JAVA动态代理 - JDK -- 纯JAVA代码

快来打我* 2022-07-18 04:21 106阅读 0赞

静态代理：编译时就已经确定了代理关系，代理类和被代理类均实现同一个接口，且代理类持有被代理类的引用。

动态代理：运行时确定代理关系，生成代理类，代理类持有特定的Handler类的引用，并由此特定类的引用通过反射调用被代理类的方法，在调用被代理类方法时，在被代理类方法前后插入代理类方法。

JDK动态代理：

接口：

/** 
     * @projectName:JavaProxy 
     * @fileName:People.java 
     * @packageName:club.younge.proxy 
     * @date:2016年9月4日上午11:29:44 
     * @copyright (c) 2016, heqy@finansir.nt All Rights Reserved. 
     * 
     */  
      
    package club.younge.proxy;  
    /** 
     * @className:People 
     * @function: TODO ADD FUNCTION.  
     * @reason:   TODO ADD REASON. 
     * @date:     2016年9月4日 上午11:29:44
     * @author   Younge 
     * @version   
     * @since    JDK 1.8 
     * @see       
     */
    public interface People {
    	public void eat() throws Throwable;
    	public void sleep() throws Throwable;
    	public void sport() throws Throwable;
    }

被代理类：

/** 
     * @projectName:JavaProxy 
     * @fileName:Jason.java 
     * @packageName:club.younge.proxy 
     * @date:2016年9月4日上午11:31:55 
     * @copyright (c) 2016, heqy@finansir.nt All Rights Reserved. 
     * 
     */  
      
    package club.younge.proxy;  
    /** 
     * @className:Jason 
     * @function: TODO ADD FUNCTION.  
     * @reason:   TODO ADD REASON. 
     * @date:     2016年9月4日 上午11:31:55
     * @author   Younge 
     * @version   
     * @since    JDK 1.8 
     * @see       
     */
    public class Jason implements People{
    
    	@Override
    	public void eat() {
    		System.out.println("Jason is eating now.");
    		
    	}
    
    	@Override
    	public void sleep() {
    		System.out.println("Jason is sleeping now.");
    		
    	}
    
    	@Override
    	public void sport() {
    		System.out.println("Jason is sporting now.");
    		
    	}
    
    }

实现JDK的一个调用接口ProxyHandler:

/** 
     * @projectName:JavaProxy 
     * @fileName:ProxyHandler.java 
     * @packageName:club.younge.proxy.jdk 
     * @date:2016年9月4日上午11:34:57 
     * @copyright (c) 2016, heqy@finansir.nt All Rights Reserved. 
     * 
     */  
      
    package club.younge.proxy.jdk;
    
    import java.lang.reflect.InvocationHandler;
    import java.lang.reflect.Method;
    
    import club.younge.proxy.People;
    
    /** 
     * @className:ProxyHandler 
     * @function: TODO ADD FUNCTION.  
     * @reason:   TODO ADD REASON. 
     * @date:     2016年9月4日 上午11:34:57
     * @author   Younge 
     * @version   
     * @since    JDK 1.8 
     * @see       
     */
    public class ProxyHandler implements InvocationHandler {
    
    	private People people;
    	public ProxyHandler(People people) {
    		this.people = people;
    	}
    	@Override
    	public Object invoke(Object obj, Method method, Object[] objArray) throws Throwable {
    		
    		before();
    		method.invoke(people, objArray);
    		after();
    		return null;
    	}
    	
    	private void before(){
    		System.out.println("Before eat you should washes hands!");
    	}
    	
    	private void after(){
    		System.out.println("After eat you should do some work!");
    	}
    
    }

JDK动态代理测试类：

/** 
     * @projectName:JavaProxy 
     * @fileName:SelfTest.java 
     * @packageName:club.younge.test 
     * @date:2016年9月4日上午11:44:37 
     * @copyright (c) 2016, heqy@finansir.nt All Rights Reserved. 
     * 
     */  
      
    package club.younge.test;
    
    import java.io.FileOutputStream;
    import java.io.IOException;
    import java.lang.reflect.Proxy;
    
    import club.younge.proxy.Jason;
    import club.younge.proxy.People;
    import club.younge.proxy.jdk.ProxyHandler;
    import sun.misc.ProxyGenerator;
    
