【JAVA】附件工具类 文件转base64、文件输入流转为base64、通过base64下载文件、通过图片src下载图片

import sun.misc.BASE64Decoder;

import java.io.*;
import java.net.URL;
import java.net.URLConnection;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.util.Base64;
import java.util.HashMap;
import java.util.Map;


public class FileUtils {

    private static final String filePathRoot = "D:\yzy";

    
    public static String encryptToBase64(String filePath) {
        if (filePath == null) {
            return null;
        }
        try {
            byte[] b = Files.readAllBytes(Paths.get(filePath));
            return Base64.getEncoder().encodeToString(b);
        } catch (IOException e) {
            e.printStackTrace();
        }

        return null;
    }

    
    public static String getBase64FromInputStream(InputStream in) {
        // 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 = in.read(buff, 0, 100)) > 0) {
                swapStream.write(buff, 0, rc);
            }
            data = swapStream.toByteArray();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (in != null) {
                try {
                    in.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return Base64.getEncoder().encodeToString(data);
    }

    public static File getFileFromBase64(String base, String suffix) {
        String base64Pic = base;
        File file = null;
        Map resultMap = new HashMap();
        // 图像数据为空
        if (base64Pic == null) {
            resultMap.put("resultCode", 0);
            resultMap.put("msg", "图片为空");
        } else {
            try {
                BASE64Decoder decoder = new BASE64Decoder();
                //前台在用Ajax传base64值的时候会把base64中的+换成空格，所以需要替换回来。
                String baseValue = base64Pic.replaceAll(" ", "+");
                //去除base64中无用的部分
                byte[] b = decoder.decodeBuffer(baseValue.replace("data:image/jpeg;base64,", ""));
                base64Pic = base64Pic.replace("base64,", "");
                String nowDateStr = LocalDate.now().format(DateTimeFormatter.ofPattern("yyyy-MM-dd"));
                String imgFilePath = filePathRoot + "\" + nowDateStr;
                File file1 = new File(imgFilePath);
                //判断文件路径下的文件夹是否存在，不存在则创建
                if (!file1.exists() && !file1.isDirectory()) {
                    file1.mkdirs();
                }
                for (int i = 0; i < b.length; ++i) {
                    // 调整异常数据
                    if (b[i] < 0) {
                        b[i] += 256;
                    }
                }
                file = new File(imgFilePath + "\" + System.currentTimeMillis() + "." + suffix);
                // 如果要返回file文件这边return就可以了,存到临时文件中
                OutputStream out = new FileOutputStream(file.getPath());
                out.write(b);
                out.flush();
                out.close();
            } catch (Exception e) {
                resultMap.put("resultCode", 0);
                resultMap.put("msg", "存储异常");
            }
        }
        return file;
    }

    
    public static void download(String urlString, String filename) throws Exception {
        // 构造URL
        URL url = new URL(urlString);
        // 打开连接
        URLConnection con = url.openConnection();
        //设置请求超时为5s
        con.setConnectTimeout(5 * 1000);
        // 输入流
        InputStream is = con.getInputStream();
        

        // base64转文件
        String base64FromInputStream = getBase64FromInputStream(is);
        // 获取图片的扩展名
        String extensionName = filename.substring(filename.lastIndexOf(".") + 1);
        getFileFromBase64(base64FromInputStream, extensionName);
    }

    public static void inputStreamToFile(InputStream ins, File file) {
        try {
            OutputStream os = new FileOutputStream(file);
            int bytesRead = 0;
            byte[] buffer = new byte[8192];
            while ((bytesRead = ins.read(buffer, 0, 8192)) != -1) {
                os.write(buffer, 0, bytesRead);
            }
            os.close();
            ins.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) throws Exception {
        String url = "https://www.baidu.com/img/PCtm_d9c8750bed0b3c7d089fa7d55720d6cf.png";
        String fileName = "sftp_test.png";
        // String savePath = filePathRoot + "\testDownload";
        download(url, fileName);
        // 文件转Base64
        String filePath = filePathRoot + "\testDownload\af4616c312d.png";
        String dd = encryptToBase64(filePath);
        System.out.println(dd);
        System.out.println("---------------------------------------");
        // Base64转文件
        System.out.println("---------------------------------------" + filePath.substring(filePath.lastIndexOf(".") + 1));
        getFileFromBase64(dd, filePath.substring(filePath.lastIndexOf(".") + 1));
    }

}