定义
属于行为型模式的一种,一个请求由多个对象来处理,这些对象形成一条链,请求沿着该链传递,直到该链上的某个对象处理它为止。
角色
- 抽象处理者 定义了处理方法,并且可以设置和返回下一个处理者。为接口或抽象类
- 具体处理者 抽象处理者的实现
实现
/**
* desc : 抽象处理者
* Created by tiantian on 2018/8/19
*/
public interface IHandler {
void handle();
void setNextHandler(IHandler handler);
IHandler getNextHandler();
}
package design.patten.chain;
/**
* desc : 具体处理者A
* Created by tiantian on 2018/8/19
*/
public class HandlerA implements IHandler {
private IHandler nextHandler = null;
@Override
public void handle() {
System.out.println("HandlerA do something");
if (this.hasNext()) {
nextHandler.handle();
}
}
@Override
public void setNextHandler(IHandler handler) {
this.nextHandler = handler ;
}
@Override
public IHandler getNextHandler() {
return nextHandler;
}
private boolean hasNext() {
return nextHandler != null;
}
}
package design.patten.chain;
/**
* desc : 具体处理者B
* Created by tiantian on 2018/8/19
*/
public class HandlerB implements IHandler {
private IHandler nextHandler = null;
@Override
public void handle() {
System.out.println("HandlerB do something");
if (this.hasNext()) {
nextHandler.handle();
}
}
@Override
public void setNextHandler(IHandler handler) {
this.nextHandler = handler;
}
@Override
public IHandler getNextHandler() {
return nextHandler;
}
private boolean hasNext() {
return nextHandler != null;
}
}
package design.patten.chain;
/**
* desc : 具体处理者C
* Created by tiantian on 2018/8/19
*/
public class HandlerC implements IHandler {
private IHandler nextHandler = null;
@Override
public void handle() {
System.out.println("HandlerC do something");
if (this.hasNext()) {
nextHandler.handle();
}
}
@Override
public void setNextHandler(IHandler handler) {
this.nextHandler = handler;
}
@Override
public IHandler getNextHandler() {
return null;
}
private boolean hasNext() {
return nextHandler != null;
}
}
public class Test {
public static void main(String[] args) {
IHandler handlerA = new HandlerA();
IHandler handlerB = new HandlerB();
IHandler iHandlerC = new HandlerC();
handlerA.setNextHandler(handlerB);
handlerB.setNextHandler(iHandlerC);
handlerA.handle();
}
// output:
//HandlerA do something
//HandlerB do something
//HandlerC do something
}
应用
JS 中的事件冒泡。 Servlet中的Filter等。
总结
优点: 分离了请求和处理,降低了耦合。请求的处理是在链上的某个处理者处理,请求者不知道具体处理者;处理者亦不知请求的全部细节。
缺点: 请求链较长时性能受到影响。调试不太方便。