Java实现断点续传

时间 2019-11-20

标签 java 实现断点栏目 Java 繁體版

原文原文链接

原理：java

断点续传的关键是断点，因此在制定传输协议的时候要设计好，如上图，我自定义了一个交互协议，每次下载请求都会带上下载的起始点，这样就能够支持从断点下载了，其实HTTP里的断点续传也是这个原理，在HTTP的头里有个可选的字段RANGE，表示下载的范围，下面是我用Java语言实现的下载断点续传示例。网络

提供下载的服务端代码：多线程

         String path = "文件地址";
         BufferedInputStream bis = null;
         try {
             File file = new File(path);
             if (file.exists()) {
                 long p = 0L;
                 long toLength = 0L;
                 long contentLength = 0L;
                 int rangeSwitch = 0; // 0,从头开始的全文下载；1,从某字节开始的下载（bytes=27000-）；2,从某字节开始到某字节结束的下载（bytes=27000-39000）
                 long fileLength;
                 String rangBytes = "";
                 fileLength = file.length();
       
                 // get file content 
                 InputStream ins = new FileInputStream(file);
                 bis = new BufferedInputStream(ins);
//                 String d = new SimpleDateFormat("EEE,d MMM yyyy hh:mm:ss 'GMT' ",Locale.US).format(new Date());
//                 System.out.println(d);
                 // tell the client to allow accept-ranges
                 response.reset();
                 response.setHeader("Accept-Ranges", "bytes");
                 /*DateTime dateTime = DateTime.now();
                 System.out.println(dateTime.toString("r"));*/
                 response.setHeader("Last-Modified","Sat, 27 Jul 2017 12:14:58 GMT");
                 /*response.setHeader("HTTP/1.0 206 Partial Content", "206");*/
                 // client requests a file block download start byte
          
                 String range = request.getHeader("Range");
                log.info("range : "+range);
                 
                 if (range != null && range.trim().length() > 0 && !"null".equals(range)) {
                     response.setStatus(javax.servlet.http.HttpServletResponse.SC_PARTIAL_CONTENT);
                     rangBytes = range.replaceAll("bytes=", "");
                     if (rangBytes.endsWith("-")) {  // bytes=270000-
                         rangeSwitch = 1;
                         p = Long.parseLong(rangBytes.substring(0, rangBytes.indexOf("-")));
                         contentLength = fileLength - p;  // 客户端请求的是270000以后的字节（包括bytes下标索引为270000的字节）
                     } else { // bytes=270000-320000
                         rangeSwitch = 2;
                         String temp1 = rangBytes.substring(0, rangBytes.indexOf("-"));
                         String temp2 = rangBytes.substring(rangBytes.indexOf("-") + 1, rangBytes.length());
                         p = Long.parseLong(temp1);
                         toLength = Long.parseLong(temp2);
                         contentLength = toLength - p + 1; // 客户端请求的是 270000-320000 之间的字节
                     }
                 } else {
                     contentLength = fileLength;
                 }
                
                 // 若是设设置了Content-Length，则客户端会自动进行多线程下载。若是不但愿支持多线程，则不要设置这个参数。
                 // Content-Length: [文件的总大小] - [客户端请求的下载的文件块的开始字节]
                 response.setHeader("Content-Length", new Long(contentLength).toString());
       
                 // 断点开始
                 // 响应的格式是:
                 // Content-Range: bytes [文件块的开始字节]-[文件的总大小 - 1]/[文件的总大小]
                 if (rangeSwitch == 1) {
                     String contentRange = new StringBuffer("bytes ").append(new Long(p).toString()).append("-")
                             .append(new Long(fileLength - 1).toString()).append("/")
                             .append(new Long(fileLength).toString()).toString();
                     response.setHeader("Content-Range", contentRange);
                     bis.skip(p);
                 } else if (rangeSwitch == 2) {
                     String contentRange = range.replace("=", " ") + "/" + new Long(fileLength).toString();
                     response.setHeader("Content-Range", contentRange);
                     bis.skip(p);
                 } else {
                     String contentRange = new StringBuffer("bytes ").append("0-")
                             .append(fileLength - 1).append("/")
                             .append(fileLength).toString();
                     response.setHeader("Content-Range", contentRange);
                 }
       
