如何将JSON转换为Java对象

Question

我正在使用Jackson ObjectMapper 我有JSON和Java Class。我越来越异常了。有人能告诉我我的Java类错误吗

JSON：

{"name":
    [
        {
            "field1":"value1",
            "field2":"value2"
        },
        {
            "field1":"value1",
            "field2":"value2"
        },
        {
            "field1":"value1",
            "field2":"value2"
        }
    ]
}

Java类： AnyJsonObject.java：

public class AnyJsonObject {
    private List<Name> name;

    public List<Name> getName() {
        return name;
    }

    public void setName(List<Name> name) {
        this.name = name;
    }
}

Name.java：

public class Name {

    @JsonProperty("field1")
    public String fieldOne;

    public String field2;

}

代码：

ObjectMapper mapper = new ObjectMapper();
mapper.readValue(json, AnyJsonObject.class);

我得到java.lang.Exception：反序列化json时发生错误

Answer 1

在AnyJsonObject class中，您有以下几行：

private List<Name> name;

// wrong place here
public Name getName() {
    return name;
}

您正在返回List<Name>类型，但方法签名为public Name getName()。您应该修复返回类型：

public List<Name> getName() {
    return name;
}

修改

我修改了您的源代码并使用了Jackson 2 lib。以下是我执行此任务的内容：

以下是class Name：

import com.fasterxml.jackson.annotation.JsonProperty;

public class Name {

    @JsonProperty("field1")
    public String fieldOne;

    @JsonIgnore
    public String field2; // this field will be ignored

    @Override
    public String toString() {
        return "field1: " + fieldOne + ", field2: " + field2;
    }
} 

以下是AnyJsonObject class：

import java.util.List;

public class AnyJsonObject {
    private List<Name> name;

    public List<Name> getName() {
        return name;
    }

    public void setName(List<Name> name) {
        this.name = name;
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        for (Name n : name) sb.append(n.toString());

        return sb.toString();
    }
}

这是Test class：

import com.fasterxml.jackson.databind.ObjectMapper;
import java.io.IOException;

public class Test {

    public static void main(String[] args) {
        String json = "{\"name\":\n" +
                "    [\n" +
                "        {\n" +
                "            \"field1\":\"value1\",\n" +
                "            \"field2\":\"value2\"\n" +
                "        },\n" +
                "        {\n" +
                "            \"field1\":\"value1\",\n" +
                "            \"field2\":\"value2\"\n" +
                "        },\n" +
                "        {\n" +
                "            \"field1\":\"value1\",\n" +
                "            \"field2\":\"value2\"\n" +
                "        }\n" +
                "    ]\n" +
                "}";

        ObjectMapper mapper = new ObjectMapper();

        try {
            AnyJsonObject any = mapper.readValue(json, AnyJsonObject.class);
            System.out.println(any);

        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

  

执行输出：

     

field1：value1，field2：value2field1：value1，field2：value2field1：value1，field2：value2

Answer 2

作为替代建议使用gson（https://github.com/google/gson） 它还有助于将json读取到Java对象，例如：

public List<Class_to_create_json_of> readJsonToObject(String jsonContent) {

    JSONObject json = new JSONObject();
    try {
         json = (JSONObject) new JSONParser().parse(jsonContent);
    } catch (Exception e) {
         handleException(e);
    }
    return gson.fromJson(json.toString(),
                new TypeToken<List<Class_to_create_json_of>>() {}.getType());
}

Class_to_create_json_of是表示字符串值的Json - String字段的类，布尔值的布尔值等等.... 例如：

{
  "some_key" : "some_velue",
  "some_other_key" : 1,
  "some_third_key" : true
}

public class jsonContent {
   private String some_key;
   private int some_other_key;
   privtae boolean some_third_key;

   public setSome_key(String some_key) {
       this.some_key = some_key;
   }
   public setSome_other_key(int some_other_key) {
      this.some_other_key = some_other_key;
   }
   public setSome_third_key(boolean some_third_key) {
      this.some_third_key = some_third_key;
   }

   public getSome_key() {
       return some_key;
   }
   public getSome_other_key(i) {
      return some_other_key;
   }
   public getSome_third_key() {
      return some_third_key;
   }
}

Answer 3

import com.fasterxml.jackson.core.JsonProcessingException; import com.fasterxml.jackson.databind.JavaType; import com.fasterxml.jackson.databind.JsonNode; import com.fasterxml.jackson.databind.ObjectMapper; import com。 fasterxml.jackson.databind.node.ArrayNode; public static T jsonToPojo（String jsonData，Class beanType）{try {T t = MAPPER.readValue（jsonData，beanType）; return t;} catch（Exception e）{e.printStackTrace（ ）;} return null;}