    /** 
     * @className:SelfTest 
     * @function: TODO ADD FUNCTION.  
     * @reason:   TODO ADD REASON. 
     * @date:     2016年9月4日 上午11:44:37
     * @author   Younge 
     * @version   
     * @since    JDK 1.8 
     * @see       
     */
    public class JdkTest {
    
    	public static void main(String[] args) throws Throwable {
    		People people = (People) Proxy.newProxyInstance(People.class.getClassLoader(), new Class[]{People.class}, new ProxyHandler(new Jason()));
    		people.eat();
    		System.out.println("People's actual class:" + people.getClass().getName());
    		System.out.println("Game over!");
    		//createProxyFile();
    	}
    	
    	public static void createProxyFile() throws IOException{
    		String proxyName = "ProxyPeople";
    		byte[] data = ProxyGenerator.generateProxyClass(proxyName, new Class[]{People.class}); //调试时的名称为$Proxy0
    		FileOutputStream fos = new FileOutputStream(proxyName + ".class");
    		fos.write(data);
    		fos.close();
    	}
    	
    
    }

测试结果：

Before eat you should washes hands!  
Jason is eating now.  
After eat you should do some work!  
People's actual class:com.sun.proxy.$Proxy0  
Game over!

从测试结果可以看出，JDK动态生成的代理类为com.sun.proxy.$Proxy0(类全名)，将此动态生成的代理类的字节码输出为文件，然后通过JD-GUI反编译为java文件，代码如下：

package club.younge.proxy.jdk;
    
    import java.lang.reflect.InvocationHandler;
    import java.lang.reflect.Method;
    import java.lang.reflect.Proxy;
    import java.lang.reflect.UndeclaredThrowableException;
    
    import club.younge.proxy.People;
    /**
     * generated by jdkTest and decompiled by jd-gui.
     * @author Younge
     *
     */
    public final class ProxyPeople extends Proxy implements People {
    	
    	private static final long serialVersionUID = 1L;
    	private static Method m1;
    	private static Method m4;
    	private static Method m2;
    	private static Method m5;
    	private static Method m3;
    	private static Method m0;
    	static {
    		try {
    			m1 = Class.forName("java.lang.Object").getMethod("equals",
    					new Class[] { Class.forName("java.lang.Object") });
    			m4 = Class.forName("club.younge.proxy.People").getMethod("eat", new Class[0]);
    			m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
    			m5 = Class.forName("club.younge.proxy.People").getMethod("sport", new Class[0]);
    			m3 = Class.forName("club.younge.proxy.People").getMethod("sleep", 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());
    		}
    	}
    
    	public ProxyPeople(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 void eat() {
    		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 void sport() {
    		try {
    			this.h.invoke(this, m5, null);
    			return;
    		} catch (Error | RuntimeException localError) {
    			throw localError;
    		} catch (Throwable localThrowable) {
    			throw new UndeclaredThrowableException(localThrowable);
    		}
    	}
    
    	public final void sleep() {
    		try {
    			this.h.invoke(this, m3, null);
    			return;
    		} 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);
    		}
    	}
    
    }

从反编译的代码看出，动态生成的代理类，继承JDK的Proxy类，并实现了我们自定义的People接口，并持有，我们实现的ProxyHandler类的引用。在调用代理类方法时，实则调用了ProxyHandler的invoke方法，然后在此invoke方法中，反射调用被代理类方法。最终代理类调用了被代理类的方法。

自己实现JDK的动态代理过程：

接口和被代理类如上。

我们需要手动实现JDK定义的Proxy的newProxyInstance()方法。

/** 
     * @projectName:JavaProxy 
     * @fileName:MyProxy.java 
     * @packageName:club.younge.proxy.self 
     * @date:2016年9月5日下午5:34:24 
     * @copyright (c) 2016, heqy@finansir.nt All Rights Reserved. 
     * 
     */
    
    package club.younge.proxy.self;
    
    import java.io.File;
    import java.io.FileWriter;
    import java.io.IOException;
    import java.lang.reflect.Constructor;
    import java.lang.reflect.InvocationTargetException;
    import java.lang.reflect.Method;
    
    import javax.tools.JavaCompiler;
    import javax.tools.JavaCompiler.CompilationTask;
    import javax.tools.StandardJavaFileManager;
    import javax.tools.ToolProvider;
    
    /**
     * @className:MyProxy
     * @function: TODO ADD FUNCTION.
     * @reason: TODO ADD REASON.
     * @date: 2016年9月5日 下午5:34:24
     * @author Younge
     * @version
     * @since JDK 1.8
     * @see
     */
    public class MyProxy {
    	private static String rt = "\r\n";
    
    	@SuppressWarnings({ "rawtypes", "unchecked" })
    	public static Object newProxyInstance(ClassLoader classLoader, Class interfs,
    			MyInvocationHandler invocationHandler) {
    		try {
    			Method[] methods = interfs.getMethods();
    			
    			// 1.创建一个JAVA文件，用流的方式创建一个JAVA文件，生成JAVA文件String内容
    			String proxyClass = "package club.younge.proxy.self;" + rt + "import java.lang.reflect.Method;" + rt
    					+ "public class $Proxy0 implements " + interfs.getName() + "{" + rt + "MyInvocationHandler h;" + rt
    					+ "public $Proxy0(MyInvocationHandler h) {" + rt + "this.h = h;" + rt + "}"
    					+ getMethodStr(methods, interfs) + rt + "}";
    			
    			// 2.类生成文件
    			String fileName = "E:/GitLocal/Java/JavaProxy/JavaProxy"  //请务必注意文件路径是否正确，检查您的工程目录
    					+ "/src/club/younge/proxy/self/$Proxy0.java";
    			File file = new File(fileName);
    			FileWriter fileWriter = new FileWriter(file);
    
    			fileWriter.write(proxyClass);
    			fileWriter.flush();
    			fileWriter.close();
    			
    			// 3. 编译JAVA文件
    			JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
    			StandardJavaFileManager stdFileMgr = compiler.getStandardFileManager(null, null, null);
    			Iterable units = stdFileMgr.getJavaFileObjects(fileName);
    			CompilationTask task = compiler.getTask(null, stdFileMgr, null, null, null, units);
    			task.call();
    			stdFileMgr.close();
    			//file.delete(); //编译后可将该文件删除，造成与JDK动态代理一样的效果
    			
    			// 4.把class字节码加载到内存中  请务必注意文件路径是否正确，检查您的工程目录
    			MyClassLoader classLoader2 = new MyClassLoader("E:/GitLocal/Java/JavaProxy/JavaProxy"
    					+ "/src/club/younge/proxy/self/");
    			Class proxy0Class = classLoader2.findClass("$Proxy0");
    			Constructor constructor = proxy0Class.getConstructor(MyInvocationHandler.class);
    			Object object = constructor.newInstance(invocationHandler);
    			return object;
    		} catch (IOException e) {
    			e.printStackTrace();
    		} catch (ClassNotFoundException e) {
    			e.printStackTrace();
    		} catch (NoSuchMethodException e) {
    			e.printStackTrace();
    		} catch (SecurityException e) {
    			e.printStackTrace();
    		} catch (InstantiationException e) {
    			e.printStackTrace();
    		} catch (IllegalAccessException e) {
    			e.printStackTrace();
    		} catch (IllegalArgumentException e) {
    			e.printStackTrace();
    		} catch (InvocationTargetException e) {
    			e.printStackTrace();
    		}
    		
    		return null;
    	}
    
    	@SuppressWarnings("rawtypes")
    	private static String getMethodStr(Method[] methods, Class interfs) {
    		StringBuilder builder = new StringBuilder();
    		builder.append(rt);
    		for (Method method : methods) {
    			builder.append("public void ").append(method.getName()).append("() throws Throwable {").append(rt)
    					.append("Method md = ").append(interfs.getName()).append(".class.getMethod(\"")
    					.append(method.getName()).append("\", new Class[]{});").append(rt)
    					.append("this.h.invoke(this, md, null);").append(rt).append("}").append(rt);
    		}
    		return builder.toString();
    	}
    }

此方法主要做：

1.拼凑动态代理类的字符串

2.将上述字符串写入.java文件中

3.编译.java文件为class字节码，

4.将字节码文件加载到内存中

自定义invocationhandler接口及对应接口实现类和ClassLoader类：

/** 
     * @projectName:JavaProxy 
     * @fileName:MyInvocationHandler.java 
     * @packageName:club.younge.proxy.self 
     * @date:2016年9月5日下午5:30:26 
     * @copyright (c) 2016, heqy@finansir.nt All Rights Reserved. 
     * 
     */
    
    package club.younge.proxy.self;
    
    import java.lang.reflect.Method;
    
    /**
     * @className:MyInvocationHandler
     * @function: TODO ADD FUNCTION.
     * @reason: TODO ADD REASON.
     * @date: 2016年9月5日 下午5:30:26
     * @author Younge
     * @version
     * @since JDK 1.8
     * @see
     */
    public interface MyInvocationHandler {
    	public Object invoke(Object obj, Method method, Object[] objArray) throws Throwable;
    }

