java中代理模式详解

最新推荐文章于 2025-06-20 22:08:45 发布

原创最新推荐文章于 2025-06-20 22:08:45 发布 · 214 阅读

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本文详细介绍了Java中的代理模式，包括其应用场景、特点。重点讲解了JDK动态代理的实现步骤，强调被代理类需要实现接口，代理类实现InvocationHandler接口并重写invoke方法。此外，还提到了手写JDK动态代理的过程，涉及代码生成、编译及加载到JVM的流程。

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代理模式：

1.事情必须做,而自己有没有时间做或者想做；2.持有被代理对象的引用。

分为静态代理，动态代理。

特点:

1.执行者，被代理人

2.对于被代理人来说，这件事情是一定要做的，但是自己又不想去做或者没时间做，找代理。

3.需要获取被代理人的个人资料

jdk动态代理：

1.被代理类需要一个接口

package jdk;

public interface Person {
	//寻找真爱
	void findLove();
	public String getSex();
	public String getName();
}

2.被代理类需要实现这个接口

package jdk;

//小星星，单身
public class XiaoXingXing implements Person {
	private String sex="女";
	private String name="小星星";
	
	public String getSex() {
		return sex;
	}

	public void setSex(String sex) {
		this.sex = sex;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	@Override
	public void findLove() {
		System.out.println("我叫"+this.name+",性别:"+this.sex+".我找对象的要求是：");
		System.out.println("高富帅");
		System.out.println("有车有房");
		System.out.println("身高要求180cm,体重70kg");
		
	}
}

3.代理类需要实现InvocationHandler接口，重写invoke方法

package jdk;

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

//媒婆
public class Meipo implements InvocationHandler {
	private Person target;
	public Object getInstance(Person target)throws  Exception{
		this.target=target;
		Class clazz = target.getClass();
		System.out.println("被代理对象的class是："+clazz);
		return Proxy.newProxyInstance(clazz.getClassLoader(), clazz.getInterfaces(), this);
	}

	@Override
	public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
		System.out.println("我是媒婆：你的性别是:"+this.target.getSex()+"得给你找个异性");
		System.out.println("开始进行海选。。。。");
		System.out.println("-----------------------------");
		method.invoke(this.target, args);
		System.out.println("-----------------------------");
		System.out.println("如果合适的话准备办事吧");
		return null;
	}

}

4.测试

package jdk;

import java.io.FileOutputStream;

import sun.misc.ProxyGenerator;

public class TestFindLove {
	public static void main(String[] args){
		//new XiaoXingXing().findLove();
		try {
			Person obj =(Person) new Meipo().getInstance(new XiaoXingXing());
			System.out.println(obj.getClass());
			obj.findLove();
			
			//代理对象的实现原理
			//1.拿到被代理对象的引用，然后获取它的接口、
			//2.JDK代理 就会重新生成一个类同时实现我们给的代理对象的所实现的接口
			//3.把被代理对象的引用也拿到了
			//4.重新生成一个class字节码
			//5.然后编译
			
			//获取字节码内容
			byte[] data = ProxyGenerator.generateProxyClass("$Proxy0", new Class[]{Person.class});
			FileOutputStream os = new FileOutputStream("E:/GP_WORKSPACE/$Proxy0.class");
			os.write(data);
			os.close();
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

}

5，输出的内容

被代理对象的class是：class jdk.XiaoXingXing
class com.sun.proxy.$Proxy0
我是媒婆：你的性别是:女得给你找个异性
开始进行海选。。。。
-----------------------------
我叫小星星,性别:女.我找对象的要求是：
高富帅
有车有房
身高要求180cm,体重70kg
-----------------------------
如果合适的话准备办事吧

