如何在 Java 使用 Gson 运用 @Since 注解?


@Since 注解可与 GsonBuilder 类的 setVersion() 方法一起使用。此注释可应用到 java 类中的字段并接受浮点数作为参数。此参数表示字段已序列化的版本号。相同的注解可应用于反序列化过程。

语法

@Documented
@Retention(value=RUNTIME)
@Target(value={FIELD,TYPE})
public @interface Since

示例

import com.google.gson.annotations.Since;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
public class GsonSinceAnnotationTest {
   public static void main(String[] args) {
      Employee emp = new Employee();
      emp.setEmployeeName("Raja Ramesh");
      emp.setEmployeeId(125);
      emp.setEmployeeTechnology("Java");
      emp.setEmploeeAddress("Hyderabad");
      System.out.println("Since version 0.5");
      GsonBuilder gsonBuilder = new GsonBuilder();
      Gson gson = gsonBuilder.setPrettyPrinting().setVersion(0.5).create();
      String jsonString = gson.toJson(emp);
      System.out.println(jsonString);
      System.out.println("Since version 1.0");
      gsonBuilder = new GsonBuilder();
      gson = gsonBuilder.setPrettyPrinting().setVersion(1.0).create();
      jsonString = gson.toJson(emp);
      System.out.println(jsonString);
      System.out.println("Since version 1.1");
      gsonBuilder = new GsonBuilder();
      gson = gsonBuilder.setPrettyPrinting().setVersion(1.1).create();
      jsonString = gson.toJson(emp);
      System.out.println(jsonString);
   }
}
// Employee class
class Employee {
   private String empName;
   private int empId;
   @Since(1.0)
   private String empTech;
   @Since(1.1)
   private String empAddress;
   public String getEmployeeName() {
      return empName;
   }
   public void setEmployeeName(String empName) {
      this.empName = empName;
   }
   public int getEmployeeId() {
      return empId;
   }
   public void setEmployeeId(int empId) {
      this.empId = empId;
   }
   public String getEmployeeTechnology() {
      return empTech;
   }
   public void setEmployeeTechnology(String empTech) {
      this.empTech = empTech;
   }
   public String getEmploeeAddress() {
      return empAddress;
   }
   public void setEmploeeAddress(String empAddress) {
      this.empAddress = empAddress;
   }
}

输出

Since version 0.5
{
   "empName": "Raja Ramesh",
   "empId": 125
}
Since version 1.0
{
   "empName": "Raja Ramesh",
   "empId": 125,
   "empTech": "Java"
}
Since version 1.1
{
   "empName": "Raja Ramesh",
   "empId": 125,
   "empTech": "Java",
   "empAddress": "Hyderabad"
}

更新于: 2020 年 7 月 8 日

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