📄 入門 07 - 使用actionform類別 - javaworld@tw.htm
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<SPAN class=java-keyword>public</SPAN> class LoginAction <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> name = ((UserForm) form).getName();
<SPAN class=java-object>String</SPAN> password = ((UserForm) form).getPassword();
<SPAN class=java-keyword>if</SPAN>(name.equals(<SPAN class=java-quote>"caterpillar"</SPAN>) && password.equals(<SPAN class=java-quote>"1234"</SPAN>)) {
request.setAttribute(<SPAN class=java-quote>"valid_user"</SPAN>, form);
<SPAN class=java-keyword>return</SPAN> mapping.findForward(<SPAN class=java-quote>"greeting"</SPAN>);
}
<SPAN class=java-keyword>return</SPAN> mapping.findForward(<SPAN class=java-quote>"welcome"</SPAN>);
}
}</PRE></DIV></DIV><BR> ActionForm被作為參數傳遞至execute()方法，我們必須轉換為其原來的形態UserForm，這樣才可以取出當中的屬性值，在驗證使用者的名稱與密碼無誤後，我們查找greeting的ActionForward對象並傳回，這會使得ActionServlet將請求
forward至greeting.jsp：
<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>greeting.jsp</B></DIV>
<DIV class=codeContent><PRE><%@ taglib uri=<SPAN class=java-quote>"/tags/struts-bean"</SPAN> prefix=<SPAN class=java-quote>"bean"</SPAN> %>
<%@ taglib uri=<SPAN class=java-quote>"/tags/struts-html"</SPAN> prefix=<SPAN class=java-quote>"html"</SPAN> %>
<%@ taglib uri=<SPAN class=java-quote>"/tags/struts-logic"</SPAN> prefix=<SPAN class=java-quote>"logic"</SPAN> %>
<%@page contentType=<SPAN class=java-quote>"text/html; charset=Big5"</SPAN>%>
<html:html locale=<SPAN class=java-quote>"<SPAN class=java-keyword>true</SPAN>"</SPAN>>
<head>
<title><bean:message key=<SPAN class=java-quote>"welcome.title"</SPAN>/></title>
<html:base/>
</head>
<body bgcolor=<SPAN class=java-quote>"white"</SPAN>>
<logic:present scope=<SPAN class=java-quote>"request"</SPAN> name=<SPAN class=java-quote>"valid_user"</SPAN>>
<bean:write name=<SPAN class=java-quote>"valid_user"</SPAN> property=<SPAN class=java-quote>"name"</SPAN>/>您好，這是您的神秘禮物！
</logic:present>
<logic:notPresent scope=<SPAN class=java-quote>"request"</SPAN> name=<SPAN class=java-quote>"valid_user"</SPAN>>
<html:link forward=<SPAN class=java-quote>"welcome"</SPAN>>請先登入</html:link>
</logic:notPresent>
</body>
</html:html></PRE></DIV></DIV><BR> <login:present>標籤會查看指定的範圍中是不是有指定名稱的JavaBean物件，如果有的話就使用<
bean:write>寫出指定的屬性，而<login:notPresent>的作用恰恰相反，如果沒有指定名稱的JavaBean
物件，就給出一個超連結要求先進行登入，<html:link>的forward屬性會查找struts-config.xml中的<
global-forward>的welcome設定。<BR>如果驗證失敗，則查找welcome的ActionForward對象並傳回，也就是Welcome.jsp，我們用之為登入表單：
<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>Welcome.jsp</B></DIV>
<DIV class=codeContent><PRE><%@ taglib uri=<SPAN class=java-quote>"/tags/struts-bean"</SPAN> prefix=<SPAN class=java-quote>"bean"</SPAN> %>
<%@ taglib uri=<SPAN class=java-quote>"/tags/struts-html"</SPAN> prefix=<SPAN class=java-quote>"html"</SPAN> %>
<%@page contentType=<SPAN class=java-quote>"text/html; charset=Big5"</SPAN>%>
<html:html locale=<SPAN class=java-quote>"<SPAN class=java-keyword>true</SPAN>"</SPAN>>
<head>
<title><bean:message key=<SPAN class=java-quote>"welcome.title"</SPAN>/></title>
<html:base/>
</head>
<body bgcolor=<SPAN class=java-quote>"white"</SPAN>>
<html:form action=<SPAN class=java-quote>"/LoginAction"</SPAN> focus=<SPAN class=java-quote>"name"</SPAN>>
名稱：<html:text property=<SPAN class=java-quote>"name"</SPAN> size=<SPAN class=java-quote>"20"</SPAN>/><br>
密碼：<html:password property=<SPAN class=java-quote>"password"</SPAN> size=<SPAN class=java-quote>"20"</SPAN>/><br>
<html:submit/> <html:reset/>
</html:form>
</body>
</html:html></PRE></DIV></DIV><BR> <html:form>指定的LoginAction必須在struts-config.xml中有定義，<html:
text>與<html:password>會取出對應的ActionForm物件中對應的屬性值，如果使用者填寫的內容不正確而被送回Welcome.jsp，使用者將可以看到先前所填寫的值，如果不想顯示先前所填寫的值，則將<html:text>與<html:
password>的redisplay屬性設定為false即可，這幾個Struts標籤必須與Action物件及ActionForm物件搭配使用。<BR> 接下來您可以測試一下程式，連上http://localhost:8080/HelloStruts/，如果您填寫了正確的表單欄位並送出，則結果會如下：
<DIV class=code
style="BORDER-TOP-STYLE: solid; BORDER-RIGHT-STYLE: solid; BORDER-LEFT-STYLE: solid; BORDER-BOTTOM-STYLE: solid">
<DIV class=codeContent><PRE><html lang=<SPAN class=java-quote>"zh"</SPAN>>
<head>
<title>哈囉！Struts！</title>
<base href=<SPAN class=java-quote>"http:<SPAN class=java-comment>//localhost:8080/HelloStruts/pages/greeting.jsp"</SPAN>></SPAN>
</head>
<body bgcolor=<SPAN class=java-quote>"white"</SPAN>>
caterpillar您好，這是您的神秘禮物！
</body>
</html></PRE></DIV></DIV><BR> ActionForm在Struts中是屬於視圖組件的一部份，它是表單的物件化表單，表單的參數會自動設定給ActionForm，無法對應的就加以忽略，您可以定義validate()方法來驗證表單設定的內容，這在下一個主題中將加以說明，在ActionForm中您可以填入表單值，作一些適當的值轉換，進行基本的資料驗證，ActionForm是表單資料發送至應用程式前的緩衝區，在某些程度上，它是應用程式的防火牆，您可以在
ActionForm中避免不正確或不安全的資料進入應用程式。<BR> 綜合一下，ActionForm擔任以下的幾個職責：<BR>*表單欄位的耕耘者<BR>*資料的緩衝區<BR>*資料的驗證<BR>*進行屬性值的轉換<BR>*應用程式防火牆
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