java怎么取json里面的数据

Java中如何从JSON数据中提取信息的全面指南

在Java开发中，处理JSON数据是一项非常常见的任务，无论是从API响应中获取数据，还是解析配置文件，如何从JSON中提取信息都是必不可少的技能，本文将详细介绍几种在Java中获取JSON数据的方法，从传统的库到现代的函数式编程方式,帮助你根据不同场景选择最适合的解决方案。

使用org.json库解析JSON

org.json是一个轻量级的JSON处理库,适合简单的JSON操作。

添加Maven依赖：

<dependency>
    <groupId>org.json</groupId>
    <artifactId>json</artifactId>
    <version>20231013</version>
</dependency>

示例代码：

import org.json.JSONObject;
import org.json.JSONArray;
public class JsonExample {
    public static void main(String[] args) {
        String jsonStr = "{\"name\":\"张三\",\"age\":30,\"hobbies\":[\"阅读\",\"旅行\"]}";
        // 解析JSON对象
        JSONObject jsonObject = new JSONObject(jsonStr);
        // 获取简单值
        String name = jsonObject.getString("name");
        int age = jsonObject.getInt("age");
        System.out.println("姓名: " + name + ", 年龄: " + age);
        // 获取数组
        JSONArray hobbies = jsonObject.getJSONArray("hobbies");
        System.out.print("爱好: ");
        for (int i = 0; i < hobbies.length(); i++) {
            System.out.print(hobbies.getString(i) + " ");
        }
    }
}

使用Gson库解析JSON

Gson是Google开发的JSON处理库,功能强大且易于使用。

添加Maven依赖：

<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.10.1</version>
</dependency>

1 将JSON映射到Java对象

import com.google.gson.Gson;
class Person {
    private String name;
    private int age;
    private String[] hobbies;
    // getters and setters
}
public class GsonExample {
    public static void main(String[] args) {
        String jsonStr = "{\"name\":\"李四\",\"age\":25,\"hobbies\":[\"音乐\",\"电影\"]}";
        Gson gson = new Gson();
        Person person = gson.fromJson(jsonStr, Person.class);
        System.out.println("姓名: " + person.getName());
        System.out.println("年龄: " + person.getAge());
        System.out.print("爱好: ");
        for (String hobby : person.getHobbies()) {
            System.out.print(hobby + " ");
        }
    }
}

2 解析嵌套JSON

class Address {
    private String city;
    private String street;
}
class PersonWithAddress {
    private String name;
    private Address address;
}
public class NestedJsonExample {
    public static void main(String[] args) {
        String jsonStr = "{\"name\":\"王五\",\"address\":{\"city\":\"北京\",\"street\":\"长安街\"}}";
        Gson gson = new Gson();
        PersonWithAddress person = gson.fromJson(jsonStr, PersonWithAddress.class);
        System.out.println("姓名: " + person.getName());
        System.out.println("城市: " + person.getAddress().getCity());
        System.out.println("街道: " + person.getAddress().getStreet());
    }
}

使用Jackson库解析JSON

Jackson是另一个流行的JSON处理库，性能优异,功能全面。

添加Maven依赖：

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.15.2</version>
</dependency>

1 基本用法

import com.fasterxml.jackson.databind.ObjectMapper;
class User {
    private String username;
    private int userId;
    // getters and setters
}
public class JacksonExample {
    public static void main(String[] args) throws Exception {
        String jsonStr = "{\"username\":\"johndoe\",\"userId\":123}";
        ObjectMapper objectMapper = new ObjectMapper();
        User user = objectMapper.readValue(jsonStr, User.class);
        System.out.println("用户名: " + user.getUsername());
        System.out.println("用户ID: " + user.getUserId());
    }
}

2 处理JSON数组

import com.fasterxml.jackson.core.type.TypeReference;
import java.util.List;
public class JsonArrayExample {
    public static void main(String[] args) throws Exception {
        String jsonStr = "[{\"name\":\"商品1\",\"price\":10.5},{\"name\":\"商品2\",\"price\":20.3}]";
        ObjectMapper objectMapper = new ObjectMapper();
        List<Product> products = objectMapper.readValue(jsonStr, new TypeReference<List<Product>>() {});
        for (Product product : products) {
            System.out.println("商品: " + product.getName() + ", 价格: " + product.getPrice());
        }
    }
}
class Product {
    private String name;
    private double price;
    // getters and setters
}

使用Java内置的javax.json API

Java EE 7及以上版本提供了javax.json API来处理JSON。

添加Maven依赖：

<dependency>
    <groupId>org.glassfish</groupId>
    <artifactId>javax.json</artifactId>
    <version>1.1.4</version>
</dependency>

示例代码：

import javax.json.Json;
import javax.json.JsonObject;
import javax.json.JsonReader;
import java.io.StringReader;
public class JsonpExample {
    public static void main(String[] args) {
        String jsonStr = "{\"name\":\"赵六\",\"age\":35}";
        JsonReader reader = Json.createReader(new StringReader(jsonStr));
        JsonObject jsonObject = reader.readObject();
        String name = jsonObject.getString("name");
        int age = jsonObject.getInt("age");
        System.out.println("姓名: " + name + ", 年龄: " + age);
    }
}

使用Java 11+的HttpClient和JSON解析

Java 11引入了HttpClient和轻量级的JSON API（虽然这个API在Java 14中被移除了）。

import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.util.Map;
public class Java11JsonExample {
    public static void main(String[] args) throws Exception {
        HttpClient client = HttpClient.newHttpClient();
        HttpRequest request = HttpRequest.newBuilder()
                .uri(URI.create("https://api.example.com/data"))
                .build();
        HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());
        String jsonStr = response.body();
        // 使用简单的字符串处理提取数据
        String name = jsonStr.split("\"name\":")[1].split(",")[0].replace("\"", "");
        System.out.println("名称: " + name);
    }
}