使用 gson 序列化时为空 json 文件答案

【问题标题】：Empty json file when serialising with gson使用 gson 序列化时为空 json 文件
【发布时间】：2021-10-04 10:49:42
【问题描述】：

我想将一个 Student 对象序列化为一个 student.json 文件，在我的代码中是学生。

主要思想是我创建一个 json 字符串，从中创建一个学生，然后再次从学生对象创建一个 json 字符串，最后将学生对象序列化为一个 json 文件。

这是我的代码：

import com.google.gson.Gson; 
import com.google.gson.GsonBuilder;
import java.io.FileWriter;
import java.io.Writer; 
import java.nio.file.Paths;
import java.io.IOException;
import java.nio.file.Files;
public class JaJson {

    public static void main(String args[]) {  
        System.out.println("Hello");  
        String jsonString = "{\"name\":\"Mahesh\", \"age\":21}"; 

        GsonBuilder builder = new GsonBuilder(); 
        builder.setPrettyPrinting(); 

        Gson gson = builder.create(); 
        Student student = gson.fromJson(jsonString, Student.class);
        System.out.println("student object");    
        System.out.println(student);    

        jsonString = gson.toJson(student);
        System.out.println("student string");  
        System.out.println(jsonString); 
        String sFileName = "student.json";
        try{
    //Writer writer = Files.newBufferedWriter(Paths.get(sFileName));
    //gson.toJson(student, writer);
            Writer writer = new FileWriter(sFileName);
            gson.toJson(student, writer);
        } catch(IOException ex){
            System.out.println (ex.toString());
            System.out.println("Could not find file " + sFileName);
        }

    }  
    public JaJson(){
        System.out.println("what time is it ?");
    }

}

这里是 Student.java

public 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+ " ]"; 
   }  
}

这是程序的输出：

Hello
student object
Student [ name: Mahesh, age: 21 ]
student string
{
  "name": "Mahesh",
  "age": 21
}

但它会产生一个我不明白的空 student.json ...

知道缺少什么吗？

问候

【问题讨论】：

标签： java json gson

【解决方案1】：

我忘了补充：

    writer.flush(); //flush data to file   <---
    writer.close(); //close write

在我的代码中：

try{
    //Writer writer = Files.newBufferedWriter(Paths.get(sFileName));
    //gson.toJson(student, writer);
            Writer writer = new FileWriter(sFileName);
            gson.toJson(student, writer);
            writer.flush(); //flush data to file   <---
            writer.close(); //close write  
        } catch(IOException ex){
            System.out.println (ex.toString());
            System.out.println("Could not find file " + sFileName);
        }

【讨论】：