Person obj =(Person) new Meipo().getInstance(new XiaoXingXing());
System.out.println(obj.getClass());

obj是jdk代理生成的一个类class com.sun.proxy.$Proxy0，源码：

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

public final class $Proxy0
  extends Proxy
  implements Person
{
  private static Method m1;
  private static Method m5;
  private static Method m3;
  private static Method m4;
  private static Method m2;
  private static Method m0;
  
  public $Proxy0(InvocationHandler paramInvocationHandler)
  {
    super(paramInvocationHandler);
  }
  
  public final boolean equals(Object paramObject)
  {
    try
    {
      return ((Boolean)this.h.invoke(this, m1, new Object[] { paramObject })).booleanValue();
    }
    catch (Error|RuntimeException localError)
    {
      throw localError;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }
  
  public final String getSex()
  {
    try
    {
      return (String)this.h.invoke(this, m5, null);
    }
    catch (Error|RuntimeException localError)
    {
      throw localError;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }
  
  public final String getName()
  {
    try
    {
      return (String)this.h.invoke(this, m3, null);
    }
    catch (Error|RuntimeException localError)
    {
      throw localError;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }
  
  public final void findLove()
  {
    try
    {
      this.h.invoke(this, m4, null);
      return;
    }
    catch (Error|RuntimeException localError)
    {
      throw localError;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }
  
  public final String toString()
  {
    try
    {
      return (String)this.h.invoke(this, m2, null);
    }
    catch (Error|RuntimeException localError)
    {
      throw localError;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }
  
  public final int hashCode()
  {
    try
    {
      return ((Integer)this.h.invoke(this, m0, null)).intValue();
    }
    catch (Error|RuntimeException localError)
    {
      throw localError;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }
  
  static
  {
    try
    {
      m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] { Class.forName("java.lang.Object") });
      m5 = Class.forName("jdk.Person").getMethod("getSex", new Class[0]);
      m3 = Class.forName("jdk.Person").getMethod("getName", new Class[0]);
      m4 = Class.forName("jdk.Person").getMethod("findLove", new Class[0]);
      m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
      m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
      return;
    }
    catch (NoSuchMethodException localNoSuchMethodException)
    {
      throw new NoSuchMethodError(localNoSuchMethodException.getMessage());
    }
    catch (ClassNotFoundException localClassNotFoundException)
    {
      throw new NoClassDefFoundError(localClassNotFoundException.getMessage());
    }
  }
}

手写一个jdk动态代理

1.被代理类实现的接口：

package jdk;

public interface Person {
	//寻找真爱
	void findLove();
	public String getSex();
	public String getName();
}

2.被代理类：

package jdk;

//小星星，单身
public class XiaoXingXing implements Person {
	private String sex="女";
	private String name="小星星";
	
	public String getSex() {
		return sex;
	}

	public void setSex(String sex) {
		this.sex = sex;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	@Override
	public void findLove() {
		System.out.println("我叫"+this.name+",性别:"+this.sex+".我找对象的要求是：");
		System.out.println("高富帅");
		System.out.println("有车有房");
		System.out.println("身高要求180cm,体重70kg");
		
	}
}

3.代理类实现的接口

package customer;

import java.lang.reflect.Method;

public interface GPInvocationHandler {
	public Object invoke(Object proxy, Method method, Object[] args)
	        throws Throwable;
}

4.生成代码类

package customer;

import java.io.File;
import java.io.FileWriter;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;

import javax.tools.JavaCompiler;
import javax.tools.JavaCompiler.CompilationTask;
import javax.tools.JavaFileObject;
import javax.tools.StandardJavaFileManager;
import javax.tools.ToolProvider;

//生成对象的代码
public class GPProxy {
	private static String ln="\r\n";
	public static Object newProxyInstance(GPClassLoader classLoader,Class<?>[] interfaces,GPInvocationHandler h){
		
