将JSON数据转换为Java对象 [英] Converting JSON data to Java object

问题描述

我希望能够在我的Java操作方法中从JSON字符串访问属性。该字符串可通过简单说 myJsonString = object.getJson（）来使用。下面是一个字符串的例子：

  {
'title'：'ComputingandInformationsystems'，
'id'：1，
'children'：'true'，
'groups'：[{
'title'：'LeveloneCIS'，
'id' ：2，
'children'：'true'，
'groups'：[{
'title'：'IntroToComputingandInternet'，
'id'：3，
'children'：'false'，
'groups'：[] 
}] 
}] 
} 
  

在此字符串中，每个JSON对象都包含其他JSON对象的数组。目的是提取任何给定对象拥有包含其他JSON对象的组属性的ID列表。我将Google的Gson视为潜在的JSON插件。任何人都可以提供某种形式的指导，以了解如何从这个JSON字符串中生成Java？

解决方案

我将Google的Gson看作潜在的JSON插件。任何人都可以提供某种形式的指导，以了解如何从此JSON字符串生成Java？

Google Gson 支持泛型和嵌套bean。 JSON中的 [] 代表一个数组，并且应该映射到一个Java集合，比如 List 或者只是一个普通的Java数组。 JSON中的 {} 代表一个对象，并且应该映射到Java Map 或者只是一些JavaBean类。

您有一个JSON对象，其中有几个属性，其中 groups 属性表示具有相同类型的嵌套对象数组。这可以用Gson按以下方式解析：

  package com.stackoverflow.q1688099; 
 
 import java.util.List; 
 import com.google.gson.Gson; 
 
 public class Test {
 
 public static void main（String ... args）throws Exception {
 String json = 
{
 +''title'：'计算和信息系统'，'
 +''id'：1，'
 +''children'：'true'，'
 +' 'groups'：[{
 +'title'：'Level 1 CIS'，'
 +''id'：2，'
 +''children'：'true' ，
 +'groups'：[{
 +'title'：'介绍到计算和互联网'，'
 +''id'：3，
 +''children'：'false'，'
 +''groups'：[]
 +}]
 +}]
 +} ; 
 
 //现在做魔术。 
 Data data = new Gson（）。fromJson（json，Data.class）; 
 
 //显示它。 
 System.out.println（data）; 
} 
 
} 
 
 class数据{
私有字符串标题; 
私人长ID; 
私人布尔儿童; 
私人列表< Data>组; 
 
 public String getTitle（）{return title; } 
 public Long getId（）{return id; } 
 public Boolean getChildren（）{return children; } 
 public List< Data> getGroups（）{返回组; } 
 
 public void setTitle（String title）{this.title = title; } 
 public void setId（Long id）{this.id = id; } 
 public void setChildren（Boolean children）{this.children = children; } 
 public void setGroups（List< Data> groups）{this.groups = groups; } 
 $ b $ public String toString（）{
 return String.format（title：％s，id：％d，children：％s，groups：％s，title，id，儿童，团体）; 
} 
} 
  

相当简单，不是吗？只需要有一个合适的JavaBean，并调用 Gson＃fromJson（） 。

参见：

• Json.org - JSON简介


• Gson用户指南 - Gson简介

I want to be able to access properties from a JSON string within my Java action method. The string is available by simply saying myJsonString = object.getJson(). Below is an example of what the string can look like:

{
    'title': 'ComputingandInformationsystems',
    'id': 1,
    'children': 'true',
    'groups': [{
        'title': 'LeveloneCIS',
        'id': 2,
        'children': 'true',
        'groups': [{
            'title': 'IntroToComputingandInternet',
            'id': 3,
            'children': 'false',
            'groups': []
        }]
    }]
}

In this string every JSON object contains an array of other JSON objects. The intention is to extract a list of IDs where any given object possessing a group property that contains other JSON objects. I looked at Google's Gson as a potential JSON plugin. Can anyone offer some form of guidance as to how I can generate Java from this JSON string?

解决方案

I looked at Google's Gson as a potential JSON plugin. Can anyone offer some form of guidance as to how I can generate Java from this JSON string?

Google Gson supports generics and nested beans. The [] in JSON represents an array and should map to a Java collection such as List or just a plain Java array. The {} in JSON represents an object and should map to a Java Map or just some JavaBean class.

You have a JSON object with several properties of which the groups property represents an array of nested objects of the very same type. This can be parsed with Gson the following way:

package com.stackoverflow.q1688099;

import java.util.List;
import com.google.gson.Gson;

public class Test {

    public static void main(String... args) throws Exception {
        String json = 
            "{"
                + "'title': 'Computing and Information systems',"
                + "'id' : 1,"
                + "'children' : 'true',"
                + "'groups' : [{"
                    + "'title' : 'Level one CIS',"
                    + "'id' : 2,"
                    + "'children' : 'true',"
                    + "'groups' : [{"
                        + "'title' : 'Intro To Computing and Internet',"
                        + "'id' : 3,"
                        + "'children': 'false',"
                        + "'groups':[]"
                    + "}]" 
                + "}]"
            + "}";

        // Now do the magic.
        Data data = new Gson().fromJson(json, Data.class);

        // Show it.
        System.out.println(data);
    }

}

class Data {
    private String title;
    private Long id;
    private Boolean children;
    private List<Data> groups;

    public String getTitle() { return title; }
    public Long getId() { return id; }
    public Boolean getChildren() { return children; }
    public List<Data> getGroups() { return groups; }

    public void setTitle(String title) { this.title = title; }
    public void setId(Long id) { this.id = id; }
    public void setChildren(Boolean children) { this.children = children; }
    public void setGroups(List<Data> groups) { this.groups = groups; }

    public String toString() {
        return String.format("title:%s,id:%d,children:%s,groups:%s", title, id, children, groups);
    }
}

Fairly simple, isn't it? Just have a suitable JavaBean and call Gson#fromJson().

See also:

• Json.org - Introduction to JSON
• Gson User Guide - Introduction to Gson

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