Java 设计模式-责任链模式

需求分析:
一个公司的审批流程是层层递进的. 假设现在你有一个请假的请求, 请假两天及以内经理同意就可以了, 请假五天及以内需要总监同意, 请假大于五天需要总经理同意.

/**
 * 请求
 */
public class Request {
    public static final String REQUEST_TYPE_DAY_OFF = "day_off";
    private String requestType;
    private String int number;
    
    public void setRequestType(String requestType) {
        this.requestType = requestType;
    }
    
    public String getRequestType() {
        return this.requestType;
    }
    
    public void setNumber(int number) {
        this.number = number;
    }
    
    public int getNumber() {
        return this.number;
    }
}

/**
 * 管理者
 */
public class Manager {
    private String name;
    
    public Manager(String name) {
        this.name = name;
    }
    
    public void getResult(String managerLevel, Request request) {
        if (managerLevel == "经理") {
            if (request.getRequestType() == Request.REQUEST_TYPE_DAY_OFF && request.getNumber() <= 2) {
                System.out.println(String.format("%s同意请假, 请假天数为%d", this.name, request.getNumber()));
            } else {
                System.out.println(String.format("请假天数大于两天, %s无权处理", this.name));
            }
        } else if (managerLevel == "总监") {
            if (request.getType() ==  Request.REQUEST_TYPE_DAY_OFF && request.getNumber() <= 5) {
                System.out.println(String.format("%s同意请假, 请假天数为%d", this.name, request.getNumber()));
            } else {
                System.out.println(String.format("请假天数大于两天, %s无权处理", this.name));
            }
        } else if (managerLevel == "总经理") {
            if (request.getRequestType() ==  Request.REQUEST_TYPE_DAY_OFF) {
                 System.out.println(String.format("%s同意请假, 请假天数为%d", this.name, request.getNumber()));
            }
        }
    }
}

public class Client {
    public static void main(String[] args) {
        Manager commonManager = new Manager("王经理");
        Manager majordomo = new Manager("李总监");
        Manager generalManager = new Manager("周总经理");
        Request request = new Request(Request.REQUEST_TYPE_DAY_OFF);
        commonManager.getResult(request);
        majordomo.getResult(request);
        generalManager.getResult(request);
    }
}

现在存在的问题是所有处理的判断都是在Manager#getResult()方法里面进行的. 如果需要增加审批中间人, 就需要对Manager#getResult()方法进行改动. 采用职责链对审批处理进行改动, 让审批流程形成一条审批链.

/**
 * 抽象的管理者类
 */
public abstract class Manager {
    protected String name;
    protected Manager superior;
    
    public Manager(String name) {
        this.name = name;
    }
    
    public void setSuperior(Manager superior) {
        this.superior = superior;
    }
    
    public abstract void handleRequest(Request request);
}

/**
 * 经理
 */
public class CommonManager extends Manager {
    public CommonManager(String name) {
        super(name);
    }
    
    @Override
    public void handleRequest(Request request) {
        if (request.getRequestType() == Request.REQUEST_TYPE_DAY_OFF && request.getNumber() <= 2) {
            System.out.println(String.format("%s同意请假, 请假天数为%d", this.name, request.getNumber()));
        } else {
            if (superior != null) {
                superior.handleRequest(request);
            }
        }
    }
}

/**
 * 总监
 */
public class Majordomo extends Manager {
    
    public Majordomo(String name) {
        super(name);
    }
    
    @Override
    public void handleRequest(Request request) {
        if (request.getRequestType() == Request.REQUEST_TYPE_DAY_OFF && request.getNumber() <= 5) {
            System.out.println(String.format("%s同意请假, 请假天数为%d", this.name, request.getNumber()));
        } else {
            if (superior != null) {
                superior.handleRequest(request);
            }
        }
    }
}

/**
 * 总经理
 */
public class GeneralManager extends Manager {
    
    public GeneralManager(String name) {
        super(name);
    }
    
    @Override
    public void handleRequest(Request request) {
        if (request.getRequestType() == Request.REQUEST_TYPE_DAY_OFF) {
            System.out.println(String.format("%s同意请假, 请假天数为%d", this.name, request.getNumber()));
        }
    }
}

public class Client {
    public static void main(String[] args) {
        Manager commonManager = new Manager("王经理");
        Manager majordomo = new Manager("李总监");
        Manager generalManager = new Manager("周总经理");
        // 这里上级是可以动态设置的, 可以根据需求调整
        commonManager.setSuperior(majordomo);
        majordomo.setSuperior(generalManager);
        Request request = new Request(Request.REQUEST_TYPE_DAY_OFF);
        // 这里只需要调用一次方法, 整个需要就会沿着责任连进行传递
        commonManager.handleRequest(request);
    }
}

责任连模式的定义:
Avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request.Chain the receiving objects and pass the request along the chain util an object handle it(使多个对象都有机会处理请求, 从而避免了请求的发送者和接受者之间的耦合关 系. 将这些对象连成一条链, 并沿着这条链传递该请求， 直到有对象处理它为止).

责任连模式的应用: javax.servlet.Filter#doFilter() 方法

参考:
[1] : Java 库中的设计模式
[2] : 设计模式之禅
[3] : Head First 设计模式
[4] : 大话设计模式