Java 序列化(Serialization)

序列化的意思就是把物件儲存後(file or database)，在從中取出還會是原物件狀況，包含屬性等。

首先必須實作 Serializable interface，這個介面沒有任何method。

該物件的屬性如果是 primitive type會自動被序列化。

如果非primitive type沒有實作Serializable就會丟出 Runtime Exception

或者我們不想讓這個非primitive type不被序列化，就在這屬性加上transient

如果兩個物件共同指向相同非privitive type的A物件，且儲存時使用相同ObjectOutputStream，此時只會存一份A物件。如果儲存時分別使用不同ObjectOutputStream，當然就會有各自一份不同的A物件。

細節說明和範例可參考這

Got an UiBinder useSafeHtmlTemplates warning on GWT compiling

When I was running a sample MVP application of GWT , show an error

[WARN] [helloMVP] Configuration property UiBinder.useSafeHtmlTemplates is false! UiBinder SafeHtml integration is off,
leaving your users more vulnerable to cross-site scripting attacks. This property will default to true in future releases of GWT

Solution is add one line in Contacts.gwt.xml

To decorate java code in google blogger with SyntaxHighlighter

• Go to SyntaxHighlighter and download ( I used 3.0.83 release )
• Unzip the file you download and  upload 

               the files(shCore.js、shBrushJava.js) in syntaxhighlighter_3.0.83\scripts               and (shCore.css、shCoreEclipse.css、shThemeEclipse.css) in syntaxhighlighter_3.0.83\styles
              to your web space ( On-line ) or https://sites.google.com/site/yours/

                                             I upload these files to my google site

 

 

                                              change the template in your blogger

 

add some html code as below

 

save the setting!

So , now you can decorate your code in blogger !

In editor of blogger , as following

<pre class="brush:java" name="code" >
      java code
</pre >

It is easy to use for html and javaScript and so on as above . See the configuration of SyntaxHighlighter for more advanced feature.

GWT Note 2

Event and Event handler

有四種方式來實作UI介面與事件觸發處理的關係
1.handler獨立成一個class，這樣會多很多class file不好review code和維護。

public class GwtEvents implements EntryPoint {
   ...
   public void onModuleLoad() {
     textfield = new TextBox();
     textfield.addKeyUpHandler(new MyHandler(this));
     ...
   }//end onModuleLoad
}//end class

public class MyHandler implements KeyUpHandler {
   ...
   public void onKeyUp(KeyUpEvent event) {
   ...
   }
}//end class

2.直接實作handler

public class GwtEvents implements EntryPoint, KeyUpHandler {
   ...
   public void onModuleLoad() {
     textfield = new TextBox();
     textfield.addKeyUpHandler(this);
     ...
    }

   public void onKeyUp(KeyUpEvent event) {
   ...
   }

}//end class

3. (Named)Inner class

public class GwtEvents implements EntryPoint { 
   public void onModuleLoad() { 
      textfield = new TextBox(); 
      textfield.addKeyUpHandler(new MyHandler()); 

   private class MyHandler implements KeyUpHandler { 
     public void onKeyUp(KeyUpEvent event) { 
     ... 
    } 

   }//end onModuleLoad 
}//end class 

4.Anonymous inner classes

public class GwtEvents implements EntryPoint { 
   ... 
   public void onModuleLoad() { 
     textfield = new TextBox(); 
     textfield.addKeyUpHandler(new KeyUpHandler() { 
     @Override 
     public void onKeyUp(KeyUpEvent event) { 
      ... 
     } 
    }); 
   }//end onModuleLoad 
}//end class 

請依情況選擇2、3的作法，避免用方法4。

GWT Note 1

今天遇到一個很怪的情況，怎麼加xxx.gwt.xml在已含有*.gwt.xml的project內就是會跑不起來，訊息如下:
[ERROR] [gwtevents1] - Unable to find 'gwtevents1.gwt.xml' on your classpath; could be a typo, or maybe you forgot to include a classpath entry for source?
...
[ERROR] [gwtevents4] - Unable to find 'gwtevents4.gwt.xml' on your classpath; could be a typo, or maybe you forgot to include a classpath entry for source?

這四個新加入的都出現一樣的錯誤，後來才找到問題:就是不要跑原先存留在eclipse內的執行設定，也就是刪除舊的執行設定 Run => Run Configurations => delete old configuration 或對project按右鍵=>Run As => Web Application

這種問題的解決挺難找的= = ，如果習慣用ant或maven來build，不要仰賴eclipse就不會遇到這種鳥事。

GWT Note

最近開始進入GWT的開發模式，所以一定會有不熟悉的地方，也就容易產生錯誤。
這邊就來把遇到的問題記起來吧!

在eclipse建立一個練習的GWT專案後，想要在這個專案跑一個以上的entry http://www.blogger.com/img/blank.gifpoint，http://www.blogger.com/img/blank.gif所以就會有一個以上的xxx.gwt.xml，那不想讓這兩個module(GWT是定義一個module一個entry point，討論1、2)包到彼此的client code，很簡單的方式就是切不同的path(或說package)

for example :
gwtapp1.gwt.xml
...
<module rename-to='gwtapp1'>
<source path='client/app1'/>
</module>

gwtapp2.gwt.xml
...
<module rename-to='gwtapp2'>
<source path='client/app2'/>
</module>

就是path不同，這樣就不會把gwtapp1的clinet code也被compile成gwtapp2的code了!

注意rename-to的值就是war內的一個目錄專放java to javaScipt的地方，還有就是path是用 / 斜線(slash or forward slash。 \ 反斜線是叫 backslash)，我一開始是用"點" 所以會被google plugin的compiler說 "GWT compilation failed" 。= =;;;