java的动态代理如何实现

一. JdkProxy

jdkproxy动态代理必须基于接口(interface)实现

1. 接口UserInterface.java

public interface UserService {String getUserName(String userCde);
}

1. 原始实现类：UseServiceImpl.java

public class UserServiceImpl implements UserSerice {@Overridepublic String getUserName(String userCde) {System.out.println("the name of " + userCde + "is Austin");return "Austin";}
}

1. 代理类 ：UserProxyFactoryBJdk.java

public class UserProxyFactoryBJdk {public static UserService getUserServiceProxy(UserService origin) {UserService userService = (UserService) Proxy.newProxyInstance(UserService.class.getClassLoader(), new Class[]{UserService.class}, new InvocationHandler() { //动态代理实现类@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {System.out.println("before");Object o = method.invoke(origin, args);System.out.println("after");return o;}});return userService;}public static void main(String[] args) {UserService userService = getUserServiceProxy(new UserServiceImpl());userService.getUserName("123");}
}

执行结果：
before
the name of 123is Austin
after

二. Cglib动态代理

Cglib实现动态代理与JdkProxy不同， 是通过构建继承类实现

1. 原始类UseServiceImpl.java

public class UserServiceImpl implements UserSerice {@Overridepublic String getUserName(String userCde) {System.out.println("the name of " + userCde + "is Austin");return "Austin";}
}

1. 代理类 ：UserProxyFactoryByCglib.java

public static UserServiceImpl getUserServiceProxy(UserService origin) {Enhancer enhancer = new Enhancer();// 设置debug信息System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "/home/aa/dev/testfile/com/austin/meta/cxf/");// 设置父类：UserServiceImplenhancer.setSuperclass(UserServiceImpl.class);//设置代理实现逻辑enhancer.setCallback(new CglibInterCeptor() {public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {System.out.println("CglibInterCeptor.intercept-before");Object o = proxy.invokeSuper(obj, args);System.out.println("CglibInterCeptor.intercept-after");return o;}});UserServiceImpl userService = ((UserServiceImpl) enhancer.create());return userService;}public static void main(String[] args) {UserService userService = getUserServiceProxy(new UserServiceImpl());userService.getUserName("123");}

1. 执行结果
   CglibInterCeptor.intercept-before
   the name of 123is Austin
   CglibInterCeptor.intercept-after

三. Java动态编译

通过JavaCompiler动态编译java源文件，并将相应字节码加载到JVM中，其编译底层通过javac -d 命令进行编译

1. 需要动态编译的类文件

package com.austin.meta.dynamiccompiler;
public class UserServiceImplE extends UserServiceImpl {public UserServiceImplE() {}public String getUserName(String userCde) {System.out.println("before");super.getUserName(userCde);System.out.println("after");return "Austin";}
}

1. 动态编译类

public class JavaCompilerTest {private static String basePath = "";public static void main(String[] args) throws Exception{System.out.println(ClassLoader.getSystemResource(""));Class<?> userServiceImplE = compiler("UserServiceImplE");UserServiceImpl o = (UserServiceImpl)userServiceImplE.getConstructor(null).newInstance(null);o.getUserName("235");}private static Class<?> getClass(String pakcge, String className) {Class<?> clazz = null;try {clazz = Class.forName(pakcge + "." +className, true, JavaCompilerTest.class.getClassLoader());} catch (ClassNotFoundException e) {e.printStackTrace();}return clazz;}/*** 动态编译java类，并通加载到JVM*/
private static Class<?> compiler(String className) throws IOException {File javaSrcFile = new File(basePath+ "/" + className + ".java");JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();StandardJavaFileManager standardFileManager = compiler.getStandardFileManager(null, null, null);List<String> options = Arrays.asList("-d", ClassLoader.getSystemResource("").toString());JavaCompiler.CompilationTask task = compiler.getTask(null, standardFileManager, null, options, null, standardFileManager.getJavaFileObjects(javaSrcFile));Boolean isCompilerSuccess = task.call();if(!isCompilerSuccess) {return null;}Class<?> clazz = getClass("com.austin.meta.dynamiccompiler", className);return clazz;}
}

1. 执行结果
   before
   the name of 235is Austin
   after