几个问题（九）-------序列化的作用，应用场景，除了网路传输

关于更多java序列化的问题可以参见JAVA系列之对象的序列化与反序列化
      Java的序列化机制只序列化对象的属性值，而不会去序列化什么所谓的方法。其实这个问题简单思考一下就可以搞清楚，方法是不带状态的，就是一些指令，指令是不需要序列化的，只要你的JVM classloader可以load到这个类，那么类方法指令自然就可以获得。序列化真正需要保存的只是对象属性的值，和对象的类型。

我们可以做一个简单的小试验，来证实一下：

Java代码 < type="application/x-shockwave-flash" width="14" height="15" src="javascripts/syntaxhighlighter/clipboard_new.swf" pluginspage="http://www.macromedia.com/go/getflashplayer" allowscriptaccess="always" quality="high" flashvars="clipboard=package%20com.javaeye%3B%0A%0Aimport%20java.io.Serializable%3B%0A%0Apublic%20class%20DomainObject%20%20implements%20Serializable%20%7B%0A%0A%09private%20String%20name%3B%0A%09%0A%09private%20int%20age%20%3B%0A%0A%09public%20int%20getAge()%3B%20%7B%0A%09%09return%20age%3B%0A%09%7D%0A%0A%09public%20void%20setAge(int%20age)%3B%20%7B%0A%09%09this.age%20%3D%20age%3B%0A%09%7D%0A%0A%09public%20String%20getName()%3B%20%7B%0A%09%09return%20name%3B%0A%09%7D%0A%0A%09public%20void%20setName(String%20name)%3B%20%7B%0A%09%09this.name%20%3D%20name%3B%0A%09%7D%0A%09%0A%09%0A%7D">
package com.javaeye;

import java.io.Serializable;

public class DomainObject  implements Serializable {

 private String name;
 
 private int age ;

 public int getAge(); {
  return age;
 }

 public void setAge(int age); {
  this.age = age;
 }

 public String getName(); {
  return name;
 }

 public void setName(String name); {
  this.name = name;
 }
 
 
}view plaincopy to clipboardprint?
package com.javaeye;    
    
import java.io.Serializable;    
    
public class DomainObject  implements Serializable {    
    
    private String name;    
        
    private int age ;    
    
    public int getAge(); {    
        return age;    
    }    
    
    public void setAge(int age); {    
        this.age = age;    
    }    
    
    public String getName(); {    
        return name;    
    }    
    
    public void setName(String name); {    
        this.name = name;    
    }    
        
        
}   
 package com.javaeye; 
  
 import java.io.Serializable; 
  
 public class DomainObject  implements Serializable { 
  
     private String name; 
      
     private int age ; 
  
     public int getAge(); { 
         return age; 
     } 
  
     public void setAge(int age); { 
         this.age = age; 
     } 
  
     public String getName(); { 
         return name; 
     } 
  
     public void setName(String name); { 
         this.name = name; 
     } 
      
      
 }  
Java代码
package com.javaeye;

import java.io.FileOutputStream;
import java.io.ObjectOutputStream;

public class Main {

 public static void main(String[] args); throws Exception {
  DomainObject obj = new DomainObject();;
  obj.setAge(29);;
  obj.setName("fankai");;
  FileOutputStream fos = new FileOutputStream("DomainObject");;
  ObjectOutputStream oos = new ObjectOutputStream(fos);;
  oos.writeObject(obj);;
  oos.close();;
  fos.close();;
 }

}view plaincopy to clipboardprint?
package com.javaeye;    
    
import java.io.FileOutputStream;    
import java.io.ObjectOutputStream;    
    
public class Main {    
    
    public static void main(String[] args); throws Exception {    
        DomainObject obj = new DomainObject();;    
        obj.setAge(29);;    
        obj.setName("fankai");;    
        FileOutputStream fos = new FileOutputStream("DomainObject");;    
        ObjectOutputStream oos = new ObjectOutputStream(fos);;    
        oos.writeObject(obj);;    
        oos.close();;    
        fos.close();;    
    }    
    
}  
 package com.javaeye; 
  
 import java.io.FileOutputStream; 
 import java.io.ObjectOutputStream; 
  
 public class Main { 
  
     public static void main(String[] args); throws Exception { 
         DomainObject obj = new DomainObject();; 
         obj.setAge(29);; 
         obj.setName("fankai");; 
         FileOutputStream fos = new FileOutputStream("DomainObject");; 
         ObjectOutputStream oos = new ObjectOutputStream(fos);; 
         oos.writeObject(obj);; 
         oos.close();; 
         fos.close();; 
     } 
  
