30 Oracle XML DB Repository Events

This chapter describes repository events and how to use them. It contains these topics:

Overview of Repository Events

You can use Oracle XML DB Repository to store and access data of any kind in the form of repository resources: files and folders. Repository resource operations include creating, deleting, locking, unlocking, rendering, linking, unlinking, placing under version control, checking in, checking out, unchecking out (reverting a checked out version), opening, and updating. You can access data in the repository from any application. Sometimes your application needs to perform certain actions whenever a particular repository operation occurs. For example, you might want to perform some move-to-wastebasket or other backup action whenever a resource is deleted.

Repository Events: Use Cases

The following are examples of cases where repository events can be used:

  • Wastebasket – You can use an UnLink pre-event handler to effectively move a resource to a wastebasket instead of deleting it. Create a link in a wastebasket folder before removing the original link. The link in the wastebasket ensures that the resource is not removed. When you subsequently undelete a resource from the waste basket, the original link can be created again and the wastebasket link removed. The wastebasket link name can be different from the name of the link being removed because a resource at a certain path could be unlinked more than once from that path. The wastebasket would then have multiple links corresponding to that path, with different link properties and possibly pointing to different resources.

  • Categorization – An application might categorize the resources it manages based on MIME type or other properties. It might keep track of GIF, text, and XML files by maintaining links to them from repository folders /my-app/gif, /my-app/txt, and /my-app/xml. Three post-event handlers could be used here: LinkIn, UnlinkIn, and Update. The LinkIn post-event handler would examine the resource and create a link in the appropriate category folder, if not already present. The UnlinkIn post-event handler would remove the link from the category folder. The Update post-event handler would effectively move the resource from one category folder to another if its category changes.

Repository Events and Database Triggers

Repository events are reminiscent of database triggers, but they offer additional functionality. You cannot use a database trigger to let your application react to repository operations. A given repository operation can consist of multiple database operations on multiple underlying, internal tables. Because these underlying tables are internal to Oracle XML DB, you cannot easily map them to specific repository operations. For example, internal table XDB$H_INDEX might be updated by either a database update operation, if an ACL is changed, or a link operation. Even in cases where you might be able to accomplish the same thing using database triggers, you would not want to do that: A repository event is a higher-level abstraction than would be a set of database triggers on the underlying tables.

When a repository event occurs, information associated with the operation, such as the resource path used, can be passed to the corresponding event handler. Such information is not readily available using database triggers.

Repository events and database triggers can both be applied to XML data. You can use triggers on XMLType tables, for instance. However, if an XMLType table is also a repository table (hierarchy-enabled), then do not duplicate in an event handler any trigger code that applies to the table. Otherwise, that code is executed twice.

Repository Event Listeners and Event Handlers

Each repository operation is associated with one or more repository events. Your application can configure listeners for the events associated with resources it is concerned with. A repository event listener is a Java class or a PL/SQL package or object type. It comprises a set of PL/SQL procedures or Java methods, each of which is called an event handler. Each event handler processes a single event. A repository event listener can be configured for a particular resource or for the entire repository. A listener can be further restricted to apply only when a given node-existence precondition is met.

You associate a repository event listener with a resource by mapping a resource configuration file to the resource. You use PL/SQL package DBMS_RESCONFIG to manipulate resource configuration files, including associating them with the resources they configure. In particular, PL/SQL function DBMS_RESCONFIG.getListeners lists all event listeners for a given resource.

Repository Event Configuration

A given resource can be configured by multiple resource configuration files. These are stored in a resource configuration list, and they are processed in list order. The repository as a whole can also be configured by multiple resource configuration files. The repository itself has a resource configuration list. Event handling that is configured for the repository as a whole takes effect before any resource-specific event handling. All applicable repository-wide events are processed before any resource-specific events.

A given resource configuration file can define multiple event listeners for the resources it configures, and each event listener can define multiple event handlers.

See Also:

Possible Repository Events

A rendering operation is associated with a single repository event. Except for rendering, all repository operations are associated with one or more pairs of events. For example, a resource creation is associated with three pairs of events, with the events occurring in this order:

  1. Pre-creation event

  2. Post-creation event

  3. Pre-link-in event

  4. Pre-link-to event

  5. Post-link-to event

  6. Post-link-in event

Table 30-1 lists the events associated with each repository operation. Their order is indicated in the handler columns.

