130 lines
3.0 KiB
Java
130 lines
3.0 KiB
Java
## 责任链（Chain Of Responsibility）
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### Intent
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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。将这些对象连成一条链，并沿着这条链发送该请求，直到有一个对象处理它为止。
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### Class Diagram
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- Handler：定义处理请求的接口，并且实现后继链（successor）
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<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/ca9f23bf-55a4-47b2-9534-a28e35397988.png"/> </div><br>
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### Implementation
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```java
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public abstract class Handler {
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protected Handler successor;
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public Handler(Handler successor) {
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this.successor = successor;
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}
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protected abstract void handleRequest(Request request);
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}
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```
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```java
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public class ConcreteHandler1 extends Handler {
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public ConcreteHandler1(Handler successor) {
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super(successor);
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}
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@Override
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protected void handleRequest(Request request) {
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if (request.getType() == RequestType.TYPE1) {
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System.out.println(request.getName() + " is handle by ConcreteHandler1");
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return;
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}
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if (successor != null) {
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successor.handleRequest(request);
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}
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}
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}
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```
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```java
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public class ConcreteHandler2 extends Handler {
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public ConcreteHandler2(Handler successor) {
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super(successor);
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}
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@Override
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protected void handleRequest(Request request) {
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if (request.getType() == RequestType.TYPE2) {
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System.out.println(request.getName() + " is handle by ConcreteHandler2");
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return;
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}
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if (successor != null) {
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successor.handleRequest(request);
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}
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}
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}
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```
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```java
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public class Request {
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private RequestType type;
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private String name;
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public Request(RequestType type, String name) {
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this.type = type;
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this.name = name;
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}
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public RequestType getType() {
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return type;
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}
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public String getName() {
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return name;
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}
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}
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```
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```java
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public enum RequestType {
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TYPE1, TYPE2
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}
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```
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```java
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public class Client {
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public static void main(String[] args) {
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Handler handler1 = new ConcreteHandler1(null);
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Handler handler2 = new ConcreteHandler2(handler1);
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Request request1 = new Request(RequestType.TYPE1, "request1");
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handler2.handleRequest(request1);
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Request request2 = new Request(RequestType.TYPE2, "request2");
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handler2.handleRequest(request2);
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}
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}
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```
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```html
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request1 is handle by ConcreteHandler1
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request2 is handle by ConcreteHandler2
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```
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### JDK
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- [java.util.logging.Logger#log()](http://docs.oracle.com/javase/8/docs/api/java/util/logging/Logger.html#log%28java.util.logging.Level,%20java.lang.String%29)
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- [Apache Commons Chain](https://commons.apache.org/proper/commons-chain/index.html)
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- [javax.servlet.Filter#doFilter()](http://docs.oracle.com/javaee/7/api/javax/servlet/Filter.html#doFilter-javax.servlet.ServletRequest-javax.servlet.ServletResponse-javax.servlet.FilterChain-)
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