JMSReader

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Short Description
Ports
Metadata
JMSReader Attributes
Details
Examples
Best Practices
See also

Short Description

JMSReader converts JMS messages into Clover data records.

Component Data source Input ports Output ports Each to all outputs Different to different outputs Transformation Transf. req. Java CTL Auto-propagated metadata
JMSReaderjms messages01
yes
no
yes
no
yes
no
no

Icon

Ports

Port typeNumberRequiredDescriptionMetadata
Output0
yes
For correct data recordsAny

All the connected output ports send out all data records.

Metadata

JMSReader does not propagate metadata.

JMSReader has no metadata templates.

Metadata on the output port may contain a field specified in the Message body field attribute. Metadata can also use Autofilling Functions.

JMSReader Attributes

AttributeReqDescriptionPossible values
Basic
JMS connectionyesID of the JMS connection to be used. See JMS Connections. 
Processor code [1] Transformation of JMS messages to records written in the graph in Java. 
Processor URL[1]Name of an external file, including the path, containing the transformation of JMS messages to records written in Java. 
Processor class[1]Name of an external class defining the transformation of JMS messages to records. The default processor value is sufficient for most cases. It can process both javax.jms.TextMessage and javax.jms.BytesMessage.JmsMsg2DataRecordProperties (default) | other class
JMS message selector Standard JMX "query" used to filter the JMS messages that should be processed. In effect, it is a string query using message properties and syntax that is a subset of SQL expressions. For more information, see Interface Message .  
Message charset Encoding of JMS messages contents. This attribute is also used by the default processor implementation (JmsMsg2DataRecordProperties). And it is used for javax.jms.BytesMessage only.ISO-8859-1 (default) | other encoding
Advanced
Processor source charset Encoding of external file containing the transformation in Java.ISO-8859-1 (default) | other encoding
Max msg count  Maximum number of messages to be received. 0 means without limitation. For more information, see Limit of Run. 0 (default) | 1-N
Timeout Maximum time to receive messages in milliseconds. 0 means without limitation. For more information, see Limit of Run. 0 (default) | 1-N
Message body field Name of the field to which message body should be written. This attribute is used by the default processor implementation (JmsMsg2DataRecordProperties). If no Message body field is specified, the field whose name is bodyField will be filled with the body of the message. If no field for the body of the message is contained in metadata, the body will not be written to any field.bodyField (default) | other name

[1]  One of these may be set. Any of these transformation attributes implements a JmsMsg2DataRecord interface.

For more information, see Java Interfaces for JMSReader.

For detailed information about transformations, see also Defining Transformations.

Details

JMSReader receives JMS messages, converts them into Clover data records and sends these records to the connected output port. The component uses a processor transformation which implements a JmsMsg2DataRecord interface or inherits from a JmsMsg2DataRecordBase superclass. Methods of JmsMsg2DataRecord interface are described below in Java Interfaces for JMSReader.

Limit of Run

You can choose to limit the number of received messages and/or time of processing.

  • Limited Run

    If you specify the maximum number of messages (Max msg count), the timeout (Timeout) or both, the processing will be limited by the number of messages, or time of processing, or both of these attributes. They need to be set to positive values.

    When the specified number of messages is received, or when the process lasts some defined time, the process stops. Whichever of them will be achieved first, such attribute will be applied.

    [Note]Note

    Remember that you can also limit the graph run by using the endOfInput() method of JmsMsg2DataReader interface. It returns a boolean value and can also limit the run of the graph. Whenever it returns false, the processing stops.

  • Unlimited Run

    If you do not specify either of these two attributes (Max msg count and Timeout), the processing will never stop.

    This is the default setting of JMSReader. Both the attributes are set to 0 by default. Thus, the processing is limited by neither the number of messages nor the elapsed time.

Thread Safety and Parallel Access

Each JMS Connection used in a graph creates one JMS session in AUTO_ACKNOWLEDGE mode. All JMS components get the "consumer" or "producer" from the shared session. It's possible to use more consumers/producers in parallel, but the session is single-threaded, so the requests for JMS broker are synchronized. To achieve really parallel access, each JMS component should have its own JMS connection.

Message Body, Message Header etc.

Data that is inserted into the body or header of a message depends on the implementation of the Processor class. The default implementation is org.jetel.component.jms.JmsMsg2DataRecordProperties. It is the class transforming JMS messages (TextMessage or BytesMessage) to data records.

One field of the record may be filled with body of the message. The name of the field is specified by component attribute Message body field.

If message is of type BytesMessage, use attribute "msgCharset" to specify encoding of characters in the message.

All the other fields are saved using string properties in the message header. Property names are same as respective field names. Values contain textual representation of field values. Default property field of Map<StringÎ may be defined to which all "unmappable" properties of header are saved as [key=property name]-Î[value=property value]

Last message has a same format as all the others. Terminating message is not supported.

Java Interfaces for JMSReader

The transformation implements methods of the JmsMsg2DataRecord interface and inherits other common methods from the Transform interface. See Common Java Interfaces. See Public Clover API.

Following are the methods of JmsMsg2DataRecord interface:

  • void init(DataRecordMetadata metadata, Properties props)

    Initializes the processor.

  • boolean endOfInput()

    May be used to end processing of input JMS messages when it returns false. See Limit of Run for more information.

  • DataRecord extractRecord(Message msg)

    Transforms JMS message to data record. null indicates that the message is not accepted by the processor.

  • String getErrorMsg()

    Returns error message.

Examples

Read Text Message from Message Queue

There is a message queue clover-queue accessible at localhost:61616. Read 5 records from the queue.

Solution

Create a JMS connection MyJMSConnection:

PropertyValue
NameMyJMSConnection
Librariese.g. C:/opt/apache-activemq-5.12.0/activemq-all-5.12.0.jar
Initial ctx factory classorg.apache.activemq.jndi.ActiveMQInitialContextFactory
URLtcp://localhost:61616
Connection factory JNDI nameQueueConnectionFactory
Destination JNDIdynamicQueues/clover-queue
User nameActiveMQ_user_name
PasswordActiveMQ_password

User name and Password are credentials for reading messages from message queue. E.g. Apache ActiveMQ has default values admin:admin.

The activemq-all-5.12.0.jar file is a JMS provider. The library file must be available on your file system and accessible to CloverETL. You can use another message provider.

Configure JMSReader component. Use the above mentioned connection in the component configuration.

AttributeValue
JMS ConnectionMyJMSConnection
Max msg count5
Message body fielde.g. field1

Best Practices

We recommend users to explicitly specify the Message charset attribute.

If the transformation is specified in an external file (with Processor URL), Processor source charset should be specified too.

See also

JMSWriter
JMS Connections
Common Properties of Components
Specific Attribute Types
Common Properties of Readers
Readers Comparison