使用ServiceComb客户端轻松调用ServiceCenter

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问题/背景

在微服务架构中，服务注册中心是必不可少的组件，主要提供服务注册与管理的能力。目前使用ServiceComb服用中心的 java 微服务开发者，不仅需要写微服务业务代码，还要写客户端代码去调用 ServiceCenter 的 openAPI 。开发者首先需要熟悉 ServiceCenter 的 openAPI 文档，然后代码实现 http 客户端用于发起请求和接收响应，并绑定 ServiceCenter 配置参数，最后代码实现对服务中心 API 的调用，才能使用上 ServiceCenter 。为了简单化开发者使用 ServiceCenter ， ServiceCenter 客户端实现了上述步骤。开发者只需要添加客户端 jar 包调用 API 就能轻松使用 ServiceCenter ，不需要过多关注 openAPI 文档、不需要写 http 客户端层代码。使用 ServiceComb 客户端，开发者可以轻松调用 ServiceCenter ，更专注于写微服务业务代码。

了解更多ServiceComb-Service-Center： https://docs.servicecomb.io/service-center/zh_CN/index.html

了解更多ServiceCenter客户端： https://github.com/apache/s ervicecomb-java- chassis/tree/master/clients/service-center-client

客户端原理及关键代码解读

1

基于httpClient设计ServiceCenter客户端

客户端发起请求和接收响应

客户端选择httpclient作为底层组件，用于实际发起请求和接收响应，并对请求和响应类进行了封装。代码中get方法对应发起GET请求，调用doRequest方法首先添加服务注册中心信息到封装过的httpRequest请求头部，再基于httpclient组件发起实际的http请求，最后将请求响应结果转化为封装过的httpResponse对象返回。

//make GET request
@Override
public HttpResponse get(HttpRequest request) throws IOException {
    request.setMethod(HttpRequest.GET);
    return doRequest(request);
}
......

//make http request with httpClient component
public HttpResponse doRequest(HttpRequest httpRequest) throws IOException {
    //add cse-serviceregistry-client header to identify client
    httpRequest.addHeader(HEADER_CONTENT_TYPE, "application/json");
    httpRequest.addHeader(HEADER_USER_AGENT, "cse-serviceregistry-client/1.0.0");
    
    if (globalHeaders != null) {
    globalHeaders.forEach(httpRequest::addHeader);
    }
    
    //make http request
    org.apache.http.HttpResponse response = httpClient.execute(httpRequest.getRealRequest());
    
    int statusCode = response.getStatusLine().getStatusCode();
    String messgae = response.getStatusLine().getReasonPhrase();
    String context = EntityUtils.toString(response.getEntity(), "UTF-8");
    
    return new HttpResponse(statusCode, messgae, context);
}

/**
* Customized host, port, projectName, tenantName, TLSConf, headers and any one parameter can be null.
*/
public ServiceCenterClient(String host, int port, String projectName, String tenantName, TLSConfig tlsConfig,
  Map<String, String> extraGlobalHeaders) {
    HttpTransport httpTransport = HttpTransportFactory.getDefaultHttpTransport();
    if (tlsConfig != null) {
      httpTransport = new TLSHttpsTransport(tlsConfig);
    }
    httpTransport.addHeaders(extraGlobalHeaders);
    
    //set configuration parameters
    this.httpClient = new ServiceCenterRawClient.Builder()
        .setHost(host)
        .setPort(port)
        .setProjectName(projectName)
        .setTenantName(tenantName)
        .setHttpTransport(httpTransport).build();
}

2

ServiceCenter客户端核心API

服务注册与发现，注册服务和实例到服务注册中心，根据服务ID发现服务实例。registerMicroserviceInstance方法用于注册服务实例，发起httpPOST请求访问服务实例注册URL，并将实例注入到请求body中，返回服务ID字符串; getMicroserviceInstanceList方法用于发现服务的所有实例，根据服务ID，发起httpGET请求访问服务发现URL，返回MicroserviceInstancesResponse对象。

