Class ContentCoding

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

public abstract class ContentCoding extends 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:
  • Field Details

    • 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:
    • CONTENT_ENCODING

      public static final String CONTENT_ENCODING
      Name of HTTP response header to mark coded response ("Content-Encoding").
      See Also:
  • Constructor Details

    • ContentCoding

      protected ContentCoding()
      Constructor.
  • Method Details

    • 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:
    • 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:
    • 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