Jackson - 全資料繫結

全資料繫結是指將 JSON 對映到任何 JAVA 物件。

//Create an ObjectMapper instance
ObjectMapper mapper = new ObjectMapper();	
//map JSON content to Student object
Student student = mapper.readValue(new File("student.json"), Student.class);
//map Student object to JSON content
mapper.writeValue(new File("student.json"), student);

我們來看看簡單的實際資料繫結。這裡我們將把 JAVA 物件直接對映到 JSON，反之亦然。

在 C:\>Jackson_WORKSPACE 中建立一個名為 JacksonTester 的 java 類檔案。

檔案：JacksonTester.java

import java.io.File;
import java.io.IOException;

import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class JacksonTester {
   public static void main(String args[]){
      JacksonTester tester = new JacksonTester();
      try {
         Student student = new Student();
         student.setAge(10);
         student.setName("Mahesh");
         tester.writeJSON(student);

         Student student1 = tester.readJSON();
         System.out.println(student1);

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

   private void writeJSON(Student student) throws JsonGenerationException, JsonMappingException, IOException{
      ObjectMapper mapper = new ObjectMapper();	
      mapper.writeValue(new File("student.json"), student);
   }

   private Student readJSON() throws JsonParseException, JsonMappingException, IOException{
      ObjectMapper mapper = new ObjectMapper();
      Student student = mapper.readValue(new File("student.json"), Student.class);
      return student;
   }
}

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+ " ]";
   }	
}

驗證結果

使用 javac 編譯器編譯類，如下所示

C:\Jackson_WORKSPACE>javac JacksonTester.java

現在執行 jacksonTester 以檢視結果

C:\Jackson_WORKSPACE>java JacksonTester

驗證輸出

Student [ name: Mahesh, age: 10 ]