import sun.misc.BASE64Encoder;

import java.io.*;

import java.net.*;

public class Main {

    public static void main(String[] args) throws IOException {

        String filePath = "image.jpg";

        URL realUrl = new URL("https://aip.baidubce.com/rest/2.0/ocr/v1/idcard?access_token=your_access_token");

        HttpURLConnection connection = (HttpURLConnection)realUrl.openConnection();

        connection.setRequestMethod("POST");

        connection.setDoOutput(true);

        String body = String.format("id_card_side=front&image=%s", URLEncoder.encode(new BASE64Encoder().encode(readImage(filePath)).replaceAll("\r|\n", "")));

        connection.getOutputStream().write(body.getBytes("UTF-8"));

        connection.connect();

        System.out.println(

                new BufferedReader(new InputStreamReader(connection.getInputStream())).readLine()

        );

    }

    public static byte[] readImage(String filePath){

        File file = new File(filePath);

        byte[] content = new byte[new Long(file.length()).intValue()];

        try {

            FileInputStream in = new FileInputStream(file);

            in.read(content);

            in.close();

        } catch (FileNotFoundException e) {

            e.printStackTrace();

        } catch (IOException e) {

            e.printStackTrace();

        }

        return content;

    }

}

问题注意事项：

1. sun.misc.BASE64Encoder返回的编码含有换行回车，请使用.replaceAll("\r|\n", "")将其替换，否则无法识别。

2. HTTP body 里面参数值一定要经过URLEncoder.encode，否则无法识别。