无法写入请求：找不到适合请求类型[org.json.JSONObject]和内容类型[应用程序/json]的HttpMessageConverter

Question

我正在努力将带有JSON有效负载的POST请求发送到远程服务器。

此GET curl命令工作正常：

curl -H "Accept:application/json" --user [e-mail]:aaa "http://www.aaa.com:8080/aaa-project-rest/api/users/1" -i

这个POST也很好：

curl -H "Accept:application/json" -H "Content-Type: application/json" "http://www.aaa.com:8080/aaa-project-rest/api/users/login" -X POST -d "{ \"email\" : \"[e-mail]\", \"password\" : \"aaa\" }" -i

所以我试着在我的Android应用程序中模仿它。

该应用程序在第一个GET请求上运行良好，但在第二个POST请求上发出400个错误请求。

下面是用于GET请求的代码：

  RestTemplate restTemplate = new RestTemplate();
  restTemplate.getMessageConverters().add(new MappingJackson2HttpMessageConverter());
  HttpHeaders httpHeaders = Common.createAuthenticationHeaders("[e-mail]" + ":" + "aaa");
  User user = null;
  ResponseEntity<User> responseEntity = restTemplate.exchange("http://" + REST_HOST + ":8080/aaa-project-rest/api/users/" + 1L, HttpMethod.GET, new HttpEntity<Object>(httpHeaders), User.class);

以下是POST请求的源代码：

RestTemplate restTemplate = new RestTemplate();
restTemplate.getMessageConverters().add(new MappingJackson2HttpMessageConverter());
User user = null;
HttpHeaders headers = new HttpHeaders();
headers.setContentType(MediaType.APPLICATION_JSON);
httpHeaders.setAccept(Arrays.asList(MediaType.APPLICATION_JSON));
JSONObject jsonCredentials = new JSONObject();
jsonCredentials.put("email", REST_LOGIN);
jsonCredentials.put("password", REST_PASSWORD);
ResponseEntity<User> responseEntity = restTemplate.exchange("http://" + REST_HOST + ":" + REST_PORT + "/" + REST_APP + "/api/users/login",
        HttpMethod.POST, new HttpEntity<Object>(jsonCredentials, httpHeaders), User.class);

但它传达了这样一个信息：

Could not write request: no suitable HttpMessageConverter found for request type [org.json.JSONObject] and content type [application/json]

这是Spring座控制器：

@RequestMapping(value = RESTConstants.SLASH + RESTConstants.LOGIN, method = RequestMethod.POST, produces = MediaType.APPLICATION_JSON_VALUE)
@ResponseBody
public ResponseEntity<UserResource> login(@Valid @RequestBody CredentialsResource credentialsResource, UriComponentsBuilder builder) {
    HttpHeaders responseHeaders = new HttpHeaders();
    User user = credentialsService.checkPassword(credentialsResource);
    userService.clearReadablePassword(user);
    if (user == null) {
        return new ResponseEntity<UserResource>(responseHeaders, HttpStatus.NOT_FOUND);
    } else {
        tokenAuthenticationService.addTokenToResponseHeader(responseHeaders, credentialsResource.getEmail());
        responseHeaders.setLocation(builder.path(RESTConstants.SLASH + RESTConstants.USERS + RESTConstants.SLASH + "{id}").buildAndExpand(user.getId()).toUri());
        UserResource createdUserResource = userResourceAssembler.toResource(user);
        ResponseEntity<UserResource> responseEntity = new ResponseEntity<UserResource>(createdUserResource, responseHeaders, HttpStatus.CREATED);
        return responseEntity;
    }
}

@RequestMapping(value = RESTConstants.SLASH + "{id}", method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_VALUE)
@ResponseBody
public ResponseEntity<UserResource> findById(@PathVariable Long id, UriComponentsBuilder builder) {
    HttpHeaders responseHeaders = new HttpHeaders();
    User user = userService.findById(id);
    if (user == null) {
        return new ResponseEntity<UserResource>(responseHeaders, HttpStatus.NOT_FOUND);
    } else {
        UserResource userResource = userResourceAssembler.toResource(user);
        responseHeaders.setLocation(builder.path(RESTConstants.SLASH + RESTConstants.USERS + RESTConstants.SLASH + "{id}").buildAndExpand(user.getId()).toUri());
        ResponseEntity<UserResource> responseEntity = new ResponseEntity<UserResource>(userResource, responseHeaders, HttpStatus.OK);
        return responseEntity;
    }
}

