Handling downloads in Java

Question

How would I be able to handle downloads using HttpResponse in Java? I made an HttpGet request to a specific site - the site returns the file to be downloaded. How can I handle this download? InputStream doesn't seem to be able to handle it (or maybe I'm using it the wrong way.)

Answer 1

Assuming you're actually talking about HttpClient, Here's an SSCCE:

package com.stackoverflow.q2633002;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;

public class Test {

    public static void main(String... args) throws IOException {
        System.out.println("Connecting...");
        HttpClient client = new DefaultHttpClient();
        HttpGet get = new HttpGet("http://apache.cyberuse.com/httpcomponents/httpclient/binary/httpcomponents-client-4.0.1-bin.zip");
        HttpResponse response = client.execute(get);

        InputStream input = null;
        OutputStream output = null;
        byte[] buffer = new byte[1024];

        try {
            System.out.println("Downloading file...");
            input = response.getEntity().getContent();
            output = new FileOutputStream("/tmp/httpcomponents-client-4.0.1-bin.zip");
            for (int length; (length = input.read(buffer)) > 0;) {
                output.write(buffer, 0, length);
            }
            System.out.println("File successfully downloaded!");
        } finally {
            if (output != null) try { output.close(); } catch (IOException logOrIgnore) {}
            if (input != null) try { input.close(); } catch (IOException logOrIgnore) {}
        }
    }

}

Works fine here. Your problem lies somewhere else.

Answer 2

Open a stream and send the file:

try {
    FileInputStream is = new FileInputStream( _backupDirectory + filename );
    OutputStream os = response.getOutputStream();
    byte[] buffer = new byte[65536];
    int numRead;
    while ( ( numRead = is.read( buffer, 0, buffer.length ) ) != -1 ) {
        os.write( buffer, 0, numRead );
    }
    os.close();
    is.close();
}
    catch (FileNotFoundException fnfe) {
    System.out.println( "File " + filename + " not found" );
}

Answer 3

In general when you want the browser to show the download dialog box for a file to be downloaded, you should set the incoming inputstream content directly into the response object steam and set the content type of response (HttpServletResponse object) to the relevant file type.

i.e.,

response.setContentType(.. relevant content type)

Content type can be application/pdf for pdf files as an example.

If browser has a plugin to show relevant file in the browser window, file will open and user can save then, otherwise browser will show the download box.