/** 
     * @projectName:JavaProxy 
     * @fileName:MyProxyHandler.java 
     * @packageName:club.younge.proxy.self 
     * @date:2016年9月5日下午5:31:06 
     * @copyright (c) 2016, heqy@finansir.nt All Rights Reserved. 
     * 
     */  
      
    package club.younge.proxy.self;
    
    import java.lang.reflect.Method;
    
    import club.younge.proxy.People;
    
    /** 
     * @className:MyProxyHandler 
     * @function: TODO ADD FUNCTION.  
     * @reason:   TODO ADD REASON. 
     * @date:     2016年9月5日 下午5:31:06
     * @author   Younge 
     * @version   
     * @since    JDK 1.8 
     * @see       
     */
    public class MyProxyHandler implements MyInvocationHandler{
    	private People people;
    	public MyProxyHandler(People people) {
    		this.people = people;
    	}
    	@Override
    	public Object invoke(Object obj, Method method, Object[] objArray) throws Throwable {
    		before();
    		people.eat();
    		after();
    		return null;
    	}
    	
    	private void before(){
    		System.out.println("Before eat you should washes hands!");
    	}
    	
    	private void after(){
    		System.out.println("After eat you should do some work!");
    	}
    
    }

/** 
     * @projectName:JavaProxy 
     * @fileName:MyClassLoader.java 
     * @packageName:club.younge.proxy.self 
     * @date:2016年9月5日下午11:35:07 
     * @copyright (c) 2016, heqy@finansir.nt All Rights Reserved. 
     * 
     */
    
    package club.younge.proxy.self;
    
    import java.io.ByteArrayOutputStream;
    import java.io.File;
    import java.io.FileInputStream;
    import java.io.FileNotFoundException;
    import java.io.IOException;
    
    /**
     * @className:MyClassLoader
     * @function: TODO ADD FUNCTION.
     * @reason: TODO ADD REASON.
     * @date: 2016年9月5日 下午11:35:07
     * @author Younge
     * @version
     * @since JDK 1.8
     * @see
     */
    public class MyClassLoader extends ClassLoader {
    
    	private File dir;
    
    	public MyClassLoader(String path) {
    		dir = new File(path);
    	}
    
    	@Override
    	protected Class<?> findClass(String name) throws ClassNotFoundException {
    		if (dir != null) {
    			File classFile = new File(dir, name + ".class");
    			if (classFile.exists()) {
    				FileInputStream fis = null;
    				try {
    					fis = new FileInputStream(classFile);
    					ByteArrayOutputStream baos = new ByteArrayOutputStream();
    					byte[] buffer = new byte[1024];
    					int len = 0;
    					while ((len = fis.read(buffer)) != -1) {
    						baos.write(buffer, 0, len);
    					}
    
    					return defineClass("club.younge.proxy.self." + name, baos.toByteArray(), 0, baos.size());
    				} catch (FileNotFoundException e) {
    					e.printStackTrace();
    				} catch (IOException e) {
    					e.printStackTrace();
    				} finally {
    					if (fis != null) {
    						try {
    							fis.close();
    						} catch (IOException e) {
    							e.printStackTrace();
    						}
    					}
    
    				}
    
    			}
    		}
    		return super.findClass(name);
    	}
    }

自定义动态代理测试类

/** 
     * @projectName:JavaProxy 
     * @fileName:SelfTest.java 
     * @packageName:club.younge.test 
     * @date:2016年9月5日下午5:38:08 
     * @copyright (c) 2016, heqy@finansir.nt All Rights Reserved. 
     * 
     */  
      
    package club.younge.test;
    
    import club.younge.proxy.Jason;
    import club.younge.proxy.People;
    import club.younge.proxy.self.MyProxy;
    import club.younge.proxy.self.MyProxyHandler;
    
    /** 
     * @className:SelfTest 
     * @function: TODO ADD FUNCTION.  
     * @reason:   TODO ADD REASON. 
     * @date:     2016年9月5日 下午5:38:08
     * @author   Younge 
     * @version   
     * @since    JDK 1.8 
     * @see       
     */
    public class SelfTest {
    
    	public static void main(String[] args) throws Throwable {
    		People people = (People) MyProxy.newProxyInstance(People.class.getClassLoader(), People.class, new MyProxyHandler(new Jason()));
    		people.eat();
    		System.out.println("Game over!");
    
    	}
    
    }

测试结果：

Before eat you should washes hands!  
Jason is eating now.  
After eat you should do some work!  
Game over!

与JDK动态代理效果类似。