怎么取地址栏的值？

[wws5220]

首先在一个JSP页面通过Javascript做判断，

function abc3() {

var s4 = document.getElementById("s4").value;
var s3 = document.getElementById("s3").value;
var s2 = document.getElementById("s2").value;

if (s4 != 0 ) {
window.location.href = "../selectProduct?s4=" + s4;
}else if(s3!=0 || s4==0){
s4=s3;
window.location.href = "../selectProduct?s3=" + s4;

if(s2!=0 || s4==0){
s4=s2;
window.location.href = "../selectProduct?s2=" + s4;
}


}
}

到servlet里面怎么去取判断以后的值呢？