java常见的设计模式

1、单例模式（为什么说这个很重要，面试时有、框架思想中也经常出现）

//双重检查
public class TestSingleTon {
    public static TestSingleTon testSingleTon=null;
    
    private TestSingleTon() {
        
    }
    public  static TestSingleTon  getInstance() {
        if(testSingleTon==null) {
            synchronized (TestSingleTon.class) {
                if(testSingleTon==null) {
                    testSingleTon=new TestSingleTon();
                }
            }            
        }
        return testSingleTon;
    }

}

2、代理模式

懵逼中。懵逼树下你和我。。。

代理模式其实很简单，就是中介公司。你需要得到目标对象，得靠代理对象获得。然后这个代理对象还可以帮你做其他的事。就像中介代替租客找房源，房间卫生、合同、物业都给

解决了。

关键点：代理对象是对目标对象的一个扩展，并会调用目标对象。

（1）静态代理 

public interface Excute {
    public void excute(); 
}


public class Target implements Excute{

    @Override
    public void excute() {
        System.out.println("目标方法被调用了！！！");
    }

}


public class StaticProxy implements Excute{
     
    public Excute excute;
    public StaticProxy(Excute excute) {
        this.excute=excute;
    }
    @Override
    public void excute() {
        System.out.println("目标方法执行之前！！！");
        excute.excute();
        System.out.println("目标方法执行之后！！！");
    }

}

public class Test {
    public static void main(String[] args) {
        StaticProxy staticProxy=new StaticProxy(new Target());
        staticProxy.excute();
    }

}

  (2)动态代理

public interface Excute {
    public void excute(); 
}

public class Target implements Excute{

    @Override
    public void excute() {
        System.out.println("目标方法被调用了！！！");
    }

}

public class DynamicProxy {
    private Object object;
    public DynamicProxy(Object object) {
        this.object=object;
    }
    public Object  getProxyInstance() {
         Object proxyInstance=Proxy.newProxyInstance(object.getClass().getClassLoader(), object.getClass().getInterfaces(),
                new InvocationHandler() {                
                    @Override
                    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                        // TODO Auto-generated method stub]
                        System.out.println("目标方法调用之前！！！");
                        Object invoke = method.invoke(object, args);
                        System.out.println("目标方法调用之后！！！");
                        return invoke;
                    }
                });
         return proxyInstance;
    }

}


public class Test {
    public static void main(String[] args) {       
        Excute proxyInstance = (Excute) new DynamicProxy(new Target()).getProxyInstance();
        proxyInstance.excute();
        
    }

}

  （3）Cglib代理 

public interface Excute {
    public void excute(); 
}


public class Target implements Excute{

    @Override
    public void excute() {
        System.out.println("目标方法被调用了！！！");
    }

}

public class CglibProxy implements MethodInterceptor{
    private Object object;
    public CglibProxy(Object object) {
        this.object=object;
    }
    
    public Object getCglibProxyInstance() {
        Enhancer enhancer=new Enhancer();
        enhancer.setSuperclass(object.getClass());
        enhancer.setCallback(this);
        return enhancer.create();
    }
    @Override
    public Object intercept(Object arg0, Method arg1, Object[] arg2, MethodProxy arg3) throws Throwable {
        // TODO Auto-generated method stub
        System.out.println("目标方法被调用之前！！！");
        Object returnVal = arg1.invoke(object, arg2);
        System.out.println("目标方法被调用之后！！！");
        return returnVal;
    }

}


public class Test {
    public static void main(String[] args) {        
        Excute cglibProxy=(Excute) new CglibProxy(new Target()).getCglibProxyInstance();
        cglibProxy.excute();
    }

}