Java之JSON操做（Jackson）

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與Java對象、Map等類型轉換，JSON文件的讀寫等
12  * 依賴包：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對象轉json，也支持bytes
21         String json = objectMapper.writeValueAsString(user);
22         System.out.println("Java對象轉json:" + json);
23 
24         // json轉Java對象
25         User user2 = objectMapper.readValue(json, User.class);
26         System.out.println("json轉Java對象" + user2);
27 
28         // 讀文件
29         String jsonFilePath = "src/main/java/json/jackson/JsonReader.json";
30         User user3 = objectMapper.readValue(new File(jsonFilePath), User.class);
31         System.out.println("讀取JSON文件：" + user3);
32         // 寫文件
33         objectMapper.writeValue(new File(jsonFilePath), user3);
34 
35         // json轉map，也支持List
36         Map map = objectMapper.readValue(json, Map.class);
37         System.out.println("json轉map：" + map);
38 
39         // map轉json字符串，支持全部類型轉字符串
40         String json2 = objectMapper.writeValueAsString(map);
41         System.out.println("map轉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  * 處理複雜的JSON，返回多個對象的狀況
12  * 從文件中讀取複雜的JSON，根據key找到對應value值
13  * 依賴包：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         // 以樹形態支持多對象的狀況：支持讀取多種類型
21         JsonNode jsonNode = objectMapper.readTree(new File(jsonFilePath));
22         System.out.println("jsonNode：" + jsonNode);
23         // 根據key查詢多個值，返回list
24         List<JsonNode> list = jsonNode.findValues("name");
25         System.out.println("Values：" + list);
26 
27         // 根據key查詢單個值
28         String channel = jsonNode.get("channel").asText();
29         System.out.println("查詢channel的值：" + channel);
30     }
31 }