Submit values of various inputs of the form

1.        When getting parameters on the server ,HttpServletRequest.getParameter(String name) The return result of the method is distinguished according to the following conditions ：

1.1    The request message does not contain this parameter , return null.

1.2    The request message contains this parameter , But it's not worth it . for example param1=&param2=123 Medium param1. In this case, an empty string is returned ””.

1.3    The request message contains multiple parameters with the same name . for example param1=1&param1=2 Medium param1. In this case , Returns the value of the first parameter . For example, above 1. If you use HttpServletRequest.getParameterValues(String name), Returns a containing all values with the same name Sring Array .

2.       <input type="submit" name=" " value=" ">.

There can be more than one... In a page submit Elements , Click on a submit Button time , The browser will form The data is sealed and forwarded to the server , This includes a pair of currently clicked submit Data of information , Click... For the current submit Button on the name and value. Other non clickable submit Button does not pass name and value value .

So you can judge which one is clicked by the following statement submit Button .

if(req.getParameter("submit Button on the name attribute ") != null && req.getParameter("submit Button on the name attribute ").equals("submit Button on the value attribute "))

       {

            Execute statement

    }

If a submit The button doesn't have name attribute . When you click this button , The browser will also form The data is sealed and forwarded to the server , But it doesn't include submit Button itself name and value Information . Therefore, the server cannot judge which button is clicked .

3.       <input type="button" name=" " value=" ">

Click on a submit Button time , The browser will automatically submit data to the server , But click on one Button When , The browser simply executes this Button Of onclick event . without onclick event , Just do nothing . Can be in onclick Pass in the event JavaScript Code submission form .

for example ：

function button1_click()

{

document.form1.action = “check.jsp”;

document.form1.submit();

}

Click on button Button does not pass button Of name and value value .

4.        Various input The transfer name and value The situation of ：

Premise is , As long as there is no name attribute , No transmission .

text and textarea Whether it's empty or not , Will be passed to the server , Passed when null value The value is an empty string .

checkbox and radio The situation is , Only the selected one will be passed , What is not selected is not transmitted . If no... Is selected value Of checkbox and radio, Delivered value The value is defaults to ”on”.

hidden No matter how , Will be passed to the server .

5.        A practice

5.1   jsp page

<form action="<%=request.getContextPath()%>/checkboxtest"

                            method="post" target="_blank">

                            <table>

                                     <tr>

                                               <td>

                                                        <input type="checkbox" name="selectbooks" value="1">

                                               </td>

                                               <td>

                                                        1

                                               </td>

                                     </tr>

                                     <tr>

                                               <td>

                                                        <input type="checkbox" name="selectbooks" value="2">

                                               </td>

                                               <td>

                                                        2

                                               </td>

                                     </tr>

                                     <tr>

                                               <td>

                                                        <input type="checkbox" name="selectbooks" value="3">

                                               </td>

                                               <td>

                                                        3

                                               </td>

                                     </tr>

                                     <tr>

                                               <td>

                                                        <input type="submit" name="check" value=" see ">

                                               </td>

                                               <td>

                                                        <input type="submit" name="delete" value=" Delete ">

                                               </td>

                                     </tr>

                            </table>

</form>

5.2    backstage Servlet Code ：

                   resp.setContentType("text/html;charset=UTF-8");

                   String[] selectBooks = req.getParameterValues("selectbooks");

                   StringBuffer selectBookIds = new StringBuffer();

                   int flag = 0;

                   for (String selectbook : selectBooks) {

                            if (flag == 0) {

                                     selectBookIds.append(selectbook);

                            }

                            else

                            {

                                     selectBookIds.append("," + selectbook);

                            }                

                            flag = 1;

                   }

 

                   if(req.getParameter("check") != null)

                   {

                            resp.getWriter().println(" Of the selected books id Yes ：" + selectBookIds.toString());

                   }

                   else if(req.getParameter("delete") != null)

                   {

                            resp.getWriter().println(" Deleted books id Yes ：" + selectBookIds.toString());

                   }

                   else

                   {

                            resp.getWriter().println(" Of the returned books id Yes ：" + selectBookIds.toString());

                   }