Multi-thread download in java

Package donghongyujava. gui; import java. awt. event. actionEvent; import java. awt. event. actionListener; import java. io. file; import java. io. inputStream; import java. io. randomAccessFile; import java.net. httpURLConnection; import java.net. URL; import javax. swing. JButton; import javax. swing. JFrame; import javax. swing. JLabel; import javax. swing. JTextField; import javax. swing. plaf. insetsUIResource; public class downlevels EJframe_v2 extends JFrame {private JLabel downlodeJlabel; private JTextField downlodeJTextField; private JButton downlodeJButton; public DownlodeJframe_v2 () {super ("Download page"); this. setLayout (null); downlodeJlabel = new JLabel ("Download connection:"); downlodeJlabel. setBounds (20, 30, 80, 30); downlodeJTextField = new JTextField ("http: // 172.22.65.22: 8080/day31/vedio/test. rmvb "); downlodeJTextField. setBounds (90, 30,350, 30 ); DownlodeJButton = new JButton ("Download Now"); downlodeJButton. setMargin (new InsetsUIResource (0, 0, 0, 0); downlodeJButton. setBounds (200,120,100, 40); add (downlodeJlabel); add (downlodeJTextField); add (downlodeJButton); downlodeJButton. addActionListener (new MyActionListener (); this. setSize (500,300); this. setLocationRelativeTo (null); this. setdefaclocloseoperation (JFrame. EXIT_ON_CLOSE); this. setVisible (true);} pub Lic static void main (String [] args) {new DownlodeJframe_v2 ();} // internal class of event listening MyActionListener implements ActionListener {// declare Random access File private RandomAccessFile access for random access; @ Overridepublic void actionreceivmed (ActionEvent e) {// TODO Auto-generated method stub // The downlodeJButton cannot be set. setEnabled (false); // get the download link final String path = downlodeJTextField. getText (); try {// create the url object URL = new url (Path); // HttpURLConnection supports URLConnection with specific HTTP functions. /** Each HttpURLConnection instance can be used to generate a single request, but other instances can transparently share the basic network connected to the HTTP * server. After a request, call the close () method on InputStream or OutputStream * of HttpURLConnection to release the network resources associated with the instance, but it has no effect on the shared persistent connections. If the persistent connection is idle when * disconnect () is called, the basic socket may be disabled. * /// The openConnection (Proxy proxy) in the call url is similar to openConnection (). // The difference is that the connection is established through the specified Proxy; protocol handlers that do not support proxy will ignore this proxy parameter and establish a normal connection. HttpURLConnection httpURLConnection = (HttpURLConnection) url. openConnection (); // get the size of the target resource int size = httpURLConnection. getContentLength (); // get the name of the target resource and set the corresponding save name // substring (int beginIndex) to return a new string, it is a substring of this string // It starts from the character at the specified index until the end of this string. // LastIndexOf (String str) returns the index at the rightmost of the substring. File file = new File ("E:" + path. substring (path. lastIndexOf ("/"); // create a RandomAccessFile instance based on the file name. This type of instance supports reading and writing random access files. // RandomAccessFile (File file, String mode) creates a random access File stream that reads from and writes to/(Optional). The File is specified by the file parameter. // Mode Value:/** Value Meaning ** "r" is enabled in read-only mode. Any write method that calls the result object will throw an IOException. "Rw" * open for reading and writing. If the file does not exist, try to create it. "Rws" is enabled for reading and writing. For * "rw", it is also required that each update of the file content or metadata be synchronized to the underlying storage device. "Rwd" is enabled for reading and writing. For * "rw", it is also required that each update of the file content be synchronized to the underlying storage device. */Access = new RandomAccessFile (file, "rw"); // set the file size access. setLength (size); // close the random access to the file stream and release all system resources associated with the stream. Access. close (); // indicates that the server may not have other requests in the near future. HttpURLConnection. disconnect (); // define the number of threads int threadNumber = 3; // write data to the file created with the same size and type as the target file for (int I = 1; I <= threadNumber; I ++) {// calculate the download size that each thread needs to share based on the total size of the target resource. int blockSize = size/threadNumber; // calculate the start download position of each thread. final int startSize = (I-1) * blockSize; int temp = I * blockSize-1; // determine whether the currently running thread is the last if (I = threadNumber) {if (temp <size) {temp = size ;}} // final int endSize = temp ;// Final RandomAccessFile threadFile = new RandomAccessFile (file, "rw"); // create Thread new Thread () {public void run () {// create a resource file in a connection try {// create a url object URL = new url (path) based on the path of the target resource ); // open the link HttpURLConnection httpURLConnection = (HttpURLConnection) url. openConnection (); // set general request attributes. HttpURLConnection. setRequestProperty ("Range", "bytes =" + startSize + "-" + endSize); // get the input stream object InputStream after connection is = httpURLConnection. getInputStream (); // sets the threadFile where the file starts to be written. seek (startSize); // create byte buffer in the buffer [] = new byte [1024]; // read the file length int len = 0; while (len = is. read (buffer ))! =-1) {threadFile. write (buffer, 0, len);} // release resource is. close (); threadFile. close (); httpURLConnection. disconnect ();} catch (Exception e) {// TODO Auto-generated catch blocke. printStackTrace ();}}}. start () ;}} catch (Exception e1) {// TODO Auto-generated catch blocke1.printStackTrace ();}}}}