凭据资源类代码：

public class CredentialsResource extends ResourceSupport {

    @NotEmpty
    @Email
    private String email;
    @NotEmpty
    private String password;

    public CredentialsResource() {
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

}

Answer 1

如果类路径中不存在JSON实现，则引发异常“找不到合适的HTTPMessageConverter”。查看RestTemplate源代码：

public RestTemplate() {
    this.messageConverters.add(new ByteArrayHttpMessageConverter());
    this.messageConverters.add(new StringHttpMessageConverter());
    this.messageConverters.add(new ResourceHttpMessageConverter());
    this.messageConverters.add(new SourceHttpMessageConverter<Source>());
    this.messageConverters.add(new AllEncompassingFormHttpMessageConverter());

    if (romePresent) {
        this.messageConverters.add(new AtomFeedHttpMessageConverter());
        this.messageConverters.add(new RssChannelHttpMessageConverter());
    }

    if (jackson2XmlPresent) {
        this.messageConverters.add(new MappingJackson2XmlHttpMessageConverter());
    }
    else if (jaxb2Present) {
        this.messageConverters.add(new Jaxb2RootElementHttpMessageConverter());
    }

    if (jackson2Present) {
        this.messageConverters.add(new MappingJackson2HttpMessageConverter());
    }
    else if (gsonPresent) {
        this.messageConverters.add(new GsonHttpMessageConverter());
    }
}

将JSON实现添加到您的类路径中。例如：

implementation "com.fasterxml.jackson.core:jackson-databind:2.9.0"

Answer 2

我必须做几件事才能让它工作起来。

首先，我必须将JSONObject转换为字符串，如下所示：

HttpEntity<String> entityCredentials = new HttpEntity<String>(jsonCredentials.toString(), httpHeaders);

原因是JSONObject类没有映射消息转换器，而String类有一个。

其次，我必须向RestTemplate构造函数传递一个真值。如果不这样做，我会收到400个错误的请求。

RestTemplate restTemplate = new RestTemplate(true);

true值告诉rest模板使用默认转换器。如果有人知道为什么会这样，我很乐意了解更多。

第三，我移除了不需要的Jackson转换器：

restTemplate.getMessageConverters().add(new MappingJackson2HttpMessageConverter());

完成这些工作后，请求就可以正常工作了。

以下是完整代码：

RestTemplate restTemplate = new RestTemplate(true);    
User user = null;
HttpHeaders httpHeaders = new HttpHeaders();
httpHeaders.setContentType(MediaType.APPLICATION_JSON);
httpHeaders.setAccept(Arrays.asList(MediaType.APPLICATION_JSON));
try {
    JSONObject jsonCredentials = new JSONObject();
    jsonCredentials.put("email", REST_LOGIN);
    jsonCredentials.put("password", REST_PASSWORD);
    Log.e(Constants.APP_NAME, ">>>>>>>>>>>>>>>> JSON credentials " + jsonCredentials.toString());
    HttpEntity<String> entityCredentials = new HttpEntity<String>(jsonCredentials.toString(), httpHeaders);
    ResponseEntity<User> responseEntity = restTemplate.exchange("http://" + REST_HOST + ":" + REST_PORT + "/" + REST_APP + "/api/users/login",
            HttpMethod.POST, entityCredentials, User.class);
    if (responseEntity != null) {
        user = responseEntity.getBody();
    }
    return user;
} catch (Exception e) {
    Log.e(Constants.APP_NAME, ">>>>>>>>>>>>>>>> " + e.getLocalizedMessage());
}
return null;

我怀疑可能有一种方法可以显式使用Jackson转换器并跳过rest模板构造函数中的真值，但这只是一种猜测。

Answer 3

虽然我刚刚遇到了同样的问题，并花了一些时间来解决它，但回复得很晚。所以，我想我最好分享它，并跟踪我的解决方案。

实际上，抛出的异常完全具有误导性。事实证明，问题不在于MappingJackson2HttpMessageConverter不知道如何管理我的对象——这听起来很奇怪，是JSON——而是底层ObjectMapper的配置。

我所做的是禁用属性SerializationFeature。FAIL_ON_EMPTY_BEANS像这样

restTemplate = new RestTemplate();
MappingJackson2HttpMessageConverter jsonHttpMessageConverter = new MappingJackson2HttpMessageConverter();
jsonHttpMessageConverter.getObjectMapper().configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
restTemplate.getMessageConverters().add(jsonHttpMessageConverter);

一切开始按预期进行。