Jackson json反序列化,忽略来自json的根元素

如何从json忽略父标签?

这是我的json

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

这里是从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;
  }
 }

这里是测试
       public class 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]

我发现Jackson注释给出的解决方案::

  (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!!

另一个打嗝与Jackson的反序列化方法:(

如果’DeserializationConfig.Feature.UNWRAP_ROOT_VALUE配置’,它解开所有jsons,eventhough我的类没有注释与@JsonRootName(value =“rootTagInJson”),不是weired。

我想解开根标记只有如果类用@JsonRootName注释,否则不解包。

下面是解开根标签的用例。

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

我对Jackson的ObjectMapper中的一个小改动源代码,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
https://github.com/FasterXML/jackson-databind中的TestRootName.java中获取的示例可能会提供更好的方法。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);
}

转载注明原文:Jackson json反序列化,忽略来自json的根元素 - 代码日志