代理模式

概念

中介，就是为一个实际业务对象提供控制处理的代理。

角色

• 抽象对象
• 业务处理对象
• 代理对象

分类

• 静态代理
• 动态代理

demo

// 代理类和业务类需要共同实现的接口
public interface Person {
    public void tollage();
}

//被代理的业务类
public class Employee implements Person {
    @Override
    public void tollage() {
        System.out.println("员工上缴个税");
    }
}

静态代理的实现方式

//代理对象
public class EmployeeProxy implements Person {
    private Employee  employee;
    public EmployeeProxy(Employee employee) {
        super();
        this.employee = employee;
    }
    @Override
    public void tollage() {
        System.out.println("代理上缴个税begin");
        employee.tollage();
        System.out.println("代理上缴个税end");
    }
}

//测试类
public class StaticProxyTest {
    public static void main(String[] args) {
        Employee employee = new Employee();
        EmployeeProxy employeeProxy = new EmployeeProxy(employee);
        employeeProxy.tollage();
    }
}

动态代理的实现方式

JDK proxy：代理类必须实现接口

// 动态代理类
public class EmployeeInvocationHandler implements InvocationHandler {   
    private Object target;
    public EmployeeInvocationHandler(Object target) {
        super();
        this.target = target;
    }
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
            System.out.println("代理执行" +method.getName() + "方法");
            Object result = method.invoke(target, args);
            return result;
    }
}

//测试类
public class DynamicProxyTest {
    public static void main(String[] args) {
        Employee employee = new Employee();
        EmployeeInvocationHandler employeeInvocationHandler = new EmployeeInvocationHandler(employee);
        Person person = (Person) Proxy.newProxyInstance(Person.class.getClassLoader(), new Class[] {Person.class} , employeeInvocationHandler);
        person.tollage();;
    }
}

CGLIB: 代理类不能是final,代理的方法也不能是final（继承限制）

public class CglibProxy implements MethodInterceptor {
    /* (非 Javadoc) 
    * <p>Title: intercept</p> 
    * <p>Description: </p> 
    * @param  代理对象
    * @param 拦截的方法
    * @param 方法的参数
    * @param JDK的java.lang.reflect.Method类的代理类
    * @return
    * @throws Throwable 
    * @see net.sf.cglib.proxy.MethodInterceptor#intercept(java.lang.Object, java.lang.reflect.Method, java.lang.Object[], net.sf.cglib.proxy.MethodProxy) 
    */
    @Override
    public Object intercept(Object obj, Method method, Object[] arg2, MethodProxy methodProxy) throws Throwable {
        return  methodProxy.invokeSuper(obj, arg2);
    }
}

//测试类
public class CglibProxyTest {
    public static void main(String[] args) {
        CglibProxy cglibProxy = new CglibProxy();
        
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(Employee.class);
        enhancer.setCallback(cglibProxy);
        
        Person person = (Person)enhancer.create();
        person.tollage();
    }
}