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());        

I did everything which i add dependency of rest api, this witch i did response content in application/json still; it not working i find that solution only in some stackoverflow verify..!

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)

error occurs when i add jar files in project of build path, namely rest api jar, spring frameworks...

error shows and consult with everyone which they did know about rest api.

which someone please find the solution and get the corrected output please

Answer 1

For retrieving a resource with application/json Accept Header, you need MappingJackson2HttpMessageConverter , which is one of the special HttpMessageConverters which looks like you're missing.

Try adding below just after initializing RestTemplate as :

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 is not able to parse your request payload (LinkedMultiValueMap) to JSON. Please make sure that you use a converter that can do this. So your request is not sent to the target system.

Please read this for more information: https://www.baeldung.com/spring-httpmessageconverter-rest

Answer 3

Try this -

 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;
}