Gson空對象支持

Gson默認生成優化的Json內容，忽略NULL值。 但是GsonBuilder提供的標誌使用GsonBuilder.serializeNulls()方法在Json輸出中顯示NULL值。

參考以下代碼實現 -

GsonBuilder builder = new GsonBuilder();
builder.serializeNulls();
Gson gson = builder.create();

不帶serializeNulls的示例調用

創建一個名為GsonTester的Java類檔:GsonTester.java -

import com.google.gson.Gson;

public class GsonTester {
   public static void main(String args[]) {
      Gson gson = new Gson();

      Student student = new Student();
      student.setRollNo(1);
      String jsonString = gson.toJson(student);

      System.out.println(jsonString);
      student = gson.fromJson(jsonString, Student.class);
      System.out.println(student);
   }
}
class Student {
   private int rollNo;
   private String name;

   public int getRollNo() {
      return rollNo;
   }
   public void setRollNo(int rollNo) {
      this.rollNo = rollNo;
   }
   public String getName() {
      return name;
   }
   public void setName(String name) {
      this.name = name;
   }
   public String toString() {
      return "Student[ name = "+name+", roll no: "+rollNo+ "]";
   }
}

執行上面示例代碼，得到以下結果 -

{"rollNo": 1}
Student[ name = null, roll no: 1]

使用serializeNulls調用的示例

創建一個名為GsonTester的Java類檔:GsonTester.java -

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

public class GsonTester {
   public static void main(String args[]) {
      GsonBuilder builder = new GsonBuilder();
      builder.serializeNulls();
      builder.setPrettyPrinting();
      Gson gson = builder.create();

      Student student = new Student();
      student.setRollNo(1);
      String jsonString = gson.toJson(student);

      System.out.println(jsonString);
      student = gson.fromJson(jsonString, Student.class);
      System.out.println(student);
   }
}
class Student {
   private int rollNo;
   private String name;

   public int getRollNo() {
      return rollNo;
   }
   public void setRollNo(int rollNo) {
      this.rollNo = rollNo;
   }
   public String getName() {
      return name;
   }
   public void setName(String name) {
      this.name = name;
   }
   public String toString() {
      return "Student[ name = "+name+", roll no: "+rollNo+ "]";
   }
}

執行上面示例代碼，得到以下結果 -

{
   "rollNo": 1,
   "name": null
}
Student[ name = null, roll no: 1]