JSP聊天-如何将HTML中的值解析为JSP页面？

Question

I have to make a chat with JSP, AJAX and Java and I have a problem: when I try to use my variable to store value of a input text, this variable is null. If I add 'action' property to the form, the variable 'textParam' will have the value of the input text, but, if I do that I have to redirect with action to a page and I don't what that.

I need to process something bigger in the JSP page and then to reload in the HTML page (which is a JSP page) (the reload part is not on actual probem).

How I can make to populate 'textParam' with the input text value when I press the button?

PS: I need to make it with pure javascript, not with some libraries :)

The JSP which have to process is:

String textParam = request.getParameter("chatMessage");
System.out.println("textParam = " + textParam);

My form it look like that:

<form id="frmmain" name="frmmain" onsubmit="return blockSubmit();">
        <input type="text" id="chatMessage" name="chatMessage" style="width: 447px;" />
        <input type="button" name="btn_send_chat" id="btn_send_chat" value="Send" onclick="sendChatText();" />
</form>

The .js file it's this:

var request = getXmlHttpRequestObject();
var response = getXmlHttpRequestObject();
var lastMessage = 0;
var mTimer;

function getXmlHttpRequestObject() {                
    if (window.XMLHttpRequest) {                    
        return new XMLHttpRequest();
    } else if(window.ActiveXObject) {                   
        return new ActiveXObject("Microsoft.XMLHTTP");
    }
}

function sendChatText() {
    if(document.getElementById('chatMessage').value == '') {
        alert("You have not entered a message");
        return;
    }
    if (request.readyState == 4 || request.readyState == 0) {
        request.open("POST", 'getChat2.jsp?chat=1&last=' + lastMessage, true);
        request.setRequestHeader('Content-Type','application/x-www-form-urlencoded');
        request.onreadystatechange = handleSendChat; 
        var param = 'message=' + document.getElementById('chatMessage').value;                                  
        param += '&chat=1';
        request.send(param);
        document.getElementById('chatMessage').value = '';
    }                           
}

function handleSendChat() {             
    clearInterval(mTimer);
    getChatText();
}

function blockSubmit() {
    sendChatText();
    return false;
}

Answer 1

The problem is here:

String textParam = request.getParameter("chatMessage");

I was trying to get 'chatMessage' parameter, which it was only the name of the input. The solve is to get 'message' param which it was defined and requested in js:

String textParam = request.getParameter("message");