使用Jackson映射的嵌套Json

Question

我试图动态解析一些JSON到一个Map

        String easyString = "{\"name\":\"mkyong\", \"age\":\"29\"}";
    Map<String,String> map = new HashMap<String,String>();
    ObjectMapper mapper = new ObjectMapper();

    map = mapper.readValue(easyString, 
            new TypeReference<HashMap<String,String>>(){});

    System.out.println(map);

但是当我尝试使用一些更复杂的JSON和嵌套信息时失败了。我试图从json解析示例数据。组织

{
  "glossary": {
    "title": "example glossary",
    "GlossDiv": {
      "title": "S",
      "GlossList": {
        "GlossEntry": {
          "ID": "SGML",
          "SortAs": "SGML",
          "GlossTerm": "Standard Generalized Markup Language",
          "Acronym": "SGML",
          "Abbrev": "ISO 8879:1986",
          "GlossDef": {
            "para": "A meta-markup language, used to create markup languages such as DocBook.",
            "GlossSeeAlso": [
              "GML",
              "XML"
            ]
          },
          "GlossSee": "markup"
        }
      }
    }
  }
}

我得到以下错误

异常在线程"main"com.fasterxml.jackson.databind.JsonMapping异常：不能反序列化实例的java.lang.字符串START_OBJECT令牌

有没有办法将复杂的JSON数据解析成映射？

Answer 1

将地图包装成一个哑对象作为容器，如下所示：

public class Country {
  private final Map<String,Map<String,Set<String>>> citiesAndCounties=new HashMap<>;

  // Generate getters and setters and see the magic happen.
}

剩下的就是使用你的Object mapper，例如使用Joda模块的Object mapper：

public static final ObjectMapper JSON_MAPPER=new ObjectMapper().
          disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES).
          setSerializationInclusion(JsonInclude.Include.NON_NULL).
          disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS).
          registerModule(new JodaModule());

// Calling your Object mapper
JSON_MAPPER.writeValueAsString(new Country());

希望有帮助；-）

Answer 2

我认为发生错误是因为Jackson在遇到{字符时，会将剩余的内容视为新对象，而不是字符串。请尝试将对象作为映射值，而不是字符串。

public static void main(String[] args) throws IOException {

    Map<String,String> map = new HashMap<String,String>();
    ObjectMapper mapper = new ObjectMapper();

    map = mapper.readValue(x, new TypeReference<HashMap>(){});

    System.out.println(map);
}

输出

{glossary={title=example glossary, GlossDiv={title=S, GlossList={GlossEntry={ID=SGML, SortAs=SGML, GlossTerm=Standard Generalized Markup Language, Acronym=SGML, Abbrev=ISO 8879:1986, GlossDef={para=A meta-markup language, used to create markup languages such as DocBook., GlossSeeAlso=[GML, XML]}, GlossSee=markup}}}}}