?? 入門 08 - actionerror與actionmessage - javaworld@tw.htm
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<DIV class=pageheader><SPAN class=pagetitle>入門 08 -
ActionError與ActionMessage</SPAN> </DIV>
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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 --> ActionForm是表單的物件化，有關於表單資料的完整性檢查工作該在其中進行，例如使用者是否填寫了所有的欄位，ActionForm中所有的屬性是否被設定了，您可以重新定義ActionForm的validate()方法來進行這項工作，例如：
<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>UserForm.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 UserForm <SPAN class=java-keyword>extends</SPAN> ActionForm {
<SPAN class=java-keyword>protected</SPAN> <SPAN class=java-object>String</SPAN> name;
<SPAN class=java-keyword>protected</SPAN> <SPAN class=java-object>String</SPAN> password;
<SPAN class=java-keyword>public</SPAN> void setName(<SPAN class=java-object>String</SPAN> name) {
<SPAN class=java-keyword>this</SPAN>.name = name;
}
<SPAN class=java-keyword>public</SPAN> void setPassword(<SPAN class=java-object>String</SPAN> password) {
<SPAN class=java-keyword>this</SPAN>.password = password;
}
<SPAN class=java-keyword>public</SPAN> <SPAN class=java-object>String</SPAN> getName() {
<SPAN class=java-keyword>return</SPAN> name;
}
<SPAN class=java-keyword>public</SPAN> <SPAN class=java-object>String</SPAN> getPassword() {
<SPAN class=java-keyword>return</SPAN> password;
}
<SPAN class=java-keyword>public</SPAN> void reset(ActionMapping mapping, HttpServletRequest req) {
name = <SPAN class=java-keyword>null</SPAN>;
password = <SPAN class=java-keyword>null</SPAN>;
}
<SPAN class=java-keyword>public</SPAN> ActionErrors validate(ActionMapping mapping,
HttpServletRequest request) {
ActionErrors errors = <SPAN class=java-keyword>new</SPAN> ActionErrors();
<SPAN class=java-keyword>if</SPAN>(getName() == <SPAN class=java-keyword>null</SPAN> || getUsername().length() < 1) {
errors.add(<SPAN class=java-quote>"name"</SPAN>,<SPAN class=java-keyword>new</SPAN> ActionError(<SPAN class=java-quote>"error.name.required"</SPAN>));
}
<SPAN class=java-keyword>if</SPAN>(getPassword() == <SPAN class=java-keyword>null</SPAN> || getPassword().length() < 1) {
errors.add(<SPAN class=java-quote>"password"</SPAN>,<SPAN class=java-keyword>new</SPAN> ActionError(<SPAN class=java-quote>"error.password.required"</SPAN>));
}
<SPAN class=java-keyword>return</SPAN> errors;
}
}</PRE></DIV></DIV><BR> 當使用者發送表單，而表單中有欄位沒有填寫時，則請求中會包括參數名稱，但是值為空字串，如果ActionForm具有某些屬性，而表單並沒有發送對應的參數，則不會設定ActionForm中對應的屬性，這些屬性將為null，我們的validate()中主要在檢查這兩個情況。<BR> validate()方法會傳回ActionErrors物件，ActionErrors可以儲存ActionError的訊息，每一個
ActionError會查詢資源檔中的key-value對應，當validate()丟回ActionErrors物件時，
ActionServlet就不會繼續進行接下來的工作，而是導回structs-config.xml所設定的位置，例如：
<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><global-forwards>
<forward
name=<SPAN class=java-quote>"welcome"</SPAN>
path=<SPAN class=java-quote>"/Welcome.<SPAN class=java-keyword>do</SPAN>"</SPAN>/>
</global-forwards>
<form-beans>
<form-bean
name=<SPAN class=java-quote>"userForm"</SPAN>
type=<SPAN class=java-quote>"onlyfun.caterpillar.UserForm"</SPAN>/>
</form-beans>
<action-mappings>
<action
path=<SPAN class=java-quote>"/Welcome"</SPAN>
type=<SPAN class=java-quote>"org.apache.struts.actions.ForwardAction"</SPAN>
parameter=<SPAN class=java-quote>"/pages/Welcome.jsp"</SPAN>/>
<action
path=<SPAN class=java-quote>"/LoginAction"</SPAN>
type=<SPAN class=java-quote>"onlyfun.caterpillar.LoginAction"</SPAN>
name=<SPAN class=java-quote>"userForm"</SPAN>
validate=<SPAN class=java-quote>"<SPAN class=java-keyword>true</SPAN>"</SPAN>
input=<SPAN class=java-quote>"/pages/Welcome.jsp"</SPAN>>
<forward name=<SPAN class=java-quote>"greeting"</SPAN> path=<SPAN class=java-quote>"/pages/greeting.jsp"</SPAN>/>
</action>
</action-mappings></PRE></DIV></DIV><BR> 為了要能使用validate()方法，<action>中的validate屬性必須設定為true，而input屬性也是必要的，當validate()傳回ActionErrors時，就會forward至input屬性所設定的位置，ActionErrors中的訊息，我們可以使用<html:errors/>標籤來顯示，待會就會看到。<BR> ActionForm中驗證了屬性為null及空字串的可能，這是資料完整性的驗證，接下來我們要驗證資料的正確性，是否符合我們所設定的名稱與密碼，我們改寫前一個主題的LoginAction，看看寫法有何不同：
<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>LoginAction.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>import</SPAN> org.apache.commons.beanutils.*;
<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,
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