通过GSON从JSON列表中的多个对象获取多个属性

Question

我有一个包含3个对象的json：问题，标记和选择。

[ 
    { 
     "question" : { 
      "questionId" : 01, 
      "isActive" : 1 
     }, 
     "tags" : ["tag1", "tag2"], 
     "choices" : [{ 
       "choiceId" : 0, 
       "questionId" : 0 
      }, { 
       "choiceId" : 1, 
       "questionId" : 0 
      } 
     ] 
    } 
] 

我目前使用GSON这种提取类由3级不同的对象越来越细节的意图：

public class Extractor { 

//question, tags, and choices are existing classes 
Questions question; 
List<Tags> tags; 
List<Choice> choices; 

//getters and setters 
} 

Extractor result = gson.fromJson(jsonString, Extractor.class); 

//I want to see the question, tag, and choice parts from the json 
System.out.println("Result" + result.getTags().get(0).getName() + result.getChoices().get(0).getChoiceId()); 

我在做什么错？如何分别获得问题，标记和选择的属性？另外，我如何能够遍历包含多个问题，标记和选择的JSON列表？

Answer 1

只要POJO类定义正确，下面的代码应该分别得到问题，标记和选择。有关POJO类定义，请参阅此类似的post。

public static void main(String[] args) { 

     String jsonString = "[{\"question\":{\"questionId\":01,\"isActive\":1},\"tags\":[\"tag1\",\"tag2\"],\"choices\":[{\"choiceId\":0,\"questionId\":0},{\"choiceId\":1,\"questionId\":0}]}]"; 
     Gson gson = new Gson(); 

     JsonParser parser = new JsonParser(); 
     JsonArray array = parser.parse(jsonString).getAsJsonArray(); 

     for (final JsonElement json : array) { 
      Extracter jsonModel = gson.fromJson(json, new TypeToken<Extracter>() { 
      }.getType()); 

      System.out.println(jsonModel.toString()); 

      List<Choices> choicesList = jsonModel.getChoices(); 
      //Looping the choices 
      for (Choices choice :choicesList) { 
       System.out.println("Choice :" + choice); 
       System.out.println("Choice Id :" + choice.getChoiceId()); 
       System.out.println("Question Id :" + choice.getQuestionId()); 
      } 

      //Printing the question 
      System.out.println("Question obj data :" + jsonModel.getQuestion()); 
      System.out.println("Course Id :" + jsonModel.getQuestion().getQuestionId()); 
      System.out.println("Active :" + jsonModel.getQuestion().getIsActive()); 

      //Printing the tags 
      System.out.println(jsonModel.getTags()); 

     } 

    } 

输出： -

Choice :Choices [choiceId=0, questionId=0] 
Choice Id :0 
Question Id :0 
Choice :Choices [choiceId=1, questionId=0] 
Choice Id :1 
Question Id :0 
Question obj data :Question [questionId=1, courseId=null, isActive=1] 
Course Id :1 
Active :1 
[tag1, tag2] 

POJO类： -

public class Extracter implements Serializable { 

    private static final long serialVersionUID = -2255013835370141266L; 
    private List<Choices> choices; 
    private List<String> tags; 
    private Question question; 

    public List<Choices> getChoices() { 
     return choices; 
    } 
    public void setChoices(List<Choices> choices) { 
     this.choices = choices; 
    } 
    public List<String> getTags() { 
     return tags; 
    } 
    public void setTags(List<String> tags) { 
     this.tags = tags; 
    } 
    public Question getQuestion() { 
     return question; 
    } 
    public void setQuestion(Question question) { 
     this.question = question; 
    } 
    @Override 
    public String toString() { 
     return "JsonModel [choices=" + choices + ", tags=" + tags + ", question=" + question + "]"; 
    } 

} 


public class Choices implements Serializable{ 

    private static final long serialVersionUID = 3947337014862847527L; 

    private Integer choiceId; 
    private Integer questionId; 

    public Integer getChoiceId() { 
     return choiceId; 
    } 
    public void setChoiceId(Integer choiceId) { 
     this.choiceId = choiceId; 
    } 
    public Integer getQuestionId() { 
     return questionId; 
    } 
    public void setQuestionId(Integer questionId) { 
     this.questionId = questionId; 
    } 
    @Override 
    public String toString() { 
     return "Choices [choiceId=" + choiceId + ", questionId=" + questionId + "]"; 
    } 



} 


public class Question implements Serializable{ 

    private static final long serialVersionUID = -8649775972572186614L; 

    private Integer questionId; 
    private Integer courseId; 
    private Integer isActive; 

    public Integer getQuestionId() { 
     return questionId; 
    } 
    public void setQuestionId(Integer questionId) { 
     this.questionId = questionId; 
    } 
    public Integer getCourseId() { 
     return courseId; 
    } 
    public void setCourseId(Integer courseId) { 
     this.courseId = courseId; 
    } 
    public Integer getIsActive() { 
     return isActive; 
    } 
    public void setIsActive(Integer isActive) { 
     this.isActive = isActive; 
    } 
    @Override 
    public String toString() { 
     return "Question [questionId=" + questionId + ", courseId=" + courseId + ", isActive=" + isActive + "]"; 
    } 


}