uk.ac.starlink.util

Class ContentCoding

java.lang.Object

uk.ac.starlink.util.ContentCoding

All Implemented Interfaces:

UrlConnector

public abstract class ContentCoding
extends Object
implements UrlConnector

Defines a policy for Content Codings used in HTTP connections. An instance of this class is used to prepare requests and decode responses for some HTTP-based communications in this package. It controls whether HTTP-level content codings are used; typically this means transparent gzip compression of the HTTP response stream where negotiation indicates it is allowed.

Two static instances NONE and GZIP are provided. It should be completely safe to use either of these in any context, since an instance of this class represents only an indication to an HTTP server that a particular coding scheme is supported by the client. A service is therefore always at liberty to ignore this hint/request and provide and unencoded response if, for instance, it does not support the requested compression scheme. Good practice for use of this class is therefore probably to use GZIP where the response is expected to be large and reasonably compressible (a long VOTable is a good example), and NONE where the response is expected to be short or, especially, not very gzippable (for instance noisy binary floating point data, or a byte stream that has already been compressed).

The provided instances also include some logging functionality; information about how many bytes (and where applicable the level of compression) is logged for bytestreams read through these instances. The logging level for this information is currently CONFIG.

See Also:

RFC 2616 secs 3.5, 14.3, 14.11

Field Summary

Fields

Modifier and Type	Field and Description
static String	ACCEPT_ENCODING Name of HTTP request header to request coded response ("Accept-Encoding").
static String	CONTENT_ENCODING Name of HTTP response header to mark coded response ("Content-Encoding").
static ContentCoding	GZIP Gzip encoding is requested.
static ContentCoding	NONE No encoding is requested.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	ContentCoding() Constructor.

Method Summary

Modifier and Type	Method and Description
void	connect(HttpURLConnection hconn) Opens communication to an HTTP resource.
abstract InputStream	getErrorStream(URLConnection conn) Returns the error stream response from the given connection, which was prepared using this object's prepareRequest method.
abstract InputStream	getInputStream(URLConnection conn) Returns the input stream response from the given connection, which was prepared using this object's prepareRequest method.
URLConnection	openConnection(URL url) Convenience method to open a new connection prepared in accordance with this object's encoding policy.
InputStream	openStream(URL url) Convenience method to return a byte stream from a given URL in accordance with this object's encoding policy.
InputStream	openStreamAuth(URL url, AuthManager authManager) Convenience method to return a byte stream from a given URL in accordance with this object's encoding policy and with authentication and redirects handled by a given AuthManager (typically AuthManager.getInstance()).
abstract void	prepareRequest(URLConnection conn) Sets up request headers for the given connection.

Methods inherited from class java.lang.Object

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

Field Detail

NONE

public static final ContentCoding NONE

No encoding is requested.

GZIP

public static final ContentCoding GZIP

Gzip encoding is requested.

ACCEPT_ENCODING

public static final String ACCEPT_ENCODING

Name of HTTP request header to request coded response ("Accept-Encoding").

See Also:

Constant Field Values

CONTENT_ENCODING

public static final String CONTENT_ENCODING

Name of HTTP response header to mark coded response ("Content-Encoding").

See Also:

Constant Field Values

Constructor Detail

ContentCoding

protected ContentCoding()

Constructor.

Method Detail

prepareRequest

public abstract void prepareRequest(URLConnection conn)

Sets up request headers for the given connection. The connection must not have yet been connected.

Parameters:

conn - unconnected connection

getInputStream

public abstract InputStream getInputStream(URLConnection conn)
                                    throws IOException

Returns the input stream response from the given connection, which was prepared using this object's prepareRequest method. Any required decoding will have been done transparently.

Parameters:

conn - connection

Returns:

stream decoded as required

Throws:

IOException

See Also:

URLConnection.getInputStream()

getErrorStream

public abstract InputStream getErrorStream(URLConnection conn)
                                    throws IOException

Returns the error stream response from the given connection, which was prepared using this object's prepareRequest method. Any required decoding will have been done transparently.

Parameters:

conn - connection

Returns:

stream decoded as required

Throws:

IOException

See Also:

URLConnection.getInputStream()

openConnection

public URLConnection openConnection(URL url)
                             throws IOException

Convenience method to open a new connection prepared in accordance with this object's encoding policy. Opens the connection and calls prepareRequest.

Parameters:

url - target URL

Returns:

prepared connection

Throws:

IOException

openStream

public InputStream openStream(URL url)
                       throws IOException

Convenience method to return a byte stream from a given URL in accordance with this object's encoding policy. Opens the connection, prepares the request, and decodes the result.

Parameters:

url - target URL

Returns:

unencoded stream from the URL

Throws:

IOException

openStreamAuth

public InputStream openStreamAuth(URL url,
                                  AuthManager authManager)
                           throws IOException

Convenience method to return a byte stream from a given URL in accordance with this object's encoding policy and with authentication and redirects handled by a given AuthManager (typically AuthManager.getInstance()).

Parameters:

url - target URL

authManager - authentication manager

Returns:

unencoded stream from the URL

Throws:

IOException

connect

public void connect(HttpURLConnection hconn)
             throws IOException

Description copied from interface: UrlConnector

Opens communication to an HTTP resource. The implementation will presumably at least call URLConnection.connect(), but it may optionally perform other actions as well, such as configuring the request headers as required and writing to the connection's output stream, before returning.

If this object is being used with AuthManager, it will typically be a good idea to call setInstanceFollowRedirects(false), since redirection can be handled by AuthManager.

Specified by:

connect in interface UrlConnector

Parameters:

hconn - URL connection; on entry connect() has not yet been called, but on exit it has

Throws:

IOException