Table 30-1 Predefined Repository Events

Repository Event Type Description Pre Handler Execution Post Handler Execution

Render

A Render event occurs only for file resources, never for folder resources.

Occurs when resource contents are accessed using any of the following:

  • Protocols

  • XDBURIType methods getCLOB(), getBLOB(), and getXML()

Does not occur when resource contents are accessed using any of the following:

  • SELECT ... FROM RESOURCE_VIEW

  • XDBURIType method getResource()

Only one handler for a Render event can set the rendered output. The first handler to call setRenderStream or setRenderPath controls the rendering.

N/A

N/A

Create

Occurs when a resource is created. The pre and post handlers executed are those defined on the folder of the new resource.

After pre-parsing, after validating the parent resource ACL and locks, and before assigning default values to undefined properties.

After inserting the resource into the system resource table.

Delete

Occurs when the resource and its contents are removed from disk, that is, when the resource REF count is zero (0).

After validating the resource ACL and locks and before removing the resource from disk.

After removing the resource and its contents from disk and after touching the parent folder to update its last modifier and modification time.

Update

Occurs when a resource is updated on disk.

After validating the resource ACL and locks and before updating the last modifier and modification time.

After writing the resource to disk.

Lock

Occurs during a lock-resource operation.

After validating the resource ACL and locks and before creating the new lock on the resource.

After creating the new lock.

Unlock

Occurs during an unlock-resource operation.

After validating the resource ACL and delete token.

After removing the lock.

LinkIn

Occurs before a LinkTo event during a link operation. The event target is the folder in which the link is created. Always accompanied by a LinkTo event.

After validating the resource ACL and locks and before creating the link.

After executing LinkTo post handler.

LinkTo

Occurs after a LinkIn event during a link operation. The event target is the resource that is the link destination.

After executing LinkIn pre handler and before creating the link.

After creating the link and after updating the last modifier and modification time of the parent folder.

UnLinkIn

Occurs before an UnlinkFrom event during an unlink operation. Always accompanied by an UnlinkFrom event.

After validating the resource ACL and locks and before removing the link.

After executing the UnlinkFrom post handler.

UnlinkFrom

Occurs after an UnlinkIn event during an unlink operation.

After executing the UnlinkIn pre handler.

After removing the link.

CheckIn

Occurs during check-in of a resource.

After validating the resource ACL and locks and after verifying that the resource is version-controlled and has been checked out.

After checking in the resource.

CheckOut

Occurs during check-out of a resource.

After validating the resource ACL and locks and after verifying that the resource is version-controlled and is not already checked out.

After checking out the resource.

UncheckOut

Occurs during uncheck-out of a resource.

Before removing the record that the resource is checked out.

After unchecking out the resource.

VersionControl

Occurs when a version history is created for a resource.

Note: You can call DBMS_XDB.MakeVersioned() multiple times, but the version history is created only at the first call. Subsequent calls have no effect, so no VersionControl event occurs.

Before creating the version history for the resource.

After creating the first version of the resource.

For simplicity, the presentation in this chapter generally treats both members of a repository event pair together, referring, for example, to the LinkIn event type as shorthand for the pre-link-in and post-link-in event types. For the same reason, the event-type names used here are derived from the Java interface XDBRepositoryEventListener by dropping the prefixes handlePre and handlePost.

See Also:

Oracle Database PL/SQL Packages and Types Reference for the PL/SQL repository event types

Repository Operations and Events

The same repository event can occur with different Oracle XML DB Repository operations, and a given repository operation can produce more than one repository event. Table 30-2 lists the events that are associated with each repository operation. See Table 30-1 for the event order when multiple repository events occur for the same operations.

Table 30-2 Oracle XML DB Repository Operations and Events

Operation Repository Events Occurring

Get binary representation of resource contents by path name

Render

Get XML representation of resource contents by path name

Render

Create or update a resource

If the resource already exists: Create, LinkIn, LinkTo

If resource doe not yet exist (HTTP and FTP only): Update

Create a folder

Create, LinkIn, LinkTo

Create a link to an existing resource

LinkIn on the folder containing the link target, LinkTo on the target resource to be linked

Unlink a file resource or an empty folder resource. (Decrement RefCount, and if it becomes zero then delete the resource from disk.)

