Java中动态代理技术生成的类与原始类的区别（good）

Posted 2023-01-02

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　　用动态代理的时候,对它新生成的类长什么样子感到好奇.有幸通过一些资料消除了心里的疑惑.

　　平时工作使用的Spring框架里面有一个AOP(面向切面)的机制,只知道它是把类重新生成了一遍,在切面上加上了后来定义的逻辑.这样就达到了动态的在原有类上增加一些功能.比如日志打印,拦截信息等.

　　这里只关心动态代理技术生成新的类,先不管虚拟机是如何去生成类,用了什么字节码生成技术,怎么产生字节码等这一系列动作.现在只关心最后生成的新类长什么样,它和老类有什么区别.为了获取到生成后的代理类的字节码并且反编译成我们能够看得懂的代码,需要实现一个动态代理例子.

例子

//接口

package note.com;

public interface IGirl 
    void sayHello();

//接口实现,也是需要利用动态代理扩展功能的类

package note.com;

public class MyGirl implements IGirl 
    public void sayHello() 
        System.out.println("如花似玉石榴姐");

//代理实现类

package note.com;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

public class ProxyGirl implements InvocationHandler 
    Object originalObj;

    Object bind(Object originalObj) 
        this.originalObj = originalObj;
        return Proxy.newProxyInstance(originalObj.getClass()
                .getClassLoader(), originalObj.getClass().getInterfaces(),
                this);
    

    public Object invoke(Object proxy, Method method, Object[] args)
            throws Throwable 
        System.out.println("第一美女是:");
        return method.invoke(originalObj, args);

//测试类

package note.com;

public class Test 

    public static void main(String[] args) 
        IGirl hello = (IGirl) new ProxyGirl().bind(new MyGirl());
        hello.sayHello();
　　　　　System.out.println(hello.getClass().getName());

结果:

第一美女是:
如花似玉石榴姐
com.sun.proxy.$Proxy0

这里可见hello真实类型是$Proxy0,到底它长什么样子,往下看.

代理类字节码反编译结果

package note.com;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;

/**
 * 动态生成的类字节码的反编译结果
 *
 */
public final class $Proxy0 extends Proxy implements IGirl 

    private static Method m3;
    private static Method m1;
    private static Method m0;
    private static Method m2;

    /*
     * 构造函数传入能够访问真实对象的代理类,这个实际是上例Test中的new ProxyGirl()
     */
    protected $Proxy0(InvocationHandler h) 
        super(h);
    

    /*
     * 代理实现sayHello,
     */
    public void sayHello() 
        try 
            this.h.invoke(this, m3, null);
         catch (RuntimeException localRuntimeException) 
            throw localRuntimeException;
         catch (Throwable localThrowable) 
            throw new UndeclaredThrowableException(localThrowable);
        

    

    /*
     * 代理实现继承自Object的equals
     */
    public void equals() 
        try 
            this.h.invoke(this, m1, null);
         catch (RuntimeException localRuntimeException) 
            throw localRuntimeException;
         catch (Throwable localThrowable) 
            throw new UndeclaredThrowableException(localThrowable);
        
    

    /*
     * 代理实现继承自Object的hashCode
     */
    public int hashCode() 
        try 
            return (Integer) this.h.invoke(this, m0, null);
         catch (RuntimeException localRuntimeException) 
            throw localRuntimeException;
         catch (Throwable localThrowable) 
            throw new UndeclaredThrowableException(localThrowable);
        
    

    /*
     * 代理实现继承自Object的toString
     */
    public String toString() 
        try 
            return (String) this.h.invoke(this, m2, null);
         catch (RuntimeException localRuntimeException) 
            throw localRuntimeException;
         catch (Throwable localThrowable) 
            throw new UndeclaredThrowableException(localThrowable);
        
    

    /*
     * 初始化真实对象中的所有方法
     */
    static 
        try 
            m3 = Class.forName("note.com.IGirl").getMethod("sayHello",
                    new Class[0]);
            m1 = Class.forName("java.lang.Object").getMethod("equals",
                    new Class[]  Class.forName("java.lang.Object") );
            m0 =  Class.forName("java.lang.Object").getMethod("equals",
                    new Class[0]);
            m2 =  Class.forName("java.lang.Object").getMethod("equals",
                    new Class[0]);
         catch (NoSuchMethodException localNoSuchMethodException) 
            throw new NoSuchMethodError(localNoSuchMethodException.getMessage());
         catch (ClassNotFoundException localClassNotFoundException) 
            throw new NoClassDefFoundError(
                    localClassNotFoundException.getMessage());