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

问题描述

我希望能够从我的 Java 操作方法中的 JSON 字符串访问属性.只需说 myJsonString = object.getJson() 即可获得该字符串.以下是字符串外观的示例:

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': []
        }]
    }]
}

在这个字符串中，每个 JSON 对象都包含其他 JSON 对象的数组.目的是提取 ID 列表，其中任何给定对象拥有包含其他 JSON 对象的组属性.我将 Google 的 Gson 视为一个潜在的 JSON 插件.任何人都可以就如何从这个 JSON 字符串生成 Java 提供某种形式的指导吗?

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?

推荐答案

我将 Google 的 Gson 视为潜在的 JSON 插件.任何人都可以就如何从这个 JSON 字符串生成 Java 提供某种形式的指导吗?

Google Gson 支持泛型和嵌套 bean.JSON 中的 [] 表示一个数组，应该映射到一个 Java 集合，例如 List 或只是一个普通的 Java 数组.JSON 中的 {} 表示一个对象，应该映射到 Java Map 或只是一些 JavaBean 类.

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.

您有一个具有多个属性的 JSON 对象，其中 groups 属性表示一组相同类型的嵌套对象.这可以通过以下方式用 Gson 解析:

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);
    }
}

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

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

• Json.org - JSON 简介
• Gson 用户指南 - Gson 简介

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

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