Ribbon之IPing

IPing是Ribbon 框架中，负责检查服务实例是否存活（UP）。

• IPing
  

public interface IPing {    // 检查是否存活的接口    public boolean isAlive(Server server);}

• DummyPing

一个虚设的IPing实现，永远返回true。

public class DummyPing extends AbstractLoadBalancerPing {    public DummyPing() {    }    // 直接返回true    public boolean isAlive(Server server) {        return true;    }    @Override    public void initWithNiwsConfig(IClientConfig clientConfig) {    }}

• NoOpPing
  

什么也不做，直接返回true。

public class NoOpPing implements IPing {    @Override    public boolean isAlive(Server server) {        return true;    }}

• PingConstant
  

一个工具类的IPing实现，只要常量参数为true，则表示服务存活，否则都是失效的服务实例。

public class PingConstant implements IPing {      boolean constant = true;      public void setConstant(String constantStr) {            constant = (constantStr != null) && (constantStr.toLowerCase().equals("true"));      }      public void setConstant(boolean constant) {            this.constant = constant;      }      public boolean getConstant() {            return constant;      }      public boolean isAlive(Server server) {            return constant;      }}

• PingUrl
  

通过request访问服务返回的状态码来判定服务是否存活。

public class PingUrl implements IPing {    public boolean isAlive(Server server) {          String urlStr   = "";          if (isSecure){             urlStr = "https://";          }else{             urlStr = "http://";          }          urlStr += server.getId();          urlStr += getPingAppendString();              boolean isAlive = false;              HttpClient httpClient = new DefaultHttpClient();          HttpUriRequest getRequest = new HttpGet(urlStr);          String content=null;          try {             HttpResponse response = httpClient.execute(getRequest);             content = EntityUtils.toString(response.getEntity());             isAlive = (response.getStatusLine().getStatusCode() == 200); // 根据状态码和返回的内容来判定服务实例是否有效             if (getExpectedContent()!=null){                LOGGER.debug("content:" + content);                if (content == null){                   isAlive = false;                }else{                   if (content.equals(getExpectedContent())){                      isAlive = true;                   }else{                      isAlive = false;                   }                }             }          } catch (IOException e) {             e.printStackTrace();          }finally{             // Release the connection.             getRequest.abort();          }              return isAlive;    }}

• NIWSDiscoveryPing
  

通过Eureka来判定服务实例是否存活。

public class NIWSDiscoveryPing extends AbstractLoadBalancerPing {    public boolean isAlive(Server server) {        boolean isAlive = true;        if (server!=null && server instanceof DiscoveryEnabledServer){               DiscoveryEnabledServer dServer = (DiscoveryEnabledServer)server; // 通过Eureka的服务机制来判定服务是否存活                            InstanceInfo instanceInfo = dServer.getInstanceInfo();               if (instanceInfo!=null){                                       InstanceStatus status = instanceInfo.getStatus();                   if (status!=null){                       isAlive = status.equals(InstanceStatus.UP);                   }               }           }        return isAlive;    }}