org.fcrepo.server.storage.lowlevel.akubra
Class HashPathIdMapper

java.lang.Object
  org.fcrepo.server.storage.lowlevel.akubra.HashPathIdMapper

All Implemented Interfaces:

org.akubraproject.map.IdMapper

public class HashPathIdMapper
extends Object
implements org.akubraproject.map.IdMapper

Provides a hash-based file: mapping for any URI.

The path component of each internal URI is derived from an MD5 hash of the external URI. The filename component is a reversible encoding of the external URI that is safe to use as a filename on modern filesystems.

Hash Path Patterns

The pattern given at construction time determines how the path component of each internal URI will be composed. Within the pattern, the # character is a stand-in for a hexadecimal [0-f] digit from the MD5 hash of the external id.

Patterns:

• must consist only of # and / characters.
• must contain between 1 and 32 # characters.
• must not begin or end with the / character.
• must not contain consecutive / characters.

Example patterns:

• Good: #
• Good: ##/#
• Good: ##/##/##
• Bad: a
• Bad: ##/
• Bad: ##//##

Filesystem-Safe Encoding

The last part of the internal URI is a "filesystem-safe" encoding of the external URI. All characters will be UTF-8 percent-encoded ("URI escaped") except for the following: a-z A-Z 0-9 = ( ) [ ] - In addition, . (period) will be escaped as %2E when it occurs as the last character of the URI.

Example Mappings

With pattern #/#:

• urn:example1 becomes file:0/8/urn%3Aexample1
• http://tinyurl.com/cxzzf becomes file:6/2/http%3A%2F%2Ftinyurl.com%2Fcxzzf

With pattern ##/##:

• urn:example1 becomes file:08/86/urn%3Aexample1
• http://tinyurl.com/cxzzf becomes file:62/ca/http%3A%2F%2Ftinyurl.com%2Fcxzzf

Author:

Chris Wilper

Constructor Summary

HashPathIdMapper(String pattern)
Creates an instance that will use the given pattern.

Method Summary

URI	getExternalId(URI internalId)
URI	getInternalId(URI externalId)
String	getInternalPrefix(String externalPrefix)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

HashPathIdMapper

public HashPathIdMapper(String pattern)

Creates an instance that will use the given pattern.

Parameters:

pathPattern - the pattern to use, possibly null or "".

Throws:

IllegalArgumentException - if the pattern is invalid.

Method Detail

getExternalId

public URI getExternalId(URI internalId)
                  throws NullPointerException

Specified by:

getExternalId in interface org.akubraproject.map.IdMapper

Throws:

NullPointerException

getInternalId

public URI getInternalId(URI externalId)
                  throws NullPointerException

Specified by:

getInternalId in interface org.akubraproject.map.IdMapper

Throws:

NullPointerException

getInternalPrefix

public String getInternalPrefix(String externalPrefix)
                         throws NullPointerException

Specified by:

getInternalPrefix in interface org.akubraproject.map.IdMapper

Throws:

NullPointerException