UnlinkIn, UnlinkFrom, and, if RefCount is zero, Delete

Forcibly delete a folder and its contents

Recursively produce events for unlinking a resource. Folder child resources are deleted recursively, then the folder is deleted.

Forcibly remove all links to a resource

Produce unlinking events for each link removed.

Update the contents, properties, or ACL of a resource by path name

Update

Put a depth-zero WebDAV lock on a resource

Lock

Remove a depth-zero WebDAV lock from a resource

Lock

Rename (move) a resource

LinkIn and LinkTo on the new location, UnlinkIn and UnlinkFrom on the old location

Copy a resource

Create, LinkIn, and LinkTo on the new location

Check out a resource

CheckOut

Check in a resource

CheckIn

Place a resource under version control

VersionControl

Uncheck out a resource

UncheckOut

All operations listed in Table 30-2 are atomic, except for these:

  • Forced deletion of a folder and its contents

  • Update of resource properties by path name using HTTP (only)

  • Copy of a folder using HTTP (only)

See Also:

Table 21-3, "Accessing Oracle XML DB Repository: API Options" for information on accessing resources using APIs and protocols

Repository Event Handler Considerations

This section mentions some things to keep in mind when you define handlers for Oracle XML DB Repository events.

  • In any handler: Do not use COMMIT, ROLLBACK, or data definition language (DDL) statements in a handler. Do not call PL/SQL functions or procedures, such as DBMS_XMLSCHEMA.registerSchema, that behave similarly to DDL statements. In a Render handler: Do not use data manipulation language (DML) statements.

    To work around these restrictions, a handler can use such statements inside an autonomous transaction, but it must ensure that lock conflicts cannot arise.

  • In a Render handler, do not close an output stream. (You can append to a stream.)

  • Do not use modifier methods from class XDBResource in a handler, unless it is a Pre-Create or Pre-Update handler. Do not use method XDBResource.save() in any handler.

  • Oracle recommends that you develop only safe repository event handlers. In particular:

    • Write only resource properties that are in namespaces owned by your application, never in the xdb namespace.

    • Do not delete a resource while it is being created.

  • A repository event handler is passed an XDBRepositoryEvent object, which exists only during the current SQL statement or protocol operation. You can use PL/SQL procedures and Java methods on this object to obtain information about the resource, the event, and the associated event handlers.

  • When an event handler performs operations that cause other repository events to occur, those cascading events occur immediately. They are not queued to occur after the handlers for the current event are finished. Each event thus occurs in the context of its corresponding operation.

  • Repository event handlers are called synchronously. They are executed in the process, session, and transaction context of the corresponding operation. However, handlers can use Oracle Streams Advanced Queuing (AQ) to queue repository events that are then handled asynchronously by some other process.

  • Because a repository event handler is executed in the transaction context of its corresponding operation, any locks acquired by that operation, or by other operations run previously in the transaction, are still active. An event handler must not start a separate session or transaction that tries to acquire such a lock. Otherwise, the handler hangs.

  • Repository event handlers are called in the order that they appear in a resource configuration file. If preconditions are defined for a resource configuration, then only those handlers are called for which the precondition is satisfied.

  • Although handlers are called in the order they are defined in a configuration file, avoid letting your code depend upon this. If the user who is current when a handler is invoked has privilege write-config, then the handler invocation order could be changed inside an executing handler.

  • The entire list of handlers applicable to a given repository event occurrence is determined before any of the handlers is invoked. This means, in particular, that the precondition for each handler is evaluated before any handlers are invoked.

  • The following considerations apply to error handling for repository events:

    • A pre-operation event handler is never invoked if access checks for the operation fail.

    • All handlers for a given event are checked before any of them are called. If any of them is not usable (for example, no longer exists), then none of them are called.

    • If an error is raised during event handling, then other, subsequent event handlers are not invoked for the same SQL statement or protocol operation. The current statement or operation is canceled and all of its changes are rolled back.

