📄 入門 06 - 使用action類別 - javaworld@tw.htm
字号:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<!-- saved from url=(0071)http://www.javaworld.com.tw/confluence/pages/viewpage.action?pageId=424 -->
<HTML><HEAD><TITLE>入門 06 - 使用Action類別 - JAVAWORLD@TW</TITLE>
<META http-equiv=Content-Type content="text/html; charset=utf-8"><!-- CONFL-BEGIN standardHeader -->
<META http-equiv=Pragma content=no-cache>
<META http-equiv=Expires content=-1>
<SCRIPT language=javascript> var contextPath = '/confluence';</SCRIPT>
<LINK href="入門 06 - 使用Action類別 - JAVAWORLD@TW.files/main-action.css"
type=text/css rel=stylesheet><LINK href="/confluence/images/icons/favicon.ico"
rel="shortcut icon"><LINK href="/confluence/images/icons/favicon.png"
type=image/png rel=icon>
<SCRIPT src="入門 06 - 使用Action類別 - JAVAWORLD@TW.files/effects.js"></SCRIPT>
<!-- CONF-END standardHeader -->
<META content="MSHTML 6.00.2800.1491" name=GENERATOR></HEAD>
<BODY onload=placeFocus()>
<DIV id=Content>
<TABLE cellSpacing=0 cellPadding=0 width="100%" border=0>
<TBODY>
<TR>
<TD class=logocell width="60%" rowSpan=2>
<DIV class=spacenametitle><A
href="http://www.javaworld.com.tw/confluence/display/opensrc"><IMG
src="入門 06 - 使用Action類別 - JAVAWORLD@TW.files/confluence_logo.gif"
align=bottom border=0></A> <A
href="http://www.javaworld.com.tw/confluence/display/opensrc">OpenSource
Project</A></DIV></TD>
<TD vAlign=top align=right width="40%">
<TABLE cellSpacing=1 cellPadding=2 align=right bgColor=#ffffff border=0>
<TBODY>
<TR>
<TD class=navItem onmouseover="this.className='navItemOver'"
onclick="window.document.location='/confluence/'"
onmouseout="this.className='navItem'" vAlign=center noWrap
align=middle> <A title="Go to the Confluence Dashboard"
accessKey=h onclick="return false"
href="http://www.javaworld.com.tw/confluence/"><U>H</U>OME</A>
</TD>
<TD class=navItem onmouseover="this.className='navItemOver'"
onclick="window.document.location='/confluence/spaces/listspaces.action'"
onmouseout="this.className='navItem'" vAlign=center noWrap
align=middle> <A title="The spaces available for you"
accessKey=s onclick="return false"
href="http://www.javaworld.com.tw/confluence/spaces/listspaces.action"><U>S</U>PACES</A>
</TD></TR></TBODY></TABLE></TD></TR>
<TR>
<TD vAlign=bottom align=right><SPAN class=smalltext><A
href="http://www.javaworld.com.tw/confluence/login.action?os_destination=/pages/viewpage.action?pageId=424">Log
In</A> </SPAN><A
href="http://www.javaworld.com.tw/confluence/pages/viewpage.action?pageId=424&decorator=printable"><IMG
title="View a printable version of the current page." height=16
alt="View a printable version of the current page." hspace=1
src="入門 06 - 使用Action類別 - JAVAWORLD@TW.files/print_16.gif" width=16
align=absMiddle vspace=1 border=0></A> <A
href="http://confluence.atlassian.com/display/DOC"><IMG
title="Get help from the Confluence website." height=16
alt="Get help from the Confluence website." hspace=1
src="入門 06 - 使用Action類別 - JAVAWORLD@TW.files/help_16.gif" width=16
align=absMiddle vspace=1 border=0></A> </TD></TR></TBODY></TABLE><!-- CONF-BEGIN breadcrumbsAndSearch -->
<DIV class=breadcrumbs width="100%">
<TABLE cellSpacing=0 cellPadding=0 width="100%" border=0>
<TBODY>
<TR>
<TD> Location: <A
href="http://www.javaworld.com.tw/confluence/dashboard.action">Dashboard</A>
> <A
href="http://www.javaworld.com.tw/confluence/spaces/viewspacesummary.action?key=opensrc">opensrc</A>
> <A
href="http://www.javaworld.com.tw/confluence/pages/listpages.action?key=opensrc">Pages</A>
> <A
href="http://www.javaworld.com.tw/confluence/display/opensrc/Home">Home</A>
> <A
href="http://www.javaworld.com.tw/confluence/display/opensrc/Struts">Struts</A>
> <A
href="http://www.javaworld.com.tw/confluence/pages/viewpage.action?pageId=1958">Struts入門</A>
> <A
href="http://www.javaworld.com.tw/confluence/pages/viewpage.action?pageId=424">入門
06 - 使用Action類別</A> </TD>
<FORM name=searchForm action=/confluence/dosearchsite.action
method=get><INPUT type=hidden value=true name=quickSearch>
<TD vAlign=bottom align=right width=200><A style="TEXT-DECORATION: none"
href="http://www.javaworld.com.tw/confluence/searchsite.action"><U>Q</U>uick
