Desig Pattern - Chain Of Responsiblity

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Mybatis中的Plugin是依赖Interceptor接口实现的，这里面还用到了责任链模式 Chain of responsibility

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interceptorChain.addInterceptor(interceptor);


public class InterceptorChain {

  private final List<Interceptor> interceptors = new ArrayList<>();

  public Object pluginAll(Object target) {
    for (Interceptor interceptor : interceptors) {
      target = interceptor.plugin(target);
    }
    return target;
  }

  public void addInterceptor(Interceptor interceptor) {
    interceptors.add(interceptor);
  }
}

上面的InterceptorChain在调用pluginAll的时候会应用所有的plugin

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default Object plugin(Object target) {
    return Plugin.wrap(target, this);
 }

具体的就是，依次生成JDK dynamic proxy对象，并且将对具体statement的调用应用拦截器，形成调用链，及责任链模式。

如图所示

举个栗子：

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# Reviewer基础类
public abstract class Reviewer {
    public Reviewer nextReviewer;
    Reviewer addReviewer(Reviewer nextReviewer){
        return this.nextReviewer=nextReviewer;
    }
    
    abstract void reviewCode(String code);
    public void review(String code){
        reviewCode(code);
        if(nextReviewer!=null){
            nextReviewer.review(code);
        }
    }
}
#几种实现
public class SelfReview extends Reviewer {
    @Override
    public void reviewCode(String code) {
        System.out.println(code + " \n self review done \n");
    }
}
public class PeerReviewer extends Reviewer {
    @Override
    public void reviewCode(String code) {
        System.out.println(code + " \n peer review done \n");
    }
}
public class TeamLeadReviewer extends Reviewer {
    @Override
    public void reviewCode(String code) {
        System.out.println(code + "\n team lead review done \n");
    }
}
#测试
public static void main(String[] args){
    String code = "hello world";
    Reviewer selfReviewer = new SelfReview();
    Reviewer peerReviewer = new PeerReviewer();
    Reviewer teamLeadReviewer = new TeamLeadReviewer();
    selfReviewer.addReviewer(peerReviewer);
    peerReviewer.addReviewer(teamLeadReviewer);
    selfReviewer.review("Hello world");
}

责任链的作用很明显了，解藕，可以在sender和receiver之间添加更多的逻辑