java 获取 长期有效的 access_token 代码示例

以下是Java获取长期有效的access_token的代码示例：

 class MyAccessToken {
    修改为自己的app和appsecret
    private static final StringID = "your appid";
    private static final String APPSECRET = "yoursecret";

    // 获取access_token的接口
    private static final String ACCESS_TOKEN_URL = "https://api.weixin.qq.com/cgi-bin/token";

    // access_token保存时间（单位：毫秒）
    private static final long ACCESS_TOKEN_EXPIRE_TIME = 7200000; // 2小时

    private static String access_token = null;
    private static long access_token_create_time = 0;

    /**
     * 获取access_token
     * 
     * @return access_token字符串
     */
    public static String getAccessToken() {
        // 判断是否超过保存时间
        long now_time = System.currentTimeMillis() / 1000;
        if (now_time - access_token_create_time > ACCESS_TOKEN_EXPIRE_TIME || access_token == null) {
            JSONObject json = new JSONObject();
            try {
                json.put("grant_type", "client_credential");
                json.put("appid", APPID);
                json.put("secret", APPSECRET);

                String result = HttpUtil.post(ACCESS_TOKEN_URL, json.toString());
                JSONObject resultJson = new JSONObject(result);
                if (resultJson.has("access_token")) {
                    access_token = resultJson.getString("access_token");
                    access_token_create_time = System.currentTimeMillis() / 1000;
                } else {
                    throw new Exception(result);
                }
            } catch (Exception e) {
                System.out.println("获取access_token出现错误：" + e.getMessage());
            }
        }
        return access_token;
    }

    /**
     * 发起HTTP请求获取返回结果
     * 
     * @param url  HTTP请求URL
     * @param json HTTP请求body
     * @return 返回结果字符串
     * @throws Exception
     */
    private static String post(String url, String json) throws Exception {
        String result = null;
        CloseableHttpClient httpClient = HttpClients.createDefault();
        HttpPost httpPost = new HttpPost(url);
        StringEntity entity = new StringEntity(json, "utf-8");
        entity.setContentEncoding("UTF-8");
        entity.setContentType("application/json");
        httpPost.setEntity(entity);
        HttpResponse httpResponse = httpClient.execute(httpPost);
        if (httpResponse.getStatusLine().getStatusCode() == 200) {
            HttpEntity httpEntity = httpResponse.getEntity();
            if (httpEntity != null) {
                result = EntityUtils.toString(httpEntity, "UTF-8");
            }
        }
        httpClient.close();
        return result;
    }
}

请注意，如果要使用上述示例代码，需要替换APPID和APPSECRET为真实的值。