您需要使用JsonNode和来自jackson库的ObjectMapper类来获取Json树的节点。在pom.xml中添加以下依赖项以获得对Jackson类的访问权。

<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.9.5</version>
</dependency>

你应该尝试下面的代码，这将工作:

import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;

class JsonNodeExtractor{

    public void convertToJson(){

        String filepath = "c:\\data.json";
        ObjectMapper mapper = new ObjectMapper();
        JsonNode node =  mapper.readTree(filepath);

        // create a JsonNode for every root or subroot element in the Json String
        JsonNode pageInfoRoot = node.path("pageInfo");

        // Fetching elements under 'pageInfo'
        String pageName =  pageInfoRoot.path("pageName").asText();
        String pagePic = pageInfoRoot.path("pagePic").asText();

        // Now fetching elements under posts
        JsonNode  postsNode = node.path("posts");
        String post_id = postsNode .path("post_id").asText();
        String nameOfPersonWhoPosted = postsNode 
        .path("nameOfPersonWhoPosted").asText();
    }
}

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);

我相信最好的做法应该是通过仍在开发中的官方Java JSON API。

几乎所有给出的答案都要求在访问感兴趣的属性中的值之前，将JSON完全反序列化为Java对象。另一种不走这条路的替代方法是使用JsonPATH，它类似于JSON的XPath，允许遍历JSON对象。

它是一个规范，JayWay的优秀人员已经为该规范创建了一个Java实现，您可以在这里找到:https://github.com/jayway/JsonPath

所以基本上要使用它，把它添加到你的项目中，例如:

<dependency>
    <groupId>com.jayway.jsonpath</groupId>
    <artifactId>json-path</artifactId>
    <version>${version}</version>
</dependency>

并使用:

String pageName = JsonPath.read(yourJsonString, "$.pageInfo.pageName");
String pagePic = JsonPath.read(yourJsonString, "$.pageInfo.pagePic");
String post_id = JsonPath.read(yourJsonString, "$.pagePosts[0].post_id");

等等……

查看JsonPath规范页面，了解横向JSON的其他方法的更多信息。

如果你有maven项目，那么添加下面的依赖项或普通项目添加json-simple jar。

<dependency>
    <groupId>org.json</groupId>
    <artifactId>json</artifactId>
    <version>20180813</version>
</dependency>

写下面的java代码转换JSON字符串到JSON数组。

JSONArray ja = new JSONArray(String jsonString);

除了其他答案，我推荐这个在线开源服务jsonschema2pojo.org，它可以从json或json模式快速生成Java类，用于GSON, Jackson 1。或者Jackson 2.x。例如，如果你有:

{
   "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
         }
    ]
}

GSON的jsonschema2pojo.org生成:

@Generated("org.jsonschema2pojo")
public class Container {
    @SerializedName("pageInfo")
    @Expose
    public PageInfo pageInfo;
    @SerializedName("posts")
    @Expose
    public List<Post> posts = new ArrayList<Post>();
}

@Generated("org.jsonschema2pojo")
public class PageInfo {
    @SerializedName("pageName")
    @Expose
    public String pageName;
    @SerializedName("pagePic")
    @Expose
    public String pagePic;
}

@Generated("org.jsonschema2pojo")
public class Post {
    @SerializedName("post_id")
    @Expose
    public String postId;
    @SerializedName("actor_id")
    @Expose
    public long actorId;
    @SerializedName("picOfPersonWhoPosted")
    @Expose
    public String picOfPersonWhoPosted;
    @SerializedName("nameOfPersonWhoPosted")
    @Expose
    public String nameOfPersonWhoPosted;
    @SerializedName("message")
    @Expose
    public String message;
    @SerializedName("likesCount")
    @Expose
    public long likesCount;
    @SerializedName("comments")
    @Expose
    public List<Object> comments = new ArrayList<Object>();
    @SerializedName("timeOfPost")
    @Expose
    public long timeOfPost;
}