# Create a Java-based Transformer Service blade

Here we explain how to create a simple Service blade for Transformer, where the blade is written as a Transformer modulein the Java programming language. The core of Transformer is written in C, so to create a module in Java, you use Transformer’s Java Module API.

 If you’ve already read How Can I…​ Create a Lua-based Transformer Service blade, you’ll notice that the Lua blade described there does exactly the same thing as the blade we create here. This is entirely deliberate, and should allow you to see the differences and similarities between using Java and Lua for creating Transformer Service blades.

## Before you start

This example shows how to create a Java-based Service blade called SpreadJavaBlade that calculates the spread between Bid and Ask prices. At run time, the Transformer receives the prices from a Pricing Adapter (an Integration Adapter), and passes them on to the SpreadJavaBlade Transformer module, which calculates the price spread from the Bid and Ask prices. The Transformer sends the prices, including the new `spread` field, on to a Liberator, which forwards them to subscribing client applications, as shown in this diagram:

You’ll need a Transformer and Liberator to help test your Service blade while you develop it, and a Pricing Adapter that can supply the Bid and Ask prices. In this example we’ve assumed that the corresponding record fields are called `bidPrice` and `askPrice` respectively.

If you don’t have Transformer and Liberator already deployed on a machine for this purpose, you’ll need to deploy one or both of these components to the Deployment Framework on your development machine. To do this, follow the instructions in How can I…​ Deploy Platform components to the Framework. You won’t need to set up HTTPS connections or KeyMaster while you’re developing the blade, so you can ignore the topics about those things.

If you need to develop a suitable Pricing Adapter first, see How can I…​ Create a Java-based Adapter blade.

### Blade structure

What’s in a Java Service blade? Assuming the blade is located in in the Deployment Framework at <Framework-root>/kits/<blade_name>/<blade_name>/, relative to this path:

• the blade type and blade compatibility information are in the control file

• the blade’s field definitions are in blade_config/fields.conf

• Liberator related configuration for the blade is in Liberator/etc/rttpd.conf

• Transformer related configuration for the blade is in Transformer/etc/java.conf and Transformer/etc/spreadjava.conf

• the Transformer module’s Java JAR file compiled from the Java source file is in Transformer/lib/java

## Overview

In brief, you create the blade using the following steps, which are given in more detail further down the page:

## Create the blade’s directory structure

In a directory that’s outside the Deployment Framework (say Temp_Java_blade), create the following directory structure:

At this stage, you don’t need to create the control file and the .conf and .jar files that are also shown in the structure - you’ll do that in subsequent steps.

## Define the new fields

The blade must define any new fields that it will use, which in this instance means our new `Spread` field.

1. Create a text file called fields.conf in Temp_Java_blade/SpreadJavaBlade/blade_config/

2. Using a suitable text editor, add the following configuration to fields.conf

```#
# Field definitions for the Transformer SpreadJavaBlade
#
add-field Spread 45036```
 You don’t have to use the field number we’ve shown here; you can choose your own value as long as it’s unique within your particular Caplin Platform installation.

You don’t have to list in the fields.conf file all the fields belonging to the incoming records that the blade will receive, because they’re already defined in the Pricing Adapter’s fields.conf file. For example, The `BidPrice` and `AskPrice` fields used in the code samples further down this page would have been defined there. When you deploy your new SpreadJavaBlade blade, the Deployment Framework will make the Pricing Adapter’s field definitions available to it (since the Pricing Adapter will also have been deployed as a blade).

For more about defining fields, see Field definitions in the DataSource Features and Concepts, and Field definition format.

## Include configuration for Liberator and Transformer

The new blade has to include configuration for the core Platform components that it interacts with. In this case, the core components are: Liberator, which will subscribe to data supplied by the Transformer module, and Transformer, which houses the module.

### Define additional Liberator configuration

Configuration details for the Liberator are stored in the rttpd.conf file

1. Create a text file called rttpd.conf in Temp_Java_blade/SpreadLuaBlade/Liberator/etc/

2. Using a suitable text editor, add the following configuration to rttpd.conf

