info.dmtree.spi
Interface DataPlugin

public interface DataPlugin

An implementation of this interface takes the responsibility of handling data requests in a subtree of the DMT.

In an OSGi environment such implementations should be registered at the OSGi service registry specifying the list of root node URIs in a String array in the dataRootURIs registration parameter.

When the first reference in a session is made to a node handled by this plugin, the DmtAdmin calls one of the open... methods to retrieve a plugin session object for processing the request. The called method depends on the lock type of the current session. In case of openReadWriteSession(String[], DmtSession) and openAtomicSession(String[], DmtSession), the plugin may return null to indicate that the specified lock type is not supported. In this case the DmtAdmin may call openReadOnlySession(String[], DmtSession) to start a read-only plugin session, which can be used as long as there are no write operations on the nodes handled by this plugin.

The sessionRoot parameter of each method is a String array containing the segments of the URI pointing to the root of the session. This is an absolute path, so the first segment is always ".". Special characters appear escaped in the segments.

Method Summary

TransactionalDataSession	openAtomicSession(java.lang.String[] sessionRoot, DmtSession session) This method is called to signal the start of an atomic read-write session when the first reference is made within a DmtSession to a node which is handled by this plugin.
ReadableDataSession	openReadOnlySession(java.lang.String[] sessionRoot, DmtSession session) This method is called to signal the start of a read-only session when the first reference is made within a DmtSession to a node which is handled by this plugin.
ReadWriteDataSession	openReadWriteSession(java.lang.String[] sessionRoot, DmtSession session) This method is called to signal the start of a non-atomic read-write session when the first reference is made within a DmtSession to a node which is handled by this plugin.

Method Detail

openReadOnlySession

public ReadableDataSession openReadOnlySession(java.lang.String[] sessionRoot,
                                               DmtSession session)
                                        throws DmtException

This method is called to signal the start of a read-only session when the first reference is made within a DmtSession to a node which is handled by this plugin. Session information is given as it is needed for sending alerts back from the plugin.

The plugin can assume that there are no writing sessions open on any subtree that has any overlap with the subtree of this session.

Parameters:

sessionRoot - the path to the subtree which is accessed in the current session, must not be null

session - the session from which this plugin instance is accessed, must not be null

Returns:

a plugin session capable of executing read operations

Throws:

DmtException - with the following possible error codes:

• NODE_NOT_FOUND if sessionRoot points to a non-existing node
• COMMAND_FAILED if some unspecified error is encountered while attempting to complete the command

java.lang.SecurityException - if some underlying operation failed because of lack of permissions

openReadWriteSession

public ReadWriteDataSession openReadWriteSession(java.lang.String[] sessionRoot,
                                                 DmtSession session)
                                          throws DmtException

This method is called to signal the start of a non-atomic read-write session when the first reference is made within a DmtSession to a node which is handled by this plugin. Session information is given as it is needed for sending alerts back from the plugin.

The plugin can assume that there are no other sessions open on any subtree that has any overlap with the subtree of this session.

Parameters:

sessionRoot - the path to the subtree which is locked in the current session, must not be null

session - the session from which this plugin instance is accessed, must not be null

Returns:

a plugin session capable of executing read-write operations, or null if the plugin does not support non-atomic read-write sessions

Throws:

DmtException - with the following possible error codes:

• NODE_NOT_FOUND if sessionRoot points to a non-existing node
• COMMAND_FAILED if some unspecified error is encountered while attempting to complete the command

java.lang.SecurityException - if some underlying operation failed because of lack of permissions

openAtomicSession

public TransactionalDataSession openAtomicSession(java.lang.String[] sessionRoot,
                                                  DmtSession session)
                                           throws DmtException

This method is called to signal the start of an atomic read-write session when the first reference is made within a DmtSession to a node which is handled by this plugin. Session information is given as it is needed for sending alerts back from the plugin.

The plugin can assume that there are no other sessions open on any subtree that has any overlap with the subtree of this session.

Parameters:

sessionRoot - the path to the subtree which is locked in the current session, must not be null

session - the session from which this plugin instance is accessed, must not be null

Returns:

a plugin session capable of executing read-write operations in an atomic block, or null if the plugin does not support atomic read-write sessions

Throws:

DmtException - with the following possible error codes:

• NODE_NOT_FOUND if sessionRoot points to a non-existing node
• COMMAND_FAILED if some unspecified error is encountered while attempting to complete the command

java.lang.SecurityException - if some underlying operation failed because of lack of permissions