Jackson - 使用泛型进行数据绑定

简述

在简单的数据绑定中，我们使用 Map 类，它使用 String 作为键，将 Object 用作值对象。相反，我们可以让具体的java对象和类型将其转换为用于JSON绑定。

请考虑下面带有类 UserData 的示例，该类用于保存用户特定的数据。

在 C：\>Jackson_WORKSPACE 中创建一个名为“JacksonTester”的 Java 类文件。

文件： JacksonTester.java

import java.io.File;
import java.io.IOException;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.core.type.TypeReference;
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 {
            ObjectMapper mapper = new ObjectMapper();
            Map<String, UserData> userDataMap = new HashMap<String, UserData>();
            UserData studentData = new UserData(); 
            int[] marks = {1,2,3};
            Student student = new Student();
            student.setAge(10);
            student.setName("Mahesh");
            // JAVA Object
            studentData.setStudent(student);
            // JAVA String
            studentData.setName("Mahesh Kumar");
            // JAVA Boolean
            studentData.setVerified(Boolean.FALSE);
            // Array
            studentData.setMarks(marks);
            TypeReference ref = new TypeReference<Map<String,UserData>>() { };
            userDataMap.put("studentData1", studentData);
            mapper.writeValue(new File("student.json"), userDataMap);
            //{
            //   "studentData1":
            //   {
            //      "student":
            //      {
            //          "name":"Mahesh",
            //          "age":10
            //      },
            //      "name":"Mahesh Kumar",
            //      "verified":false,
            //      "marks":[1,2,3]
            //   }
            //}
            userDataMap = mapper.readValue(new File("student.json"), ref);
            System.out.println(userDataMap.get("studentData1").getStudent());
            System.out.println(userDataMap.get("studentData1").getName());
            System.out.println(userDataMap.get("studentData1").getVerified());
            System.out.println(Arrays.toString(userDataMap.get("studentData1").getMarks()));
      } catch (JsonParseException e) {
         e.printStackTrace();
      } catch (JsonMappingException e) {
         e.printStackTrace();
      } catch (IOException e) {
            e.printStackTrace();
      }
   }
}
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+ " ]";
   }    
}
class UserData {
   private Student student;
   private String name;
   private Boolean verified;
   private int[] marks;
   public UserData(){}
   public Student getStudent() {
      return student;
   }
   public void setStudent(Student student) {
      this.student = student;
   }
   public String getName() {
      return name;
   }
   public void setName(String name) {
      this.name = name;
   }
   public Boolean getVerified() {
      return verified;
   }
   public void setVerified(Boolean verified) {
      this.verified = verified;
   }
   public int[] getMarks() {
      return marks;
   }
   public void setMarks(int[] marks) {
      this.marks = marks;
   }        
}

验证结果

使用 javac 编译器编译类，如下所示：


C:\Jackson_WORKSPACE>javac JacksonTester.java

现在运行 JacksonTest 以查看结果：


C:\Jackson_WORKSPACE>java JacksonTester

验证输出


Student [ name: Mahesh, age: 10 ]
Mahesh Kumar
false
[1, 2, 3]