Get hidden value set by JavaScript in JSF backing bean

I want to get a JavaScript value in a JSF backing bean. I've tried the following:

JSF:

<h:inputHidden id="fileName" value="#{TestBean.fileName}" />
<a4j:commandButton id="button" value="Send Mail" action="#{TestBean.send}" onclick="onCall()"/>

Bean:

public String send() {
    System.out.println("File Name: " + fileName);
}

JS:

function onCall(){
    //value changes dynamically everytime this function is called
    document.getElementById('case:fileName').value = '123';
}

Problem with this code is: for the fir开发者_开发知识库st time it is fetching empty string in backing bean from the second time onwards it is getting previously generated value in the java script function.

Where did I go wrong and how can I solve it?

I just tried this code and it works fine on my machine. As I can see the code is not exactly copy-pasted, because there is mistake in send() method. It declares return type String, but it doesn't return anything.

Maybe your mistake is somewhere in the part of code you didn't copy here.

You will need to use a4j's commandButton with a actionParam inside. Refer to this answer: https://stackoverflow.com/a/10534779/268016