文件下载转码处理类

import org.apache.commons.codec.binary.Base64;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.net.HttpURLConnection;
import java.net.URL;


//1.文件下载（postman可试）
public static void postmanLoad(String url, HttpServletResponse response) throws Exception {

        File file = new File(url);

        byte [] bytes = File2byte(file);
        try {

            response.setHeader("Content-Disposition",
                    "attachment; filename="" + "123.jpg" + """);
            OutputStream out = response.getOutputStream();
            if (bytes != null) {
                out.write(bytes);
            }
            out.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    /**
     * 将文件转换成byte数组
     */
    public static byte[] File2byte(File tradeFile){
        byte[] buffer = null;
        try
        {
            FileInputStream fis = new FileInputStream(tradeFile);
            ByteArrayOutputStream bos = new ByteArrayOutputStream();
            byte[] b = new byte[10240];
            int n;
            while ((n = fis.read(b)) != -1)
            {
                bos.write(b, 0, n);
            }
            fis.close();
            bos.close();
            buffer = bos.toByteArray();
        }catch (FileNotFoundException e){
            e.printStackTrace();
        }catch (IOException e){
            e.printStackTrace();
        }
        return buffer;
    }




    //2.从地址下载转成Base64编码
    public static String downLoadFromUrlBase64(String urlStr) throws Exception {
        URL url = new URL(urlStr);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        //设置超时间为10秒
        conn.setConnectTimeout(10 * 1000);
        //得到输入流
        InputStream inputStream = conn.getInputStream();
        return DownLoadFileUtil.getBase64FromInputStream(inputStream);
    }


    /**
     * 将inputstream转为Base64
    public static String getBase64FromInputStream(InputStream is) throws Exception {
        // 将图片文件转化为字节数组字符串，并对其进行Base64编码处理
        byte[] data = null;

        // 读取图片字节数组
        try {
            ByteArrayOutputStream swapStream = new ByteArrayOutputStream();
            byte[] buff = new byte[100];
            int rc = 0;
            while ((rc = is.read(buff, 0, 100)) > 0) {
                swapStream.write(buff, 0, rc);
            }
            data = swapStream.toByteArray();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (is != null) {
                try {
                    is.close();
                } catch (IOException e) {
                    throw new Exception("输入流关闭异常");
                }
            }
        }
        return Base64.encodeBase64String(data);
    }