org.springframework.web.client.RestClientException：无法写入请求：找不到适合请求类型的 HttpMessageConverter

Question

response.setContentType("application/json");
response.setCharacterEncoding("UTF-8");
PrintWriter out = response.getWriter();  

String Empcode="10743";
String password="IsaiVanan";

final String uri = "https://vtop9.vit.ac.in/vtoplogin/employeeLoginPost";

RestTemplate restTemplate = new RestTemplate();

HttpHeaders headers = new HttpHeaders();
headers.setAccept(Arrays.asList(MediaType.APPLICATION_JSON));
headers.setContentType(MediaType.APPLICATION_JSON);

MultiValueMap<String, String> postParams = new LinkedMultiValueMap<String, String>();
postParams.add("userid",Empcode);
postParams.add("pwd",password);

HttpEntity<MultiValueMap<String, String>> entity = new HttpEntity<> (postParams,headers);
System.out.println("Try coming1..!");

ResponseEntity<UserValidation> result = restTemplate.exchange(uri, HttpMethod.POST,entity, UserValidation.class);

System.out.print("result..."+result.getBody().getResponseMsg());        

我做了所有我添加rest api依赖的事情， 这个女巫我仍然在 application/json 中做了响应内容；它不起作用我只在一些stackoverflow验证中找到该解决方案..！

public class UserValidation {

    private String responseMsg ;
    private Integer responseCode;
    public String getResponseMsg() {
        return responseMsg;
    }
    public void setResponseMsg(String responseMsg) {
        this.responseMsg = responseMsg;
    }
    public Integer getResponseCode() {
        return responseCode;
    }
    public void setResponseCode(Integer responseCode) {
        this.responseCode = responseCode;
    }

}


org.springframework.web.client.RestClientException: Could not write request: no suitable HttpMessageConverter found for request type [org.springframework.util.LinkedMultiValueMap] and content type [application/json]
    at org.springframework.web.client.RestTemplate$HttpEntityRequestCallback.doWithRequest(RestTemplate.java:597)
    at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:436)
    at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:401)
    at org.springframework.web.client.RestTemplate.exchange(RestTemplate.java:377)
    at sample.doGet(sample.java:82)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:475)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:80)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:625)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:498)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:796)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1372)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Unknown Source)

当我在构建路径的项目中添加jar文件时发生错误，即rest api jar，spring frameworks...

错误显示并咨询他们确实知道rest api的每个人。

请哪位大神找到解决方案并得到正确的输出

Answer 1

要检索带有application/json 接受标头的资源，您需要MappingJackson2HttpMessageConverter，它是特殊的HttpMessageConverters 之一，看起来好像您丢失了。

在初始化RestTemplate 之后尝试在下面添加：

RestTemplate restTemplate = new RestTemplate();
List<HttpMessageConverter<?>> converters = new ArrayList<HttpMessageConverter<?>>();
converters.add(new MappingJackson2HttpMessageConverter());
restTemplate.setMessageConverters(converters);
// carry on with your code

Answer 2

Spring 无法将您的请求负载 (LinkedMultiValueMap) 解析为 JSON。请确保您使用可以执行此操作的转换器。所以你的请求不会发送到目标系统。

更多信息请阅读：https://www.baeldung.com/spring-httpmessageconverter-rest

Answer 3

试试这个 -

 private HttpEntity<MultiValueMap<String, Object>> makeExportRequestEntity(RequestObject requestObject ) throws IOException {
    MultiValueMap<String, Object> bodyMap = new LinkedMultiValueMap<>();
    bodyMap.add("DataOne", requestObject .getDataOne());
    bodyMap.add("DataTwo", requestObject .getDataTwo());

    HttpHeaders headers = new HttpHeaders();
    headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED);
    HttpEntity<MultiValueMap<String, Object>> requestEntity = new HttpEntity<>(bodyMap, headers);

    return requestEntity;
}