为了便于示例，让我们假设您有一个只有名称的Person类。

private class Person {
    public String name;

    public Person(String name) {
        this.name = name;
    }
}

谷歌GSON (Maven)

我个人最喜欢的JSON对象序列化/反序列化。

Gson g = new Gson();

Person person = g.fromJson("{\"name\": \"John\"}", Person.class);
System.out.println(person.name); //John

System.out.println(g.toJson(person)); // {"name":"John"}

更新

如果你想获取单个属性，你可以很容易地使用谷歌库:

JsonObject jsonObject = new JsonParser().parse("{\"name\": \"John\"}").getAsJsonObject();

System.out.println(jsonObject.get("name").getAsString()); //John

Org。JSON (Maven)

如果您不需要对象反序列化，而只是获得一个属性，您可以尝试org。json(或查看上面的GSON示例!)

JSONObject obj = new JSONObject("{\"name\": \"John\"}");

System.out.println(obj.getString("name")); //John

杰克逊(Maven)

ObjectMapper mapper = new ObjectMapper();
Person user = mapper.readValue("{\"name\": \"John\"}", Person.class);

System.out.println(user.name); //John

你可以用谷歌Gson。

使用这个库，您只需要创建一个具有相同JSON结构的模型。然后自动填充模型。你必须调用你的变量作为你的JSON键，或者使用@SerializedName如果你想使用不同的名字。

JSON

从你的例子中:

{
    "pageInfo": {
        "pageName": "abc",
        "pagePic": "http://example.com/content.jpg"
    }
    "posts": [
        {
            "post_id": "123456789012_123456789012",
            "actor_id": "1234567890",
            "picOfPersonWhoPosted": "http://example.com/photo.jpg",
            "nameOfPersonWhoPosted": "Jane Doe",
            "message": "Sounds cool. Can't wait to see it!",
            "likesCount": "2",
            "comments": [],
            "timeOfPost": "1234567890"
        }
    ]
}

模型

class MyModel {

    private PageInfo pageInfo;
    private ArrayList<Post> posts = new ArrayList<>();
}

class PageInfo {

    private String pageName;
    private String pagePic;
}

class Post {

    private String post_id;

    @SerializedName("actor_id") // <- example SerializedName
    private String actorId;

    private String picOfPersonWhoPosted;
    private String nameOfPersonWhoPosted;
    private String message;
    private String likesCount;
    private ArrayList<String> comments;
    private String timeOfPost;
}

解析

现在你可以使用Gson库进行解析:

MyModel model = gson.fromJson(jsonString, MyModel.class);

Gradle进口

记得在应用的Gradle文件中导入这个库

implementation 'com.google.code.gson:gson:2.8.6' // or earlier versions

自动生成模型

您可以使用这样的在线工具从JSON自动生成模型。

Quick-json解析器非常简单，灵活，快速，可定制。试一试

特点:

Compliant with JSON specification (RFC4627) High-Performance JSON parser Supports Flexible/Configurable parsing approach Configurable validation of key/value pairs of any JSON Hierarchy Easy to use # Very small footprint Raises developer friendly and easy to trace exceptions Pluggable Custom Validation support - Keys/Values can be validated by configuring custom validators as and when encountered Validating and Non-Validating parser support Support for two types of configuration (JSON/XML) for using quick-JSON validating parser Requires JDK 1.5 No dependency on external libraries Support for JSON Generation through object serialisation Support for collection type selection during parsing process

它可以这样使用:

JsonParserFactory factory=JsonParserFactory.getInstance();
JSONParser parser=factory.newJsonParser();
Map jsonMap=parser.parseJson(jsonString);

由于还没有人提到它，这里是一个使用Nashorn (Java 8的JavaScript运行时部分，但在Java 11中已弃用)的解决方案的开始。

解决方案

private static final String EXTRACTOR_SCRIPT =
    "var fun = function(raw) { " +
    "var json = JSON.parse(raw); " +
    "return [json.pageInfo.pageName, json.pageInfo.pagePic, json.posts[0].post_id];};";

public void run() throws ScriptException, NoSuchMethodException {
    ScriptEngine engine = new ScriptEngineManager().getEngineByName("nashorn");
    engine.eval(EXTRACTOR_SCRIPT);
    Invocable invocable = (Invocable) engine;
    JSObject result = (JSObject) invocable.invokeFunction("fun", JSON);
    result.values().forEach(e -> System.out.println(e));
}