  • The following considerations apply to resource security for repository events:

    • An event handler can have invoker's rights or definer rights. You specify the execution rights of a PL/SQL package when you create the package. You specify the execution rights of Java classes when you load them into the database using the loadjava utility. If you specify invoker's rights, but a given handler is not configured for invoker's rights, then an insufficient-privilege error is raised.

    • Within an event handler, the current user privileges, whether obtained by invoker or definer rights, are determined in detail for a given resource by its ACL. These privileges determine what the handler can do with the resource. For example, if the current user has privileges read-properties and read-contents for a particular resource, then an event handler can read that resource.

  • The following considerations apply to repository events for linking and unlinking:

    • After creating a link to a resource, if you want any resource configuration files of the parent folder to also apply to the linked resource, then use procedure DBMS_RESCONFIG.appendResConfig to add the configuration files to the linked resource. You can invoke this procedure from a Post-LinkTo event handler for the linked resource.

    • After unlinking a resource, if you want to remove any such resource configuration files added when linking, then use procedure DBMS_RESCONFIG.deleteResConfig to remove them from the unlinked resource. You can invoke this procedure from a Post-UnlinkFrom event handler for the unlinked resource.

  • Do not define handlers for events on folder /sys/schemas or on resources under this folder. Events do not occur for any such resources, so such event handlers are ignored. This implies that XML schema operations that affect the repository (registration, deletion, and so on) do not produce events.

See Also:

Configuring Repository Events

You configure event treatment for Oracle XML DB Repository resources as you would configure any other treatment of repository resources — see "Configuring a Resource".

By default, repository events are enabled, but you can disable them by setting parameter XML_DB_EVENTS to DISABLE. To disable repository events at the session level, use the following SQL*Plus command. You must have role XDBADMIN to do this.

ALTER SESSION SET XML_DB_EVENTS = DISABLE;

To disable repository events at the system level, use the following SQL*Plus command, and then restart your database. Repository events are disabled for subsequent sessions. You must have privilege ALTER SYSTEM to do this.

ALTER SYSTEM SET XML_DB_EVENTS = DISABLE;

To enable repository events again, set the value of XML_DB_EVENTS to ENABLE.

The rest of this section describes the resource configuration file that you use as a resource to configure event processing for other resources.

A resource configuration file is an XML file that conforms to the XML schema XDBResConfig.xsd, which is accessible in Oracle XML DB Repository at path /sys/schemas/PUBLIC/xmlns.oracle.com/xdb/XDBResConfig.xsd. You use element event-listeners, child of element ResConfig, to configure repository event handling.

See Also:

Chapter 22, "Configuring Oracle XML DB Repository" for general information about configuring repository resources

Configuration Element event-listeners

Each resource configuration file can have one event-listeners element, as a child of element ResConfig. This configures all event handling for the target resource. If the resource configuration file applies to the entire repository, not to a particular resource, then it defines event handling for all resources in the repository.

Element event-listeners has the following optional attributes:

  • set-invoker – Set this to true to if the resource configuration defines one or more repository event handlers to have invoker's rights. The default value is false, meaning that definer rights are used.

    To define an invoker-rights repository event handler, you must have database role XDB_SET_INVOKER. This role is granted to DBA, but not to XDBADMIN. Role XDB_SET_INVOKER is checked only when a resource configuration file is created or updated. Only attribute set-invoker, not role XDB_SET_INVOKER, is checked at run time to ensure sufficient privilege.

    See Also:

    "Repository Event Handler Considerations" for information about insufficient-privilege errors

  • default-schema – The default schema value, used for listeners for which no schema element is defined.

  • default-language –The default language value, used for listeners for which no language element is defined.

Element event-listeners has a sequence of listener elements as children. These configure individual repository event listeners. The listeners are processed at run time in the order of the listener elements.

Configuration Element listener

Each listener element has the following child elements. All of these are optional except source, and they can appear in any order (their order is irrelevant).

  • description – Description of the listener.

  • schema – Database schema for the Java or PL/SQL implementation of the repository event handlers. If neither this nor default-schema is defined, then an error is raised.

