Struts中使用 DynaActionForm

使用表单是网页里面经常遇到的事情．利用struts的标签可以很好的完成这一功能．在struts中表单分为两种．一种是ActionForm..另外一种是DynaActionForm.所谓动态是在使用表单时不需要创建对就的bean文件．ActionForm很简单，在此只说说DynaActionForm．因为在这个小项目中在很多的用户输入．数据验证部分我放到了Action中进行．于是在表示层Form中只是接收数据．用DynaActionForm实现是个很好的选择．

DynaActionForm提供了一种方便的机制，从根本上消除了编写ActionForm的需要。DynaActionForm可允许动态的表单属性。这意味着你能够在你的struts-config.xml文件中定义属性并且将表单类型设置为org.apache.struts.action.DynaActionForm。什么都不需要写。DynaActionForm使用Apache公共项目中的DynaBean完成这些操作。这一动态的行为是通过反射（reflection）与哈希图（Hashmaps）提供的。

index.jsp

<TABLE border="0" width="100%" height="40px">
                <TR>
                    <TD >
                        <html:form action="/selectAction" method="POST">    
                                       选择文法：
                                    <html:select property="select_grammar" >
                                        <html:options collection="grammarCollection"
                                                      　　　      property="label"
                                                       　　　     labelProperty="label"/>
                                    </html:select>
                                    <p>
                                       输入文法：                  
                                    <logic:present name="SELECTED_GRAMMAR" scope="request">
                                    <span id="thegrammar">         
                                        <html:textarea   cols="40"value="${SELECTED_GRAMMAR}">
                                        </html:textarea>*     
                                    </span>      
                                    </logic:present>
                                    <p>
                                <html:checkbox property="first" value="true" />:求first集合 <br>
                                <html:checkbox property="follow" value="true" />:求follow集合<br>
                                <html:checkbox property="select" value="true" />:求select集合 <br>
                                <html:submit/>
                                <html:reset/>
                                </html:form>                    
                    </TD>
                </TR>
</TABLE>

这个页面中和使用静态表单没什么区别，只是在struts-config.xm配置稍微有些不同．

<form-bean name="selectForm" type="org.apache.struts.action.DynaActionForm">
      <form-property name="select_grammar" type="java.lang.String" />
      <form-property name="selected_grammar" type="java.lang.String" />
      <form-property name="first" type="java.lang.Boolean" />
      <form-property name="select" type="java.lang.Boolean"/>  
      <form-property name="follow" type="java.lang.Boolean"/>       
</form-bean>

对应此表单的Action的配置：

<action path="/selectAction"
                    type="ysu.cs.icai.action.selectAction"　//定义的处理提交的类
                    input="/index.jsp"
                    name="selectForm"
                    validate="false"
                    scope="request">
                 <forward name="SUCCESS_PATH" path="/selectindex.do"/>
</action>

和ActionForm的不同之处还在于在Action中获取提交的参数时要将ActionForm强制转换为DynaActionForm:

DynaActionForm analyzeForm = (DynaActionForm) form;

如何获取各参数如下：

import org.apache.struts.action.DynaActionForm;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
/**
        * Method execute
        * @param mapping
        * @param form
        * @param request
        * @param response
        * @return ActionForward
     */
public class selectAction extends Action {

public ActionForward execute(
           ActionMapping mapping,
           ActionForm form,
           HttpServletRequest request,
       HttpServletResponse response) {
           DynaActionForm analyzeForm = (DynaActionForm) form;//强制
           String grammar=(String)analyzeForm.get("selected_grammar");    
           Boolean first=(Boolean)analyzeForm.get("first");//
           Boolean follow=(Boolean)analyzeForm.get("follow");//
           Boolean select=(Boolean)analyzeForm.get("select");//获取提交的各个参数．
　　//......something about what     you what todo.........
    return mapping.findForward("SUCCESS_PATH");
}
}

动态表单有很多优点．比如可以实现跨页的表单提交．还过也有缺点比如此时它就不能将validate框架集成到里面．有个方法就是可心自己继承DynaActionForm类在其中添加validate方法．再将实际的应用中的Form继承此类．不过此时的将失去使用DynaActionForm的灵活性．只好自己权衡了。