性能比较

我编写的JSON内容包含三个数组，分别为20、20和100个元素。我只想从第三个数组中获取100个元素。我使用下面的JavaScript函数来解析和获取我的条目。

var fun = function(raw) {JSON.parse(raw).entries};

使用Nashorn运行一百万次调用需要7.5~7.8秒

(JSObject) invocable.invokeFunction("fun", json);

org。Json需要20~21秒

new JSONObject(JSON).getJSONArray("entries");

杰克逊用时6.5~7秒

mapper.readValue(JSON, Entries.class).getEntries();

在这种情况下，Jackson的性能比Nashorn好，后者的性能比org.json好得多。 Nashorn API比org更难使用。json或Jackson的。根据您的需求，Jackson和Nashorn都是可行的解决方案。

A -解释

您可以使用Jackson库，将JSON字符串绑定到POJO(普通旧Java对象)实例中。POJO只是一个只有私有字段和公共getter/setter方法的类。Jackson将遍历这些方法(使用反射)，并将JSON对象映射到POJO实例，因为类的字段名与JSON对象的字段名相匹配。

在JSON对象中，它实际上是一个复合对象，主对象由两个子对象组成。因此，我们的POJO类应该具有相同的层次结构。我将把整个JSON对象称为Page对象。Page对象由PageInfo对象和Post对象数组组成。

所以我们必须创建三个不同的POJO类;

页面类，PageInfo类和Post实例数组的组合 PageInfo类 文章类

我唯一用过的包是Jackson ObjectMapper，我们做的是绑定数据;

com.fasterxml.jackson.databind.ObjectMapper

所需的依赖项，jar文件如下所示;

jackson-core-2.5.1.jar jackson-databind-2.5.1.jar jackson-annotations-2.5.0.jar

这里是所需的代码;

主POJO类:页

package com.levo.jsonex.model;

public class Page {
    
    private PageInfo pageInfo;
    private Post[] posts;

    public PageInfo getPageInfo() {
        return pageInfo;
    }

    public void setPageInfo(PageInfo pageInfo) {
        this.pageInfo = pageInfo;
    }

    public Post[] getPosts() {
        return posts;
    }

    public void setPosts(Post[] posts) {
        this.posts = posts;
    }
    
}

C -儿童POJO类:PageInfo

package com.levo.jsonex.model;

public class PageInfo {
    
    private String pageName;
    private String pagePic;
    
    public String getPageName() {
        return pageName;
    }
    
    public void setPageName(String pageName) {
        this.pageName = pageName;
    }
    
    public String getPagePic() {
        return pagePic;
    }
    
    public void setPagePic(String pagePic) {
        this.pagePic = pagePic;
    }
    
}

D -儿童POJO类:Post

package com.levo.jsonex.model;

public class Post {
    
    private String post_id;
    private String actor_id;
    private String picOfPersonWhoPosted;
    private String nameOfPersonWhoPosted;
    private String message;
    private int likesCount;
    private String[] comments;
    private int timeOfPost;

    public String getPost_id() {
        return post_id;
    }

    public void setPost_id(String post_id) {
        this.post_id = post_id;
    }

    public String getActor_id() {
        return actor_id;
    }

    public void setActor_id(String actor_id) {
        this.actor_id = actor_id;
    }

    public String getPicOfPersonWhoPosted() {
        return picOfPersonWhoPosted;
    }
    
    public void setPicOfPersonWhoPosted(String picOfPersonWhoPosted) {
        this.picOfPersonWhoPosted = picOfPersonWhoPosted;
    }

    public String getNameOfPersonWhoPosted() {
        return nameOfPersonWhoPosted;
    }

    public void setNameOfPersonWhoPosted(String nameOfPersonWhoPosted) {
        this.nameOfPersonWhoPosted = nameOfPersonWhoPosted;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    public int getLikesCount() {
        return likesCount;
    }

    public void setLikesCount(int likesCount) {
        this.likesCount = likesCount;
    }

    public String[] getComments() {
        return comments;
    }

    public void setComments(String[] comments) {
        this.comments = comments;
    }

    public int getTimeOfPost() {
        return timeOfPost;
    }

    public void setTimeOfPost(int timeOfPost) {
        this.timeOfPost = timeOfPost;
    }
    