  • source (required) – Name of the Java class, PL/SQL package, or object type that provides the handler methods. Java class names must be qualified with a package name. Use an empty source element to indicate that the repository event handlers are standalone PL/SQL stored procedures.

  • language – Implementation language of the listener class (Java) or package (PL/SQL). If neither this nor default-language is defined, then an error is raised.

  • pre-condition – Precondition to be met for any repository event handlers in this listener to be executed. This is identical to the pre-condition child of general resource configuration element configuration – see "Configuration Element defaultChildConfig".

  • events – Sequence of unique repository event type names: Render, Pre-Create, and so on. Only handlers for repository events of these types are enabled for the listener. See "Possible Repository Events" for the list of possible repository event types. If element events is not present, then handlers of repository events of all types are enabled for the listener, which can be wasteful. Provide element events to eliminate handler invocations for insignificant repository events.

Repository Events Configuration Examples

Example 30-1 shows the content of a resource configuration file that defines two listeners. Each listener defines handlers for repository events of types Post-LinkIn, Post-UnlinkIn, and Post-Update. It defines preconditions, the default language (Java) and default database schema.

Example 30-1 Resource Configuration File for Java Event Listeners with Preconditions

<ResConfig xmlns="http://xmlns.oracle.com/xdb/XDBResConfig.xsd"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="http://xmlns.oracle.com/xdb/XDBResConfig.xsd
                               http://xmlns.oracle.com/xdb/XDBResConfig.xsd">
  <event-listeners default-language="Java" default-schema="IFS">
    <listener>
      <description>Category application</description>
      <schema>CM</schema>
      <source>oracle.cm.category</source>
      <events>
        <Post-LinkIn/>
        <Post-UnlinkIn/>
        <Post-Update/>
      </events>
      <pre-condition>
        <existsNode>
          <XPath>/Resource[ContentType="image/gif"]</XPath>
        </existsNode>
      </pre-condition>
    </listener>
    <listener>
      <description>Check quota</description>
      <source>oracle.ifs.quota</source>
      <events>
        <Post-LinkIn/>
        <Post-UnlinkIn/>
        <Post-Update/>
      </events>
      <pre-condition>
        <existsNode>
          <XPath>r:/Resource/[ns:type="ifs-file"]</XPath>
          <namespace>xmlns:r="http://xmlns.oracle.com/xdb/XDBResource.xsd"
                     xmlns:ns="http://foo.xsd"
          </namespace>
        </existsNode>
      </pre-condition>
    </listener>
  </event-listeners>
  <defaultChildConfig>
    <configuration>
      <path>/sys/xdb/resconfig/user_rc.xml</path>
    </configuration>
  </defaultChildConfig>
  <applicationData>
    <foo:data xmlns:foo="http://foo.xsd">
      <foo:item1>1234</foo:item1>
    </foo:data>
  </applicationData>
</ResConfig>

The implementation of the handlers of the first listener is in Java class oracle.cm.quota defined in database schema CM. These handlers are invoked only for events on resources of ContentType image/gif.

The implementation of the handlers of the second listener is in Java class oracle.ifs.quota defined in database schema IFS (the default schema for this resource configuration file). These handlers are invoked only for events on resources of type ifs-file in namespace http://foo.xsd.

See Also:

"Configuration Element defaultChildConfig" for a description of elements defaultChildConfig and applicationData

As a simple end-to-end illustration, suppose that an application needs to categorize the resources in folder /public/res-app according to their MIME types. It creates links to resources in folders /public/app/XML-TXT, /public/app/IMG, and /public/app/FOLDER, depending on whether the resource MIME type is text/xml, image/gif, or application/octet-stream, respectively. This is illustrated in Example 30-2, Example 30-3, and Example 30-5.

Example 30-2 shows the PL/SQL code to create the configuration file for this categorization illustration. It defines a single listener that handles events of types Pre-UnlinkIn and Post-LinkIn. It explicitly defines the language (PL/SQL) and database schema. No preconditions are defined.

