Spring Cloud Zuul 网关服务的fallback

当我们的zuul进行路由分发时，如果后端服务没有启动，或者调用超时，这时候我们希望Zuul提供一种降级功能，而不是将异常暴露出来。

Spring cloud zuul提供这种降级功能，操作步骤如下：

package microService.app.filter;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import javax.servlet.http.HttpServletRequest;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.cloud.netflix.zuul.filters.route.ZuulFallbackProvider;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.client.ClientHttpResponse;
import org.springframework.stereotype.Component;
import com.netflix.zuul.context.RequestContext;
import net.sf.json.JSONObject;
/**
 * 向用户管理路由发起请求失败时的回滚处理 hystrix的回滚能力
 *
 */
@Component
public class MsgCollectionFilter implements ZuulFallbackProvider {
  private final Logger logger = LoggerFactory.getLogger(MsgCollectionFilter.class);
  @Override
  public String getRoute() {
    return "*";// api服务id，如果需要所有调用都支持回退，则return "*"或return null
  }
  /**
   * 如果请求用户服务失败，返回什么信息给消费者客户端
   */
  @Override
  public ClientHttpResponse fallbackResponse() {
        RequestContext ctx = RequestContext.getCurrentContext();
        HttpServletRequest request = ctx.getRequest();
    return new ClientHttpResponse() {
      @Override
      public InputStream getBody() throws IOException {
        JSONObject r = new JSONObject();
        r.put("state", "8888");
        r.put("msg", "系统错误，请求失败");
        logger.error("降级"+r.toString());
        return new ByteArrayInputStream(r.toString().getBytes("UTF-8"));
      }
      @Override
      public HttpHeaders getHeaders() {
        HttpHeaders headers = new HttpHeaders();
        // 和body中的内容编码一致，否则容易乱码
        headers.setContentType(MediaType.APPLICATION_JSON_UTF8);
        return headers;
      }
      /**
       * 网关向api服务请求是失败了，但是消费者客户端向网关发起的请求是OK的， 不应该把api的404,500等问题抛给客户端
       * 网关和api服务集群对于客户端来说是黑盒子
       */
      @Override
      public HttpStatus getStatusCode() throws IOException {
        return HttpStatus.OK;
      }
      @Override
      public int getRawStatusCode() throws IOException {
        return HttpStatus.OK.value();
      }
      @Override
      public String getStatusText() throws IOException {
        return HttpStatus.OK.getReasonPhrase();
      }
      @Override
      public void close() {
      }
    };
  }
}