Java

S3 Resume Download

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Suppose an S3 download of a very large file failed for some reason and you have a partial file on disk. Rather than restart the entire download, you wish to download the remaining portion. This example demonstrates how to finish a previously failed download.

Note: This example requires Chilkat v9.5.0.83 or above.

Chilkat2 Java

import com.chilkatsoft.chilkat2.AuthAws;
import com.chilkatsoft.chilkat2.ChilkatException;
import com.chilkatsoft.chilkat2.FileAccess;
import com.chilkatsoft.chilkat2.Rest;
import com.chilkatsoft.chilkat2.Stream;
import com.chilkatsoft.chilkat2.StringBuilder;

public class ChilkatExample {

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

        Rest rest = new Rest();

        // Connect to the Amazon AWS REST server.
        boolean bTls = true;
        int port = 443;
        boolean bAutoReconnect = true;
        rest.connect("s3.amazonaws.com", port, bTls, bAutoReconnect);

        // ---------------------------------------------------------------------------
        // Important: For buckets created in regions outside us-east-1,
        // there are three important changes that need to be made.
        // See Working with S3 Buckets in Non-us-east-1 Regions for the details.
        // ---------------------------------------------------------------------------

        // Provide AWS credentials for the REST call.
        AuthAws authAws = new AuthAws();
        authAws.setAccessKey("AWS_ACCESS_KEY");
        authAws.setSecretKey("AWS_SECRET_KEY");
        authAws.setServiceName("s3");
        rest.setAuthAws(authAws);

        // Set the bucket name via the HOST header.
        // In this case, the bucket name is "chilkat100".
        rest.setHost("chilkat100.s3.amazonaws.com");

        // We want to continue downloading a file.
        // The relative local filepath of our previously partially downoaded file is: qa_output/hamlet.xml
        // Let's find out how many bytes are already downloaded.
        FileAccess fac = new FileAccess();
        String localFilepath = "qa_output/hamlet.xml";
        // Note: The FileSize method returns a signed 32-bit integer.  If the file is potentially larger than 2GB, call FileSizeStr instead to return
        // the size of the file as a string, then convert to an integer value.
        int sz = fac.fileSize(localFilepath);
        if (sz > 0) {
            System.out.println("sz = " + sz);

            // If the sz equals 42375 bytes, then we want to add a Range header that looks like this:
            // Range: bytes=42375-
            StringBuilder sbRange = new StringBuilder();
            sbRange.append("bytes=");
            sbRange.appendInt(sz);
            sbRange.append("-");
            rest.addHeader("Range", sbRange.getAsString());
            System.out.println("Added Range: " + sbRange.getAsString());
        }

        // Send the request to download the remainder of the file.
        try {
            rest.sendReqNoBody("GET", "/hamlet.xml");
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        // Read the response header.
        int responseStatusCode = rest.readResponseHeader();
        if (responseStatusCode < 0) {
            System.out.println(rest.getLastErrorText());
            return;
        }

        System.out.println("Response status code = " + responseStatusCode);

        // We expect a 200 or 206 response status if the file data is coming.
        // Otherwise, we'll get a string response body with an error message(or no response body).
        if ((responseStatusCode == 200) || (responseStatusCode == 206)) {
            Stream bodyStream = new Stream();

            // The stream's sink will be a file.
            // We will append to the file..
            bodyStream.setSinkFile(localFilepath);

            // Indicate that we wish to append to the output file.
            // The SinkFileAppend property was added in Chilkat v9.50.83
            bodyStream.setSinkFileAppend(true);

            // Read the response body to the stream.  Given that we've
            // set the stream's sink to a file, it will stream directly
            // to the file.
            try {
                rest.readRespBodyStream(bodyStream, true);
            } catch (ChilkatException e) {
                System.out.println(e.getLastErrorText());
                return;
            }

            System.out.println("Successfully downloaded the file.");
        } else {
            String errResponse = null;
            try {
                errResponse = rest.readRespBodyString();
                System.out.println(errResponse);
            } catch (ChilkatException e) {
                System.out.println(e.getLastErrorText());
            }
        }
    }
}