Example 30-2 Resource Configuration File for PL/SQL Event Listeners with No Preconditions

DECLARE
  b BOOLEAN := FALSE;
BEGIN
  b := DBMS_XDB.createFolder('/public/resconfig');
  b := DBMS_XDB.createResource(
         '/public/resconfig/appcatg-rc1.xml',
         '<ResConfig xmlns="http://xmlns.oracle.com/xdb/XDBResConfig.xsd"
                     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                     xsi:schemaLocation="http://xmlns.oracle.com/xdb/XDBResConfig.xsd
                                         http://xmlns.oracle.com/xdb/XDBResConfig.xsd">
            <event-listeners>
              <listener>
                <description>Category application</description>
                <schema>APPCATGUSER1</schema>
                <source>APPCATG_EVT_PKG1</source>
                <language>PL/SQL</language>
                <events>
                  <Pre-UnlinkIn/>
                  <Post-LinkIn/>
                </events>
              </listener>
            </event-listeners>
            <defaultChildConfig>
              <configuration>
                <path>/public/resconfig/appcatg-rc1.xml</path>
              </configuration>
            </defaultChildConfig>
          </ResConfig>',
         'http://xmlns.oracle.com/xdb/XDBResConfig.xsd',
         'ResConfig');
END;
/
BEGIN
  DBMS_RESCONFIG.appendResConfig('/public/res-app', 
                                 '/public/resconfig/appcatg-rc1.xml',
                                 DBMS_RESCONFIG.APPEND_RECURSIVE);
END;
/

Example 30-3 shows the PL/SQL code that implements the event handlers that are configured in Example 30-2. The Post-LinkIn event handler creates a link to the eventObject resource in one of the folders /public/app/XML-TXT, /public/app/IMG, and /public/app/FOLDER, depending on the resource MIME type. The Pre-UnlinkIn event handler deletes the links that are created by the Post-LinkIn event handler.

Example 30-3 PL/SQL Code Implementing Event Listeners

CREATE OR REPLACE PACKAGE appcatg_evt_pkg1 AS
 
  PROCEDURE handlePreUnlinkIn (eventObject DBMS_XEVENT.XDBRepositoryEvent);
  PROCEDURE handlePostLinkIn (eventObject DBMS_XEVENT.XDBRepositoryEvent);
 
END;
/
CREATE OR REPLACE PACKAGE BODY appcatg_evt_pkg1 AS
 
  PROCEDURE handlePreUnlinkIn (eventObject DBMS_XEVENT.XDBRepositoryEvent) AS
      XDBResourceObj DBMS_XDBRESOURCE.XDBResource;
      ResDisplayName VARCHAR2(100);
      ResPath        VARCHAR2(1000);
      ResOwner       VARCHAR2(1000);
      ResDeletedBy   VARCHAR2(1000);
      XDBPathobj     DBMS_XEVENT.XDBPath;
      XDBEventobj    DBMS_XEVENT.XDBEvent;
      SeqChar        VARCHAR2(1000);
      LinkName       VARCHAR2(10000);
      ResType        VARCHAR2(100);
      LinkFolder     VARCHAR2(100);
    BEGIN
      XDBResourceObj := DBMS_XEVENT.getResource(eventObject);
      ResDisplayName := DBMS_XDBRESOURCE.getDisplayName(XDBResourceObj);
      ResOwner       := DBMS_XDBRESOURCE.getOwner(XDBResourceObj);
      XDBPathobj     := DBMS_XEVENT.getPath(eventObject);
      ResPath        := DBMS_XEVENT.getName(XDBPathObj);
      XDBEventobj    := DBMS_XEVENT.getXDBEvent(eventObject);
      ResDeletedBy   := DBMS_XEVENT.getCurrentUser(XDBEventobj);
      BEGIN
        SELECT XMLCast(
                 XMLQuery(
                   'declare namespace ns = "http://xmlns.oracle.com/xdb/XDBResource.xsd";
                    /ns:Resource/ns:ContentType'
                   PASSING r.RES RETURNING CONTENT) AS VARCHAR2(100))
          INTO ResType
          FROM PATH_VIEW r WHERE r.PATH=ResPath;
          EXCEPTION WHEN OTHERS THEN NULL;
      END;
      IF ResType = 'text/xml' THEN LinkFolder := '/public/app/XML-TXT/';
      END IF;
      IF ResType = 'image/gif' THEN LinkFolder := '/public/app/IMG/';
      END IF;
      IF ResType = 'application/octet-stream' THEN LinkFolder := '/public/app/FOLDER/';
      END IF;
      DBMS_XDB.deleteResource(LinkFolder || ResDisplayName);
  END;
 