}

E -样本JSON文件:sampleJSONFile.json

我刚刚将JSON示例复制到这个文件中，并将其放在项目文件夹下。

{
   "pageInfo": {
         "pageName": "abc",
         "pagePic": "http://example.com/content.jpg"
    },
    "posts": [
         {
              "post_id": "123456789012_123456789012",
              "actor_id": "1234567890",
              "picOfPersonWhoPosted": "http://example.com/photo.jpg",
              "nameOfPersonWhoPosted": "Jane Doe",
              "message": "Sounds cool. Can't wait to see it!",
              "likesCount": "2",
              "comments": [],
              "timeOfPost": "1234567890"
         }
    ]
}

F -演示代码

package com.levo.jsonex;

import java.io.File;
import java.io.IOException;
import java.util.Arrays;

import com.fasterxml.jackson.databind.ObjectMapper;
import com.levo.jsonex.model.Page;
import com.levo.jsonex.model.PageInfo;
import com.levo.jsonex.model.Post;

public class JSONDemo {
    
    public static void main(String[] args) {
        ObjectMapper objectMapper = new ObjectMapper();
        
        try {
            Page page = objectMapper.readValue(new File("sampleJSONFile.json"), Page.class);
            
            printParsedObject(page);
        } catch (IOException e) {
            e.printStackTrace();
        }
        
    }
    
    private static void printParsedObject(Page page) {
        printPageInfo(page.getPageInfo());
        System.out.println();
        printPosts(page.getPosts());
    }

    private static void printPageInfo(PageInfo pageInfo) {
        System.out.println("Page Info;");
        System.out.println("**********");
        System.out.println("\tPage Name : " + pageInfo.getPageName());
        System.out.println("\tPage Pic  : " + pageInfo.getPagePic());
    }
    
    private static void printPosts(Post[] posts) {
        System.out.println("Page Posts;");
        System.out.println("**********");
        for(Post post : posts) {
            printPost(post);
        }
    }
    
    private static void printPost(Post post) {
        System.out.println("\tPost Id                   : " + post.getPost_id());
        System.out.println("\tActor Id                  : " + post.getActor_id());
        System.out.println("\tPic Of Person Who Posted  : " + post.getPicOfPersonWhoPosted());
        System.out.println("\tName Of Person Who Posted : " + post.getNameOfPersonWhoPosted());
        System.out.println("\tMessage                   : " + post.getMessage());
        System.out.println("\tLikes Count               : " + post.getLikesCount());
        System.out.println("\tComments                  : " + Arrays.toString(post.getComments()));
        System.out.println("\tTime Of Post              : " + post.getTimeOfPost());
    }
    
}

G -演示输出

Page Info;
****(*****
    Page Name : abc
    Page Pic  : http://example.com/content.jpg
Page Posts;
**********
    Post Id                   : 123456789012_123456789012
    Actor Id                  : 1234567890
    Pic Of Person Who Posted  : http://example.com/photo.jpg
    Name Of Person Who Posted : Jane Doe
    Message                   : Sounds cool. Can't wait to see it!
    Likes Count               : 2
    Comments                  : []
    Time Of Post              : 1234567890

The below example shows how to read the text in the question, represented as the "jsonText" variable. This solution uses the Java EE7 javax.json API (which is mentioned in some of the other answers). The reason I've added it as a separate answer is that the following code shows how to actually access some of the values shown in the question. An implementation of the javax.json API would be required to make this code run. The full package for each of the classes required was included as I didn't want to declare "import" statements.

javax.json.JsonReader jr = 
    javax.json.Json.createReader(new StringReader(jsonText));
javax.json.JsonObject jo = jr.readObject();

//Read the page info.
javax.json.JsonObject pageInfo = jo.getJsonObject("pageInfo");
System.out.println(pageInfo.getString("pageName"));

//Read the posts.
javax.json.JsonArray posts = jo.getJsonArray("posts");
//Read the first post.
javax.json.JsonObject post = posts.getJsonObject(0);
//Read the post_id field.
String postId = post.getString("post_id");

现在，在大家对这个答案投反对票之前因为它没有使用GSON, org。json, Jackson或任何其他可用的第三方框架，它是每个问题解析所提供文本的“所需代码”的示例。我很清楚JDK 9没有考虑遵守当前标准JSR 353，因此JSR 353规范应该与任何其他第三方JSON处理实现一样对待。