		try{
			//1.生成源代码
			String proxySrc=generateSrc(interfaces[0]);
			//2.将生成的源代码输出到磁盘，保存为.java文件
			String filePath = GPProxy.class.getResource("").getPath();
			File f = new File(filePath+"$Proxy0.java");
			FileWriter fw = new FileWriter(f);
			fw.write(proxySrc);
			fw.flush();
			fw.close();
			//3.编译源代码。并且生成.class文件
			JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
			StandardJavaFileManager manager = compiler.getStandardFileManager(null, null, null);
			Iterable iterable = manager.getJavaFileObjects(f);
			CompilationTask task = compiler.getTask(null, manager, null, null, null, iterable);
			task.call();
			manager.close();
			//4.将class文件中的内容，动态加载到JVM中来
			//5.返回被代理后的代理对象
			Class proxyClass = classLoader.findClass("$Proxy0");
			Constructor c=proxyClass.getConstructor(GPInvocationHandler.class);
			f.delete();
			return c.newInstance(h); 
		}catch (Exception e) {
			e.printStackTrace();
		}
		return null;
	}
	private static String generateSrc(Class<?> interfaces){
		StringBuffer src = new StringBuffer();
		src.append("package customer;"+ln);
		src.append("import java.lang.reflect.Method;"+ln);
		src.append("public final class $Proxy0  implements "+interfaces.getName()+"{"+ln);
		src.append("GPInvocationHandler h;"+ln);
		src.append("public $Proxy0(GPInvocationHandler h) {"+ln);
		src.append("this.h=h;"+ln);
		src.append("}"+ln);
		
		for (Method m : interfaces.getMethods()) {
			src.append("public "+m.getReturnType().getName()+" "+m.getName()+"() {"+ln);
			src.append("try{"+ln);
			
			src.append("Method m="+interfaces.getName()+".class.getMethod(\""+m.getName()+"\",new Class[]{});"+ln);
			src.append("this.h.invoke(this,m,null);"+ln);
			if(!m.getReturnType().getName().equals("void")){
				src.append("return \"测试\";"); 
			}
			src.append("}catch(Throwable e){e.printStackTrace();}"+ln);
			if(!m.getReturnType().getName().equals("void")){
				src.append("return \"测试\";"); 
			}
			src.append("}"+ln);
  		}
		src.append("}");
		return src.toString();
	}
}

5.代码生成，编译，重新动态load到JVM

package customer;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;

//代码生成，编译，重新动态load到JVM
public class GPClassLoader extends ClassLoader {
	private File baseDir;
    public GPClassLoader() {
    	String basePath = GPClassLoader.class.getResource("").getPath();
    	this.baseDir=new File(basePath);
	}

	@Override
	protected Class<?> findClass(String name) throws ClassNotFoundException {
		String className =GPClassLoader.class.getPackage().getName()+"."+name;
		if(baseDir!=null){
			File classFile = new File(baseDir,name.replace("\\.", "/")+".class");
			if(classFile.exists()){
				FileInputStream  in=null;
				ByteArrayOutputStream out=null;
				try {
					in=new FileInputStream(classFile);
					out=new ByteArrayOutputStream();
					byte[] buff=new byte[1024];
					int len;
					while((len=in.read(buff))!=-1){
						out.write(buff, 0, len);
					}
					return defineClass(className, out.toByteArray(), 0, out.size());
				} catch (Exception e) {
					e.printStackTrace();
				}finally{
					if(null!=in){
						try {
							in.close();
						} catch (Exception e) {
							e.printStackTrace();
						}
					}
					if(null!=out){
						try {
							out.close();
						} catch (Exception e) {
							e.printStackTrace();
						}
					}
					classFile.delete();
				}
			}
		}
		return null;
	}

}

6.代理类

package customer;

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

import jdk.Person;

public class GPMeipo implements GPInvocationHandler {
	private Person target;
	public Object getInstance(Person target)throws  Exception{
		this.target=target;
		Class clazz = target.getClass();
		System.out.println("被代理对象的class是："+clazz);
		return GPProxy.newProxyInstance(new GPClassLoader(), clazz.getInterfaces(), this);
	} 
	@Override
	public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
		System.out.println("我是媒婆：你的性别是:"+this.target.getSex()+"得给你找个异性");
		System.out.println("开始进行海选。。。。");
		System.out.println("-----------------------------");
		method.invoke(this.target, args);
		System.out.println("-----------------------------");
		System.out.println("如果合适的话准备办事吧");
		return null;
	}

}

7.测试

package customer;


import jdk.Person;
import jdk.XiaoXingXing;

public class GPTestFindLove {
	public static void main(String[] args){
		try {
		    Person obj = (Person)new GPMeipo().getInstance(new XiaoXingXing());
			System.out.println(obj.getClass());
			obj.findLove();
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

}