclaredMethod() throws an exception if g() is not defined in sample.Test.
			 */
			CtMethod fMethod = cc.getDeclaredMethod("f");
			CtMethod gMethod = CtNewMethod.copy(fMethod, "g", cc, null);
			cc.addMethod(gMethod);
			cc.writeFile(); // update the class file
			System.out.println("g() was added.");
		}
	}
}

运行后:

g() was added.

验证结果:
a. class 的修改时间已经修改
b. 反编译 class 文件 ,查看源码已经修改

package sample;

import java.io.PrintStream;
import javassist.ClassPool;
import javassist.CtClass;
import javassist.CtMethod;
import javassist.CtNewMethod;
import javassist.NotFoundException;

public class Test
{
  public int f(int i)
  {
    return (i + 1);
  }

  public static void main(String[] args) throws Exception {
    ClassPool pool = ClassPool.getDefault();

    CtClass cc = pool.get("sample.Test");
    try {
      cc.getDeclaredMethod("g");
      System.out.println("g() is already defined in sample.Test.");
    }
    catch (NotFoundException e)
    {
      CtMethod fMethod = cc.getDeclaredMethod("f");
      CtMethod gMethod = CtNewMethod.copy(fMethod, "g", cc, null);
      cc.addMethod(gMethod);
      cc.writeFile();
      System.out.println("g() was added.");
    }
  }

[b]  public int g(int i)
  {
    return (i + 1);
  }
[/b]
}

5
例子2