如何通过google map api实现地图定位

本人想开发一个网站，希望可以通过google map api实现：
获取访问者的IP，然后定位到google map的相应区域，如广州的用户访问，则定位到广州的地图

请问要怎么实现，希望能给出可以发布到tomcat下相应的例子，谢谢！

1. 通过 IP 得到地址
2. JavaScript下使用地理译码

[url]http://www.codechina.org/doc/google/gmapapi/[/url]

[code="javascript"]
var map = new GMap2(document.getElementById("map"));
var geocoder = new GClientGeocoder();

function showAddress(address) {
geocoder.getLatLng(
address,
function(point) {
if (!point) {
alert(address + " not found");
} else {
map.setCenter(point, 13);
var marker = new GMarker(point);
map.addOverlay(marker);
marker.openInfoWindowHtml(address);
}
}
);
}
[/code]

java 获得访问者IP

package com.util;

import javax.servlet.http.HttpServletRequest;

public class GetIPAddr {
public String getIP(HttpServletRequest request) {
String ip = request.getHeader(" x-forwarded-for ");
if (ip == null || ip.length() == 0 || " unknown ".equalsIgnoreCase(ip)) {
ip = request.getHeader(" Proxy-Client-IP ");
}
if (ip == null || ip.length() == 0 || " unknown ".equalsIgnoreCase(ip)) {
ip = request.getHeader(" WL-Proxy-Client-IP ");
}
if (ip == null || ip.length() == 0 || " unknown ".equalsIgnoreCase(ip)) {
ip = request.getRemoteAddr();
}
String[] arg=ip.split(",");
return arg[0];
}
}