org.osgi.service.dmt.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 or in case of a single value as String 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.

Field Summary

Fields

Modifier and Type	Field and Description
static java.lang.String	DATA_ROOT_URIS The string to be used as key for the "dataRootURIs" property when an DataPlugin is registered.
static java.lang.String	MOUNT_POINTS The string to be used as key for the mount points property when a DataPlugin is registered with mount points.

Method Summary

Modifier and Type	Method and Description
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.

Field Detail

MOUNT_POINTS

static final java.lang.String MOUNT_POINTS

The string to be used as key for the mount points property when a DataPlugin is registered with mount points.

See Also:

Constant Field Values

DATA_ROOT_URIS

static final java.lang.String DATA_ROOT_URIS

The string to be used as key for the "dataRootURIs" property when an DataPlugin is registered.

Since:

2.0

See Also:

Constant Field Values

Method Detail

openReadOnlySession

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

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

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