688笔记

反射

/**
 * 反射
 */
public class Test {
    public static ReflectServiceImpl getInstance(){
        ReflectServiceImpl obj = null;
        try {
            //getConstructor 获取构造函数
            //newInstance 实例化
            obj = (ReflectServiceImpl) Class.forName("proxy.demo.ReflectServiceImpl").getConstructor(String.class).newInstance("张三");

        } catch (Exception e) {
            e.printStackTrace();
        }
        return obj;
    }
    public static void main(String[] args){
        ReflectServiceImpl instance = getInstance();
        instance.sayHello();
    }
}

动态代理：略

• jdk implements InvocationHandler
• cglib implements MethodInterceptor

jdk动态代理实现拦截器

public interface Interceptor {
    public boolean before(Object proxy, Object target, Method method, Object[] args);

    public void around(Object proxy, Object target, Method method, Object[] args);

    public void after(Object proxy, Object target, Method method, Object[] args);
}

public class MyInterceptor implements Interceptor {
    @Override
    public boolean before(Object proxy, Object target, Method method, Object[] args) {
        System.out.println("反射before...");
        return true;//返回true执行原有方法
    }

    @Override
    public void around(Object proxy, Object target, Method method, Object[] args) {
        System.out.println("不执行原有方法，执行代理方法");
    }

    @Override
    public void after(Object proxy, Object target, Method method, Object[] args) {
        System.out.println("反射after...");
    }
}

public class InterceptorJdkProxy implements InvocationHandler {
    private Object target;
    private String interceptorClass = null;

    public InterceptorJdkProxy(Object target,String interceptorClass){
        this.target = target;
        this.interceptorClass = interceptorClass;
    }

    public static Object getInstance(Object target,String interceptorClass){
        return Proxy.newProxyInstance(
                target.getClass().getClassLoader(),
                target.getClass().getInterfaces(),
                new InterceptorJdkProxy(target,interceptorClass));
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        if (interceptorClass==null){
            //没有拦截器，执行原有方法
            return method.invoke(target,args);
        }
        Object result = null;
        Interceptor interceptor = (Interceptor) Class.forName(interceptorClass).newInstance();
        if (interceptor.before(proxy,target,method,args)){
            //执行原有方法
            result = method.invoke(target,args);
        }else {
            //执行拦截方法
            interceptor.around(proxy,target,method,args);
        }
        interceptor.after(proxy,target,method,args);
        return result;
    }
}

public class Test {
    public static void main(String[] args){
        Inter inter = (Inter) InterceptorJdkProxy.getInstance(new Boss(),"proxy.Interceptor.MyInterceptor");
        inter.findPerson();
    }
}

观察者模式实例：通过java.util.Observer实现

import java.util.ArrayList;
import java.util.List;
import java.util.Observable;
import java.util.Observer;

public class ProductList extends Observable {
    private List<String> productList = null;
    private static ProductList instance;
    private ProductList(){}

    public static ProductList getInstance(){
        if (instance == null){
            instance = new ProductList();
            instance.productList = new ArrayList<>();
        }
        return instance;
    }

    public void addProductListObserver(Observer observer){
        this.addObserver(observer);
    }
    public void addProduct(String newProduct){
        productList.add(newProduct);
        System.out.println("新增产品"+newProduct);
        this.setChanged();//设置被观察对象发生变化
        this.notifyObservers(newProduct);//通知观察者
    }
}

import java.util.Observable;
import java.util.Observer;

public class Observer1 implements Observer {
    @Override
    public void update(Observable o, Object arg) {
        String newProduct = (String) arg;
        System.out.println("有新产品了:"+newProduct);
    }
}

public class Test {
    public static void main(String[] args){
        ProductList instance = ProductList.getInstance();
        Observer1 observer1 = new Observer1();
        Observer2 observer2 = new Observer2();
        instance.addProductListObserver(observer1);
        instance.addProductListObserver(observer2);
        instance.addProduct("新增xxx");
    }
}