Jackson - 使用泛型进行数据绑定

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  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]