Gateways and Streamers - Streamer

This page shows you how to create a Streamer.

Creating a Streamer

To create a Streamer:

1. Add the process configuration for the Streamer to the applicationName-processes.xml file. For example:

<process name="POSITION_APP_STREAMER">
    <start>true</start>
    <options>-Xmx128m -DXSD_VALIDATE=false</options>
    <module>genesis-pal-streamer</module>
    <package>global.genesis.streamer.pal</package>
    <script>position_app-streamer.kts</script>
	<language>pal</language>
</process>

For more information on the above process tags, see the page on configuring runtime processes.

2. Create a Kotlin script file named app-name-streamer.kts under jvm/app-name-script-config. Add the following information:
   • A stream name
   • A GPAL index reference for a unique index with a single LONG field, this could refer to a table index or a view index.

The simplest Streamer definition is:

streams {
    stream("ORDERS_OUT", ORDER_OUT.BY_TIMESTAMP)
}

This example creates a stream called ORDERS_OUT, based on the ORDER_OUT table (or view). The data will be streamed, ordered by timestamp.

Parameters

You can also specify the following optional parameters in a stream block:

• batchSize - default value 100

• logoffTimeout - default value 5000

• maxLogons - default value 1

Transforming the stream

You can define the following blocks to transform the stream:

• where
• fields
• toGenesisSet

Where

The where tag enables the stream to be filtered. It is available in two versions: one that has the streamed row as a parameter, and one that also has the logon message.

Here, we only stream orders with a quantity greater than 1,000.

streams {
    stream("ORDERS_OUT", ORDER_OUT.BY_TIMESTAMP) {
        where { ordersOut ->
            ordersOut.quantity > 1_000
        }
    }
}

In this example, we only stream orders with a quantity greater than 1,000 and where the logon message has provided a secret key.

streams {
    stream("ORDERS_OUT", ORDER_OUT.BY_TIMESTAMP) {
        where { ordersOut, logonMessage ->
            ordersOut.quanity > 1_000 && logonMessage.getString("KEY") == "SECRET"
        }
    }
}

Fields

The fields tag enables you to transform the output in a similar way to views, data server and req rep definitions. For example, here we output three fields:

streams {
    stream("ORDERS_OUT", ORDER_OUT.BY_TIMESTAMP) {
        fields {
            ORDERS_OUT.CLIENT_ID
            ORDERS_OUT.QUANTITY withPrefix "ORDER"
            ORDERS_OUT.CLIENT_ID withAlias "CLIENT"
        }
    }
}

toGenesisSet

The toGenesisSet tag enables you to create a custom GenesisSet from the entity:

streams {
    stream("ORDERS_OUT", ORDER_OUT.BY_TIMESTAMP) {
        toGenesisSet { ordersOut ->
            genesisSet {
                "ORDER_QUANTITY" with ordersOut.quantity
                "ORDER" with ordersOut.orderId
            }
        }
    }
}

Metrics

You can find details of how to use metrics with Streamer in our pages on metrics.