[HDFS-8101] DFSClient use of non-constant DFSConfigKeys pulls in WebHDFS classes at runtime

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 2.7.0
• Fix Version/s: 2.8.0, 2.7.3, 3.0.0-alpha1
• Component/s: hdfs-client
• Target Version/s: 2.8.0
• Hadoop Flags: Reviewed
• Assignee: Sean Busbey
• Reporter: Sean Busbey
• Created: 08/Apr/15 21:29
• Updated: 06/Jan/17 01:53
• Resolved: 09/Apr/15 16:49

Description

Previously, all references to DFSConfigKeys in DFSClient were compile time constants which meant that normal users of DFSClient wouldn't resolve DFSConfigKeys at run time. As of HDFS-7718, DFSClient has a reference to a member of DFSConfigKeys that isn't compile time constant (DFS_CLIENT_KEY_PROVIDER_CACHE_EXPIRY_DEFAULT).

Since the class must be resolved now, this particular member

public static final String  DFS_WEBHDFS_AUTHENTICATION_FILTER_DEFAULT = AuthFilter.class.getName();

means that javax.servlet.Filter needs to be on the classpath.

javax-servlet-api is one of the properly listed dependencies for HDFS, however if we replace AuthFilter.class.getName() with the equivalent String literal then downstream folks can avoid including it while maintaining compatibility.