```#
# Liberator configuration for data from
# the SpreadJavaBlade Java-based Transformer Service blade.
#
add-data-service
service-name SpreadJavaBlade${THIS_LEG} include-pattern ^/FX/ add-source-group required true add-priority remote-label transformer${THIS_LEG}
end-priority
if "${FAILOVER}" == "ENABLED" add-priority remote-label transformer${OTHER_LEG}
end-priority
endif
end-source-group
end-data-service```

This configuration defines a data service through which the Liberator requests the data supplied by the SpreadJavaBlade. It also defines, through the `add-source-group …​ end-source-group` block, how the Liberator should fail the data service over to an alternate Liberator (this only applies if failover has been enabled for the deployment - see How can I…​ Set up server failover capability).

This is fairly standard configuration. The important points to note are:

• The `service-name` configuration item defines the name of the data service, which in this case is (by convention) the name of the blade, SpreadJavaBlade, that supplies the data.

• The `include-pattern` item specifies that the data service is to supply data for all subscriptions whose subjects start with the string `/FX/`

• The macros `THIS_LEG` and `OTHER_LEG` are used to differentiate the configuration of primary and secondary failover legs.

### Define the Java module configuration in Transformer

Configuring Transformer for a Java module is a bit more involved than doing so for a Lua module, as the Transformer has to know the location of the Java Virtual Machine (JVM) in order to start it.

1. Create a java.conf file in Temp_Java_blade/SpreadJavaBlade/Transformer/etc/

2. Using a suitable text editor, add the following configuration to java.conf

```#
# Java module configuration for the
# SpreadJavaBlade Java-based Transformer Service blade.
#
jvm-location       "${JVM_LOCATION}" jvm-global-classpath %r/lib/java/transformermodule.jar modules-dir${ccd}/../lib
add-module SpreadJavaBlade

add-javaclass
class-name example.spreadmodule.SpreadModule
class-id   SpreadJavaBlade
classpath  "${ccd}/../lib/java/SpreadModule.jar" end-javaclass``` The important points to note about this configuration are: `jvm-location` defines the path of the JVM. It refers to the master definition through the macro `JVM_LOCATION`, which is defined in <Framework-root>/global_config/environment-defaults.conf `jvm-global-classpath` defines the classpath of the Java library underlying Transformer’s Java Module API. ** `modules-dir` defines the directory path to the java directory, which contains the Java module’s JAR file. + NOTE: The `ccd` macro in the path name defines the current directory path of the file in which it is referenced. So in this example, because the `ccd` reference is in the file SpreadLuaBlade/Transformer/etc/java.conf, the macro defines the path SpreadLuaBlade/Transformer/etc/ The directory path for the Java Module is therefore SpreadLuaBlade/Transformer/lib • `add-module` defines an identifier for the Transformer Java module. This must be the blade name, so in this example it’s `SpreadJavaBlade`. • `add-javaclass` defines: • The fully qualified name of the Java class that implements the Java module (`class-name example.spreadmodule.SpreadModule`). • `class-id` — a short identifier of the Java class. For blade implementations this must be the blade name, so in this example it’s set to `SpreadJavaBlade`. • The classpath on which the module’s JAR file can be found (`classpath "${ccd}/../lib/java/SpreadModule.jar"`). You generate the JAR from the SpreadModule.java file where the Java source code for the module resides.

3. Create a configuration file spreadjava.conf in Temp_Java_blade/SpreadJavaBlade/Transformer/etc/ and add the following lines:

```include-file ${ENV:CONFIG_BASE}bootstrap.conf module-logfile spreadjava.log module-classid spreadjava include-file${BASE}/global_config/overrides/SpreadJavaBlade/Transformer/etc/spreadjava.conf```
• `include-file \${ENV:CONFIG_BASE}bootstrap.conf` allows access to some common definitions that the blade requires.

