通过url传参在Struts2的Action中得不到值的问题

xmlhttp.open("GET", "queryForChannelnode.action?nAddress=" + nAddress,true);

这个nAddress在Action中得不到值，我将变量private改成public后，成功。

public String nAddress;
	
	public String getnAddress() {
		return nAddress;
	}

	public void setnAddress(String nAddress) {
		this.nAddress = nAddress;
	}