如何判断get传的参数为空?

Question

if(request.getParameter("tool")==null)
resp.sendRedirect("aa.jsp");是这个意思么？

Answer 1

tool的是String 怎么能用"=="呢

Answer 2

String tool = request.getParameter("tool");if(tool.equals(null)&&tool.equals(""))
resp.sendRedirect("aa.jsp");

Answer 3

String tool = request.getParameter("tool");if(tool.equals("null")&&tool.equals(""))
resp.sendRedirect("aa.jsp");

Answer 4

String tool = request.getParameter("tool");if(tool.equals(null)&&tool.equals(""))
resp.sendRedirect("aa.jsp");判空的方法可不能这么写啊
NULL这个对象是没有equals方法的，JAVA会出现溢常的

Answer 5

能把JSP的页面发一下吗？那个应该是可以的

Answer 6

空值的比较当然用"=="
要么这么写String tool = request.getParameter("tool");
if(tool.equals＝＝null||tool.equals(""))
resp.sendRedirect("aa.jsp");

Answer 7

JSP: table width="577" height="98" border="0" cellpadding="0" cellspacing="0" onKeypress="if (event.keyCode<48||event.keyCode>57) event.returnValue=false"; >
  
<%  Collection temp = Tool_info.getAlltoolInformation();
   Iterator its=temp.iterator(); while(its.hasNext())
{
 
out.print("<tr>");
out.print("<td height=18></td></tr>");
out.print("<form name=form1 action=manage_food method=POST>"); Tool_info tool=(Tool_info)its.next();
String input_value;
out.print("<tr>");
out.print("<td width=63 rowspan=2 valign=top><img src="+tool.getToolImg()+" width=56 height=70></td>");
                out.print("<td width=380 height=59 valign=top>");
                out.print("<strong>FoodName:</strong>"+tool.getToolType()+"<br>");
                        out.print("<input type=hidden name=type_id value="+tool.getToolTypeID()+">");
out.print("<strong>About Tool:</strong>"+tool.getToolIntro()+"<br>");
                        out.print("<input type=hidden name=type_power value="+tool.getToolPower()+">");
  out.print("<strong>Energy number value:</strong>"+tool.getToolPower()+"<br>");
out.print("<strong>Price</strong>:$"+tool.getToolPrice()+"/one"+"</td>"); out.print("<td colspan=2 valign=top> <p></p></td>");
out.print("</tr>");
out.print("<tr>");
out.print("<td colspan=3>要购买的数量:");
out.print("<input type=text name=tool> &nbsp;&nbsp;&nbsp; <input type=submit value=buy></td>");
out.print("</tr>");
                out.print("</form>");
out.print("<tr>");
out.print("<td height=18></td></tr>");

}   %>
</table>
Servlet:      HttpSession session = request.getSession(false);
      String chk_buyfood = request.getParameter("food");
      System.out.println(chk_buyfood);
      int food_count=Integer.parseInt(chk_buyfood);      if(food_count==0||(chk_buyfood.equals("")&&chk_buyfood.equals(null)))
      {
        response.sendRedirect("process_error.jsp");
      }

Answer 8

if(food_count==0||(chk_buyfood.equals("")&&chk_buyfood.equals(null)))
      {
        response.sendRedirect("process_error.jsp");
      }
你的这句话有问题！~
if(food_count==0||(chk_buyfood==null&&chk_buyfood.equals("")))
      {
        response.sendRedirect("process_error.jsp");
      }