Random volume randomaccessfile-multi-thread download

Random random class randomaccessfile

The input stream fileinputstream and output stream fileoutputstream implement sequential read and write of disk files, and create different objects for read and write respectively.

In contrast, the randomaccessfile class can perform random read/write operations on files.
The file position pointer of the randomaccessfile object follows the following rules:
· The file position pointer of the new randomaccessfile object is located at the beginning of the file;
· After each read/write operation, the pointer to the file location is corresponding to the number of bytes that are moved to read/write;
· You can use the getfilepointer method to obtain the position of the file pointer, and use the seek method to set the position of the file pointer.
If a file contains 30 bytes, you can use the SKIP () // skip method to read data from 20-30, the previous bytes are deleted,

If the user needs to read 10-20 bytes, then read the number between 1-10, and then between 20-30,

Multi-thread download

Public void threaddownload (string path, int threadsize) throws exception {
URL url = new URL (PATH );
Httpurlconnection connection = (httpurlconnection) URL. openconnection ();
Connection. setrequestmethod ("get ");
If (connection. getresponsecode ()! = 200 ){
Throw new runtimeexception ("responsecode! = 200 ");
}
// The total size to download
Int datalength = connection. getcontentlength ();
Connection. Disconnect ();
// Number of threads
Threadsize = 0? 5: threadsize;
Threadsize = datalength % threadsize = 0? Threadsize: threadsize + 1;
// Number of chunks to be downloaded per Thread
Int blocksize = datalength/threadsize;
String newfilename = Rename (PATH );
System. Out. println ("points" + threadsize + "Threads start downloading ");
For (INT I = 0; I <threadsize; I ++ ){
Randomaccessfile accessfile = new randomaccessfile (newfilename, "RW ");
Int startsize = blocksize * I;
Accessfile. Seek (startsize );
Thread thread = new thread (new download (startsize, path, blocksize, accessfile, I + 1 ));
Thread. Start ();
}
}

Defined thread download class

Private class download implements runnable {
Private string path;
Private randomaccessfile accessfile;
Private int startsize;
Private int blocksize;
Private int threadname;
Public download (INT startsize, string path, int blocksize, randomaccessfile accessfile, int threadname ){
This. Path = path;
This. accessfile = accessfile;
This. startsize = startsize;
This. blocksize = blocksize;
This. threadname = threadname;
}
@ Override
Public void run (){
Try {
System. Out. println ("Thread" + threadname + "start to download .....");
URL url = new URL (PATH );
Httpurlconnection connection = (httpurlconnection) URL. openconnection ();
Connection. setrequestmethod ("get ");
Connection. setreadtimeout (6*1000 );
Connection. setrequestproperty ("range", "bytes =" + startsize + "-");
If (connection. getresponsecode ()! = 206 ){
Throw new runtimeexception ("responsecode! = 206 ");
}
Inputstream = connection. getinputstream ();
Inputstream = new bufferedinputstream (inputstream );
Byte [] buffer = new byte [1024];
Int Len =-1;
Int length = 0;
While (length <blocksize & (LEN = inputstream. Read (buffer ))! =-1 )){
Accessfile. Write (buffer, 0, Len );
Length + = Len;
}
Accessfile. Close ();
Inputstream. Close ();
Connection. Disconnect ();
System. Out. println ("Thread" + threadname + "Download successful! ");
} Catch (exception e ){
E. printstacktrace ();
}
}
}