[HADOOP-14267] Make DistCpOptions class immutable

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 3.0.0-alpha4
• Component/s: tools/distcp
• Target Version/s: 3.0.0-alpha4
• Hadoop Flags: Incompatible change, Reviewed
• Release Note: DistCpOptions has been changed to be constructed with a Builder pattern. This potentially affects applications that invoke DistCp with the Java API.
• Assignee: Mingliang Liu
• Reporter: Mingliang Liu
• Created: 15/Jun/16 20:51
• Updated: 31/Jan/18 20:15
• Resolved: 01/Apr/17 03:34

Description

Currently the DistCpOptions class encapsulates all DistCp options, which may be set from command-line (via the OptionsParser) or may be set manually (eg construct an instance and call setters). As there are multiple option fields and more (e.g. HDFS-9868, HDFS-10314) to add, validating them can be cumbersome. Ideally, the DistCpOptions object should be immutable. The benefits are:

1. DistCpOptions is simple and easier to use and share, plus it scales well
2. validation is automatic, e.g. manually constructed DistCpOptions gets validated before usage
3. validation error message is well-defined which does not depend on the order of setters

This jira is to track the effort of making the DistCpOptions immutable by using a Builder pattern for creation.

Issue Links

• blocks: FALCON-2029 HDFS-8828 requires Falcon to update Snapshot based mirroring extension
• breaks: HBASE-18896 Work around incompatible change to DistCpOptions for hadoop-3
• breaks: HADOOP-15200 Missing DistCpOptions constructor breaks downstream DistCp projects in 3.0
• relates to: HDFS-10556 DistCpOptions should be validated automatically