<U>Search</U></A>:<INPUT accessKey=q size=10 name=searchQuery.queryString><INPUT type=submit value=Go><BR><IMG height=1
src="入門 06 - 使用Action類別 - JAVAWORLD@TW.files/spacer.gif"
width=200></TD></FORM></TR></TBODY></TABLE></DIV><!-- CONF-END breadcrumbsAndSearch -->
<TABLE cellSpacing=0 cellPadding=5 width="100%" border=0>
<TBODY>
<TR>
<TD>
<TABLE cellSpacing=0 cellPadding=0 width="100%" border=0>
<TBODY>
<TR>
<TD class=pagebody vAlign=top>
<DIV class=pageheader><SPAN class=pagetitle>入門 06 -
使用Action類別</SPAN> </DIV>
<SCRIPT language=javascript> function toggle(id) { var oldAttachmentVersionsBlock = document.getElementById('attachment' + id); with (oldAttachmentVersionsBlock.style) { if ( display == "none" ) display = "" else display = "none" } var arrowIcon = document.getElementById('arrow' + id); with (arrowIcon) { if (src != null && (src.indexOf('/confluence/images/icons/arrow_closed_active_16.gif') != -1 || src.indexOf('/confluence/images/icons/arrow_closing_active_16.gif') != -1)) { src = '/confluence/images/icons/arrow_opening_active_16.gif'; } else { src = '/confluence/images/icons/arrow_closing_active_16.gif'; } } } </SCRIPT>
<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 --> 在Struts中，ActionServlet擔任分配工作的控制器角色，實際上的工作是交給
Action物件來進行，ActionServlet由ActionMapping得知所使用的Action物件，將工作交給它，並在最後由Action
物件得到一個ActionForward物件，ActionServlet使用這個ActionForward來知道下一個forward的對象。<BR> 對於Struts，一個ActionMapping只會生成一個Action物件，當請求到達時，會檢查所需的Action物件是否存在，如果不存在則生成一個，之後一直使用它，由於Action物件會一直存在，所以使用Action物件必須注意到執行緒安全問題。<BR> 我們透過繼承Action類別來使用它，在Struts
1.1中，我們會重新定義execute()方法，在Struts
1.0中的perform()方法已經不建議使用；execute()方法有兩個接收不同參數的版本：
<DIV class=code
style="BORDER-TOP-STYLE: solid; BORDER-RIGHT-STYLE: solid; BORDER-LEFT-STYLE: solid; BORDER-BOTTOM-STYLE: solid">
<DIV class=codeContent><PRE><SPAN class=java-keyword>public</SPAN> ActionForward execute(ActionMapping mapping,
ActionForm form,
ServletRequest request,
ServletResponse response)
<SPAN class=java-keyword>throws</SPAN> Exception;
<SPAN class=java-keyword>public</SPAN> ActionForward execute(ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response)
<SPAN class=java-keyword>throws</SPAN> Exception;</PRE></DIV></DIV><BR> 由於Action通常處理HTTP相關請求，所以我們通常會使用第二個，execute()方法最後要傳回ActionForward物件給ActionServlet。<BR> 在MVC/Model
2中，理想上所有的請求都經由ActionServlet來協調轉發，客戶端不會直接指定真正的位址來請求資源，我們下面直接來看個例子，使用Action物件處理這個功能，首先撰寫一個Action類別：
<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>GetAction.java</B></DIV>
<DIV class=codeContent><PRE><SPAN class=java-keyword>package</SPAN> onlyfun.caterpillar;
<SPAN class=java-keyword>import</SPAN> javax.servlet.http.*;
<SPAN class=java-keyword>import</SPAN> org.apache.struts.action.*;
<SPAN class=java-keyword>public</SPAN> class GetAction <SPAN class=java-keyword>extends</SPAN> Action {
<SPAN class=java-keyword>public</SPAN> ActionForward execute(ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response)
<SPAN class=java-keyword>throws</SPAN> Exception {
<SPAN class=java-object>String</SPAN> resource = request.getParameter(<SPAN class=java-quote>"resource"</SPAN>);
<SPAN class=java-keyword>if</SPAN>(resource != <SPAN class=java-keyword>null</SPAN> && resource.length() != 0) {
request.setAttribute(<SPAN class=java-quote>"resource"</SPAN>, resource);
<SPAN class=java-keyword>return</SPAN> mapping.findForward(<SPAN class=java-quote>"resource"</SPAN>);
<SPAN class=java-comment>// <SPAN class=java-keyword>return</SPAN> <SPAN class=java-keyword>new</SPAN> ActionForward(<SPAN class=java-quote>"resource"</SPAN>);</SPAN>
}
<SPAN class=java-keyword>return</SPAN> mapping.findForward(<SPAN class=java-quote>"welcome"</SPAN>);
}
}</PRE></DIV></DIV><BR> 在這個類別中，如果客戶端的請求中包括了請求參數resource，則直接返回一個ActionForward，對象為請求參數的內容，原本我們應該是return
new
ActionForward("resource")，不過為了說明方便，我們將查找struts-config.xml中的forward對象，如果客戶端沒有包括resource對象，則直接查找"welcome"的forward對象。<BR> 這個類別編譯過後，應該位於WEB-INF下並包括package階層，接著我們要在struts-config.xml中加以定義：
<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>struts-config.xml</B></DIV>
<DIV class=codeContent><PRE><struts-config>
⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -