从序列化中排除字段（Excluding fields from Serialization）

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2023-12-01

默认情况下，GSON从序列化/反序列化过程中排除瞬态和静态字段。我们来看看下面的例子。

例子 (Example)

在C:\“GSON_WORKSPACE中创建名为GsonTester的Java类文件。

File: 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();     
      Gson gson = builder.create();  
      Student student = new Student(); 
      student.setRollNo(1); 
      student.setName("Mahesh Kumar"); 
      student.setVerified(true); 
      student.setId(1); 
      student.className = "VI";  
      String jsonString = gson.toJson(student); 
      System.out.println(jsonString);    
   }      
} 
class Student { 
   private int rollNo; 
   private String name; 
   private boolean verified;  
   private transient int id; 
   public static String className;  
   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 void setVerified(boolean verified) { 
      this.verified = verified; 
   }  
   public boolean isVerified() { 
      return verified; 
   }  
   public int getId() { 
      return id; 
   }  
   public void setId(int id) { 
      this.id = id; 
   } 
}

验证结果

使用javac编译器编译类如下 -

C:\GSON_WORKSPACE>javac GsonTester.java

现在运行GsonTester查看结果 -

C:\GSON_WORKSPACE>java GsonTester

验证输出

{"rollNo":1,"name":"Mahesh Kumar","verified":true}

使用excludeFieldsWithModifiers

GsonBuilder使用来自序列化/反序列化过程的excludeFieldsWithModifiers（）方法控制使用特定修饰符排除字段。请参阅以下示例。

例子 (Example)

在C:\> GSON_WORKSPACE中创建名为GsonTester的Java类文件。

File: GsonTester.java

import java.lang.reflect.Modifier; 
import com.google.gson.Gson; 
import com.google.gson.GsonBuilder;  
public class GsonTester { 
   public static void main(String args[]) { 
      GsonBuilder builder = new GsonBuilder(); 
      builder.excludeFieldsWithModifiers(Modifier.TRANSIENT);    
      Gson gson = builder.create();  
      Student student = new Student(); 
      student.setRollNo(1); 
      student.setName("Mahesh Kumar"); 
      student.setVerified(true); 
      student.setId(1); 
      student.className = "VI";  
      String jsonString = gson.toJson(student); 
      System.out.println(jsonString);    
   }      
} 
class Student { 
   private int rollNo; 
   private String name;
   private boolean verified;  
   private transient int id; 
   public static String className;  
   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 void setVerified(boolean verified) { 
      this.verified = verified; 
   }  
   public boolean isVerified() { 
      return verified; 
   }  
   public int getId() { 
      return id; 
   }  
   public void setId(int id) { 
      this.id = id; 
   } 
}

验证结果

使用javac编译器编译类如下 -

C:\GSON_WORKSPACE>javac GsonTester.java

现在运行GsonTester查看结果 -

C:\GSON_WORKSPACE>java GsonTester

验证输出

{"rollNo":1,"name":"Mahesh Kumar","verified":true,"className":"VI"}

使用@Expose Annotation

Gson提供@Expose注释来根据其范围控制类的Json序列化/反序列化。考虑以下具有@Expose支持的变量的类。在此类中，将公开name和rollno变量以进行序列化。然后我们使用GsonBuilder.excludeFieldsWithoutExposeAnnotation()方法来指示只有序列化/反序列化的公开变量。请参阅以下示例。

例子 (Example)

在C:\“GSON_WORKSPACE中创建名为GsonTester的Java类文件。

File: GsonTester.java

import com.google.gson.Gson; 
import com.google.gson.GsonBuilder; 
import com.google.gson.annotations.Expose;  
public class GsonTester { 
   public static void main(String args[]) { 
      GsonBuilder builder = new GsonBuilder();     
      builder.excludeFieldsWithoutExposeAnnotation(); 
      Gson gson = builder.create();  
      Student student = new Student(); 
      student.setRollNo(1); 
      student.setName("Mahesh Kumar"); 
      student.setVerified(true); 
      student.setId(1); 
      student.className = "VI"; 
      String jsonString = gson.toJson(student); 
      System.out.println(jsonString);    
   }      
} 
class Student { 
   @Expose 
   private int rollNo; 
   @Expose 
   private String name; 
   private boolean verified;  
   private int id; 
   public static String className;  
   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 void setVerified(boolean verified) { 
      this.verified = verified; 
   }  
   public boolean isVerified() { 
      return verified; 
   }  
   public int getId() { 
      return id; 
   }  
   public void setId(int id) { 
      this.id = id; 
   } 
}

验证结果

使用javac编译器编译类如下 -

C:\GSON_WORKSPACE>javac GsonTester.java

现在运行GsonTester查看结果 -

C:\GSON_WORKSPACE>java GsonTester

验证输出

{"rollNo":1,"name":"Mahesh Kumar"}