入門 10 - Map-backed ActionForm

入門 10 - Map-backed ActionForm
参考：http://www.jajakarta.org/struts/struts1.2/documentation/ja/target/userGuide/building_controller.html
原文:http://www.javaworld.com.tw/confluence/pages/viewpage.action?pageId=502
有的時候您的表單內容可能是由程式動態產生的，這時候表單上的欄位與參數我們事先並無法得知，因而無法事先決定好ActionForm的屬性，在Struts 1.1中，您可以使用Map-backed ActionForm，這樣的ActionForm使用Map來儲存表單的欄位值，一個例子如下：

UserForm.java
package onlyfun.caterpillar;
                                                                                              
import java.util.*;
import javax.servlet.http.*;
import org.apache.struts.action.*;
                                                                                              
public class UserForm extends ActionForm {
    protected Map map = new HashMap();
                                                                                              
    public void setValue(String key, Object value) {
        map.put(key, value);
    }
                                                                                              
    public Object getValue(String key) {
        return map.get(key);
    }
                                                                                              
    public Map getMap() {
        return map;
    }
                                                                                              
    public void reset(ActionMapping mapping, HttpServletRequest req) {
        map.clear();
    }
}　在Action類別中，您可以如下面的方式來取值：

LoginAction.java
package onlyfun.caterpillar;
                                                                                              
import javax.servlet.http.*;
import org.apache.struts.action.*;
                                                                                              
public class LoginAction extends Action {
    public ActionForward execute(ActionMapping mapping,
                                 ActionForm form,
                                 HttpServletRequest request,
                                 HttpServletResponse response)
    throws Exception {
        UserForm userForm = (UserForm) form;
        String name = (String) userForm.getValue("name");
        String password = (String) userForm.getValue("password");
                                                                                              
        if(name.equals("caterpillar") && password.equals("1234")) {
            request.setAttribute("valid_user", form);
            return mapping.findForward("greeting");
        }
                                                                                              
        return mapping.findForward("welcome");
    }
}　為了要能夠設定值給這個ActionForm，在表單上，您要使用name="value(key)"來設定欄位名稱，例如：

<html:form action="/LoginAction" focus="name">
    名稱：<html:text property="value(name)" size="20"/><br>
    密碼：<html:password property="value(password)" size="20"/><br>
    <html:submit/> <html:reset/>
</html:form>　同樣的，如果要使用<bean:write>標籤來寫出ActionForm的值，我們也要使用value(key)的方法來取值，例如：

<logic:present scope="request" name="valid_user">
    <bean:write name="valid_user" property="value(name)"/>您好，這是您的神秘禮物！
</logic:present>　在我們的ActionForm中，我們提供了getMap()方法，這樣作可以方便透過EL來取值，例如：

${valid_user.map.name}
${valid_user.map.password}