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/* Glazed Lists (c) 2003-2006 */
/* http://publicobject.com/glazedlists/ publicobject.com,*/
/* O'Dell Engineering Ltd.*/
package ca.odell.glazedlists.impl;
import java.io.*;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
/**
* Overcome flaws in {@link HttpURLConnection} to download files from http://java.net,
* which requires cookies to be passed between redirects for downloads to work.
*
* @author <a href="jesse@swank.ca">Jesse Wilson</a>
*/
public class HttpClient {
public static final int MAX_REDIRECTS = 20;
public static void main(String[] args) throws Exception {
// expect a single argument starting with "http" or "https"
if(args.length != 2 || !args[0].startsWith("http")) {
System.out.println("Usage: HttpClient <url> <filename>");
System.out.println();
System.out.println("This program demonstrates how to download from java.net's");
System.out.println("Documents & Files area using URLConnection");
return;
}
// fast fail if the file already exists
File targetFile = new File(args[1]);
if(targetFile.exists()) {
System.out.println("Skipping " + args[0] + ", file already exists");
return;
}
// read from the webserver specified
InputStream httpIn = getInputStream(args[0]);
// write from the stream to our target file
System.out.println("Downloading " + args[0]);
OutputStream fileOut = new BufferedOutputStream(new FileOutputStream(args[1]));
pushStreams(httpIn, fileOut);
fileOut.close();
}
/**
* Move bytes from the specified input stream to the specified output
* stream until the input stream is exhaused.
*
* <p>We could optimize this to use byte buffers if it ever became a bottleneck.
*/
private static void pushStreams(InputStream source, OutputStream target) throws IOException {
while(true) {
int aByte = source.read();
if(aByte < 0) break;
target.write(aByte);
}
}
/**
* Follow redirects as necessary to get an InputStream from the specified URL.
*/
private static InputStream getInputStream(String url) throws IOException {
List cookies = new ArrayList();
for(int i = 0; i < MAX_REDIRECTS; i++) {
// prepare the connection
HttpURLConnection urlConnection = (HttpURLConnection)new URL(url).openConnection();
urlConnection.setInstanceFollowRedirects(false);
writeCookies(cookies, urlConnection);
urlConnection.connect();
// if this is a redirect, keep the cookies
// and load the next location
if(urlConnection.getResponseCode() == HttpURLConnection.HTTP_MOVED_TEMP
|| urlConnection.getResponseCode() == HttpURLConnection.HTTP_MOVED_PERM) {
url = urlConnection.getHeaderField("Location");
acceptCookies(cookies, urlConnection);
// success!
} else {
return urlConnection.getInputStream();
}
}
throw new IOException("Max redirects " + MAX_REDIRECTS + " exceeded!");
}
/**
* Accept all cookies provided by the HTTP response.
*
* <p>This method fails to perform some important aspects of cookie management,
* and is potentially dangerous for all but the most basic of cookie problems.
* This method fails at:
* <li>Ensuring cookie names are unique
* <li>Handling cookie expiry dates
* <li>Keeping cookies private to the hosts that provide them
* <li>Verifying the hosts specified match the hosts providing the cookies
*/
private static void acceptCookies(List cookies, HttpURLConnection urlConnection) {
for(Iterator i = urlConnection.getHeaderFields().entrySet().iterator(); i.hasNext(); ) {
Map.Entry entry = (Map.Entry)i.next();
String key = (String)entry.getKey();
if(!"Set-Cookie".equalsIgnoreCase(key)) continue;
List values = (List)entry.getValue();
for(Iterator v = values.iterator(); v.hasNext(); ) {
String value = (String)v.next();
String cookie = value.split(";")[0];
cookies.add(cookie);
}
}
}
/**
* Encode the cookie header for the specified connection.
*/
private static void writeCookies(List cookies, HttpURLConnection urlConnection) {
StringBuffer cookiesString = new StringBuffer();
for(Iterator i = cookies.iterator(); i.hasNext(); ) {
if(cookiesString.length() > 0) cookiesString.append("; ");
cookiesString.append(i.next());
}
if(cookiesString.length() > 0) urlConnection.addRequestProperty("Cookie", cookiesString.toString());
}
}
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