//service register
public String registerMicroserviceInstance(MicroserviceInstance instance, String serviceId) {
    try {
      ObjectMapper mapper = new ObjectMapper();
      mapper.configure(SerializationFeature.WRAP_ROOT_VALUE, true);
      HttpResponse response = httpClient.postHttpRequest("/registry/microservices/" + serviceId + "/instances", null,
          mapper.writeValueAsString(instance));
      if (response.getStatusCode() == HttpStatus.SC_OK) {
        return response.getContent();
      } else {
        throw new OperationException(
            "register service instance fails, statusCode = " + response.getStatusCode() + "; message = " + response
                .getMessage()
                + "; content = " + response.getContent());
      }
    } catch (IOException e) {
      throw new OperationException(
          "register service instance fails", e);
    }
}
//service discovery
public MicroserviceInstancesResponse getMicroserviceInstanceList(String serviceId) {
    try {
      HttpResponse response = httpClient
          .getHttpRequest("/registry/microservices/" + serviceId + "/instances", null, null);
      if (response.getStatusCode() == HttpStatus.SC_OK) {
        ObjectMapper mapper = new ObjectMapper();
        return mapper.readValue(response.getContent(), MicroserviceInstancesResponse.class);
      } else {
        throw new OperationException(
            "get service instances list fails, statusCode = " + response.getStatusCode() + "; message = " + response
                .getMessage()
                + "; content = " + response.getContent());
      }
    } catch (IOException e) {
      throw new OperationException(
          "get service instances list fails", e);
    }
}

//heartBeats
public void sendHeartBeats(HeartbeatsRequest heartbeatsRequest) {
  try {
    ObjectMapper mapper = new ObjectMapper();
    HttpResponse response = httpClient
        .putHttpRequest("/registry/heartbeats", null, mapper.writeValueAsString(heartbeatsRequest));

    if (response.getStatusCode() == HttpStatus.SC_OK) {
      LOGGER.info("HEARTBEATS SUCCESS");
    } else {
      throw new OperationException(
          "heartbeats fails, statusCode = " + response.getStatusCode() + "; message = " + response.getMessage()
              + "; content = " + response.getContent());
    }
  } catch (IOException e) {
    throw new OperationException(
        "heartbeats fails ", e);
  }
}

3

更多客户端API介绍

参考客户端说明文档  https://github.com/apache/servicecomb-java-chassis/tree/master/clients/service-center-client

ServiceCenter客户端实践

1

实践准备

• 启动ServiceComb服务中心： http://servicecomb.apache.org/cn/docs/service-center/install/

• 下载演示代码： https://github.com/zaneChou1/spring-boot-servicecenter

2

provider端启动服务，通过客户端注册到ServiceCenter

运行provider模块，启动helloServer服务，并调用客户端API创建客户端对象、创建helloServer服务和实例对象、注册服务和实例到servicecomb 服务中心，并保持30s一次心跳，代码实现如下。

public static void registerMicroservice(){
   //new ServiceCenterClient object
   ServiceCenterClient sc = new ServiceCenterClient();
  
   //new Microservice object and setting properties and serviceName is necessary
   Microservice microservice = new Microservice();
   microservice.setServiceId("1111");
   microservice.setServiceName("HelloServer");
   //register microservice to service-center
   sc.registerMicroservice(microservice);
  
   //new MicroserviceInstance object and bind server IP and port
   MicroserviceInstance instance = new MicroserviceInstance();
   List<String> endPoints = new ArrayList<String>();
   endPoints.add("rest://127.0.0.1:8080/");
   instance.setEndpoints(endPoints);
   //setting instance hostName, instanceId and hostName is necessary
   instance.setHostName("test");
   instance.setInstanceId("2222");
   //register microservice instance to service-center
   sc.registerMicroserviceInstance(instance,microservice.getServiceId());
  
   //send a heartbeat every 30s
   HeartbeatsRequest heartbeatsRequest = new HeartbeatsRequest("1111","2222");
   while(true){
     sc.sendHeartBeats(heartbeatsRequest);
     try {
       Thread.sleep(30000);
     } catch (InterruptedException e) {
       e.printStackTrace();
     }
   }
}

查看service-center的UI显示如下，helloServer服务注册到服务中心成功，且有一个服务实例test。

访问provider服务监听的8080端口，返回“Hello Spring-Boot-ServiceCenter !”。

3

consumer端通过客户端发现服务实例，发起服务调用

运行 consumer模块，启动consumer服务，调用客户端API新建客户端对象、发现helloServer服务实例、获取服务监听的IP和端口，最后调用provider端helloServer服务返回结果。

//find service instance
ServiceCenterClient sc = new ServiceCenterClient();
MicroserviceInstancesResponse instances = sc.getMicroserviceInstanceList("1111");
//get IP and port that service is listening on
URI endpointURIBuilder = new URIBuilder(instances.getInstances().get(0).getEndpoints().get(0)).build();
int port = endpointURIBuilder.getPort();
String host = endpointURIBuilder.getHost();

//call service
RestTemplate restTemplate = new RestTemplate();
ResponseEntity<String> result = restTemplate.getForEntity("http://"+host+":"+port,String.class);
return result.getBody();

访问consumer端监听的8081端口，返回helloServer的响应结果“Hello Spring-Boot-ServiceCenter !”，consumer端通过ServiceComb服务注册中心调用provider端服务成功。

在看一点，BUG退散

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