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Writing a simple custom partition for ApacheDS
On the mailing list, people ask regularly on how to write a custom partition. If you simply plan to add another suffix to ApacheDS (besides dc=example,dc=com, for instance) in order to store data, it is not necessary to write any code. You can simply add some lines to the configuration. The following is for developers who plan to implement another storage mechanism than the provided default.
What exactly is a partition?
Within ApacheDS, a partition is a physically distinct store for a subset of the entries contained within the server. A partition can be implemented using any storage mechanism or can even be backed in memory. The default storage mechanism for a partition is JDBM.
Implementing your own partition is basically implementing the Partition interface from the org.apache.directory.server.core.partition package. Please note that this is not an easy task. Nevertheless I try to give you a starting point with some simple examples.
Hello world. A minimal partition
Let's start with a minimal partition, the hello world. Minimal means here, that it is possible to add it to ApacheDS and see it with an LDAP browser. The partition ...
- correctly implements the Partition interface
- is pluggable in the server (embedded and declarative in the configuration)
- is visible for clients like ldapsearch or Apache Directory Studio
- contains one entry, which contains the famous "hello, world" message in an attribute value
- does not support any modification operations like delete, add etc.
- does not take account of filters in search requests, ...
The sources
Currently, the sources are checked in here
In order to build it, simply check it out and type "mvn install".
Implementing the class HelloWorldPartition
The following UML class diagram depicts the structure of the little example.
In order to be a partition, class HelloWorldPartition implements the corresponding interface from org.apache.directory.server.core.partition. It has an association to it's only entry (which will hold the "hello, world" method). This entry is created in the init life cycle method of the partition, which looks like this:
...
public void init(DirectoryService core) throws Exception {
// Create LDAP DN
suffixDn = new LdapDN(suffix);
suffixDn.normalize(core.getRegistries().getAttributeTypeRegistry().getNormalizerMapping());
Rdn rdn = suffixDn.getRdn();
// Create the only entry in this partition
ServerEntry entry = new DefaultServerEntry(core
.getRegistries(), this.suffixDn);
entry.put(SchemaConstants.OBJECT_CLASS_AT, SchemaConstants.TOP_OC,
SchemaConstants.ORGANIZATIONAL_UNIT_OC);
entry.put(SchemaConstants.OU_AT, rdn.getUpValue().toString());
entry.put("description", "hello, world", "a minimal partition");
this.helloEntry = entry;
}
...
We assume that the suffix starts with "ou=" in order to create an entry of object class organizational unit. If someone tries to set a suffix which starts with another attribute for the RDN, the setSuffix will throw an exception.
The Partition interface requires to implement many methods for all the operations a partition should support (adding, deleting, modifying entries ...). Due to the fact, that this is a read only partition, the implementation in our case is minimalistic. Here is the delete method as an example.
...
public void delete(DeleteOperationContext opContext)
throws LdapOperationNotSupportedException {
throw new LdapOperationNotSupportedException(
MODIFICATION_NOT_ALLOWED_MSG, ResultCodeEnum.UNWILLING_TO_PERFORM);
}
...
Although this example should be minimal, some methods need more attention. At least if we want to see the partitiion in an LDAP and not only in the error logs ...
The important methods are hasEntry, lookup and search. The following code is the search method. Please note that it ignores search scopes other than BASE and search filters completely in order to have simple code.
public EntryFilteringCursor search(SearchOperationContext ctx)
throws Exception {
if (ctx.getDn().equals(this.suffixDn)) {
switch (ctx.getScope()) {
case OBJECT:
// return a result with the only entry we have
return new BaseEntryFilteringCursor(
new SingletonCursor<ServerEntry>(this.helloEntry), ctx);
}
}
// return an empty result
return new BaseEntryFilteringCursor(new EmptyCursor<ServerEntry>(), ctx);
}
For the other methods, take a look in the source code.
Using the partition
Embedded mode
package org.apache.directory.samples.partition.hello;
import org.apache.directory.server.core.DefaultDirectoryService;
import org.apache.directory.server.core.DirectoryService;
import org.apache.directory.server.ldap.LdapServer;
import org.apache.directory.server.protocol.shared.transport.TcpTransport;
/**
* Starts the server with the HelloWorld partition.
*/
public class Main {
public static void main(String[] args) throws Exception {
DirectoryService directoryService = new DefaultDirectoryService();
directoryService.setShutdownHookEnabled(true);
LdapServer ldapServer = new LdapServer();
ldapServer.setDirectoryService(directoryService);
ldapServer.setAllowAnonymousAccess(true);
TcpTransport ldapTransport = new TcpTransport(10389);
ldapServer.setTransports(ldapTransport);
HelloWorldPartition helloPartition = new HelloWorldPartition();
helloPartition.setSuffix("ou=helloWorld");
helloPartition.init(directoryService);
directoryService.addPartition(helloPartition);
directoryService.startup();
ldapServer.start();
}
}
Adding it to a server.xml file
In order to use the partition in a standard installation of ApacheDS, simply add it to the server.xml configuration. Provide a "native" Spring bean like this.
<spring:beans xmlns:spring="http://xbean.apache.org/schemas/spring/1.0"
xmlns:s="http://www.springframework.org/schema/beans"
xmlns="http://apacheds.org/config/1.0">
...
<defaultDirectoryService ...>
...
<partitions>
...
<s:bean
id="helloPartition"
class="org.apache.directory.samples.partition.hello.HelloWorldPartition">
<s:property name="suffix" value="ou=helloWorld" />
</s:bean>
</partitions>
...
</defaultDirectoryService>
...
Note that the class HelloWorldPartition has to be in the class path of the server. Without, starting the server leads to a ClassNotFoundException. You can copy the jar file which results from the build to the lib/ext directory.
Verification
After adding the HelloWorldPartition to the directory service like above (embedded or via configuration in server.xml), you can browse it with an LDAP browser like the one from Apache Directory Studio. Here are some screen shots.
Of course using a command line tool works as well ...
$ ldapsearch -h localhost -p 10389 -D "uid=admin,ou=system" -w secret \\
-b "" -s base "(objectclass=*)" namingContexts
version: 1
dn:
namingContexts: ou=system
namingContexts: ou=helloWorld
namingContexts: ou=schema
$
$ ldapsearch -h localhost -p 10389 -D "uid=admin,ou=system" -w secret \\
-b "ou=helloWorld" -s base "(objectclass=*)"
version: 1
dn: ou=helloWorld
objectClass: organizationalUnit
objectClass: top
description: hello, world
description: a minimal partition
ou: helloWorld
$
To be continued
We plan to add more sophistic examples on this topic in the near feature. Stay tuned on the mailing lists.
Here is an older example on the topic:
http://svn.apache.org/viewvc/directory/sandbox/akarasulu/custom-partition
It is outdated, but may still inspire you.