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);
     }
 }