java实现文件加密解密

一、对于文件流读写取的方式对比：


inputStream.read()与OutputStream.write()	单字节读取，效率低下
inputStream.read(new byte[801024])与OutputStream.write(new byte[801024])	固定数组读取，经测试数组增加到80k左右性能最佳
nputStream.read(inputStream.available()) 与OutputStream.write(inputStream.available())	按文件大小一次性读取，如文件过大有内存溢出风险
BufferedInputStream.read()与BufferedOutputStream.write()	默认有一个8K的缓存数组

二、循环每个字节加解密（此方法效率最低）：

1.通过inputStream.read()单字节加密，inputStream.read()返回的是一个字节的内容（0-255之间的数字），可直接异或加密：

    @PostMapping("/swlUpload")
    public void swlUpload(MultipartFile file) throws IOException {
        String originalFilename = file.getOriginalFilename();
        InputStream inputStream = file.getInputStream();
        //FileInputStream inputStream = new FileInputStream((File) file);
        byte[] b = new byte[1024];
        FileOutputStream fileOutputStream = new FileOutputStream(new File("D:\\"+originalFilename));
        BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(fileOutputStream);
        int  swl = 0;
        while((swl=inputStream.read())!=-1){
            //System.out.println(b);
            bufferedOutputStream.write(swl^9527);
        }
        //6.2用来刷新缓冲区，刷新后可以再次写出
        bufferedOutputStream.flush();
        inputStream.close();
        bufferedOutputStream.close();
    }
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2.通过inputStream.read()单字节解密：

    @PostMapping("/swlDownload")
    public void swlDownload(HttpServletResponse response) throws IOException {
        File f2= new File("D:\\108B计划.xlsx");
        boolean exists = f2.exists();
        FileInputStream inputStream = new FileInputStream(f2);
        //byte[] b = new byte[1024];

        String filePath = "108B计划.xlsx";
        //6.1清除buffer缓存
        response.reset();
        response.setContentType("application/octet-stream;charset=UTF-8");
        //response.setHeader("Content-Disposition", "inline; filename="+ new String(filePath.getBytes("UTF-8"), "ISO-8859-1"));// 定义文件名
        //response.setHeader("Content-Disposition", "attachment; filename="+ new String(filePath.getBytes("UTF-8"), "ISO-8859-1"));// 定义文件名
        response.setHeader("Content-Disposition", "attachment; filename=" + java.net.URLEncoder.encode(filePath, "UTF-8"));
        response.setHeader("Pragma", "no-cache");
        response.setHeader("Cache-Control", "no-cache");
        response.setHeader("Expires", " 0");
        ServletOutputStream outputStream = response.getOutputStream();
        BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(outputStream);
        int swl = 0;
        while((swl = inputStream.read())!=-1){
            bufferedOutputStream.write(swl^9527);
        }
        //6.2用来刷新缓冲区，刷新后可以再次写出
        bufferedOutputStream.flush();
        inputStream.close();
        bufferedOutputStream.close();
    }

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三、加载整个文件加解密（效率快，有内存溢出风险）：

1.通过inputStream.read(bytes) 加载整个文件，inputStream.read(bytes)返回bytes大小的字节，放入bytes数组中，循环异或加密：

    @PostMapping("/swlUpload")
    public void swlUpload(MultipartFile file) throws IOException {
        String originalFilename = file.getOriginalFilename();
        InputStream inputStream = file.getInputStream();
        //FileInputStream inputStream = new FileInputStream((File) file);
        byte[] b = new byte[8*1024];
        
        FileOutputStream fileOutputStream = new FileOutputStream(new File("D:\\"+originalFilename));
        BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(fileOutputStream);

        //一、整体io读取、循环加密
        long l = System.currentTimeMillis();
        log.info(String.valueOf(System.currentTimeMillis()));
        int  swl = 0;
        byte[] bytes = new byte[inputStream.available()];
        while((inputStream.read(bytes))!=-1){
            //System.out.println(b);
            for(int i=0;i<bytes.length;i++){
                bufferedOutputStream.write(bytes[i]^9527);
            }
        }
        //6.2用来刷新缓冲区，刷新后可以再次写出
        bufferedOutputStream.flush();
        inputStream.close();
        bufferedOutputStream.close();
        log.info(String.valueOf(System.currentTimeMillis()));
        log.info(String.valueOf(System.currentTimeMillis()-l));

    }
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2.通过inputStream.read(bytes) 加载整个文件解密：

    @PostMapping("/swlDownloadAll")
    public void swlDownloadAll(HttpServletResponse response) throws IOException {
        File f2= new File("D:\\84333c1377d99d970a0984049db926ae.mp4");
        boolean exists = f2.exists();
        FileInputStream inputStream = new FileInputStream(f2);
        //byte[] b = new byte[1024];

