Java 如何使用 request.getParameterValues？
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How to use request.getParameterValues?
提问by Dan S.
I'm trying to pass an array from one jsp page to another using a hidden form.
我正在尝试使用隐藏表单将数组从一个 jsp 页面传递到另一个页面。
Here is the relevant code of my jsp files.
这是我的jsp文件的相关代码。
<td style="vertical-align: top;"><button onclick="getPlayerNames()"id="generate">Generate</button><br></td>
<form id="playerNames" method="post" action="lineups.jsp">
<input type="hidden" id="players" />
</form>
<script>
function getPlayerNames(){
var selected = document.querySelectorAll("#selected-players > tr > td");
var playernames = [];
for(var i=0; i<selected.length; ++i){
//alert(selected[i].textContent);
var num = (i-1)%6;
if(num==0){
playernames.push(selected[i].textContent);
}
}
document.getElementById("players").values=playernames;
alert(document.getElementById("players").values);
document.getElementById("playerNames").submit();
}</script>
The alert message does show that the correct values are being placed in "players"
警报消息确实显示正确的值被放置在“玩家”中
Then on my lineup.jsp I have:
然后在我的 lineup.jsp 上我有：
<%String[] s = request.getParameterValues("players");
System.out.println(s[0]);%>
and I get a null pointer exception on the line with 'System.out.println(s[0]);'
我在“System.out.println(s[0]);”行上得到一个空指针异常
采纳答案by Srinu
name attribute is not specified to input tag, if name attribute not specified then no value will be sent.
In your case
request.getParameterandrequest.getParameterValuesreturn same value becauseplayerselement is specified only one. When you userequest.getParameterit'll return directstring,request.getParameterValueswill returnstring[]with length1.
未为输入标签指定名称属性，如果未指定名称属性，则不会发送任何值。
在您的情况下
request.getParameter并request.getParameterValues返回相同的值，因为playerselement 仅指定了一个。当您使用request.getParameter它时string，request.getParameterValues它将直接返回，将返回string[]length1。
If you want to send multiple players and you don't want to repeat element in your jsp, then concat the playerswith some special character like the following:
如果您想发送多个玩家并且不想在您的 jsp 中重复元素，则将其players与一些特殊字符连接起来，如下所示：
document.getElementById("players").value=playernames.join("::");
You can get is as string in lineup.jspand you can split it with the same special characters like the following:
您可以获取 is as string in，lineup.jsp并且可以使用相同的特殊字符将其拆分，如下所示：
<%
String players = request.getParameter("players");
String[] s = players.split("::");
%>
回答by RishikeshD
String[] players = request.getParametervalues("nameOfTheHiddenField");
String[] 玩家 = request.getParametervalues("nameOfTheHiddenField");
Please try specifying a name for the hidden field and it will work.
请尝试为隐藏字段指定一个名称，它会起作用。
回答by sbur
OK, s is null here hence s[0]throws NullPointerException
好的，这里 s 为空，因此s[0]抛出NullPointerException
The method getParameterValues()will generally come into picture if there is a chance of getting multiple values for any input parameter,
this method will retrieve all of it values and return it as string array.
该方法getParameterValues()通常将进入画面，如果有越来越多值任何输入参数的机会，这种方法会检索所有的IT价值，并返回作为字符串数组。
but in your case I think you have only one value to fetch, use request.getAttributeand try to print the result i.e. s and not s[0]
但就您而言，我认为您只有一个值可以获取、使用request.getAttribute并尝试打印结果，即 s 而不是 s[0]
once s is not null , you can go for s[0]
一旦 s 不为 null ，你可以去 s[0]
