设计模式之责任链模式

责任链模式的核心思想是让请求对象(Request)沿着链(chain)按照一定顺序(ordered)依次传递下去，链上的每个处理器(Filter)都有机会去处理请求(request)。 客户端只需把请求传递给链(chain)上的第一个处理器(filter)即可，至于被谁处理，客户端不care。

/**
* Test.java
*
* @author zhanghui
*
*/
public class Test {

public static void main(String[] args) {
FilterManager.service(new Request(), new Response());
}

}

class Request {
}
class Response {
}
class FilterManager {

private static Filter firstFilter = null;

static {
// 可以把所有的filter放到配置文件中，然后这里从配置文件中初始化所有filter
Filter f1 = new MyFilter1();
Filter f2 = new MyFilter2();
Filter f3 = new MyFilter3();
f1.setNextFilter(f2);
f2.setNextFilter(f3);
f3.setNextFilter(new NullFilter());

firstFilter = f1;
}

public static void service(Request req, Response resp) {
if (firstFilter != null) {
firstFilter.process(req, resp);
}
}
}
interface Filter {
void setNextFilter(Filter filter);
void process(Request req, Response resp);
}

abstract class AbstractFilter implements Filter {
protected Filter next;

public void setNextFilter(Filter next) {
this.next = next;
}
}
class MyFilter1 extends AbstractFilter {
public void process(Request req, Response resp) {
System.out.println("before MyFilter1...");
next.process(req, resp);
System.out.println("after MyFilter1...");
}
}
class MyFilter2 extends AbstractFilter {
public void process(Request req, Response resp) {
System.out.println("before MyFilter2...");
next.process(req, resp);
System.out.println("after MyFilter2...");
}
}
class MyFilter3 extends AbstractFilter {
public void process(Request req, Response resp) {
System.out.println("before MyFilter3...");
next.process(req, resp);
System.out.println("after MyFilter3...");
}
}
class NullFilter extends AbstractFilter {
public void process(Request req, Response resp) {
// do nothing
}
}

运行结果：

before MyFilter1...

before MyFilter2...

before MyFilter3...

after MyFilter3...

after MyFilter2...

after MyFilter1...