        String filePath = "84333c1377d99d970a0984049db926ae.mp4";
        //6.1清除buffer缓存
        response.reset();
        response.setContentType("application/octet-stream;charset=UTF-8");
        //response.setHeader("Content-Disposition", "inline; filename="+ new String(filePath.getBytes("UTF-8"), "ISO-8859-1"));// 定义文件名
        //response.setHeader("Content-Disposition", "attachment; filename="+ new String(filePath.getBytes("UTF-8"), "ISO-8859-1"));// 定义文件名
        response.setHeader("Content-Disposition", "attachment; filename=" + java.net.URLEncoder.encode(filePath, "UTF-8"));
        response.setHeader("Pragma", "no-cache");
        response.setHeader("Cache-Control", "no-cache");
        response.setHeader("Expires", " 0");
        ServletOutputStream outputStream = response.getOutputStream();
        BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(outputStream);

        long l = System.currentTimeMillis();
        log.info(String.valueOf(System.currentTimeMillis()));
        int swl = 0;
        byte[] bytes = new byte[inputStream.available()];
        while((inputStream.read(bytes))!=-1){
            for(int i=0;i<bytes.length;i++){
                bufferedOutputStream.write(bytes[i]^9527);
            }
        }
        //6.2用来刷新缓冲区，刷新后可以再次写出
        bufferedOutputStream.flush();
        inputStream.close();
        bufferedOutputStream.close();
        log.info(String.valueOf(System.currentTimeMillis()));
        log.info(String.valueOf(System.currentTimeMillis()-l));
    }
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四、小数组加载文件加解密（效率快，无内存溢出风险）【推荐】：

1.通过inputStream.read(b) 加载整个文件，inputStream.read(b)返回b大小的字节，放入b数组中，循环异或加密：

    @PostMapping("/swlUploadArray")
    public void swlUploadArray(MultipartFile file) throws IOException {
        String originalFilename = file.getOriginalFilename();
        InputStream inputStream = file.getInputStream();
        //FileInputStream inputStream = new FileInputStream((File) file);
        byte[] b = new byte[8*1024];
        FileOutputStream fileOutputStream = new FileOutputStream(new File("D:\\"+originalFilename));
        BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(fileOutputStream);

        //三、小数组循环io读取、循环加密
        long l = System.currentTimeMillis();
        log.info(String.valueOf(System.currentTimeMillis()));
        while((inputStream.read(b))!=-1){
            //System.out.println(b);
            for(int i=0;i<b.length;i++){
                bufferedOutputStream.write(b[i]^9527);
            }
        }
        //6.2用来刷新缓冲区，刷新后可以再次写出
        bufferedOutputStream.flush();
        inputStream.close();
        bufferedOutputStream.close();
        log.info(String.valueOf(System.currentTimeMillis()));
        log.info(String.valueOf(System.currentTimeMillis()-l));

    }
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2.通过inputStream.read(b) 加载整个文件解密：

    @PostMapping("/swlDownloadArray")
    public void swlDownloadArray(HttpServletResponse response) throws IOException {
        File f2= new File("D:\\84333c1377d99d970a0984049db926ae.mp4");
        boolean exists = f2.exists();
        FileInputStream inputStream = new FileInputStream(f2);
        byte[] b = new byte[8*1024];

        String filePath = "84333c1377d99d970a0984049db926ae.mp4";
        //6.1清除buffer缓存
        response.reset();
        response.setContentType("application/octet-stream;charset=UTF-8");
        //response.setHeader("Content-Disposition", "inline; filename="+ new String(filePath.getBytes("UTF-8"), "ISO-8859-1"));// 定义文件名
        //response.setHeader("Content-Disposition", "attachment; filename="+ new String(filePath.getBytes("UTF-8"), "ISO-8859-1"));// 定义文件名
        response.setHeader("Content-Disposition", "attachment; filename=" + java.net.URLEncoder.encode(filePath, "UTF-8"));
        response.setHeader("Pragma", "no-cache");
        response.setHeader("Cache-Control", "no-cache");
        response.setHeader("Expires", " 0");
        ServletOutputStream outputStream = response.getOutputStream();
        BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(outputStream);
        long l = System.currentTimeMillis();
        log.info(String.valueOf(System.currentTimeMillis()));
        int swl = 0;
        while((inputStream.read(b))!=-1){
            for(int i=0;i<b.length;i++){
                bufferedOutputStream.write(b[i]^9527);
            }
        }
        //6.2用来刷新缓冲区，刷新后可以再次写出
        bufferedOutputStream.flush();
        inputStream.close();
        bufferedOutputStream.close();
        log.info(String.valueOf(System.currentTimeMillis()));
        log.info(String.valueOf(System.currentTimeMillis()-l));
    }
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五、解决小数组读取文件流后，office文档打开异常的问题：

注意看下面的代码：
在这里插入图片描述

原因：这是文档最后一次读取文件，剩余的文件流不足b.length造成的，不足时会在数组中补0，造成上传后的文件与原文件有出入。
解决方案1：采用byte[] bytes = new byte[inputStream.available()];
解决方案2（推荐）：

        int j;
        while((j=(inputStream.read(b)))!=-1){
            for(int i=0;i<j;i++){
                bufferedOutputStream.write(b[i]^9527);
            }
        }
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原文地址：https://blog.csdn.net/qq_38837032/article/details/127751291