Springboot HttpMessageNotWritableException:没有用于[.]的转换器与预设内容-类型'null']

Question

我尝试用XML创建web，用Springboot 2.2.4.RELEASE + JDK11和Java8编译创建JSON。

my模型：

@XmlRootElement
public class DataModel {

    private List<String> columns;

    private List<Row> rows;

    public List<String> getColumns() {
        return columns;
    }

    public void setColumns(List<String> columns) {
        this.columns = columns;
    }

    public List<Row> getRows() {
        return rows;
    }

    public void setRows(List<Row> rows) {
        this.rows = rows;
    }

}

我的控制器：

@RequestMapping(value = "/{model}/columns", method = RequestMethod.GET, consumes = MediaType.ALL_VALUE, produces = { MediaType.APPLICATION_XML_VALUE, MediaType.APPLICATION_JSON_VALUE })
public ResponseEntity<DataModel> getColumnsModel(@PathVariable String model) {
    LOGGER.info("getColumnsModel : model[{}]", model);
    DataModel dataModel = modelService.getColumns(model);
    return Optional.ofNullable(dataModel).map(result -> new ResponseEntity<>(result, HttpStatus.OK)).orElse(new ResponseEntity<>(HttpStatus.NO_CONTENT));
}

我用卷发：

curl -s -v --header "Accept: application/xml" http://localhost:8084/api/foo/columns

在我的电脑(windows 10)上，结果是可以的。

* TCP_NODELAY set
* Connected to localhost (::1) port 8084 (#0)
> GET /noraui/api/hello/columns HTTP/1.1
> Host: localhost:8084
> User-Agent: curl/7.67.0
> Accept: application/xml
>
* Mark bundle as not supporting multiuse
< HTTP/1.1 200
< X-Content-Type-Options: nosniff
< X-XSS-Protection: 1; mode=block
< Cache-Control: no-cache, no-store, max-age=0, must-revalidate
< Pragma: no-cache
< Expires: 0
< X-Frame-Options: DENY
< Content-Type: application/xml
< Transfer-Encoding: chunked
< Date: Tue, 03 Mar 2020 08:38:20 GMT
<
{ [254 bytes data]
* Connection #0 to host localhost left intact

我在Unix (travis-ci)上的错误：

Resolved [org.springframework.http.converter.HttpMessageNotWritableException: No converter for [class com.github.noraui.data.rest.DataModel] with preset Content-Type 'null']

< HTTP/1.1 500 
< X-Content-Type-Options: nosniff
< X-XSS-Protection: 1; mode=block
< Cache-Control: no-cache, no-store, max-age=0, must-revalidate
< Pragma: no-cache
< Expires: 0
< X-Frame-Options: DENY
< Content-Length: 0
< Date: Tue, 03 Mar 2020 08:41:28 GMT
< Connection: close
< 
* Closing connection 0

Answer 1

我通过添加以下依赖项解决了这个问题：

<dependency>
  <groupId>com.fasterxml.jackson.dataformat</groupId>
  <artifactId>jackson-dataformat-xml</artifactId>
  <version>2.12.3</version>
</dependency>

Answer 2

我也犯了一个类似的错误，但是使用了JSON。

我的问题之所以发生，是因为我试图转换为JSON的POJO必须具有相同的名称

@JsonProperty("my_property")
[...]
@JsonProperty("my_property")  // duplicated property name in the same POJO.

在修复复制后，可以正确地转换对象。

Answer 3

在我的例子中，我正在开发一个现有的api，该api生成一个PDF，必须将响应更改为JSON。我忘了从produces = "application/pdf"注释中删除@GetMapping。