Further Readings on Custom Adapters

This is done in the custom transporter module. SAP documentation regarding the process can be found in section Enabling Guaranteed Delivery for an Input Transporter.

1. Add the following two commands to your .cnxml file:

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   <Internal id="x_unixCmdDisc"
     label="Discovery Command"
     type="string"
     default="&quot;$STREAMING_HOME/adapters/framework/bin/discover.sh&quot;
     &quot;$STREAMING_HOME/adapters/framework/instances/mqtt_input/adapter_config.xml&quot;"/>
   <Internal id="x_winCmdDisc"
     label="Discovery Command"
     type="string"
     default="&quot;%STREAMING_HOME%/adapters/framework/bin/discover.bat&quot;
     &quot;%STREAMING_HOME%/adapters/framework/instances/mqtt_input/adapter_con fig.xml&quot;"/>

2. Implement sampling or non-sampling schema discovery in your custom transporter module. Consult section Implementing Schema Discovery in a Custom Adapter for more details.

For the question below, select the correct answer, and click Validate.

If you have followed this tutorial to create an input adapter, only minor changes will have to be applied to convert it into an output adapter.

1. EspConnector

   • You will need to choose either EspSubscriber or EspMultiStreamSubscriber instead of the EspPublisher we have used.

   • To make this change, edit the <Module type="espconnector"> element of your .cnxml file. Specifically, specify the chosen EspSubscriber in the <InstanceName> element

2. Formatter module

   The convert(AdapterRow in) method will need to be edited to convert Streaming Analytics objects to Strings. You can change it to something along the lines of the following:

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   Object obj = in.getData(0);
   in.setData(0, obj.toString());
   return in;

3. Transporter module

   Instead of the following in execute():

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   AdapterRow row = utility.createRow(msg);
   utility.sendRow(row);

   You will need something along the lines of the following:

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   AepRecord record = (AepRecord)row.getData(0);
   if(record != null) {
       String value = record.getValues().toString();
       myDataSink.send(value);
   }

   Where myDataSink is the object you are outputting your data to.

4. Mqtt_input.cnxml

   • Particularly the type attribute for the Adapter element should be changed to “output”

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     <Adapter type="output" …>

   • You may consider find > replace all from input to output. This will require changing the mqtt_input folder name in %STREAMING_HOME%/adapters/framework/instances/mqtt_input

   • Consider changing the name of this file to mqtt_output.cnxml

5. Adapter_config.xml, modulesdefine.xml, parametersdefine.xsd

   You may consider changing “Input” to “Output” in names

   • <MQTTInputTransporterParameters>

   • <Name>MQTT Input</Name>

6. Mqtt.ccl

   This project assumes the adapter is an input adapter, you will need to make a new project. However, doing so is outside the scope of this tutorial.

1. Transporter

   Change Execute() function according to following:

   • For input stream based transporters:

     • Create a ByteBuffer object and load data into it by calling <ByteBuffer>.put<Type>(data)

     • Call utility.sendRowsBuffer()

   • For output stream based transporters:

     • Call utility.getRowsBuffer() which will return a ByteBuffer object.

     • Call ByteBuffer.get<Type>() to get data from the object.

Full ByteBuffer documentation can be found at ByteBuffer

Documentation regarding custom Transporter modules can be found in section Building a Custom Transporter Module.

2. Formatter

- Have your custom formatter class extend `com.sybase.esp.adapter.framework.module.StreamingFormatter`

- Implement the following functions:

  - The `init()` function.

    Prepare your formatter module to convert between data formats; for example, obtain properties from the adapter configuration file and perform any required initialization tasks.

  - The `start()` function.

    Perform any necessary tasks when the adapter is started.

- The `execute()` function.

    Here is an example of the execute() function for a formatter that converts row-based data into stream-based:

    ```java

    public void execute() throws Exception {
      OutputStream output = utility.getOutputStream();  while(!utility.isStopRequested())  {
        AdapterRow row = utility.getRow();
        if(row != null) {
          AepRecord record = (AepRecord)row.getData(0);
          String str = record.getValues().toString() + "\n";   output.write(str.getBytes());
        }
      }
    }

    ```

- For a formatter that converts from stream-based data into row-based, use:

    - `utility.getInputStream()` to obtain the `InputStream`

    - `utility.createRow()` to create the `AdapterRow` objects

    - `utility.sendRow()` to send the rows to the next module specified in the adapter configuration file

- The `stop()` function

    Perform any necessary tasks when the adapter is stopped.

- The `destroy()` function.

    Perform clean-up actions for your formatter.

Documentation regarding custom Formatter modules can be found in section Building a Custom Formatter Module.

See the $STREAMING_HOME/adapters/framework/examples/src directory for source code for sample modules

If your transporter or formatter modules don’t require very complex implementation, they may already be provided with your Streaming Analytics installation.

You can find a listing of the predefined Formatter modules in section Formatters Currently Available from SAP as well as their location.

You can find a listing of the predefined Transporter modules in section Transporters Currently Available from SAP as well as their location.

1. Comment out the ATTACH INPUT ADAPTER statement in the ccl code provided in the Appendix of this tutorial. The ccl should simply be as follows:

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   CREATE INPUT WINDOW InputWindow1 SCHEMA (
     Message string ) PRIMARY KEY ( Message ) KEEP ALL ROWS ;

2. Uncomment the <ProjectName> and <StreamName> elements in <EspPublisherParameters>

3. Start the project in Studio by pressing the deploy button.

![Deploy Streaming Project](https://raw.githubusercontent.com/sap-tutorials/Tutorials/master/tutorials/hsa-java-toolkit-adapter-part7/deploy-project.png)

4. Start the adapter by running start.sh and pass it the full path to your adapter_config.xml.

`%STREAMING_HOME%\adapters\framework\bin\start.bat`
`%STREAMING_HOME%\adapters\framework\instances\mqtt_input\adapter_config.xml`

5. The adapter will use the <EspProject> element properties set in your adapter_config.xml file to connect to the project in studio and will use the <MQTTInputTransporterParameters> element properties as arguments.

There are two main ways to debug custom adapters:

1. The first is to use the Eclipse debugger. Steps for accomplishing this are outlined in this documentation. This debugger can be used to set break points and/or step through code.

2. The second is to simply use print statements.

   • For adapter run using the ATTACH statement

     Use utility.getAdapterLogger().info(String) in your custom Transporter and Formatter modules to log information.

     Streaming Analytics log info can be found using HANA Studio.

     • In the SAP HANA Administration Console perspective, double click your SYSTEM in the Systems panel

     • Navigate to the Diagnosis Files tab.

     • Look for a .out file corresponding to the project you are working on. You can open the file for read in HANA Studio by double clicking it.

     • utility.getAdapterLogger().info() will log messages to <working-directory>\ projects\default.mqtt.0\logs\adapterframework.log.

   • For standalone adapter run without the ATTACH statement

     • utility.getAdapterLogger().info() can also be used

     • utility.getAdapterLogger().info() will log messages to the console in which the adapter start command was issued as well as %STREAMING_HOME%/adapters/framework/bin/frameworkadapter.log

     • System.out.println() messages will also appear in the console.

Click the Done button below once you have completed this tutorial.