设计模式——职责链模式

职责链模式

使多个对象都有机会处理请求，从而避免请求的发送者和接收者之间的耦合关系。将这个对象练成一条链，并沿着这条链传递该请求，知道有一个对象处理它为止

职责链模式解决什么问题？

如请假请求需要主管、经理、总经理批准

public class Request {private String type;private String content;private int number;public String getType() {return type;}public void setType(String type) {this.type = type;}public String getContent() {return content;}public void setContent(String content) {this.content = content;}public int getNumber() {return number;}public void setNumber(int number) {this.number = number;}
}

创建类处理请求

public class Manager {protected String name;public Manager(String name) {this.name = name;}public void getResult(Request request) {if (name.equals("主管")) {if (request.getNumber() <= 2) {System.out.println(name + "批准" + request.getContent() + "," + request.getType() + request.getNumber() + "天");} else {System.out.println(name + "无权处理");}} else if (name.equals("经理")) {if (request.getNumber() <= 5) {System.out.println(name + "批准" + request.getContent() + "," + request.getType() + request.getNumber() + "天");} else {System.out.println(name + "无权处理");}} else if (name.equals("总经理")) {System.out.println(name + "批准" + request.getContent() + "," + request.getType() + request.getNumber() + "天");}}
}

当提出请求时

Request request = new Request();
request.setContent("家里有事");
request.setType("请假");
request.setNumber(10);Manager manager = new Manager("主管");
manager.getResult(request);
Manager director = new Manager("经理");
director.getResult(request);
Manager generalDirector = new Manager("总经理");
generalDirector.getResult(request);

• problem1：分支判断过长
• problem2：当新增新的管理类别时，都要更改类

职责链模式实现

创建管理者类

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 requestApplications(Request request);
}

创建职责链处理请求

class CommonManager extends Manager {public CommonManager(String name) {super(name);}@Overridepublic void requestApplications(Request request) {if (request.getNumber() <= 2) {System.out.println(name + "批准" + request.getContent() + "," + request.getType() + request.getNumber() + "天");} else {System.out.println(name + "无权处理");if (superior != null) {superior.requestApplications(request);}}}
}class Direct extends Manager {public Direct(String name) {super(name);}@Overridepublic void requestApplications(Request request) {if (request.getNumber() <= 5) {System.out.println(name + "批准" + request.getContent() + "," + request.getType() + request.getNumber() + "天");} else {System.out.println(name + "无权处理");if (superior != null) {superior.requestApplications(request);}}}
}class GeneralDirector extends Manager {public GeneralDirector(String name) {super(name);}@Overridepublic void requestApplications(Request request) {System.out.println(name + "批准" + request.getContent() + "," + request.getType() + request.getNumber() + "天");}
}

传递过程

CommonManager manager = new CommonManager("主管");
Direct director = new Direct("经理");
GeneralDirector generalDirector = new GeneralDirector("总经理");manager.setSuperior(director);
director.setSuperior(generalDirector);Request request = new Request();
request.setContent("家里有事");
request.setType("请假");
request.setNumber(10);manager.requestApplications(request);