【Java基础之网络编程】代码库(七)

单线程下载.java

/** * FileOutputStream 类创建输出流对象, 然后使用 write() 方法, 将从输入流获得的网络资源保存到磁盘上, 实现网络资源的单线程下载.**/public void download(String urlAddr) {    try {        URL url = new URL(urlAddr); //创建 url 对象        URLConnection urlConn = url.openConnection(); //打开 url 连接        urlConn.connect(); //连接        InputStream in = urlConn.getInputStream(); //获取字节流        String filePath = url.getFile(); //获取完整路径        int pos = filePath.lastIndexOf("/") //获得路径中最后一个斜杠的位置        String fileName = filePath.substring(pos + 1); //截取文件名        FileOutputStream out = new FileOutputStream("D:/" + fileName);//创建输出流对象        byte[] bt = new byte[1024]; //声明存放下载内容的字节数组        int len = in.read(bt); //从输入流中读取内容        while(len != -1) {            out.write(bt, 0, len); //将读取的内容全部写入到输出流            len = in.read(bt); //继续从输入流中读取内容        }        //关闭资源        out.close();        in.close();    } catch (Exception e) {        e.printStackTrace();    }}//注意: 在网络下载时, 通常需要及时的关闭 I/O 流, 因为每个 I/O 流都会占用较多的系统资源, 且不能被垃圾回收机制回收, 当下载资源的用户较多时容易造成系统崩溃.

断点续传.java

public void download(long startPosition, long endPosition) {    try {        URL url = new URL(urlAddress);        HttpURLConnection conn = (HttpURLConnection)url.openConnection();        //设置请求属性和范围        conn.setRequestProperty("User-Agent", "NetFox");        String rangeProperty = "bytes=" + startPosition + "-";        if (endPosition > 0) {            rangeProperty += endPosition;        }        conn.setRequestProperty("RANGE", rangeProperty);        conn.connect();        InputStream in = conn.getInputStream();        String file = url.getFile();        String name = file.substring(file.lastIndexOf("/") + 1);        FileOutputStream out = new FileOutputStream("D:/" + name, true);        byte[] buff = new byte[2048];        int len = 0;        len = in.read(buff);        while (len != -1) {            out.write(buff, 0, len);            len = in.read(buff);        }        out.close();        in.close();        conn.disconnect();        if ( readToPos > 0 && readToPos == totalLength ) {            System.exit(0);        }    } catch (Exception e) {        e.printStackTrace();    }}

多线程下载.java

public class DownloadMultiThread implements Runnable {    private String sURL = null;    private File desFile;    private long startPos;    private long endPos;    public DownloadMultiThread() {    }    public DownloadMultiThread(String sURL, File desFile, long startPos, long endPos) {        this.sURL = sURL;        this.desFile = desFile;        this.startPos = startPos;        this.endPos = endPos;    }    public void run() {        RandomAccessFile out = new RandomAccessFile(desFile, "rw");        out.seek(startPos);        InputStream in = conn.getInputStream();        BufferedInputStream bin = new BufferedInputStream(in);        byte[] buff = new byte[2048];        int len = -1;        //读取到内存并添加到字节数组        len = bin.read(buff);        while (len != -1) {            out.write(buff, 0, len);            len = bin.read(buff);        }    }}public void download(String url, String dest, int threadNum) throws Exception {    URL downURL = new URL(url);    HttpURLConnection conn = (HttpURLConnection)downURL.openConnection(); //打开网络连接    long fileLength = -1;    int stateFlagCode = conn.getResponseCode(); //获得连续状态标记代码    //网络连接正常    if (stateFlagCode == 200) {        fileLength = conn.getContentLength(); //获得文件的长度        conn.disconnect();    }    if (fileLength > 0) {        long byteCounts = fileLength / threadNum + 1; //计算每个线程的字节数        File file = new File(dest);        int i = 0;        while (i < threadNum) {            //定义开始和结束位置            long startPosition = byteCounts * i;            long endPosition = byteCounts * (i + 1);            if (i == threadNum -1) {                /* 创建 DownloadMultiThread 线程的实例 */                DownloadMultiThread fileThread = new DownloadMultiThread(url, file, startPosition, 0);                 new Thread(fileThread).start(); //启动一个线程对象            } else {                DownloadMultiThread fileThread = new DownloadMultiThread(url, file, startPosition, endPosition);                 new Thread(fileThread).start(); //启动一个线程对象            }            i++;        }        JOptionPane.showMessageDialog(null, "完成网络资源下载");    }}//注意: 使用多线程下载程序时, 由于创建线程是非常消耗资源的, 如果线程的创建较多, 将极大的影响系统性能, 这时可以使用线程池来提高系统系能, 当需要创建线程时, 可以从线程池中取出空闲线程, 从而提高多线程下载的系统性能.

获取网页内容.java

public Collection<String> getURLCollection(String urlString) {    URL url = null;    URLConnection conn = null;    Collection<String> urlCollection = new ArrayList<String>();    try {        url = new URL();        conn = url.openConnection();        conn.connect();        InputStream is = conn.getInputStream();        InputStreamReader isr = new InputStreamReader(is, "UTF-8");        BufferedReader br = new BufferedReader(isr);        String nextLine = br.readLine();        //遍历读取网页的全部内容, 并添加到集合对象中        while (nextLine != null) {            urlCollection.add(nextLine);            nextLine = br.readLine();        }    } catch (Exception e) {        e.printStackTrace();    }    return urlCollection;}