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(Java) HTTP Download in Parallel with Simultaneous Range Requests

Demonstrates how to download a large file with parallel simultaneous requests, where each request downloads a segment (range) of the remote file.

Chilkat Java Downloads

Java Libs for Windows, Linux, Alpine Linux,
MAC OS X, Solaris, FreeBSD, OpenBSD,
Raspberry Pi and other single board computers

Java Libs for Android

import com.chilkatsoft.*;

public class ChilkatExample {

  static {
    try {
        System.loadLibrary("chilkat");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Native code library failed to load.\n" + e);
      System.exit(1);
    }
  }

  public static void main(String argv[])
  {
    // This requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    CkHttp http = new CkHttp();
    boolean success;

    // First get the size of the file to be downloaded.
    String url = "https://www.chilkatsoft.com/hamlet.xml";

    CkHttpResponse resp = http.GetHead(url);
    if (http.get_LastMethodSuccess() == false) {
        System.out.println(http.lastErrorText());
        return;
        }

    int remoteFileSize = resp.get_ContentLength();

    System.out.println("Downloading " + remoteFileSize + " bytes...");

    // Let's download in 4 chunks.
    // (the last chunk will be whatever remains after the 1st 3 equal sized chunks)
    int chunkSize = remoteFileSize / 4;

    // The Range header is used to download a range from a resource
    // Range: bytes=<range-start>-<range-end>
    // or
    // Range: bytes=<range-start>-

    // We're writing code this way for clarity..
    CkHttp http1 = new CkHttp();
    CkHttp http2 = new CkHttp();
    CkHttp http3 = new CkHttp();
    CkHttp http4 = new CkHttp();

    CkStringBuilder sbRange = new CkStringBuilder();
    sbRange.SetString("bytes=<range-start>-<range-end>");
    int numReplaced = sbRange.ReplaceI("<range-start>",0);
    numReplaced = sbRange.ReplaceI("<range-end>",chunkSize - 1);
    System.out.println(sbRange.getAsString());
    http1.SetRequestHeader("Range",sbRange.getAsString());

    sbRange.SetString("bytes=<range-start>-<range-end>");
    numReplaced = sbRange.ReplaceI("<range-start>",chunkSize);
    numReplaced = sbRange.ReplaceI("<range-end>",2 * chunkSize - 1);
    System.out.println(sbRange.getAsString());
    http2.SetRequestHeader("Range",sbRange.getAsString());

    sbRange.SetString("bytes=<range-start>-<range-end>");
    numReplaced = sbRange.ReplaceI("<range-start>",2 * chunkSize);
    numReplaced = sbRange.ReplaceI("<range-end>",3 * chunkSize - 1);
    System.out.println(sbRange.getAsString());
    http3.SetRequestHeader("Range",sbRange.getAsString());

    sbRange.SetString("bytes=<range-start>-");
    numReplaced = sbRange.ReplaceI("<range-start>",3 * chunkSize);
    System.out.println(sbRange.getAsString());
    http4.SetRequestHeader("Range",sbRange.getAsString());

    // Start each range download
    CkTask task1 = http1.DownloadAsync(url,"qa_output/chunk1.dat");
    task1.Run();

    CkTask task2 = http2.DownloadAsync(url,"qa_output/chunk2.dat");
    task2.Run();

    CkTask task3 = http3.DownloadAsync(url,"qa_output/chunk3.dat");
    task3.Run();

    CkTask task4 = http4.DownloadAsync(url,"qa_output/chunk4.dat");
    task4.Run();

    // Wait for the downloads to complete.
    int numLive = 4;
    while (numLive > 0) {
        numLive = 0;
        if (task1.get_Live() == true) {
            numLive = numLive+1;
            }

        if (task2.get_Live() == true) {
            numLive = numLive+1;
            }

        if (task3.get_Live() == true) {
            numLive = numLive+1;
            }

        if (task4.get_Live() == true) {
            numLive = numLive+1;
            }

        if (numLive > 0) {
            // SleepMs is a convenience method to cause the caller to sleep for N millisec.
            // It does not cause the given task to sleep..
            task1.SleepMs(10);
            }

        }

    // All should be downloaded now..
    // Examine the result of each Download.
    int numErrors = 0;
    if (task1.GetResultBool() == false) {
        System.out.println(task1.resultErrorText());
        numErrors = numErrors+1;
        }

    if (task2.GetResultBool() == false) {
        System.out.println(task2.resultErrorText());
        numErrors = numErrors+1;
        }

    if (task3.GetResultBool() == false) {
        System.out.println(task3.resultErrorText());
        numErrors = numErrors+1;
        }

    if (task4.GetResultBool() == false) {
        System.out.println(task4.resultErrorText());
        numErrors = numErrors+1;
        }

    if (numErrors > 0) {

        return;
        }

    // All downloads were successful.
    // Compose the file from the parts.
    CkFileAccess fac = new CkFileAccess();
    success = fac.ReassembleFile("qa_output","chunk","dat","qa_output/hamlet.xml");
    if (success == false) {
        System.out.println(fac.lastErrorText());
        }
    else {
        System.out.println("Success.");
        }

    // Let's download in the regular way, and then compare files..
    success = http.Download(url,"qa_output/hamletRegular.xml");

    // Compare files.
    boolean bSame = fac.FileContentsEqual("qa_output/hamlet.xml","qa_output/hamletRegular.xml");
    System.out.println("bSame = " + bSame);
  }
}

 

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