 } 
      DomainObject是我们准备序列化的类，在Main里面，我们new一个DomainObject的对象，然后赋值，最后把该对象序列化到一个硬盘文件中。然后使用一种支持二进制编辑器，例如UltraEdit打开这个文件，看看Java都对DomainObject序列化了哪些信息，你就什么都明白了。

为了更方便观察，我使用Linux下面的strings去提取文本信息，输出为：
robbin@linux:~> strings DomainObject
com.javaeye.DomainObject
ageL
namet
Ljava/lang/String;xp
fankai
这些信息很直观的告诉我们序列化都保存了些什么内容：
1）对象的类型
2）对象属性的类型
3）对象属性的值

并没有什么方法签名的信息，更不要说什么序列化方法了。
然后我们再做一个试验，给DomainObject增加两个方法：
Java代码 < type="application/x-shockwave-flash" width="14" height="15" src="javascripts/syntaxhighlighter/clipboard_new.swf" pluginspage="http://www.macromedia.com/go/getflashplayer" allowscriptaccess="always" quality="high" flashvars="clipboard=package%20com.javaeye%3B%0A%0Aimport%20java.io.Serializable%3B%0A%0Apublic%20class%20DomainObject%20%20implements%20Serializable%20%7B%0A%0A%09private%20String%20name%3B%0A%09%0A%09private%20int%20age%20%3B%0A%0A%09public%20int%20getAge()%3B%20%7B%0A%09%09return%20age%3B%0A%09%7D%0A%0A%09public%20void%20setAge(int%20age)%3B%20%7B%0A%09%09this.age%20%3D%20age%3B%0A%09%7D%0A%0A%09public%20String%20getName()%3B%20%7B%0A%09%09return%20name%3B%0A%09%7D%0A%0A%09public%20void%20setName(String%20name)%3B%20%7B%0A%09%09this.name%20%3D%20name%3B%0A%09%7D%0A%09%0A%09public%20String%20toString()%3B%20%7B%0A%09%09return%20%22This%20is%20a%20serializable%20test!%22%3B%0A%09%7D%0A%09%0A%09public%20void%20doSomeWork()%3B%20%7B%0A%09%09System.out.println(%22hello%22)%3B%3B%0A%09%7D%0A%7D">
package com.javaeye;

import java.io.Serializable;

public class DomainObject  implements Serializable {

 private String name;
 
 private int age ;

 public int getAge(); {
  return age;
 }

 public void setAge(int age); {
  this.age = age;
 }

 public String getName(); {
  return name;
 }

 public void setName(String name); {
  this.name = name;
 }
 
 public String toString(); {
  return "This is a serializable test!";
 }
 
 public void doSomeWork(); {
  System.out.println("hello");;
 }
}view plaincopy to clipboardprint?
package com.javaeye;    
    
import java.io.Serializable;    
    
public class DomainObject  implements Serializable {    
    
    private String name;    
        
    private int age ;    
    
    public int getAge(); {    
        return age;    
    }    
    
    public void setAge(int age); {    
        this.age = age;    
    }    
    
    public String getName(); {    
        return name;    
    }    
    
    public void setName(String name); {    
        this.name = name;    
    }    
        
    public String toString(); {    
        return "This is a serializable test!";    
    }    
        
    public void doSomeWork(); {    
        System.out.println("hello");;    
    }    
}    
 package com.javaeye; 
  
 import java.io.Serializable; 
  
 public class DomainObject  implements Serializable { 
  
     private String name; 
      
     private int age ; 
  
     public int getAge(); { 
         return age; 
     } 
  
     public void setAge(int age); { 
         this.age = age; 
     } 
  
     public String getName(); { 
         return name; 
     } 
  
     public void setName(String name); { 
         this.name = name; 
     } 
      
     public String toString(); { 
         return "This is a serializable test!"; 
     } 
      
     public void doSomeWork(); { 
         System.out.println("hello");; 
     } 
 }   
      我们增加了toString方法和doSomeWork方法，按照你的理论，如果序列化方法的话，产生的文件体积必然增大。记录一下文件体积，92Byte，好了，删除，运行程序，生成了新的文件，看一下体积，还是92Byte！

拿到Linux下面再提取一下字符串：
robbin@linux:~> strings DomainObject
com.javaeye.DomainObject
ageL
namet
Ljava/lang/String;xp
fankai
完全一模一样！

然后我们再做第三个试验，这次把DomainObject的两个属性以及相关方法删除掉：
Java代码 < type="application/x-shockwave-flash" width="14" height="15" src="javascripts/syntaxhighlighter/clipboard_new.swf" pluginspage="http://www.macromedia.com/go/getflashplayer" allowscriptaccess="always" quality="high" flashvars="clipboard=package%20com.javaeye%3B%0A%0Aimport%20java.io.Serializable%3B%0A%0Apublic%20class%20DomainObject%20%20implements%20Serializable%20%7B%0A%0A%09public%20String%20toString()%3B%20%7B%0A%09%09return%20%22This%20is%20a%20serializable%20test!%22%3B%0A%09%7D%0A%09%0A%09public%20void%20doSomeWork()%3B%20%7B%0A%09%09System.out.println(%22hello%22)%3B%3B%0A%09%7D%0A%7D">
package com.javaeye;

import java.io.Serializable;

public class DomainObject  implements Serializable {

 public String toString(); {
  return "This is a serializable test!";
 }
 
 public void doSomeWork(); {
  System.out.println("hello");;
 }
}view plaincopy to clipboardprint?
package com.javaeye;    
    
import java.io.Serializable;    
    
public class DomainObject  implements Serializable {    
    
    public String toString(); {    
        return "This is a serializable test!";    
    }    
        
    public void doSomeWork(); {    
        System.out.println("hello");;    
    }    
}   
 package com.javaeye; 
  
 import java.io.Serializable; 
  
 public class DomainObject  implements Serializable { 
  
     public String toString(); { 
         return "This is a serializable test!"; 
     } 
      
     public void doSomeWork(); { 
         System.out.println("hello");; 
     } 
 }  
修改Main类如下：
Java代码 < type="application/x-shockwave-flash" width="14" height="15" src="javascripts/syntaxhighlighter/clipboard_new.swf" pluginspage="http://www.macromedia.com/go/getflashplayer" allowscriptaccess="always" quality="high" flashvars="clipboard=package%20com.javaeye%3B%0A%0Aimport%20java.io.FileOutputStream%3B%0Aimport%20java.io.ObjectOutputStream%3B%0A%0Apublic%20class%20Main%20%7B%0A%0A%09public%20static%20void%20main(String%5B%5D%20args)%3B%20throws%20Exception%20%7B%0A%09%09DomainObject%20obj%20%3D%20new%20DomainObject()%3B%3B%0A%0A%09%09FileOutputStream%20fos%20%3D%20new%20FileOutputStream(%22DomainObject%22)%3B%3B%0A%09%09ObjectOutputStream%20oos%20%3D%20new%20ObjectOutputStream(fos)%3B%3B%0A%09%09oos.writeObject(obj)%3B%3B%0A%09%09oos.close()%3B%3B%0A%09%09fos.close()%3B%3B%0A%09%7D%0A%0A%7D">
package com.javaeye;

import java.io.FileOutputStream;
import java.io.ObjectOutputStream;

public class Main {

 public static void main(String[] args); throws Exception {
  DomainObject obj = new DomainObject();;

  FileOutputStream fos = new FileOutputStream("DomainObject");;
  ObjectOutputStream oos = new ObjectOutputStream(fos);;
  oos.writeObject(obj);;
  oos.close();;
  fos.close();;
 }

}view plaincopy to clipboardprint?
package com.javaeye;    
    
import java.io.FileOutputStream;    
import java.io.ObjectOutputStream;    
    
public class Main {    
    
    public static void main(String[] args); throws Exception {    
        DomainObject obj = new DomainObject();;    
    
        FileOutputStream fos = new FileOutputStream("DomainObject");;    
        ObjectOutputStream oos = new ObjectOutputStream(fos);;    
        oos.writeObject(obj);;    
        oos.close();;    
        fos.close();;    
    }    
    
}   
 package com.javaeye; 
  
 import java.io.FileOutputStream; 
 import java.io.ObjectOutputStream; 
  
 public class Main { 
  
     public static void main(String[] args); throws Exception { 
         DomainObject obj = new DomainObject();; 
  
         FileOutputStream fos = new FileOutputStream("DomainObject");; 
         ObjectOutputStream oos = new ObjectOutputStream(fos);; 
         oos.writeObject(obj);; 
         oos.close();; 
         fos.close();; 
     } 
  
 }  
      按照你的理论，如果序列化方法的话，我们必然应该在文件里面发现方法的签名信息，甚至方法里面包含的字符串，好了，再运行一遍，然后打开看一下吧！文件现在体积变成了45Byte，拿到Linux下面提取一下信息：
robbin@linux:~> strings DomainObject
com.javaeye.DomainObject
只有对象的类型信息，再无其它东西了！

      请记住序列化机制只保存对象的类型信息，属性的类型信息和属性值，和方法没有什么关系，你就是给这个类增加10000个方法，序列化内容也不会增加任何东西，不要想当然的臆测自己不了解的知识，动手去做！

本文来自CSDN博客，转载请标明出处：http://blog.csdn.net/ilibaba/archive/2009/03/10/3975680.aspx