cannot post "+" to server

cannot post "+" to server


in my js:
function testSubmit(){
    newPostData("1+2");
}
function newPostData(cmd){
    $.post("/servlet/test","cmd="+cmd);
}
in my servlet:
String data = getRequest().getParameter("cmd");
System.out.println(data);
and we got "1 2" but not "1+2" as it should be.
Is this a bug?