Step 2: Create the Siddhi Application

Let's create your first Siddhi application.

For this purpose, you can consider an example where production information is published in a database table. This information needs to be captured as and when it is published in the database, and published in a file after changing the case of the product name.

The following image depicts the procedure to be followed by the Siddhi application you create.

Open the WSO2 Integrator welcome page

1. If you have not already done so, install WSO2 Integrator and switch to the WSO2 Integrator: SI profile (see Step 1: Set up your environment and dependencies).

2. Open WSO2 Integrator. Open the command palette by pressing Ctrl + Shift + P (or Cmd + Shift + P on macOS), type WSO2 Integrator: Open Welcome Page, and select it. The welcome page opens.

   

   Note

   WSO2 Integrator: SI commands appear in the WSO2 Integrator command palette only after WSO2 Integrator: SI activates, which happens when a .siddhi file is open. If typing SI: in the palette returns no results, open or create a .siddhi file first and then reopen the palette.

3. On the welcome page, click Configure in the top right corner, and select WSO2 Integrator: SI under Select your Integration Profile (if you have not already done so).

4. Create a new project. A new .siddhi file opens for you to work in.

   

Prefer to build visually?

Siddhi applications can also be designed visually in the Graphical View by dragging and dropping flow constructs. For a worked example, see Build a Siddhi Application with the Graphical View.

Name the Siddhi application

Specify a name for the new Siddhi application via the @App:name annotation:

@App:name("SweetFactoryApp")

Define the input stream and attach the CDC source

1. Define the stream that receives the input data:

   define stream InsertSweetProductionStream (name string,amount double);
   

2. Prepend a @source annotation of type cdc to the stream definition so that inserts from the production database are captured into this stream:

   @source(type='cdc',url = "jdbc:mysql://localhost:3306/production",username = "wso2si",password = "wso2",table.name = "SweetProductionTable",operation = "insert",
       @map(type='keyvalue'))
   

   The complete stream definition now looks like:

   @source(type='cdc',url = "jdbc:mysql://localhost:3306/production",username = "wso2si",password = "wso2",table.name = "SweetProductionTable",operation = "insert",
       @map(type='keyvalue'))
   define stream InsertSweetProductionStream (name string,amount double);
   

Define the output stream and attach the file sink

1. Define an output stream for the captured data:

   define stream ProductionUpdatesStream (name string,amount double);
   

2. Prepend a @sink annotation of type file so the events are published to <YOUR_HOME>/productioninserts.csv in CSV format:

   @sink(type='file',file.uri = "<YOUR_HOME>/productioninserts.csv",
       @map(type='csv'))
   

   The complete stream definition now looks like:

   @sink(type='file',file.uri = "<YOUR_HOME>/productioninserts.csv",
       @map(type='csv'))
   define stream ProductionUpdatesStream (name string,amount double);
   

Add the processing query

Write a query that reads from the input stream, converts the product name from lower case to upper case, and inserts the converted events into the output stream:

@info(name='query1')
from InsertSweetProductionStream
select str:upper(name) as name, amount
group by name
insert  into ProductionUpdatesStream;

This query gets the information inserted into the production database table from the InsertSweetProductionStream stream. The str:upper() function included in the select clause converts the product name from lower case to upper case. Once this conversion is done, the converted events are directed to the ProductionUpdatesStream stream. These events are written into the <YOUR_HOME>/productioninserts.csv file because it is configured via the @sink annotation you previously attached to the ProductionUpdatesStream stream.

Save the Siddhi application

Save your changes.

The completed Siddhi application looks as follows:

@App:name('SweetFactoryApp')

@source(type='cdc',url = "jdbc:mysql://localhost:3306/production",username = "wso2si",password = "wso2",table.name = "SweetProductionTable",operation = "insert",
    @map(type='keyvalue'))
define stream InsertSweetProductionStream (name string,amount double);

@sink(type='file',file.uri = "<YOUR_HOME>/productioninserts.csv",
    @map(type='csv'))
define stream ProductionUpdatesStream (name string,amount double);

@info(name='query1')
from InsertSweetProductionStream
select str:upper(name) as name, amount
group by name
insert  into ProductionUpdatesStream;

Installing the required extensions

WSO2 Integrator: SI is shipped with most of the available Siddhi extensions by default. If a Siddhi extension you require is not shipped by default, you can download and install it via the Extension Installer panel. The SweetFactoryApp Siddhi application you created uses a source of the cdc type. The cdc-mysql extension that is required for this source is not shipped with WSO2 Integrator: SI by default. Therefore, let's install it as follows.

1. In WSO2 Integrator, open the command palette by pressing Ctrl + Shift + P (or Cmd + Shift + P on macOS) and type SI: Extension Installer. Then select the SI: Extension Installer option.

   

   Click Install for Change Data Capture - MySQL.

2. Reload WSO2 Integrator.

Alternative: install from the terminal

You can also install Siddhi extensions on the SI runtime directly from the terminal — useful for production setups that don't use WSO2 Integrator. From the <SI_HOME>/bin directory, run ./extension-installer.sh install cdc-mysql (on Linux/macOS) or extension-installer.bat install cdc-mysql (on Windows). When the installation completes, restart the SI server.

Testing the Siddhi application

To verify that the Siddhi queries you wrote work as expected, you can simulate events via the Event Simulator in WSO2 Integrator: SI before connecting the application to real database events. To do so, follow the steps below:

Note

MySQL must be running before you start the test. The cdc source opens its connection to MySQL on application startup, so the application will fail to deploy if MySQL is not reachable — even though you are using the Event Simulator instead of inserting real records.

1. In WSO2 Integrator: SI, click the Run button. The application is deployed to the SI runtime, and the Event Simulator panel opens on the left.

   

   

2. Enter Information in the Single Simulation panel as described below.

   

   1. In the Siddhi App Name field, select SweetFactoryApp.

   2. In the Stream Name field, select InsertSweetProductionStream.

   3. Under Attributes, enter values as follows:

      Attribute	Value
      name (STRING)	gingerbread
      amount (DOUBLE)	100

3. Click Start and Send.

4. Open the <YOUR_HOME>/productioninserts.csv. It should contain the following row.

   GINGERBREAD,100.0

What's Next?

Now you can deploy the SweetFactoryApp Siddhi application you created. To do this, proceed to Step 3: Deploy the Siddhi Application.

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Last update: May 14, 2026