Java之JSON操作（Jackson）

Posted 2020-10-24 星瑞的随笔

Java to JSON：

 1 package json.jackson;
 2 
 3 import bean.User;
 4 import com.fasterxml.jackson.databind.ObjectMapper;
 5 
 6 import java.io.File;
 7 import java.util.Map;
 8 
 9 /**
10  * Jackson – Java to JSON
11  * 功能：JSON与Java对象、Map等类型转换，JSON文件的读写等
12  * 依赖包：jackson-databind-2.8.11.1.jar、jackson-core-2.8.10.jar、jackson-annotations-2.8.0.jar
13  * https://github.com/FasterXML/jackson-databind
14  */
15 public class JavaToJSON {
16     public static void main(String[] ars) throws Exception {
17         User user = new User("tom", 25, "NO.1 street");
18         ObjectMapper objectMapper = new ObjectMapper();
19 
20         // Java对象转json，也支持bytes
21         String json = objectMapper.writeValueAsString(user);
22         System.out.println("Java对象转json:" + json);
23 
24         // json转Java对象
25         User user2 = objectMapper.readValue(json, User.class);
26         System.out.println("json转Java对象" + user2);
27 
28         // 读文件
29         String jsonFilePath = "src/main/java/json/jackson/JsonReader.json";
30         User user3 = objectMapper.readValue(new File(jsonFilePath), User.class);
31         System.out.println("读取JSON文件：" + user3);
32         // 写文件
33         objectMapper.writeValue(new File(jsonFilePath), user3);
34 
35         // json转map，也支持List
36         Map map = objectMapper.readValue(json, Map.class);
37         System.out.println("json转map：" + map);
38 
39         // map转json字符串，支持所有类型转字符串
40         String json2 = objectMapper.writeValueAsString(map);
41         System.out.println("map转json:" + json2);
42 
43     }
44 }

JsonNode：

 1 package json.jackson;
 2 
 3 import com.fasterxml.jackson.databind.JsonNode;
 4 import com.fasterxml.jackson.databind.ObjectMapper;
 5 
 6 import java.io.File;
 7 import java.util.List;
 8 
 9 /**
10  * JsonNode
11  * 处理复杂的JSON，返回多个对象的情况
12  * 从文件中读取复杂的JSON，根据key找到对应value值
13  * 依赖包：jackson-databind-2.8.11.1.jar、jackson-core-2.8.10.jar、jackson-annotations-2.8.0.jar
14  * https://github.com/FasterXML/jackson-databind
15  */
16 public class JSONTreeDemo {
17     public static void main(String[] ars) throws Exception {
18         ObjectMapper objectMapper = new ObjectMapper();
19         String jsonFilePath = "src/main/java/json/jackson/Json2.json";
20         // 以树形态支持多对象的情况：支持读取多种类型
21         JsonNode jsonNode = objectMapper.readTree(new File(jsonFilePath));
22         System.out.println("jsonNode：" + jsonNode);
23         // 根据key查询多个值，返回list
24         List<JsonNode> list = jsonNode.findValues("name");
25         System.out.println("Values：" + list);
26 
27         // 根据key查询单个值
28         String channel = jsonNode.get("channel").asText();
29         System.out.println("查询channel的值：" + channel);
30     }
31 }