使用 spring-boot-starter-web “找不到可接受的表示”

Question

我正在尝试使用 spring-boot-starter-web 创建一个服务于 Java 对象的 JSON 表示的休息服务。据我了解，这个 boot-starter-web jar 应该通过 Jackson 自动处理到 JSON 的转换，但我却收到了这个错误。

 {
  "timestamp": 1423693929568,
  "status": 406,
  "error": "Not Acceptable",
  "exception": "org.springframework.web.HttpMediaTypeNotAcceptableException",
  "message": "Could not find acceptable representation"
}

我的控制器是这个…

 @RestController
@RequestMapping(value = "/media")
public class MediaController {
    @RequestMapping(value = "/test", method = RequestMethod.POST)
    public @ResponseBody UploadResult test(@RequestParam(value="data") final String data) {
      String value = "hello, test with data [" + data + "]";
      return new UploadResult(value);
    }

    @RequestMapping(value = "/test2", method = RequestMethod.POST)
    public int test2() {
        return 42;
    }

    @RequestMapping(value = "/test3", method = RequestMethod.POST)
    public String test3(@RequestParam(value="data") final String data) {
        String value = "hello, test with data [" + data + "]";
        UploadResult upload = new UploadResult(value);
        return upload.value;
    }

    public static class UploadResult {
        private String value;
        public UploadResult(final String value)
        {
            this.value = value;
        }
    }
}

我的 pom.xml 有…

 <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <version>1.2.1.RELEASE</version>
</dependency>

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-tomcat</artifactId>
    <version>1.2.1.RELEASE</version>
    <scope>provided</scope>
</dependency>

mvn dependency:tree 显示 spring-boot-starter-web 确实依赖于 jackson2.4 数据绑定，因此应该在类路径上……

 [INFO] +- org.springframework.boot:spring-boot-starter-web:jar:1.2.1.RELEASE:compile
[INFO] |  +- org.springframework.boot:spring-boot-starter:jar:1.2.1.RELEASE:compile
[INFO] |  |  +- org.springframework.boot:spring-boot:jar:1.2.1.RELEASE:compile
[INFO] |  |  +- org.springframework.boot:spring-boot-autoconfigure:jar:1.2.1.RELEASE:compile
[INFO] |  |  +- org.springframework.boot:spring-boot-starter-logging:jar:1.2.1.RELEASE:compile
[INFO] |  |  |  +- org.slf4j:jul-to-slf4j:jar:1.7.8:compile
[INFO] |  |  |  \- org.slf4j:log4j-over-slf4j:jar:1.7.8:compile
[INFO] |  |  \- org.yaml:snakeyaml:jar:1.14:runtime
[INFO] |  +- com.fasterxml.jackson.core:jackson-databind:jar:2.4.4:compile
[INFO] |  |  +- com.fasterxml.jackson.core:jackson-annotations:jar:2.4.0:compile
[INFO] |  |  \- com.fasterxml.jackson.core:jackson-core:jar:2.4.4:compile
[INFO] |  +- org.hibernate:hibernate-validator:jar:5.1.3.Final:compile
[INFO] |  |  +- javax.validation:validation-api:jar:1.1.0.Final:compile
[INFO] |  |  +- org.jboss.logging:jboss-logging:jar:3.1.3.GA:compile
[INFO] |  |  \- com.fasterxml:classmate:jar:1.0.0:compile
[INFO] |  +- org.springframework:spring-web:jar:4.1.4.RELEASE:compile
[INFO] |  |  +- org.springframework:spring-aop:jar:4.1.4.RELEASE:compile
[INFO] |  |  |  \- aopalliance:aopalliance:jar:1.0:compile
[INFO] |  |  +- org.springframework:spring-beans:jar:4.1.4.RELEASE:compile
[INFO] |  |  \- org.springframework:spring-context:jar:4.1.4.RELEASE:compile
[INFO] |  \- org.springframework:spring-webmvc:jar:4.1.4.RELEASE:compile
[INFO] |     \- org.springframework:spring-expression:jar:4.1.4.RELEASE:compile

…但调用 test 服务会出现上述错误。 test2 和 test3 工作正常证明它一定只是尝试转换为失败的 JSON？我是否遗漏了一些配置问题或注释？从我能找到的所有示例中，不再需要为基本的 Jackson JSON 转换注释类。

非常感谢任何帮助。

原文由 crowmagnumb 发布，翻译遵循 CC BY-SA 4.0 许可协议

Answer 1

您的 UpdateResult 没有公共 getter，例如：

 public static class UploadResult {
    private String value;
    public UploadResult(final String value)
    {
        this.value = value;
    }

    public String getValue() {
       return this.value;
    }
}

我相信默认情况下自动发现是开启的，并且会尝试发现你的吸气剂。您可以使用 @JsonAutoDetect(getterVisibility=Visibility.NONE) 禁用它，在您的示例中将导致 [] 。

原文由 ikumen 发布，翻译遵循 CC BY-SA 3.0 许可协议

Answer 2

我在使用 spring/jhipster RESTful 服务时遇到了类似的错误（通过 Postman ）

端点是这样的：

 @RequestMapping(value = "/index-entries/{id}",
        method = RequestMethod.GET,
        produces = MediaType.APPLICATION_JSON_VALUE)
@Timed
public ResponseEntity<IndexEntry> getIndexEntry(@PathVariable Long id) {

I was attempting to call the restful endpoint via Postman with header Accept: text/plain but I needed to use Accept: application/json

原文由 wired00 发布，翻译遵循 CC BY-SA 4.0 许可协议