Java Transient Keyword Tutorial - 瞬態變量是不能序列化的變量

已發表: 2020-08-23

Java 瞬態關鍵字教程 - Crunchify

如果您需要序列化對象，則可以選擇通過將特定字段marking it as transient來跳過序列化特定字段。

transient是一個 Java 關鍵字，它標記成員變量在持久化為字節流時不被序列化。

什麼時候需要序列化一個對象？

當一個 Java 對象通過網絡傳輸時，該對象needs to be serialized 。 序列化將對象狀態轉換為串行字節。

讓我們看一下瞬態Java示例

  1. 首先讓我們創建一個 POJO 對象 CrunchifyTransientVariableObject 實現 Serializable。
  2. 創建主類 CrunchifyJavaTransientFieldTutorial。
    • 創建一個對象。
    • 將對象寫入文件。 文件輸出流是用於將數據寫入 File 或 FileDescriptor 的輸出流。
    • 讀取一個對象。
    • 如果字段是瞬態的——它將返回 0（對於 int）、null（對於字符串字段）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 ;
     }
 
}

這裡homeZip是一個瞬態變量。

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 ( ) ) ;
     }
 
}

運行程序：

使用瞬態關鍵字：

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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

沒有瞬態關鍵字：

刪除上述程序中的瞬態關鍵字並再次重新運行程序。

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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，現在我們可以看到郵政編碼 95112。

如果您發現序列化對象和瞬態變量有任何問題，請告訴我。