Java Transient Keyword Tutorial - 瞬态变量是不能序列化的变量

已发表: 2020-08-23

Java 瞬态关键字教程 - Crunchify

如果您需要序列化对象，则可以选择通过将特定字段marking it as transient来跳过序列化特定字段。

transient是一个 Java 关键字，它标记成员变量在持久化为字节流时不被序列化。

什么时候需要序列化一个对象？

当一个 Java 对象通过网络传输时，该对象needs to be serialized 。 序列化将对象状态转换为串行字节。

让我们看一下瞬态Java示例

  1. 首先让我们创建一个 POJO 对象 CrunchifyTransientVariableObject 实现 Serializable。
  2. 创建主类 CrunchifyJavaTransientFieldTutorial。
    • 创建一个对象。
    • 将对象写入文件。 文件输出流是用于将数据写入 File 或 FileDescriptor 的输出流。
    • 读取一个对象。
    • 如果字段是瞬态的——它将返回 0（对于 int）、null（对于字符串字段）等等。

CrunchifyTransientVariableObject.java

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package crunchify . com . tutorial ;
 
import java . io . Serializable ;
 
// Serializability of a class is enabled by the class implementing the java.io.Serializable interface.
// Warning: Deserialization of untrusted data is inherently dangerous and should be avoided.
// Untrusted data should be carefully validated according to the "Serialization and Deserialization" section of the . describes best practices for defensive use of serial filters.
public class CrunchifyTransientVariableObject implements Serializable {
 
     private static final long serialVersionUID = 1L ;
 
     private String companyName ;
 
     private int employeeCount ;
 
     // A transient variable is a variable that can not be serialized.
     // Variables may be marked transient to indicate that they are not part of the persistent state of an object.
 
     private transient int homeZip ;
     // private int homeZip;
 
     public String getName ( ) {
         return companyName ;
     }
 
     public void setName ( String companyName ) {
         this . companyName = companyName ;
     }
 
     public int getEmployeeCount ( ) {
         return employeeCount ;
     }
 
     public void setEmployeeCount ( int employeeCount ) {
         this . employeeCount = employeeCount ;
     }
 
     public int getZip ( ) {
         return homeZip ;
     }
 
     public void setZip ( int homeZip ) {
         this . homeZip = homeZip ;
     }
 
     public CrunchifyTransientVariableObject ( String companyName , int employeeCount , int homeZip ) {
         this . companyName = companyName ;
         this . employeeCount = employeeCount ;
         this . homeZip = homeZip ;
     }
 
}

这里homeZip是一个瞬态变量。

CrunchifyJavaTransientFieldTutorial.java

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package crunchify . com . tutorial ;
 
import java . io . * ;
 
/**
* @author Crunchify.com
*
*         Java Transient Keyword Tutorial - A transient variable is a variable that can not be serialized.
*
*/
public class CrunchifyJavaTransientFieldTutorial {
 
     public static void main ( String [ ] args ) {
 
         CrunchifyTransientVariableObject crunchifyCompany = new CrunchifyTransientVariableObject ( "Crunchify.com" , 5 , 95112 ) ;
 
         // A file output stream is an output stream for writing data to a File or to a FileDescriptor.
         try ( FileOutputStream crunchifyFOS = new FileOutputStream ( "crunchify.obj" ) ;
             ObjectOutputStream crunchifyOOS = new ObjectOutputStream ( crunchifyFOS ) ) {
             crunchifyOOS . writeObject ( crunchifyCompany ) ;
             crunchifyOOS . flush ( ) ;
         } catch ( FileNotFoundException e ) {
             e . printStackTrace ( ) ;
         } catch ( IOException e ) {
             e . printStackTrace ( ) ;
         }
 
         CrunchifyTransientVariableObject crunchifyResult = null ;
 
         // A FileInputStream obtains input bytes from a file in a file system. What files are available depends on the host environment.
         try ( FileInputStream crunchifyFOS = new FileInputStream ( "crunchify.obj" ) ;
             ObjectInputStream crunchifyOIS = new ObjectInputStream ( crunchifyFOS ) ) {
             crunchifyResult = ( CrunchifyTransientVariableObject ) crunchifyOIS . readObject ( ) ;
         } catch ( FileNotFoundException e ) {
             e . printStackTrace ( ) ;
         } catch ( IOException e ) {
             e . printStackTrace ( ) ;
         } catch ( ClassNotFoundException e ) {
             e . printStackTrace ( ) ;
         }
 
         System . out . println ( "Company Name: " + crunchifyResult . getName ( ) ) ;
         System . out . println ( "Number of Employee: " + crunchifyResult . getEmployeeCount ( ) ) ;
         System . out . println ( "Zip code: " + crunchifyResult . getZip ( ) ) ;
     }
 
}

运行程序：

使用瞬态关键字：

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/ Library / Java / JavaVirtualMachines / jdk - 14.0.2.jdk / Contents / Home / bin / java - javaagent
Company Name : Crunchify . com
Number of Employee : 5
Zip code : 0
 
Process finished with exit code 0

没有瞬态关键字：

删除上述程序中的瞬态关键字并再次重新运行程序。

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/ Library / Java / JavaVirtualMachines / jdk - 14.0.2.jdk / Contents / Home / bin / java - javaagent
Company Name : Crunchify . com
Number of Employee : 5
Zip code : 95112
 
Process finished with exit code 0

如您在上面看到的，现在我们可以看到邮政编码 95112。

如果您发现序列化对象和瞬态变量有任何问题，请告诉我。