【设计模式】JAVA Design Patterns——Chain of responsibility（责任链模式）

public class Request {
 
  private final RequestType requestType;
  private final String requestDescription;
  private boolean handled;
 
  public Request(final RequestType requestType, final String requestDescription) {
    this.requestType = Objects.requireNonNull(requestType);
    this.requestDescription = Objects.requireNonNull(requestDescription);
  }
 
  public String getRequestDescription() { return requestDescription; }
 
  public RequestType getRequestType() { return requestType; }
 
  public void markHandled() { this.handled = true; }
 
  public boolean isHandled() { return this.handled; }
 
  @Override
  public String toString() { return getRequestDescription(); }
}
 
public enum RequestType {
  DEFEND_CASTLE, TORTURE_PRISONER, COLLECT_TAX
}

@Slf4j
public abstract class RequestHandler {
  private final RequestHandler next;
 
  public RequestHandler(RequestHandler next) {
    this.next = next;
  }
 
  public void handleRequest(Request req) {
    if (next != null) {
      next.handleRequest(req);
    }
  }
 
  protected void printHandling(Request req) {
    LOGGER.info("{} handling request \"{}\"", this, req);
  }
 
  @Override
  public abstract String toString();
}
 
public class OrcCommander extends RequestHandler {
  public OrcCommander(RequestHandler handler) {
    super(handler);
  }
 
  @Override
  public void handleRequest(Request req) {
    if (req.getRequestType().equals(RequestType.DEFEND_CASTLE)) {
      printHandling(req);
      req.markHandled();
    } else {
      super.handleRequest(req);
    }
  }
 
  @Override
  public String toString() {
    return "Orc commander";
  }
}
 
// OrcOfficer和OrcSoldier的定义与OrcCommander类似
 

public class OrcKing {
  RequestHandler chain;
 
  public OrcKing() {
    buildChain();
  }
 
  private void buildChain() {
    chain = new OrcCommander(new OrcOfficer(new OrcSoldier(null)));
  }
 
  public void makeRequest(Request req) {
    chain.handleRequest(req);
  }
}

var king = new OrcKing();
king.makeRequest(new Request(RequestType.DEFEND_CASTLE, "defend castle")); // Orc commander handling request "defend castle"
king.makeRequest(new Request(RequestType.TORTURE_PRISONER, "torture prisoner")); // Orc officer handling request "torture prisoner"
king.makeRequest(new Request(RequestType.COLLECT_TAX, "collect tax")); // Orc soldier handling request "collect tax"