动态代理：为一堆interface或类的实现提供统一的执行通道，从含义上就像局域网电脑通过代理上网一样，走统一的通道，代理控制通道，自然可以在通道里加上自定义实现，例如像AOP切面，日志等。
JDK的动态代理只能对接口实现，代理类需要实现InvocationHandler 接口。
一、接口
public interface UserService {
User addUser();
void editUser(User user);
int deleteUser(int userId); } //假设有这么一个User类 public class User { private Integer userId; private String userName; private String password; public Integer getUserId() { return userId; } public void setUserId(Integer userId) { this.userId = userId; } public String getUserName() { return userName; } public void setUserName(String userName) { this.userName = userName; } public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } @Override public String toString() { return "User{" + "userId=" + userId + ", userName='" + userName + '\'' + ", password='" + password + '\'' + '}'; } }
二、接口的实现
public class UserServiceImpl implements UserService {
@Override
public User addUser() { User user = new User(); user.setUserId(1); user.setUserName("userTest"); user.setPassword("123456"); System.out.println("------> add user"); return user; } @Override public void editUser(User user) { System.out.println("------> edit user:" +user); } @Override public int deleteUser(int userId) { System.out.println("------> delete user:"+userId); return 1; } }
三、JDK代理类实现InvocationHandler
public class ProxyHandler implements InvocationHandler {
//被代理对象 private Object proxied; public ProxyHandler(Object proxied) { this.proxied = proxied; } private void beforeInvoke(String msg) { System.out.println("-------> beforInvoke:"+msg); } private void afterInvoke(String msg) { System.out.println("-------> afterInvoke:"+msg); } private String convertArgs(Object[] args) { if(args==null || args.length==0) { return null; } StringBuilder sb= new StringBuilder(); for(Object object : args) { sb.append(object.toString()); } return sb.toString(); } //proxy是代理对象，可以想象成代理服务器 //proxied是被代理对象，可以想象成局域网里的PC @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { beforeInvoke("proxy name:"+proxy.getClass().getName()); beforeInvoke("proxied name:"+proxied.getClass().getName()); beforeInvoke( "args:"+convertArgs(args)); Object o = method.invoke(proxied,args); afterInvoke("result:"+o); return o; } }
四、使用，实现原理是反射
public class Main {
public static void main(String[] args) { UserService userService = new UserServiceImpl(); UserService proxyUserService = (UserService) Proxy.newProxyInstance( UserService.class.getClassLoader(), new Class[]{UserService.class}, new ProxyHandler(userService) ); User user = proxyUserService.addUser(); proxyUserService.editUser(user); proxyUserService.deleteUser(user.getUserId()); } }
五、结果：符合预期的输出
六、简化一下写法，代理类的生成方式
public class DynamicProxy implements InvocationHandler {
private Object proxied; private void beforeInvoke(String msg) { System.out.println("-------> beforInvoke:"+msg); } private void afterInvoke(String msg) { System.out.println("-------> afterInvoke:"+msg); } private String convertArgs(Object[] args) { if(args==null || args.length==0) { return null; } StringBuilder sb= new StringBuilder(); for(Object object : args) { sb.append(object.toString()); } return sb.toString(); }
//在这里就把代理对象创建出来 public Object getProxyObject(Object proxied) { this.proxied = proxied; return Proxy.newProxyInstance( this.proxied.getClass().getClassLoader(), this.proxied.getClass().getInterfaces(), this ); } @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { beforeInvoke("proxy name:"+proxy.getClass().getName()); beforeInvoke("proxied name:"+proxied.getClass().getName()); beforeInvoke( "args:"+convertArgs(args)); Object o = method.invoke(proxied,args); afterInvoke("result:"+o); return o; } } //main public class Main { public static void main(String[] args) { System.out.println("##############"); System.out.println("-------> second call:"); UserService userService = (UserService) new DynamicProxy().getProxyObject(new UserServiceImpl()); User user1 = userService.addUser(); userService.editUser(user1); userService.deleteUser(user1.getUserId()); } }
六、使用cglib动态代理
cglib可以代理非接口类，但是因为其实现原理是继承，所以无法代理被代理类中final方法，也无法代理final修饰的类。
代理类需要实现MethodInterceptor 接口
<dependencies>
<dependency>
<groupId>cglib</groupId>
<artifactId>cglib</artifactId>
<version>3.2.8</version>
</dependency>
</dependencies>
public class CglibDynamicProxy implements MethodInterceptor {
private Object proxied; //Generate a new class if necessary and uses the specified callbacks (if any) to create a new object instance. //Uses the no-arg constructor of the superclass. //动态生成一个新的类，使用父类的无参构造方法创建一个指定了特定回调的代理实例 public Object getProxyObject(Object proxied) { this.proxied = proxied; //增强器，动态代码生成器 Enhancer enhancer = new Enhancer(); //回调方法 enhancer.setCallback(this); //设置生成类的父类类型 enhancer.setSuperclass(proxied.getClass()); //动态生成字节码并返回代理对象 return enhancer.create(); } public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable { beforeInvoke("Object:"+o.getClass().getName()); beforeInvoke("method:"+method.getName()); beforeInvoke("args:"+convertArgs(objects)); beforeInvoke("methodProxy:"+methodProxy.getSignature()); Object result = methodProxy.invoke(this.proxied,objects); afterInvoke("result:"+result); return result; } private void beforeInvoke(String msg) { System.out.println("-------> beforInvoke:"+msg); } private void afterInvoke(String msg) { System.out.println("-------> afterInvoke:"+msg); } private String convertArgs(Object[] args) { if(args==null || args.length==0) { return null; } StringBuilder sb= new StringBuilder(); for(Object object : args) { sb.append(object.toString()); } return sb.toString(); } }
main:
public class Main {
public static void main(String[] args) { System.out.println("##############"); System.out.println("-------> 4 call:"); UserService service4 = (UserService)new CglibDynamicProxy().getProxyObject(new UserServiceImpl()); User user4 = service4.addUser(); service4.editUser(user4); service4.deleteUser(user4.getUserId()); } }