• `module-logfile` specifies the name of the log file in Transformer/var that the spreadjava module writes errror and information messages to at run time.

• `module-classid` specifies the class ID of the Java Module. This must match the `class-id` defined in java.conf.

• The final `include-file` item allows you to override the blade’s standard configuration after it has been deployed, by putting a different spreadjava.conf configuration file in the Deployment Framework’s overrides directory for the blade.

## Add the blade control file

The Deployment Framework needs to take some specific actions to allow a Java Transformer module blade to work correctly. So the Framework needs to have a way of knowing the blade is a Java Transformer module. This is done through a blade control file located in the root directory of the blade.

1. Create a text file called control in Temp_Java_blade/SpreadJavaBlade/

This is the blade control file

2. Add the following single line to the blade control file:

`Type: JTMBlade`
3. You would normally also record any blade compatibility information in the control file as well (for details, see the Reference information about the blade control file), but for this simple example there’s nothing to record.

That’s all the configuration changes you need for the time being.

## Deploy configuration to the Deployment Framework

Now you’ve created the initial configuration for the core components that use your Transformer Service blade, you can deploy this configuration in your development environment.

1. ZIP up the blade directory structure in your temporary work area into a skeleton blade kit. The .zip file must have a name of the form <blade_name>-<version_number>.zip

The topmost directory in the .zip file must be the top level directory of the blade.

So, in our example the .zip filename is SpreadJavaBlade-<version_number>.zip (say SpreadJavaBlade-000001.zip), and the topmost directory in the .zip file is SpreadJavaBlade.

2. Navigate to <Framework-root> and deploy the skeleton blade kit:

`./dfw deploy ../Temp_Java_blade/SpreadJavaBlade-000001.zip`

The `./dfw deploy` command should respond with:

```Boot-strapping the Deployment Framework

Unpacking SpreadJavaBlade kit SpreadJavaBlade-000001.zip
SpreadJavaBlade-000001.zip successfully unpacked and stored in kits/archive

Activating SpreadJavaBlade

Blades ok```

And then `./dfw versions` should show the new blade:

```Deployment Framework           6.0.4-267113

Core components                Version
-----------------------------------------------------------
Liberator                      6.1.0-275608
Transformer                    6.1.0-275716

Deployed blades                Version            State
-----------------------------------------------------------
PricingAdapter                 2013.09.27.1138    Active
SpreadJavalade                                    Active

Built-in blades                                   State
-----------------------------------------------------------
BlotterExport                                     Inactive
DemoDataSource                                    Inactive
DirectConnection                                  Active
HTTP                                              Active
HTTPS                                             Inactive
JavaOpenPermissioning                             Inactive
LiberatorJMX                                      Active
LiberatorWebsite                                  Active
MinimalLiberatorWebsite                           Inactive
OpenPermissioning                                 Active
ServerIdentification                              Active
TransformerJMX                                    Active```

Note that deploying the skeleton SpreadJavaBlade has automatically put it in the active state.

3. Start the deployed core components and the SpreadJavaBlade blade:

`./dfw start`

At this stage, the Liberator and Transformer are running with the new configuration. The new blade won’t run of course, because no executable code has been written for the Java module.

In a Web browser, navigate to the Liberator’s status page, where you should see the SpreadJavaBlade data service:

 The URL of the Liberator is of the form http://:. You can find the and by entering the command `./dfw info`. In a development enviroment, the URL would typically be http://localhost:18080. When the Liberator home page is displayed, select the View Status button.

## Write the Java module

This is the functional part of the Java module that defines the actions you need it to perform. In this example, the Java source is in a single file called SpreadModule.java. Create this file in a suitable place within your development environment.

The example code is quite long, so we’ll break it up into sections in order to explain it. It uses Transformer’s Java Module API.

