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Esper Socket Adapter


21 January 2014

The Socket Adapter

This article discusses the EsperIO Socket adapter.
The EsperIO Socket input adapter can be used to send events into an Esper engine instance via socket client, either as Java objects or as CSV name-value pair strings.

Getting Started

You may configure the EsperIO Socket adapter either as part of your Esper configuration file in the plugin loader section or via the adapter API. Add the esperio-socket-version.jar file to your classpath. There are no other dependent jar files required.

A sample adapter configuration file is provided in esperio-socket-sample-config.xml in the etc folder of the distribution. A configuration file must be valid according to schema esperio-socket-configuration-4-0.xsd.

Plugin Loader Configuration

You may place the configuration XML directly into your Esper configuration file as the example below shows.

  <plugin-loader name="EsperIOSocketAdapter" 
	    <socket name="mysocketOne" port="7101" data="object"/>
	    <socket name="mysocketTwo" port="7102" data="csv"/>

Alternatively you can provide a URL in the Esper configuration file to point to your adapter configuration file.

  <plugin-loader name="EsperIOSocketAdapter" 
      <init-arg name="esperio.socket.configuration.file" 
          value="file:/path/esperio-socket-sample-config.xml" />

Configuration and Starting via API

If using Spring or if your application requires API access, the following code snippet configures and starts the adapter via API.

The class for configuring an EsperIO Socket adapter is com.espertech.esperio.socket.config.ConfigurationSocketAdapter. The adapter class itself is EsperIOSocketAdapter.

The code snippet below is a sample that configures using driver manager and starts the adapter via API.

ConfigurationSocketAdapter adapterConfig = new ConfigurationSocketAdapter();

SocketConfig socket = new SocketConfig();
adapterConfig.getSockets().put("SocketService", socket);

// start adapter
EsperIOSocketAdapter socketAdapter = new EsperIOSocketAdapter(adapterConfig, "engineURI");

// destroy the adapter when done

Socket Service

Add a socket configuration for each unique port that you want to expose a socket receive service for use by socket client connections.

The synopsis is as follows.

  <socket name="[name]" port="[port]" data="[csv|object]"/>

The required name attribute provides the name of the socket service for use in logging.

The required port attribute provides the port that the socket service accepts client connections.

The required data attribute specifies whether the data arriving through the socket is formatted as a Java binary object stream or as CSV string values.

If configuring via the adapter API or Spring, use the com.espertech.esperio.socket.config.SocketConfig class.

Object Data Format

When sending events as Java objects, configure the data attribute value to object and use ObjectOutputStream to write events to the client socket. When sending a java.util.Map event, your Map must contain a String value for the key stream which must denote a configured Map event type.

This example XML configures a socket accepting client connections that provide Java objects.

  <socket name="objectStreamSocket" port="8079" data="object"/>

When object data type is configured, clients connections are expected to send or objects using ObjectOutputStream.

Below is a block of sample code that for use in clients to the adapter. It assumes the MyEvent class implements either of the above interfaces.

// connect first
Socket requestSocket = new Socket("localhost", port);
ObjectOutputStream out = new ObjectOutputStream(requestSocket.getOutputStream());

// send a few events, here we send only one
out.writeObject(new MyEvent("Hello World"));

// close when done

String CSV Data Format

When sending events as CSV strings, the format of the string should be

stream=[type],[name]=[value] [,...] (newline)

The CSV string must end with a newline character: Each event is one line. Each CSV element must be in the [name]=[value] format. Your CSV must contain a value for stream which must denote a configured event type. The adapter parses each string value and populates an instance of the target type.

This next example XML configures a socket accepting client connections that provide events as CSV-formatted strings with name-value pairs :

  <socket name="csvStreamSocket" port="8079" data="csv"/>

A piece of client code that sends an event of type MyEvent may look as follows:

// connect first
String newline = System.getProperty("line.separator");
Socket requestSocket = new Socket("localhost", port);
BufferedWriter wr = new BufferedWriter(
    new OutputStreamWriter(socket.getOutputStream()));

// send a few events

// close when done

Note that if your target type is a Java object event, your event class must provide setter-methods according to JavaBean conventions. The event class should also provide a default constructor taking no parameters. If your event class does not have a default constructor, your application may configure a factory method via ConfigurationEventTypeLegacy.


[1] EsperIO Adapters, EsperIO Reference Documentation 4.0.0, 2009.

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