<script>
$(document).ready(function(){
    $("#btn_1").click(function() {
        $.post("${pageContext.request.contextPath}/LoginServlet",
                {
                    jsonData:JSON.stringify({
                        username:$("input#username").val(),
                        password:$("input#password").val()
                    })
                },
                function(data,status){
                    alert("Data: " + data + "\nStatus: " + status);
                      }

        );
    });
});
</script>