Java之JSON操作（Jackson）

Java to JSON：

package json.jackson;

import bean.User;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.File;
import java.util.Map;

/**
 * Jackson – Java to JSON
 * 功能：JSON与Java对象、Map等类型转换，JSON文件的读写等
 * 依赖包：jackson-databind-2.8.11.1.jar、jackson-core-2.8.10.jar、jackson-annotations-2.8.0.jar
 * https://github.com/FasterXML/jackson-databind
 */
public class JavaToJSON {
    public static void main(String[] ars) throws Exception {
        User user = new User("tom", 25, "NO.1 street");
        ObjectMapper objectMapper = new ObjectMapper();

        // Java对象转json，也支持bytes
        String json = objectMapper.writeValueAsString(user);
        System.out.println("Java对象转json:" + json);

        // json转Java对象
        User user2 = objectMapper.readValue(json, User.class);
        System.out.println("json转Java对象" + user2);

        // 读文件
        String jsonFilePath = "src/main/java/json/jackson/JsonReader.json";
        User user3 = objectMapper.readValue(new File(jsonFilePath), User.class);
        System.out.println("读取JSON文件：" + user3);
        // 写文件
        objectMapper.writeValue(new File(jsonFilePath), user3);

        // json转map，也支持List
        Map map = objectMapper.readValue(json, Map.class);
        System.out.println("json转map：" + map);

        // map转json字符串，支持所有类型转字符串
        String json2 = objectMapper.writeValueAsString(map);
        System.out.println("map转json:" + json2);

    }
}

JsonNode：

package json.jackson;

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.File;
import java.util.List;

/**
 * JsonNode
 * 处理复杂的JSON，返回多个对象的情况
 * 从文件中读取复杂的JSON，根据key找到对应value值
 * 依赖包：jackson-databind-2.8.11.1.jar、jackson-core-2.8.10.jar、jackson-annotations-2.8.0.jar
 * https://github.com/FasterXML/jackson-databind
 */
public class JSONTreeDemo {
    public static void main(String[] ars) throws Exception {
        ObjectMapper objectMapper = new ObjectMapper();
        String jsonFilePath = "src/main/java/json/jackson/Json2.json";
        // 以树形态支持多对象的情况：支持读取多种类型
        JsonNode jsonNode = objectMapper.readTree(new File(jsonFilePath));
        System.out.println("jsonNode：" + jsonNode);
        // 根据key查询多个值，返回list
        List<JsonNode> list = jsonNode.findValues("name");
        System.out.println("Values：" + list);

        // 根据key查询单个值
        String channel = jsonNode.get("channel").asText();
        System.out.println("查询channel的值：" + channel);
    }
}