java实现微信公众号登录，详细的步骤及有关实现代码

String appId = AppID;
String redirectUri = URLEncoder.encode(redirectUri, "UTF-8");
String state = "自己生成的标识，验证使用";
String url = WechatConstant.WECHAT_OAUTH_URL + "?appid=" + appId + "&redirect_uri=" + redirectUri + "&response_type=code&scope=snsapi_userinfo&state=" + state + "#wechat_redirect";
response.sendRedirect(url);

// 省略state验证步骤
String appId = AppID;
String secret = AppSecret;
String url = "https://api.weixin.qq.com/sns/oauth2/access_token?appid=" + appId +
                    "&secret=" + secret +
                    "&code=" + code +
                    "&grant_type=authorization_code";
String tokenInfoStr = HttpClientUtils.get(url);
if (tokenInfoStr.indexOf("openid") > -1) {
//将access_token转为json
JSONObject tokenInfoObject = new JSONObject(tokenInfoStr);
//通过access_token和openId获取用户信息
String openid = tokenInfoObject.getString("openid");
//将用户信息转为json
String userInfoUrl = "https://api.weixin.qq.com/sns/userinfo?access_token="
                        + tokenInfoObject.getString("access_token")
                        + "&openid=" + openid
                        + "&lang=zh_CN";
String userInfoStr = HttpClientUtils.get(userInfoUrl);
logger.info("用户信息信息", userInfoStr);
// 用户信息
JSONObject userInfoObject = new JSONObject(userInfoStr);
}