写一段java代码实现获取微信accesstoken

好的，下面是获取微信access token的Java代码示例：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

public class WeChatAccessToken {
    public static void main(String[] args) throws IOException {
        String appid = "your_appid";
        String secret = "your_secret";
        String grant_type = "client_credential";
        String url = "https://api.weixin.qq.com/cgi-bin/token?grant_type=" + grant_type + "&appid=" + appid + "&secret=" + secret;
        HttpURLConnection connection = (HttpURLConnection) new URL(url).openConnection();
        connection.setRequestMethod("GET");
        connection.setDoInput(true);
        InputStream inputStream = connection.getInputStream();
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
        String line;
        StringBuilder stringBuilder = new StringBuilder();
        while ((line = bufferedReader.readLine()) != null) {
            stringBuilder.append(line);
        }
        bufferedReader.close();
        inputStream.close();
        connection.disconnect();
        System.out.println(stringBuilder.toString());
    }
}

需要替换代码中的 `your_appid` 和 `your_secret` 为自己的微信公众号的 appid 和 secret。运行代码后，会返回包含 access_token 的 JSON 格式字符串。