uk.ac.starlink.util
Class ContentCoding

java.lang.Object
  extended by uk.ac.starlink.util.ContentCoding

public abstract class ContentCoding
extends java.lang.Object

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
static java.lang.String ACCEPT_ENCODING
          Name of HTTP request header to request coded response ("Accept-Encoding").
static java.lang.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
protected ContentCoding()
          Constructor.
 
Method Summary
abstract  java.io.InputStream getErrorStream(java.net.URLConnection conn)
          Returns the error stream response from the given connection, which was prepared using this object's prepareRequest method.
abstract  java.io.InputStream getInputStream(java.net.URLConnection conn)
          Returns the input stream response from the given connection, which was prepared using this object's prepareRequest method.
 java.net.URLConnection openConnection(java.net.URL url)
          Convenience method to open a new connection prepared in accordance with this object's encoding policy.
 java.io.InputStream openStream(java.net.URL url)
          Convenience method to return a byte stream from a given URL in accordance with this object's encoding policy.
abstract  void prepareRequest(java.net.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 java.lang.String ACCEPT_ENCODING
Name of HTTP request header to request coded response ("Accept-Encoding").

See Also:
Constant Field Values

CONTENT_ENCODING

public static final java.lang.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(java.net.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 java.io.InputStream getInputStream(java.net.URLConnection conn)
                                            throws java.io.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:
java.io.IOException
See Also:
URLConnection.getInputStream()

getErrorStream

public abstract java.io.InputStream getErrorStream(java.net.URLConnection conn)
                                            throws java.io.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:
java.io.IOException
See Also:
URLConnection.getInputStream()

openConnection

public java.net.URLConnection openConnection(java.net.URL url)
                                      throws java.io.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:
java.io.IOException

openStream

public java.io.InputStream openStream(java.net.URL url)
                               throws java.io.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:
java.io.IOException