请像这样做:

JSONParser jsonParser = new JSONParser();
JSONObject obj = (JSONObject) jsonParser.parse(contentString);
String product = (String) jsonObject.get("productId");

阅读下面的博文，Java中的JSON。

这篇文章有点老了，但我仍然想回答你的问题。

步骤1:创建数据的POJO类。

步骤2:现在使用JSON创建一个对象。

Employee employee = null;
ObjectMapper mapper = new ObjectMapper();
try {
    employee =  mapper.readValue(newFile("/home/sumit/employee.json"), Employee.class);
} 
catch(JsonGenerationException e) {
    e.printStackTrace();
}

如需进一步参考，请参阅以下链接。

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();
    }
}

您可以使用DSM流解析库来解析复杂的json和XML文档。DSM只解析一次数据，不会将所有数据加载到内存中。

假设我们有一个Page类来反序列化给定的json数据。

页面类

public class Page {
    private String pageName;
    private String pageImage;
    private List<Sting> postIds;

    // getter/setter

}

创建一个yaml Mapping文件。

result:
  type: object     # result is array
  path: /posts
  fields:
    pageName:
        path: /pageInfo/pageName
    pageImage:
        path: /pageInfo/pagePic
    postIds:
      path: post_id
      type: array

使用DSM提取字段。

DSM dsm=new DSMBuilder(new File("path-to-yaml-config.yaml")).create(Page.class);
Page page= (Page)dsm.toObject(new path-to-json-data.json");

页面变量序列化为json:

{
  "pageName" : "abc",
  "pageImage" : "http://example.com/content.jpg",
  "postIds" : [ "123456789012_123456789012" ]
}

DSM非常适合处理复杂的json和xml。

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。

本页的热门答案使用了太简单的例子，比如只有一个属性的对象(例如{name: value})。我认为这个简单但真实的例子可以帮助到一些人。

这是谷歌Translate API返回的JSON:

{
  "data": 
     {
        "translations": 
          [
            {
              "translatedText": "Arbeit"
             }
          ]
     }
}

我想检索“translatedText”属性的值。“Arbeit”使用谷歌的Gson。

两种可能的方法:

Retrieve just one needed attribute String json = callToTranslateApi("work", "de"); JsonObject jsonObject = new JsonParser().parse(json).getAsJsonObject(); return jsonObject.get("data").getAsJsonObject() .get("translations").getAsJsonArray() .get(0).getAsJsonObject() .get("translatedText").getAsString(); Create Java object from JSON class ApiResponse { Data data; class Data { Translation[] translations; class Translation { String translatedText; } } } ... Gson g = new Gson(); String json =callToTranslateApi("work", "de"); ApiResponse response = g.fromJson(json, ApiResponse.class); return response.data.translations[0].translatedText;