设计模式之职责链模式

工作中最喜欢的事情就是加薪了，但获得加薪可不容易，得经过层层审核。下面来代码模拟一下。

请求类

public class Request {
    private String requestType;
    private String requestContent;
    private int number;
    public String getRequestType() {
        return requestType;
    }
    public void setRequestType(String requestType) {
        this.requestType = requestType;
    }
    public String getRequestContent() {
        return requestContent;
    }
    public void setRequestContent(String requestContent) {
        this.requestContent = requestContent;
    }
    public int getNumber() {
        return number;
    }
    public void setNumber(int number) {
        this.number = number;
    }
}

public class Manager {
    protected String name;
    public Manager(String name){
        this.name = name;
    }
    public void getResult(String managerLevel, Request request){
        if(managerLevel.equals("经理")){
            if(request.getRequestType().equals("请假") && request.getNumber() <=2){
                System.out.println(name + " : " + request.getRequestContent() + "数量 " +request.getNumber() + " 被批准");
            }else{
                System.out.println(name + " : " + request.getRequestContent() + "数量 " +request.getNumber() + " 我无权处理");
            }
        }else if(managerLevel.equals("总监")){
            if(request.getRequestType().equals("请假") && request.getNumber() <=5){
                System.out.println(name + " : " + request.getRequestContent() + "数量 " +request.getNumber() + " 被批准");
            }else{
                System.out.println(name + " : " + request.getRequestContent() + "数量 " +request.getNumber() + " 我无权处理");
            }
        }else if(managerLevel.equals("总经理")){
            if(request.getRequestType().equals("请假")){
                System.out.println(name + " : " + request.getRequestContent() + "数量 " +request.getNumber() + " 被批准");
            }else if(request.getRequestType().equals("加薪") && request.getNumber() <=500){
                System.out.println(name + " : " + request.getRequestContent() + "数量 " +request.getNumber() + " 被批准");
            }else if(request.getRequestType().equals("加薪") && request.getNumber() > 500){
                System.out.println(name + " : " + request.getRequestContent() + "数量 " +request.getNumber() + " 再说吧");
            }
        }
    }
}

public class Test {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Manager m1 = new Manager("zhangsan");
        Manager m2 = new Manager("lisi");
        Manager m3 = new Manager("wangmazi");
        //加薪请求
        Request request = new Request();
        request.setRequestType("加薪");
        request.setRequestContent("xiaohe请求加薪");
        request.setNumber(600);
        
        m1.getResult("经理", request);
        m2.getResult("总监", request);
        m3.getResult("总经理", request);
        //请假请求
        Request request2 = new Request();
        request2.setRequestType("请假");
        request2.setRequestContent("xiaohe打算请假");
        request2.setNumber(3);
        
        m1.getResult("经理", request2);
        m2.getResult("总监", request2);
        m3.getResult("总经理", request2);
    }

}

可以发现，管理者类中的getResult方法中有太多的分支判断，是非常不好的设计。如果要增加其他管理者，那就需要更改这个类，这个类承担了太多的责任，违背了单一职责原则和开放封闭原则。那如何重构呢？

职责链模式：使多个对象都有机会处理请求，从而避免请求发送者和请求接收者之间的耦合关系。将这个对象连城一条链，并沿着这条链传递该请求，直到有一个对象处理它为止。

下面重构一下上面的代码：

public abstract class Manager1 {
    protected String name;
    protected Manager1 superior;
    public Manager1(String name){
        this.name = name;
    }
    public void setSuperior(Manager1 manager){
        this.superior = manager;
    }
    public abstract void requestApplications(Request request);
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Manager1 getSuperior() {
        return superior;
    }
}

public class CommonManager extends Manager1{
    public CommonManager(String name){
        super(name);
    }

    @Override
    public void requestApplications(Request request) {
        // TODO Auto-generated method stub
        if(request.getRequestType().equals("请假") && request.getNumber() <= 2){
            System.out.println(name + " : " + request.getRequestContent() + "数量 " +request.getNumber() + " 被批准");
        }else{
            if(superior != null){
                superior.requestApplications(request);
            }
        }
    }
}

public class Majordomo extends Manager1{
    public Majordomo(String name){
        super(name);
    }

    @Override
    public void requestApplications(Request request) {
        // TODO Auto-generated method stub
        if(request.getRequestType().equals("请假") && request.getNumber() <= 5){
            System.out.println(name + " : " + request.getRequestContent() + "数量 " +request.getNumber() + " 被批准");
        }else{
            if(superior != null){
                superior.requestApplications(request);
            }
        }
    }
}

public class GeneralManager extends Manager1{
    public GeneralManager(String name){
        super(name);
    }

    @Override
    public void requestApplications(Request request) {
        // TODO Auto-generated method stub
        if(request.getRequestType().equals("请假")){
            System.out.println(name + " : " + request.getRequestContent() + "数量 " +request.getNumber() + " 被批准");
        }else if(request.getRequestType().equals("加薪") && request.getNumber() <= 500){
            System.out.println(name + " : " + request.getRequestContent() + "数量 " +request.getNumber() + " 被批准");
        }else if(request.getRequestType().equals("加薪") && request.getNumber() > 500){
            System.out.println(name + " : " + request.getRequestContent() + "数量 " +request.getNumber() + " 再说吧");
        }
    }
}

public class Test3 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        CommonManager jinli = new CommonManager("jinli");
        Majordomo zongjian = new Majordomo("zongjian");
        GeneralManager zongjinli = new GeneralManager("zongjinli");
        jinli.setSuperior(zongjian);
        zongjian.setSuperior(zongjinli);
        
        Request request = new Request();
        request.setRequestType("加薪");
        request.setRequestContent("xiaohe请求加薪");
        request.setNumber(300);
        jinli.requestApplications(request);
        System.out.println("---------------------------");
        Request request2 = new Request();
        request2.setRequestType("请假");
        request2.setRequestContent("xiaohe打算请假");
        request2.setNumber(10);
        zongjian.requestApplications(request2);
    }

}

这就很好的解决了大量的分支判断造成难维护、灵活性差的问题。我们可以随时增加或修改处理一个请求的结构，增强了给对象指派职责的灵活性。不过也要担心，一个请求极有可能到了链的末端也得不到处理，或者因为没有正确配置而得不到处理，这就糟糕了，所以得考虑全面。