Processing transaction, operation and metadata events in Java works as follows:

• The Oracle GoldenGate Replicat or Extract process reads local trail data and passes the transactions, operations and database metadata to the Java Delivery Module. Metadata can come from the trail itself, a source definitions file.

• Events are fired by the Java framework, optionally filtered by custom Event Filters.

• Handlers (event listeners) process these events, and process the transactions, operations and metadata. Custom formatters may be applied for certain types of targets.

There are several existing handlers:

• Various built in Oracle GoldenGate for Distributed Applications and Analytics (GG for DAA) handlers to apply records to supported GG for DAA targets, see Replicate Data to configure various handlers supported in GG for DAA.

• JMS message handlers to send to a JMS provider using either a MapMessage, or using a TextMessage with customized formatters.

• A specialized message handler to send JMS messages to Oracle Advanced Queuing (AQ).

• A file writer handler, for writing to a single file, or a rolling file.

  Note:

  The file writer handler is particularly useful as development utility, since the file writer can take the exact same formatter as the JMS TextMessage handler. Using the file writer provides a simple way to test and tune the formatters for JMS without actually sending the messages to JMS

Event handlers can be configured using the main Java property file or they may optionally read in their own properties directly from yet another property file (depending on the handler implementation). Handler properties are set using the following syntax:

gg.handler.{name}.someproperty=somevalue

This will cause the property someproperty to be set to the value somevalue for the handler instance identified in the property file by name. This name is used in the property file to define active handlers and set their properties; it is user-defined.

Implementation note (for Java developers): Following the preceding example: when the handler is instantiated, the method void setSomeProperty(String value) will be called on the handler instance, passing in the String value somevalue. A JavaBean PropertyEditor may also be defined for the handler, in which case the string can be automatically converted to the appropriate type for the setter method. For example, in the Java application properties file, we may have the following:

# the list of active handlers: only two are active
gg.handlerlist=one, two
# set properties on 'one'
gg.handler.one.type=file
gg.handler.one.format=com.mycompany.MyFormatter
gg.handler.one.file=output.xml
# properties for handler 'two'
gg.handler.two.type=jms_text
gg.handler.two.format=com.mycompany.MyFormatter
gg.handler.two.properties=jboss.properties
# set properties for handler 'foo'; this handler is ignored
gg.handler.foo.type=com.mycompany.MyHandler
gg.handler.foo.someproperty=somevalue

The type identifies the handler class; the other properties depend on the type of handler created. If a separate properties file is used to initialize the handler (such as the JMS handlers), the properties file is found in the classpath. For example, if properties file is at: {gg_install_dir}/dirprm/foo.properties, then specify in the properties file as follows: gg.handler.name.properties=foo.properties.