1.JAVA基础——IO

public class FileInputStream extends InputStream
{
    /* File Descriptor - handle to the open file */
    private FileDescriptor fd;

......

    public FileInputStream(FileDescriptor fdObj) {
    SecurityManager security = System.getSecurityManager();
    if (fdObj == null) {
        throw new NullPointerException();
    }
    if (security != null) {
        security.checkRead(fdObj);
    }
    fd = fdObj;
    }
......

public static void main(String[] args) throws Exception {
    InputStream in = new BufferedInputStream(new URL("http://www.jd.com").openStream());
    File bdFile = new File("D:\\jd.html");
    if (!bdFile.exists()) {
        bdFile.createNewFile();
    }
    OutputStream ou = new BufferedOutputStream(new FileOutputStream(bdFile));
    byte[] b = new byte[1024];
    int len;
    while((len = in.read(b, 0, b.length)) != -1){
        ou.write(b, 0, len);
    }
}

public class Main {

    /**
     * @param args
     */
    public static void main(String[] args) throws Exception{
        String path = "xxx";//网络资源URL
        String filePath = "D:\\";//本地磁盘位置
        new Main().threadDownload(path, 5, filePath);
    }

    public void threadDownload(String path, int threadSize, String filePath) throws Exception{
        URL url = new URL(path);
        HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
        httpURLConnection.setRequestMethod("GET");
        if (httpURLConnection.getResponseCode() != 200) {
            throw new Exception("响应异常");
        }
        
        int dataLength = httpURLConnection.getContentLength();
        String fileName = Main.getFileName(httpURLConnection);
        httpURLConnection.disconnect();
        threadSize = threadSize == 0 ? 5 : threadSize;
        int blockSize = dataLength/threadSize;
        int left = dataLength % threadSize;
        for (int i = 0; i < threadSize; i++) {
            if (i == threadSize) {
                blockSize += left;
            }
            new Thread(new DownloadThread(path, new RandomAccessFile(new File(filePath + fileName), "rw"), blockSize * i, blockSize, i + 1)).start();
            
        }
    }

    private static String getFileName(HttpURLConnection httpURLConnection) throws Exception{
        Map<String, List<String>> headerFields = httpURLConnection.getHeaderFields();
        Set<Entry<String, List<String>>> set = headerFields.entrySet();
        for (Entry<String, List<String>> entry : set) {
            if (entry.toString().contains("filename")) {
                List<String> list = entry.getValue();
                for (String string : list) {
                    if (string.contains("filename")) {
                        String fileNameResult = new String(string.getBytes(), "UTF-8");
                        return fileNameResult.substring(fileNameResult.indexOf("\"") + 1, fileNameResult.lastIndexOf("\""));
                    }
                }
            }
        }
        return null;
    }
}


public class DownloadThread implements Runnable{
    
    private String path;
    private RandomAccessFile randomAccessFile;
    private int startSize;
    private int blockSize;
    private int threadName;

    public DownloadThread(String path, RandomAccessFile randomAccessFile,
            int startSize, int blockSize, int threadName) {
        this.path = path;
        this.randomAccessFile = randomAccessFile;
        this.startSize = startSize;
        this.blockSize = blockSize;
        this.threadName = threadName;
    }

    @Override
    public void run() {
        HttpURLConnection httpURLConnection = null;
        InputStream inputStream = null;
        try {
            System.out.println("线程"+threadName+"开始下载");
            URL url = new URL(path);
            httpURLConnection = (HttpURLConnection) url.openConnection();
            httpURLConnection.setRequestMethod("GET");
            httpURLConnection.setReadTimeout(10 * 1000);
            httpURLConnection.setRequestProperty("Range", "bytes=" + startSize + "-");
            if (httpURLConnection.getResponseCode() != 206) {//206 Partial Content 客户发送了一个带有Range头的GET请求，服务器完成了它（HTTP 1.1新）
                System.out.println("线程" + threadName + "响应异常，代码为" + httpURLConnection.getResponseCode());
                throw new Exception("响应异常");
            }
            
            inputStream = httpURLConnection.getInputStream();
            byte[] b = new byte[1024];
            int len = -1;
            int length = 0;
            randomAccessFile.seek(startSize);
            while(((len = inputStream.read(b)) != -1) && length < blockSize){
                randomAccessFile.write(b, 0, len);
                length += len;
            }
            randomAccessFile.close();
            inputStream.close();
            httpURLConnection.disconnect();
            System.out.println("线程"+threadName+"下载完成");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            randomAccessFile = null;
            inputStream = null;
            httpURLConnection = null;
        }
    }
}