使用 Spring Boot 和 Eureka Server 时如何修复错误 java.net.UnknownHostException？答案

【问题标题】：How to fix the error java.net.UnknownHostException while using Spring Boot and Eureka Server?使用 Spring Boot 和 Eureka Server 时如何修复错误 java.net.UnknownHostException？
【发布时间】：2020-02-09 09:36:02
【问题描述】：

我有一个名为“documents-microservice”的 Spring Boot 微服务，它在 Eureka Server 中注册。我正在尝试使用它在 URL 中的名称和 RestTemplate 访问此微服务，如下所示：

ResponseEntity<String> response =    restTemplate.exchange("http://documents-microservice/document-name", HttpMethod.POST, entity, String.class);

虽然我确定服务名称在运行在端口 8761 上的 Eureka Server 上可用（见下图），但我仍然收到以下错误：

错误：

org.springframework.web.client.ResourceAccessException: I/O error on POST request for "http://documents-microservice/document-name": documents-microservice; nested exception is java.net.UnknownHostException: documents-microservice
    at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:674)
    at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:621)
    at org.springframework.web.client.RestTemplate.exchange(RestTemplate.java:539)
    at ae.gov.adm.saeed.web.controller.util.CircularsControllerUtil.circularListView(CircularsControllerUtil.java:196)
    at ae.gov.adm.saeed.web.controller.CircularsController.viewCircularList(CircularsController.java:58)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:133)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:97)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:967)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at ae.gov.adm.saeed.web.security.AuthFilter.doFilter(AuthFilter.java:335)
    at ae.gov.adm.saeed.web.security.AuthFilter.doFilter(AuthFilter.java:610)
    at ae.gov.adm.common.web.filter.AbstractFilter.doFilter(AbstractFilter.java:47)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:651)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:417)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:754)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1376)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:748)
Caused by: java.net.UnknownHostException: documents-microservice
    at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:184)
    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
    at java.net.Socket.connect(Socket.java:589)
    at java.net.Socket.connect(Socket.java:538)
    at sun.net.NetworkClient.doConnect(NetworkClient.java:180)
    at sun.net.www.http.HttpClient.openServer(HttpClient.java:463)
    at sun.net.www.http.HttpClient.openServer(HttpClient.java:558)
    at sun.net.www.http.HttpClient.<init>(HttpClient.java:242)
    at sun.net.www.http.HttpClient.New(HttpClient.java:339)
    at sun.net.www.http.HttpClient.New(HttpClient.java:357)
    at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:1220)
    at sun.net.www.protocol.http.HttpURLConnection.plainConnect0(HttpURLConnection.java:1156)
    at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:1050)
    at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:984)
    at org.springframework.http.client.SimpleBufferingClientHttpRequest.executeInternal(SimpleBufferingClientHttpRequest.java:78)
    at org.springframework.http.client.AbstractBufferingClientHttpRequest.executeInternal(AbstractBufferingClientHttpRequest.java:48)
    at org.springframework.http.client.AbstractClientHttpRequest.execute(AbstractClientHttpRequest.java:53)
    at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:660)
    ... 52 more
I/O error on POST request for "http://documents-microservice/document-name": documents-microservice; nested exception is java.net.UnknownHostException: documents-microservice

更新：请注意，我在客户端有以下设置 RestTemplate 的方法：

    @Bean //this methods will be executed only once to avoid getting multiple instances.
    @LoadBalanced //I will not give you service URL, but rather a hint for what you need to discover.
    public RestTemplate getRestTemplate()
    {
         final RestTemplate restTemplate = new RestTemplate();

         System.out.println("rest template defined");

         return  restTemplate;
    }

更新：请注意，目前，我的客户端代码不是 Spring Boot 应用程序。

【问题讨论】：

标签： java spring-boot post resttemplate netflix-eureka

【解决方案1】：

您需要做几件事：

首先：您需要的 RestTemplate 配置不是在客户端中，而是在调用该客户端的 service(1) 中

@Configuration
public class WebClientConfiguration {

    @Bean @LoadBalanced
    public RestTemplate getRestTemplate() {
        return new RestTemplate();
    }
}

第二个：需要在同一个service(1)的pom.xml中对应的依赖关系
第三个：在你的主应用程序中添加@EnableDiscoveryClient

还有其他配置，但您必须提供一个完整的示例来为您提供更多帮助。
这个example可以帮到你

【讨论】：

【解决方案2】：

您可以通过@Feign 客户端通过名称“documents-microservice”访问它，否则您应该尝试网关 EG，hqtpm001....:8081

此外，Eureka 服务器不是应用程序的主机，它或多或少是交通警察，让您作为客户端知道去哪里获取应用程序。又名服务注册中心

【讨论】：

谢谢。是的，我对 Eureka Server 了如指掌，我使用 Eureka Server Jar 文件创建了一个服务注册表，它正在运行，正如我所展示的那样。但是根据我的知识，您只需要在客户端中包含标签 LoadBalanced 注释即可，但它在我的代码中不起作用。也许是因为我的客户不是 Spring Boot App？顺便说一句，如果您确定@Feign 客户的想法，如果您能展示它是如何通过代码完成的，我将不胜感激。谢谢。
Ribbon 是客户端负载均衡器。 ` @FeignClient("stores") 公共接口 StoreClient { @RequestMapping(method = RequestMethod.GET, value = "/stores") List getStores(); @RequestMapping(method = RequestMethod.POST, value = "/stores/{storeId}", consumes = "application/json") Store update(@PathVariable("storeId") Long storeId, Store store); `一些好文章给你。 cloud.spring.io/spring-cloud-netflix/multi/…cloud.spring.io/spring-cloud-netflix/multi/…
我认为我不需要 Ribbon 来解决我的问题，但还是谢谢

【解决方案3】：

如果你想用 OpenFeign 代替 RestTemplate

name指在eureka注册的服务名称
医生注册服务已在 eureka 服务器上注册，名称为医生注册应用程序。

@FeignClient(name = "医生注册申请") 公共接口 DoctorDetailsClient {

@GetMapping("/doctor/get-by-Id/{doctorId}") 公共医生 getDoctorDetails(@PathVariable int doctorId);
@GetMapping("/doctor/get-by-name/{name}") 公共医生 getDoctorDetailsByName(@PathVariable 字符串名称); }

【讨论】：