Java 设计模式之责任链模式
概述
- 职责链模式(Chain of Responsibility):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。将这个对象连成一条链,并沿着这条链传递该请求,直到有一个对象处理它为止。
UML图
- Handler:抽象处理者类,定义行为,冰持有下一个处理者的引用。
- ConcreteHandler:具体处理者类,实现行为,处理自己能处理的请求,否则传递给下一个处理者。
- Request:请求类,包含请求内容。
代码实现
定义抽象处理者类:
public abstract class Handler {
protected Handler nextHandler;
public void setNextHandler(Handler nextHandler) {
this.nextHandler = nextHandler;
}
public abstract void handleRequest(Request request);
}
定义具体处理者类:
public class ConcreteHandlerA extends Handler {
@Override
public void handleRequest(Request request) {
if (request.getType().equals("typeA")) {
System.out.println("ConcreteHandlerA处理请求:" + request.getContent());
} else if (nextHandler != null) {
nextHandler.handleRequest(request);
}
}
}
public class ConcreteHandlerB extends Handler {
@Override
public void handleRequest(Request request) {
if (request.getType().equals("typeB")) {
System.out.println("ConcreteHandlerB处理请求:" + request.getContent());
} else if (nextHandler != null) {
nextHandler.handleRequest(request);
}
}
}
public class ConcreteHandlerC extends Handler {
@Override
public void handleRequest(Request request) {
if (request.getType().equals("typeC")) {
System.out.println("ConcreteHandlerC处理请求:" + request.getContent());
} else if (nextHandler != null) {
nextHandler.handleRequest(request);
}
}
}
定义请求类:
public class Request {
private String type;
private String content;
public Request(String type, String content) {
this.type = type;
this.content = content;
}
public String getType() {
return type;
}
public String getContent() {
return content;
}
}
使用:
public class Client {
public static void main(String[] args) {
// 创建处理者:
Handler handlerA = new ConcreteHandlerA();
Handler handlerB = new ConcreteHandlerB();
Handler handlerC = new ConcreteHandlerC();
// 设置责任链:
handlerA.setNextHandler(handlerB);
handlerB.setNextHandler(handlerC);
// 创建请求:
Request request1 = new Request("typeA", "requestA");
Request request2 = new Request("typeB", "requestB");
Request request3 = new Request("typeC", "requestC");
Request request4 = new Request("typeD", "requestD");
// 处理请求:
handlerA.handleRequest(request1);
handlerA.handleRequest(request2);
handlerA.handleRequest(request3);
handlerA.handleRequest(request4);
}
}
输出:
ConcreteHandlerA处理请求:requestA
ConcreteHandlerB处理请求:requestB
ConcreteHandlerC处理请求:requestC