ObjectMapper的使用

Jackson ObjectMapper類

ObjectMapper類是Jackson庫的主要類
它提供一些功能將Java對象轉換成JSON結構，反之亦然
它使用JsonParser和JsonGenerator的實例實現JSON實際的讀/寫

public class ObjectMapper extends ObjectCodec implements Versioned

1.首先在pom.xml文件中，加入依賴：

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.8.3</version>
 </dependency>

 

2.使用實例

創建實體類

class Student {
   private String name;
   private int age;
   public Student(){}
   public String getName() {
      return name;
   }
   public void setName(String name) {
      this.name = name;
   }
   public int getAge() {
      return age;
   }
   public void setAge(int age) {
      this.age = age;
   }
   public String toString(){
      return "Student [ name: "+name+", age: "+age+" ]";
   }    
}

 

import java.io.IOException;
import org.codehaus.jackson.JsonParseException;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.map.SerializationConfig;

public class JacksonTester {
   public static void main(String args[]){
      ObjectMapper mapper = new ObjectMapper();
      String jsonString = "{\"name\":\"Mahesh\", \"age\":21}";

      //map json to student
      try {
         Student student = mapper.readValue(jsonString, Student.class);
         System.out.println(student);
         mapper.enable(SerializationConfig.Feature.INDENT_OUTPUT);
         //把對象轉成json string類型的
         jsonString = mapper.writeValueAsString(student);
         System.out.println(jsonString);

      } catch (JsonParseException e) {
         e.printStackTrace();
      } catch (JsonMappingException e) {
         e.printStackTrace();
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

//輸出結果
Student [ name: Mahesh, age: 21 ]
{
  "name" : "Mahesh",
  "age" : 21
}