用最简单的例子说明设计模式（三）之责任链、建造者、适配器、代理模式、享元模式

public class Chain {

    public abstract class Handler {
        private Handler nextHandler;
        // 当前领导能审批通过的最多天数
        public int maxDay;

        protected Handler(int maxDay) {
            this.maxDay = maxDay;
        }

        //设置责任链中下一个处理请求的对象
        public void setNextHandler(Handler handler) {
            nextHandler = handler;
        }

        protected void handleRequest(int day) {
            if (day <= maxDay) {
                reply(day);
            } else {
                if (nextHandler != null) {
                    //审批权限不够，继续上报
                    nextHandler.handleRequest(day);
                } else {
                    System.out.println("没有更高的领导审批了");
                }
            }
        }

        protected abstract void reply(int day);
    }

    class ProjectManager extends Handler {
        public ProjectManager(int day) {
            super(day);
        }

        @Override
        protected void reply(int day) {
            System.out.println(day + "天请假，项目经理直接审批通过");
        }
    }

    class DepartmentManager extends Handler {
        public DepartmentManager(int day) {
            super(day);
        }

        @Override
        protected void reply(int day) {
            System.out.println(day + "天请假，部门经理审批通过");
        }
    }

    class GeneralManager extends Handler {
        public GeneralManager(int day) {
            super(day);
        }

        @Override
        protected void reply(int day) {
            System.out.println(day + "天请假，总经理直接审批通过");
        }
    }

    public static void main(String[] strings) {
        Chain chain = new Chain();
        Handler projectManager = chain.new ProjectManager(3);
        Handler departmentManager = chain.new DepartmentManager(5);
        Handler generalManager = chain.new GeneralManager(15);
        //创建职责链
        projectManager.setNextHandler(departmentManager);
        departmentManager.setNextHandler(generalManager);
        //发起请假请求
        projectManager.handleRequest(4);
    }
}

/**
 * subject（抽象主题角色）：
 * 真实主题与代理主题的共同接口。
 */
interface Subject {
    void sellBook();
}

/**
 * ReaISubject（真实主题角色）：
 * 定义了代理角色所代表的真实对象。
 */
public class RealSubject implements Subject {
    @Override
    public void sellBook() {
        System.out.println("出版社卖书");
    }
}

/**
 * Proxy（代理主题角色）：
 * 含有对真实主题角色的引用，代理角色通常在将客
 * 户端调用传递给真实主题对象之前或者之后执行某些
 * 操作，而不是单纯返回真实的对象。
 */
public class ProxySubject implements Subject {

    private RealSubject realSubject;

    @Override
    public void sellBook() {
        if (realSubject == null) {
            realSubject = new RealSubject();
        }
        sale();
        realSubject.sellBook();
        give();
    }

    public void sale() {
        System.out.println("打折");
    }

    public void give() {
        System.out.println("送优惠券");
    }
}

public class Main {
    public static void main(String[] args) {
        //静态代理（我们自己静态定义的代理类)
        ProxySubject proxySubject = new ProxySubject();
        proxySubject.sellBook();

        //动态代理(通过程序动态生成代理类，该代理类不是我们自己定义的。而是由程序自动生成)
        RealSubject realSubject = new RealSubject();
        MyHandler myHandler = new MyHandler();
        myHandler.setProxySubject(realSubject);
        Subject subject = (Subject) Proxy.newProxyInstance(realSubject.getClass().getClassLoader(),
                realSubject.getClass().getInterfaces(), myHandler);
        subject.sellBook();

    }
}

public class MyHandler implements InvocationHandler {
    private RealSubject realSubject;

    public void setProxySubject(RealSubject realSubject) {
        this.realSubject = realSubject;
    }

    /**
     * @param proxy  　指代我们所代理的那个真实对象
     * @param method   指代的是我们所要调用真实对象的某个方法的Method对象
     * @param args   　指代的是调用真实对象某个方法时接受的参数
     * @return
     * @throws Throwable
     */
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        sale();
        proxy = method.invoke(realSubject, args);
        give();
        return proxy;
    }

    public void sale() {
        System.out.println("打折");
    }

    public void give() {
        System.out.println("送优惠券");
    }
}