如何忽略json中的父标签？？

这是我的json

String str = "{\"parent\": {\"a\":{\"id\": 10, \"name\":\"Foo\"}}}";

这是要从 json 映射的类。

public class RootWrapper {
  private List<Foo> foos;

  public List<Foo> getFoos() {
    return foos;
  }

  @JsonProperty("a")
  public void setFoos(List<Foo> foos) {
    this.foos = foos;
  }
 }

这是测试 公共(public)类 JacksonTest {

@Test
public void wrapRootValue() throws Exception {
    ObjectMapper mapper = new ObjectMapper();
    mapper.configure(DeserializationConfig.Feature.UNWRAP_ROOT_VALUE, true);
    mapper.configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);

    String str = "{\"parent\": {\"a\":{\"id\": 10, \"name\":\"Foo\"}}}";

    RootWrapper root = mapper.readValue(str, RootWrapper.class);

    Assert.assertNotNull(root);
}

我得到错误::

 org.codehaus.jackson.map.JsonMappingException: Root name 'parent' does not match expected ('RootWrapper') for type [simple type, class MavenProjectGroup.mavenProjectArtifact.RootWrapper]

我找到了Jackson注解给出的解决方案::

  (a) Annotate you class as below

  @JsonRootName(value = "parent")
  public class RootWrapper {

  (b) It will only work if and only if ObjectMapper is asked to wrap.
    ObjectMapper mapper = new ObjectMapper();
mapper.configure(DeserializationConfig.Feature.UNWRAP_ROOT_VALUE, true);

任务完成!!

Jackson 反序列化方式的另一个问题:(

如果“DeserializationConfig.Feature.UNWRAP_ROOT_VALUE 已配置”，它会解开所有 json，尽管我的类没有使用 @JsonRootName(value = "rootTagInJson") 进行注释，但并不奇怪。

只有当类被 @JsonRootName 注释时，我才想解开根标签，否则不要解开。

下面是展开根标签的用例。

  ###########################################################
     Unwrap only if the class is annotated with @JsonRootName.
  ############################################################

我对 Jackson 源代码的 ObjectMapper 做了一个小改动，并创建了一个新版本的 jar。 1.将此方法放在ObjectMapper中

// Ash:: Wrap json if the class being deserialized, are annotated
// with @JsonRootName else do not wrap.
private boolean hasJsonRootName(JavaType valueType) {
    if (valueType.getRawClass() == null)
        return false;

    Annotation rootAnnotation =  valueType.getRawClass().getAnnotation(JsonRootName.class);
    return rootAnnotation != null;
}


    2. Edit ObjectMapper method :: 
    Replace 
       cfg.isEnabled(DeserializationConfig.Feature.UNWRAP_ROOT_VALUE)
    with
       hasJsonRootName(valueType)

    3. Build your jar file and use it.

最佳答案

取自 https://github.com/FasterXML/jackson-databind 中的 TestRootName.java 的示例可能会提供更好的方法来做到这一点。具体使用 withRootName(""):

private ObjectMapper rootMapper()
{
    ObjectMapper mapper = new ObjectMapper();
    mapper.configure(SerializationFeature.WRAP_ROOT_VALUE, true);
    mapper.configure(DeserializationFeature.UNWRAP_ROOT_VALUE, true);
    return mapper;
}

public void testRootUsingExplicitConfig() throws Exception
{
    ObjectMapper mapper = new ObjectMapper();
    ObjectWriter writer = mapper.writer().withRootName("wrapper");
    String json = writer.writeValueAsString(new Bean());
    assertEquals("{\"wrapper\":{\"a\":3}}", json);

    ObjectReader reader = mapper.reader(Bean.class).withRootName("wrapper");
    Bean bean = reader.readValue(json);
    assertNotNull(bean);

    // also: verify that we can override SerializationFeature as well:
    ObjectMapper wrapping = rootMapper();
    json = wrapping.writer().withRootName("something").writeValueAsString(new Bean());
    assertEquals("{\"something\":{\"a\":3}}", json);
    json = wrapping.writer().withRootName("").writeValueAsString(new Bean());
    assertEquals("{\"a\":3}", json);

    bean = wrapping.reader(Bean.class).withRootName("").readValue(json);
    assertNotNull(bean);
}

https://stackoverflow.com/questions/8837018/