  PROCEDURE handlePostLinkIn (eventObject DBMS_XEVENT.XDBRepositoryEvent) AS
      XDBResourceObj DBMS_XDBRESOURCE.XDBResource;
      ResDisplayName VARCHAR2(100);
      ResPath        VARCHAR2(1000);
      ResOwner       VARCHAR2(1000);
      ResDeletedBy   VARCHAR2(1000);
      XDBPathobj     DBMS_XEVENT.XDBPath;
      XDBEventobj    DBMS_XEVENT.XDBEvent;
      SeqChar        VARCHAR2(1000);
      LinkName       VARCHAR2(10000);
      ResType        VARCHAR2(100);
      LinkFolder     VARCHAR2(100);
    BEGIN
      XDBResourceObj := DBMS_XEVENT.getResource(eventObject);
      ResDisplayName := DBMS_XDBRESOURCE.getDisplayName(XDBResourceObj);
      ResOwner       := DBMS_XDBRESOURCE.getOwner(XDBResourceObj);
      XDBPathobj     := DBMS_XEVENT.getPath(eventObject);
      ResPath        := DBMS_XEVENT.getName(XDBPathObj);
      XDBEventobj    := DBMS_XEVENT.getXDBEvent(eventObject);
      ResDeletedBy   := DBMS_XEVENT.getCurrentUser(XDBEventobj);
      SELECT XMLCast(
               XMLQuery(
                 'declare namespace ns = "http://xmlns.oracle.com/xdb/XDBResource.xsd";
                  /ns:Resource/ns:ContentType'
                 PASSING r.RES RETURNING CONTENT) AS VARCHAR2(100))
        INTO ResType
        FROM PATH_VIEW r WHERE r.PATH=ResPath;
      IF ResType = 'text/xml' THEN LinkFolder := '/public/app/XML-TXT';
      END IF;
      IF ResType = 'image/gif' THEN LinkFolder := '/public/app/IMG';
      END IF;
      IF ResType = 'application/octet-stream' THEN LinkFolder := '/public/app/FOLDER';
      END IF;
      DBMS_XDB.link(ResPath, LinkFolder, ResDisplayName);
    END;
 END;
 /

See Also:

A Java example would be configured the same as in Example 30-2, with the exception of these two lines, which would replace the elements with the same names in Example 30-2:

                <source>category</source>
                <language>Java</language>

Example 30-4 shows the Java code that implements the event handlers. The logic is identical to that in Example 30-3.

Example 30-4 Java Code Implementing Event Listeners

import oracle.xdb.event.*;
import oracle.xdb.spi.*;
import java.sql.*;
import java.io.*;
import java.net.*;
import oracle.jdbc.*;
import oracle.sql.*;
import oracle.xdb.XMLType;
import oracle.xdb.dom.*;
 
public class category
extends oracle.xdb.event.XDBBasicEventListener
{
  public Connection connectToDB() throws java.sql.SQLException
  {
    try
    {
      String strUrl="jdbc:oracle:kprb:";
      String strUname="appcatguser1";
      String strPwd="appcatguser1 ";
      Connection conn=null;
      OraclePreparedStatement stmt=null;
      DriverManager.registerDriver(new oracle.jdbc.OracleDriver());
      conn = DriverManager.getConnection(strUrl, strUname, strPwd);
      return conn;
    }
    catch(Exception e1)
    {
      System.out.println("Exception in connectToDB java function");
      System.out.println("e1:" + e1.toString());
      return null;
    }
  }
  public void handlePostLinkIn (XDBRepositoryEvent eventObject)
  {
    XDBPath objXDBPath = null;
    String strPathName="";
    objXDBPath = eventObject.getPath();
    strPathName = objXDBPath.getName();
    XDBResource objXDBResource1;
    objXDBResource1 = eventObject.getResource();
    String textResDisplayName = objXDBResource1.getDisplayName();
    String resType = objXDBResource1.getContentType();
    String linkFolder="";
    System.out.println("resType" + resType+"sumit");
    System.out.println("strPathName:" + strPathName);
    System.out.println("textResDisplayName:" + textResDisplayName);
    if (resType.equals("text/xml")) linkFolder = "/public/app/XML-TXT/";
    else if (resType.equals("image/gif")) linkFolder = "/public/app/IMG/";
    else if (resType.equals("application/octet-stream"))
            linkFolder = "/public/app/FOLDER/";
    System.out.println("linkFolder:" + linkFolder);
    try
    {
      Connection con1 = connectToDB();
      OraclePreparedStatement stmt=null;
      stmt = (OraclePreparedStatement)con1.prepareStatement(
               "CALL DBMS_XDB.link(?,?,?)");
      stmt.setString(1,strPathName);
      stmt.setString(2,linkFolder);
      stmt.setString(3,textResDisplayName);
      stmt.execute();
      stmt.close();
      con1.close();
    }
    catch(java.sql.SQLException ej1)
    {
      System.out.println("ej1:" + ej1.toString());
    }
 
