base64,file和blob相互转换

1.第一个：base64转为Blob

function dataURLtoBlob(dataurl) {
    var arr = dataurl.split(','), mime = arr[0].match(/:(.*?);/)[1],
        bstr = atob(arr[1]), n = bstr.length, u8arr = new Uint8Array(n);
    while (n--) {
        u8arr[n] = bstr.charCodeAt(n);
    }
    return new Blob([u8arr], { type: mime });
}

2.第二个：Blob转为base64

function blobToDataURL(blob, callback) {
    let a = new FileReader();
    a.onload = function (e) { callback(e.target.result); }
    a.readAsDataURL(blob);
}

3.第三个：base64转换为file

function dataURLtoFile(dataurl, filename) {//将base64转换为文件
        var arr = dataurl.split(','), mime = arr[0].match(/:(.*?);/)[1],
            bstr = atob(arr[1]), n = bstr.length, u8arr = new Uint8Array(n);
        while(n--){
            u8arr[n] = bstr.charCodeAt(n);
        }
        return new File([u8arr], filename, {type:mime});
    }

4.第四个：js图片转换为base64

function getImgToBase64(url,callback){//将图片转换为Base64
  var canvas = document.createElement('canvas'),
    ctx = canvas.getContext('2d'),
    img = new Image;
  img.crossOrigin = 'Anonymous';
  img.onload = function(){
    canvas.height = img.height;
    canvas.width = img.width;
    ctx.drawImage(img,0,0);
    var dataURL = canvas.toDataURL('image/png');
    callback(dataURL);
    canvas = null;
  };
  img.src = url;
}

第五个：在Java中base64和File相互转换

/**
     * 文件转base64字符串
     * @param file
     * @return
     */
    public static String fileToBase64(File file) {
        String base64 = null;
        InputStream in = null;
        try {
            in = new FileInputStream(file);
            byte[] bytes = new byte[in.available()];
            int length = in.read(bytes);
            base64 = Base64.encodeToString(bytes, 0, length, Base64.DEFAULT);
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            try {
                if (in != null) {
                    in.close();
                }
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        return base64;
    }
 
    /**
     * base64字符串转文件
     * @param base64
     * @return
     */
    public static File base64ToFile(String base64) {
        File file = null;
        String fileName = "/Petssions/record/testFile.amr";
        FileOutputStream out = null;
        try {
            // 解码，然后将字节转换为文件
            file = new File(Environment.getExternalStorageDirectory(), fileName);
            if (!file.exists())
                file.createNewFile();
            byte[] bytes = Base64.decode(base64, Base64.DEFAULT);// 将字符串转换为byte数组
            ByteArrayInputStream in = new ByteArrayInputStream(bytes);
            byte[] buffer = new byte[1024];
            out = new FileOutputStream(file);
            int bytesum = 0;
            int byteread = 0;
            while ((byteread = in.read(buffer)) != -1) {
                bytesum += byteread;
                out.write(buffer, 0, byteread); // 文件写操作
            }
        } catch (IOException ioe) {
            ioe.printStackTrace();
        } finally {
            try {
                if (out!= null) {
                    out.close();
                }
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        return file;
    }

其中的atob()和btoa()详见下一篇文章 JavaScript用btoa和atob来编码解码Base64

原文：https://blog.csdn.net/yayayangge/article/details/83654464