how to assign javascript variables to jsp or jstl

Can anybody tell me how to assign javascript variables to jsp request or to jsp session.

I am do开发者_如何学Cing something like this

Here deletedRows is a hidden field.

var del=45;
document.getElementById("deletedRows").value=del
alert(document.getElementById("deletedRows").value);
<%String del_values = request.getParameter("deletedRows");%>
<%request.getSession().setAttribute("del_rows", del_values);%>

I don't get the value of del in my servlet.

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JSP gets compiled on the server. All the client gets is the "output" of the JSP: the HTML, CSS and Javascript.

The Javascript gets executed after this. Meaning everything in the JSP has become HTML et all when the javascript executes. You way want to think this as the Java/JSP part has "completed" and now the HTML/Javascript part takes over.

Now you want to pass on some value calculated/manipulated via Javascript back to the server. (I think this is what you mean when you say "assingn javascript variables to jsp request or to jsp session"

For this you have to submit the page to the server, and these values should be part of the form that is being submitted.

You may already have these values in some HTML elements (like a <input> or <select>), if not you can create hidden elements and populate these with the values before submitting the <form>.

In the code you have provided, you are populating the hidden field correctly, but you have to retrieve the value in the servlet, not in the JSP itself. Also, make sure that the hidden field in in a <form> and that form is submitted.

Once the form is submitted (to a servlet) the values can be retrieved in the servlet via request.getParameter.

There are few other mechanisms to send a value to the server, using a URL parameter or via Asynchronous (AJAX) requests, but I am not sure whether you are looking at these also.

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Any form fields, including hidden fields, that are submitted from the browser will be accessible in your JSP using request.getParameter("fieldname");. Query-string parameters may be accessed the same way.

Make sure that your form fields have a name attribute specified because it is that name (not the id attribute) that becomes the parameter name in your server-side code.

What you've already done in the little bit of code shown in your question, i.e., set the hidden form field to have the value of a JavaScript variable, should allow that value to be submitted and then accessed in the server-side code. But it's hard to see why it is not working without seeing at least some of your form HTML, particularly the definition of the hidden field. It would also help to see how that is being submitted. (I'm assuming it is being submitted: if you are trying to make all of that code run just on the server it won't work, because the JavaScript is treated as document content by the server, it isn't executed. Again, I can't really tell how you're using that code without seeing more of the surrounding JSP.)

UPDATE: I see that your code has been formatted since I started typing my answer. You aren't expecting all five lines to run on the server are you? The JavaScript code only runs on the client browser after the page is rendered. The Java code in between <% %> is executed on the server before the page gets to the browser and so can't access JavaScript at all. Anything not in the <% %> tags is simply sent to the browser as is - the servlet doesn't interact with it as such.