                 String fileName = file.getName();
                 response.setContentType("application/octet-stream");
                 response.addHeader("Content-Disposition", "attachment;filename=" + fileName);
       
                 OutputStream out = response.getOutputStream();
                 
                 BufferedOutputStream buf=new BufferedOutputStream(out);
                 int n = 0;
                 long readLength = 0;
                 int bsize = 1024;
                 byte[] bytes = new byte[bsize];
                 if (rangeSwitch == 2) {
                     // 针对 bytes=27000-39000 的请求，从27000开始写数据                    
                     while (readLength <= contentLength - bsize) {
                         n = bis.read(bytes);
                         readLength += n;
                         buf.write(bytes, 0, n);
                     }
                     if (readLength <= contentLength) {
                         n = bis.read(bytes, 0, (int) (contentLength - readLength));
                         buf.write(bytes, 0, n);
                     }                   
                 } else {
                     while ((n = bis.read(bytes)) != -1) {
                         buf.write(bytes,0,n);                                                      
                     }                   
                 }
                 buf.flush();
                 buf.close();
                 out.close();
                 bis.close();
             } else {
                 if (log.isDebugEnabled()) {
                     log.debug("Error: file " + path + " not found.");
                 }                
             }
         } catch (IOException ie) {
             // 忽略 ClientAbortException 之类的异常
         } catch (Exception e) {
             log.error(e.getMessage());
             e.printStackTrace();
         }

下载的客户端代码：app

    /** 
     *  request:get0startIndex0 
     *  response:fileLength0fileBinaryStream 
     *   
     * @param filepath 
     * @throws Exception 
     */  
    public void Get(String filepath) throws Exception {  
        Socket socket = new Socket();  
        // 创建链接  
        socket.connect(new InetSocketAddress("127.0.0.1", 8888));  
        // 获取网络流  
        OutputStream out = socket.getOutputStream();  
        InputStream in = socket.getInputStream();  
        // 文件传输协定命令  
        byte[] cmd = "get".getBytes();  
        out.write(cmd);  
        out.write(0);// 分隔符  
        int startIndex = 0;  
        // 要发送的文件  
        File file = new File(filepath);  
        if(file.exists()){  
            startIndex = (int) file.length();  
        }  
        System.out.println("Client startIndex : " + startIndex);  
        // 文件写出流  
        RandomAccessFile access = new RandomAccessFile(file,"rw");  
        // 断点  
        out.write(String.valueOf(startIndex).getBytes());  
        out.write(0);  
        out.flush();  
        // 文件长度  
        int temp = 0;  
        StringWriter sw = new StringWriter();  
        while((temp = in.read()) != 0){  
            sw.write(temp);  
            sw.flush();  
        }  
        int length = Integer.parseInt(sw.toString());  
        System.out.println("Client fileLength : " + length);  
        // 二进制文件缓冲区  
        byte[] buffer = new byte[1024*10];  
        // 剩余要读取的长度  
        int tatol = length - startIndex;  
        //  
        access.skipBytes(startIndex);  
        while (true) {  
            // 若是剩余长度为0则结束  
            if (tatol == 0) {  
                break;  
            }  
            // 本次要读取的长度假设为剩余长度  
            int len = tatol;  
            // 若是本次要读取的长度大于缓冲区的容量  
            if (len > buffer.length) {  
                // 修改本次要读取的长度为缓冲区的容量  
                len = buffer.length;  
            }  
            // 读取文件，返回真正读取的长度  
            int rlength = in.read(buffer, 0, len);  
            // 将剩余要读取的长度减去本次已经读取的  
            tatol -= rlength;  
            // 若是本次读取个数不为0则写入输出流，不然结束  
            if (rlength > 0) {  
                // 将本次读取的写入输出流中  
                access.write(buffer, 0, rlength);  
            } else {  
                break;  
            }  
            System.out.println("finish : " + ((float)(length -tatol) / length) *100 + " %");  
        }  
        System.out.println("finished!");  
        // 关闭流  
        access.close();  
        out.close();  
        in.close();  
    }  
  
    public static void main(String[] args) {  
        FTPClient client = new FTPClient();  
        try {  
            client.Get("E:\\ceshi\\test\\mm.pdf");  
        } catch (Exception e) {  
            e.printStackTrace();  
        }  
    }

代码直接copy过去就能够了服务端的代码须要改下urldom