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From "Alejandro Abdelnur (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-7549) Use JDK ServiceLoader mechanism to find FileSystem implementations
Date Wed, 17 Aug 2011 19:37:27 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-7549?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13086536#comment-13086536

Alejandro Abdelnur commented on HADOOP-7549:

The current loading mechanism (from Hadoop configuration files) would be preserved and have
precedence (although it would be deprecated).

A new method {{getScheme()}} in the {{FileSystem}} class would publish the scheme handled
by the implementation.

The base {{FileSystem}} class will implement this method throwing an {{UnsupportedOperationException}}.

All {{FileSystem}} implementations in Hadoop will be retrofitted to implement this method
declaring their scheme and they will be registered as services.

Custom {{FileSystem}} implementations not part of Hadoop will not break if they don't implement
the {{getScheme()}} method. The will continue to work as before, (they just won't support
the service loading). In a future release they could be retrofitted to use the service mechanism
(if their authors choose to).

Because implementations registered in the configuration have precedence over implementations
registered as services, modified implementations of Hadoop provided implementations will still
override the service definitions.

> Use JDK ServiceLoader mechanism to find FileSystem implementations
> ------------------------------------------------------------------
>                 Key: HADOOP-7549
>                 URL: https://issues.apache.org/jira/browse/HADOOP-7549
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: fs
>    Affects Versions: 0.23.0
>            Reporter: Alejandro Abdelnur
>            Assignee: Alejandro Abdelnur
>             Fix For: 0.23.0
> Currently configuring FileSystem implementations must be done by declaring the FileSystem
class in the Hadoop configuration files (core-default.xml, ...).
> Using JDK ServiceLoader mechanism this configuration step can be avoided. Adding the
JAR file with the additional FileSystem implementation would suffice. 
> This is similar to what is being proposed for compression codecs (HADOOP-7350).

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