幾個問題（九）-------序列化的作用，應用場景，除了網路傳輸

關於更多java序列化的問題可以參見JAVA系列之對象的序列化與反序列化
Java的序列化機制只序列化對象的屬性值，而不會去序列化什麼所謂的方法。其實這個問題簡單思考一下就可以搞清楚，方法是不帶狀態的，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到這個類，那麼類方法指令自然就可以獲得。序列化真正需要保存的只是對象屬性的值，和對象的類型。

我們可以做一個簡單的小試驗，來證實一下：

Java代碼 < 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代碼
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是我們準備序列化的類，在Main裏面，我們new一個DomainObject的對象，然後賦值，最後把該對象序列化到一個硬盤文件中。然後使用一種支持二進制編輯器，例如UltraEdit打開這個文件，看看Java都對DomainObject序列化了哪些信息，你就什麼都明白了。

爲了更方便觀察，我使用Linux下面的strings去提取文本信息，輸出爲：
robbin@linux:~> strings DomainObject
com.javaeye.DomainObject
ageL
namet
Ljava/lang/String;xp
fankai
這些信息很直觀的告訴我們序列化都保存了些什麼內容：
1）對象的類型
2）對象屬性的類型
3）對象屬性的值

並沒有什麼方法簽名的信息，更不要說什麼序列化方法了。
然後我們再做一個試驗，給DomainObject增加兩個方法：
Java代碼 < 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");;
     }
}
      我們增加了toString方法和doSomeWork方法，按照你的理論，如果序列化方法的話，產生的文件體積必然增大。記錄一下文件體積，92Byte，好了，刪除，運行程序，生成了新的文件，看一下體積，還是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
完全一模一樣！

然後我們再做第三個試驗，這次把DomainObject的兩個屬性以及相關方法刪除掉：
Java代碼 < 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類如下：
Java代碼 < 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();;
     }

}
      按照你的理論，如果序列化方法的話，我們必然應該在文件裏面發現方法的簽名信息，甚至方法裏面包含的字符串，好了，再運行一遍，然後打開看一下吧！文件現在體積變成了45Byte，拿到Linux下面提取一下信息：
robbin@linux:~> strings DomainObject
com.javaeye.DomainObject
只有對象的類型信息，再無其它東西了！

請記住序列化機制只保存對象的類型信息，屬性的類型信息和屬性值，和方法沒有什麼關係，你就是給這個類增加10000個方法，序列化內容也不會增加任何東西，不要想當然的臆測自己不瞭解的知識，動手去做！

本文來自CSDN博客，轉載請標明出處：http://blog.csdn.net/ilibaba/archive/2009/03/10/3975680.aspx

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