  /* Make sure the link is not in the category folders.
     Then check the target resource's mime type and create a link
     in the appropriate category folder. */
  }
  public void handlePreUnlinkIn (XDBRepositoryEvent eventObject)
  {
    XDBPath objXDBPath = null;
    String strPathName="";
    objXDBPath = eventObject.getPath();
    strPathName = objXDBPath.getName();
    XDBResource objXDBResource1;
    objXDBResource1 = eventObject.getResource();
    String textResDisplayName = objXDBResource1.getDisplayName();
    String resType = objXDBResource1.getContentType();
    String linkFolder="";
    if (resType.equals("text/xml")) linkFolder = "/public/app/XML-TXT/";
    else if (resType.equals("image/gif")) linkFolder = "/public/app/IMG/";
    else if (resType.equals("application/octet-stream"))
            linkFolder = "/public/app/FOLDER/";
    try
    {
      Connection con1 = connectToDB();
      OraclePreparedStatement stmt=null;
      stmt = (OraclePreparedStatement)con1.prepareStatement(
               "CALL DBMS_XDB.deleteResource(?)");
      stmt.setString(1,linkFolder+textResDisplayName);
      stmt.execute();
      stmt.close();
      con1.close();
    }
    catch(java.sql.SQLException ej1)
    {
      System.out.println("ej1:" + ej1.toString());
    }
  }
}

Example 30-5 demonstrates the invocation of the event handlers that are implemented in Example 30-3 or Example 30-4.

Example 30-5 Invoking Event Handlers

DECLARE
  ret BOOLEAN;
BEGIN
  ret := DBMS_XDB.createResource('/public/res-app/res1.xml',
                                 '<name>TestForEventType-1</name>');
END;
/
DECLARE
  b BOOLEAN := FALSE;
  dummy_data CLOB := 'AAA';
BEGIN
  b := DBMS_XDB.createResource('/public/res-app/res2.gif', dummy_data);
END;
/
DECLARE
  b BOOLEAN := FALSE;
  dummy_data CLOB := 'AAA';
BEGIN
  b := DBMS_XDB.createFolder('/public/res-app/res-appfolder1');
END;
 
SELECT PATH FROM PATH_VIEW WHERE PATH LIKE '/public/app/%' ORDER BY PATH;
 
PATH
---------------------------------
/public/app/FOLDER
/public/app/FOLDER/res-appfolder1
/public/app/IMG
/public/app/IMG/res2.gif
/public/app/XML-TXT
/public/app/XML-TXT/res1.xml
 
6 rows selected.
 
-- Delete the /res-app resources. The /app resources are deleted also.
EXEC DBMS_XDB.deleteResource('/public/res-app/res2.gif');
EXEC DBMS_XDB.deleteResource('/public/res-app/res1.xml');
EXEC DBMS_XDB.deleteResource('/public/res-app/res-appfolder1');
 
SELECT PATH FROM PATH_VIEW WHERE PATH LIKE '/public/app/%' ORDER BY PATH;
 
PATH
-------------------
/public/app/FOLDER
/public/app/IMG
/public/app/XML-TXT
 
3 rows selected.