com.sptci

Class HttpDownloader

java.lang.Object

com.sptci.HttpDownloader

Direct Known Subclasses:

FileUtilities, IOUtilities, StringUtilities

public abstract class HttpDownloader
extends Object

A base class from which various utility classes that provide easy means of retrieving HTTP resources are derived. Sets up common state such as HttpDownloadListener, condition variable to allow aborting the download based on a caller specified AtomicBoolean, default logic for timeout configuration etc. Use the following properties to set up default values for all downloaders (unless over-ridden with an more specific configuration for the specific type of downloader)

• com.sptci.HttpDownloader.socket.timeout - Set the socket timeout for downloaders in milliseconds. Defaults to 5000 (5 seconds)
• com.sptci.HttpDownloader.socket.retryCount - Set the number of retries if connection attempt fails. Defaults to 1

© Copyright 2005 Sans Pareil Technologies, Inc.

Version:

$Id: HttpDownloader.java 5813 2016-03-15 13:50:05Z rakesh $

Author:

Rakesh Vidyadharan 2005-01-22

Field Summary

Fields

Modifier and Type	Field and Description
protected static Logger	logger The logger to use to log errors/messages to.

Constructor Summary

Constructors

Constructor and Description
HttpDownloader()

Method Summary

Modifier and Type	Method and Description
protected void	abortIfRequested() Check the value of the caller specified condition variable and abort the download operation as required.
void	deregisterListener() De-register any HTTP download status listener for further requests
protected HttpURLConnection	doGET(String url, String... credentials) Create a GET request to the specified url.
protected HttpURLConnection	doPOST(String url, Properties headers, byte[] body, String... credentials) Create a POST request to the specified URL.
protected HttpURLConnection	doPOST(String url, String body, String... credentials) Create a POST request to the URI specified
protected AtomicBoolean	getConditionVariable()
protected HttpURLConnection	getConnection(String url, String method, String... credentials) Open a connection to the specified URL using the specified method.
protected InputStream	getInputStream(HttpURLConnection httpConnection) Return the proper input stream to use to read the response.
protected HttpDownloadListener	getListener()
protected BufferedReader	getReader(HttpURLConnection httpConnection) Read the response from the HttpURLConnection.
void	registerConditionVariable(AtomicBoolean flag) Register the specified condition variable that will be monitored to abort download operations.
void	registerListener(HttpDownloadListener downloadListener) Register the specified listener for HTTP download status notifications.
void	resetAcceptEncoding()
protected int	retryCount() Return the number of attempts to make to fetch the response from a URI.
void	setAcceptEncoding(String encoding) Set the Accept-Encoding value for the downloader.
protected int	socketTimeout() Return the socket timeout value to set when downloading data from URL's.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

logger

protected static final Logger logger

The logger to use to log errors/messages to.

Constructor Detail

HttpDownloader

public HttpDownloader()

Method Detail

registerListener

public void registerListener(HttpDownloadListener downloadListener)

Register the specified listener for HTTP download status notifications. Note that the listener call-back methods are fired in the same thread as the executing thread. Note: The same listener instance may be used for multiple downloads, provided they are performed in the same thread.

Parameters:

downloadListener - The listener instance to send notifications to.

deregisterListener

public void deregisterListener()

De-register any HTTP download status listener for further requests

registerConditionVariable

public void registerConditionVariable(AtomicBoolean flag)

Register the specified condition variable that will be monitored to abort download operations. Callers can set the value of the condition variable to false to indicate that a download operation should abort. Note: Aborting a download will usually result in an exception which will be communiated via the HttpDownloadListener registered or a IOException.

Parameters:

flag - The externally modified condition variable to use to abort downloads.

setAcceptEncoding

public void setAcceptEncoding(String encoding)

Set the Accept-Encoding value for the downloader. Defaults to gzip.

Parameters:

encoding - The Accept-Encoding value to use.

resetAcceptEncoding

public void resetAcceptEncoding()

getListener

protected HttpDownloadListener getListener()

Returns:

The listener registered with the downloader in the current thread.

getConditionVariable

protected AtomicBoolean getConditionVariable()

Returns:

Return the condition variable registered with the current thread if set

abortIfRequested

protected void abortIfRequested()
                         throws IOException

Check the value of the caller specified condition variable and abort the download operation as required.

Throws:

IOException - If condition variable was set to false throws an exception to abort the download.

socketTimeout

protected int socketTimeout()

Return the socket timeout value to set when downloading data from URL's. Attempts to read a system property com.sptci.HttpDownloader.socket.timeout or uses a default value of 5000.

Returns:

The configured socket timeout value. Defaults to 5000 if not configured.

retryCount

protected int retryCount()

Return the number of attempts to make to fetch the response from a URI. Attempts to read a system property com.sptci.HttpDownloader.socket.retryCount or uses a default value of 1.

Returns:

The configured retry count value. Defaults to 1 if not configured.

getConnection

protected HttpURLConnection getConnection(String url,
                                          String method,
                                          String... credentials)
                                   throws IOException

Open a connection to the specified URL using the specified method.

Parameters:

url - The URL from which to retrieve the text data.

method - The HTTP method to use (GET/POST/HEAD...)

credentials - The optional credentials (username and password) to use for HTTP Basic auth

Returns:

The http connection to use

Throws:

IOException - If errors are encountered

doGET

protected HttpURLConnection doGET(String url,
                                  String... credentials)
                           throws IOException

Create a GET request to the specified url.

Parameters:

url - The URL from which to retrieve the text data.

credentials - The optional credentials (username and password) to use for HTTP Basic auth

Returns:

The GET request to the url

Throws:

IOException - If errors are encountered.

doPOST

protected HttpURLConnection doPOST(String url,
                                   String body,
                                   String... credentials)
                            throws IOException

Create a POST request to the URI specified

Parameters:

url - The URL to retrieve text data from.

credentials - The optional user and password to authenticate as using HTTP Basic Auth

body - The POST request body content.

Returns:

The POST request to the url

Throws:

IOException - If errors are encountered.

doPOST

protected HttpURLConnection doPOST(String url,
                                   Properties headers,
                                   byte[] body,
                                   String... credentials)
                            throws IOException

Create a POST request to the specified URL.

Parameters:

url - The URL to create the POST request for

headers - The headers to specify with the POST request

body - The request body to post to the server

credentials - Optional username/password combination for HTTP Basic Auth

Returns:

The http connection object

Throws:

IOException - If errors are encountered while communicating with server

getInputStream

protected InputStream getInputStream(HttpURLConnection httpConnection)
                              throws IOException

Return the proper input stream to use to read the response. The Content-encoding response header to see if the response is gzip encoded. If it is, use a GZIPInputStream to read the response. Note: Callers must check the response code returned by the connection to determine if a valid response was received or an error returned.

Parameters:

httpConnection - The HttpURLConnection from which the response is to be read.

Returns:

The input stream to use.

Throws:

IOException - If errors are encountered while reading the response from the server.

getReader

protected BufferedReader getReader(HttpURLConnection httpConnection)
                            throws IOException

Read the response from the HttpURLConnection. Check the Content-encoding response header to see if the response is gzip encoded. If it is, use a GZIPInputStream to read the response. Note: Callers must check the response code returned by the connection to determine if a valid response was received or an error returned.

Parameters:

httpConnection - The HttpURLConnection from which the response is to be read.

Returns:

The reader to use to read the character stream.

Throws:

IOException - If errors are encountered while reading the response from the server.