Section 1:

``````package example.spreadmodule;

import com.caplin.transformer.module.*;

public class SpreadModule  implements TransformerModule, SubscriptionListener
{
private int bidFieldNumber;
private int askFieldNumber;
private int spreadFieldNumber;

@Override
public void initialise(String moduleName, TransformerAccessor transformerAccessor)
{
bidFieldNumber = transformerAccessor.getFieldManager().getFieldByName("BidPrice").getNumber();
askFieldNumber = transformerAccessor.getFieldManager().getFieldByName("AskPrice").getNumber();
spreadFieldNumber = transformerAccessor.getFieldManager().getFieldByName("Spread").getNumber();

transformerAccessor.getSubscriber().addSubscriptionListener("/FX/*", this);
}``````

This first section identifies defines the `SpreadModule` class which implements the `TransformerModule` and `SubscriptionListener` interfaces of the Transformer Java Module API. It defines three integers to contain the numbers of the relevant record fields, and, in the `initialise()` method, populates these integers using the `getFieldByName()` method. `initialise()` also creates a subscription listener, to listen for messages from the Pricing Adapter that have subjects in the "/FX/" namespace.

Section 2:

``````@Override
public void setFileReading(boolean b) {
}

@Override
public void shutdown() {
}

@Override
public String getLoggerName() {
return "example.spreadmodule.SpreadModule";
}

@Override
public void objectDeleted(String objectName) {
}

@Override
public void status(String objectName, ObjectStatus objectStatus) {
}``````

The above method implementations just define the default settings for some methods of the `TransformerModule` and `SubscriptionListener` interfaces.

Section 3:

``````@Override
public void update(DataSourceUpdateEvent dataSourceUpdateEvent) {
String bidValue =
dataSourceUpdateEvent.getTransformerData().getFieldByFieldNumber(bidFieldNumber).getValue();
String askValue =
dataSourceUpdateEvent.getTransformerData().getFieldByFieldNumber(askFieldNumber).getValue();``````

This implementation of the `SubscriptionListener` interface’s `update()` method obtains the `AskPrice` and `BidPrice` field values from an incoming record message with a subject that begins with "/FX/". It uses the field numbers obtained when the module was initialised (see section 1 of the example).

Section 4:

```if ( askValue != null && bidValue != null ) {
double spreadValue =
Double.parseDouble(askValue) - Double.parseDouble(bidValue);
dataSourceUpdateEvent.getTransformerData().addData(spreadFieldNumber, spreadValue);
}
}
}```

Having retrieved the `AskPrice` and `BidPrice` field values, the subscription listener’s `update()` method checks that neither of them are null, calculates `spreadValue`, by subtracting one value from the other, and uses the `addData()` method to add this calculated spread value to the `Spread` field that was defined earlier.

When you’ve completed the code in the SpreadModule.java file, follow the steps below:

1. Compile the file and package it as a JAR file (SpreadModule.jar).

 Ensure that the JAR containing the Transformer’s Java Module API is in the compilation classpath. This JAR is called transformermodule.jar and it’s located in the lib/java directory of the deployed Transformer in the Deployment Framework.
2. Put the JAR in the directory <Framework-root>/kits/SpreadJavaBlade/SpreadJavaBlade/Transformer/lib/java/

## Start the new Transformer Service blade

Follow the steps below:

1. Follow one of the steps below to restart components on the Deployment Framework:

• If you have exclusive use of the Deployment Framework, run the command below to restart all components on the Deployment Framework:

`./dfw start`
• If you don’t have exclusive access to the Deployment Framework, run the command below to restart just Liberator and Transformer:

`./dfw start Liberator Transformer`
2. Look at the Liberator’s status page to check that the Liberator is connected to the Transformer and can see the data service (`SpreadJavaBlade` in our example) for which the new Java-based Transformer Service blade supplies data.

3. Use the Liberator’s Liberator Explorer to request data for the relevant subjects supplied by the Transformer Service blade, and check that the data is returned (via Transformer) as expected, with a correctly calculated `Spread` field included.

## Package the new blade

When you’ve developed and tested the new blade to your satisfaction, you’ll need to package it up so it can be deployed on your production system - see How can I…​ Package a custom blade.

See also: