📄 入門 18 - plugin介面 - javaworld@tw.htm
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<DIV class=pagesubheading>Last changed on Oct 27, 2004 by <A
href="http://www.javaworld.com.tw/confluence/display/~koji">koji
lin</A>
</DIV><!-- page content --> 您可以繼承ActionServlet，重新定義它的init()方法，這樣可以在ActionServlet被載入時增加一些您想要載入的資源，然而這並不是個好方法，您必須將程式碼寫死在當中，如果您要載入的資源多時是一個麻煩，想要拆除某個資源時又是一個麻煩。
<BR> Struts
1.1提供一個新的PlugIn介面，它可以讓您動態增減ActionServlet的功能，PlugIn中規定了兩個必須實作的方法：
<DIV class=code
style="BORDER-TOP-STYLE: solid; BORDER-RIGHT-STYLE: solid; BORDER-LEFT-STYLE: solid; BORDER-BOTTOM-STYLE: solid">
<DIV class=codeHeader
style="BORDER-BOTTOM-STYLE: solid"><B>PlugIn.java</B></DIV>
<DIV class=codeContent><PRE><SPAN class=java-keyword>public</SPAN> <SPAN class=java-keyword>interface</SPAN> PlugIn {
<SPAN class=java-keyword>public</SPAN> void init(ActionServlet servlet,
ModuleConfig config)
<SPAN class=java-keyword>throws</SPAN> javax.servlet.ServletException;
<SPAN class=java-keyword>public</SPAN> void destroy();
}</PRE></DIV></DIV><BR> 您可以將資源載入的動作撰寫在init()方法中，ActionServlet會載入後，會執行實作PlugIn介面的類別之init()方法，例如您可以在這邊進行資料庫資源的連結，而ActionServlet被終結前，會執行實作PlugIn介面的類別之destroy()方法，您可以在這邊撰寫一些釋放資源的方法。
<BR> 實作PlugIn介面時，必須提供一個沒有參數的建構函式給ActionServlet使用，如果初始化需要一些參數設定，您可以如同JavaBean一樣的設定setter，一個實例的例子如下：
<DIV class=code
style="BORDER-TOP-STYLE: solid; BORDER-RIGHT-STYLE: solid; BORDER-LEFT-STYLE: solid; BORDER-BOTTOM-STYLE: solid">
<DIV class=codeHeader
style="BORDER-BOTTOM-STYLE: solid"><B>MyPlugin.java</B></DIV>
<DIV class=codeContent><PRE><SPAN class=java-keyword>package</SPAN> onlyfun.caterpillar;
.......
<SPAN class=java-keyword>import</SPAN> org.apache.struts.action.*;
<SPAN class=java-keyword>public</SPAN> class MyPlugIn <SPAN class=java-keyword>implements</SPAN> PlugIn {
......
<SPAN class=java-keyword>public</SPAN> MyPlugIn() {
}
<SPAN class=java-keyword>public</SPAN> void init(ActionServlet servlet,
ModuleConfig config)
<SPAN class=java-keyword>throws</SPAN> javax.servlet.ServletException {
<SPAN class=java-comment>// 初始化資源 </SPAN>
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