方法1：

1.登录公众账号设置OAuth2.0
2.设置菜单按钮URL为OAuth链接
3.页面后台获取:

public String getopenId() {HttpServletRequest request = ServletActionContext.getRequest();HttpServletResponse response = ServletActionContext.getResponse();response.setContentType("text/html");String code = request.getParameter("code");String urlstr = "https://api.weixin.qq.com/sns/oauth2/access_token?appid=<appId>&secret=<secret>&code=" + code + "&grant_type=authorization_code";JSONObject json;    try {json = JSONObject.fromObject(HTTPTools.postToGetJson(urlstr));openId = json.getString("openid");} catch (Exception e) {        // e.printStackTrace();return "";}    return openId;
}

方法2：

//重写onresume（）方法

@Override
protected void onResume() {
if (type != null && type.equals("mwx")) {
SharedPreferences settings = getSharedPreferences("setting", 0);
String code = settings.getString("code", null);
if (code != null && !code.equals("")) {
showProgress(true);
getOpenid(code);
}
settings.edit().clear();
settings.edit().commit();
}
super.onResume();
}

// 获取微信用户的openid和access token
public void getOpenid(String code) {
final AsyncHttpClient httpClient = Gl.sharedAsyncClient();
RequestParams params = new RequestParams();
params.put("appid", Constants.wxAPP_ID);
params.put("secret", Constants.wxAppSecret);
params.put("code", code);
params.put("grant_type", "authorization_code");
String httpurl = "https://api.weixin.qq.com/sns/oauth2/access_token";
httpClient.get(httpurl, params, new JsonHttpResponseHandler() {

        @Overridepublic void onSuccess(int statusCode, Header[] headers,JSONObject response) {            try {String opendid = response.getString("openid");                if (opendid != null && !opendid.equals("")) {openid = response.getString("openid");otherLogin("mwx", opendid);}} catch (JSONException e) {e.printStackTrace();}            super.onSuccess(statusCode, headers, response);}        @Overridepublic void onFailure(int statusCode, Header[] headers,String responseString, Throwable throwable) {            super.onFailure(statusCode, headers, responseString, throwable);}});
}