czwartek, 3 grudnia 2015

KIE Server: Extend KIE Server client with new capabilities

Last but not least part of KIE Server extensions is about extending KIE Server Client with additional capabilities.

Use case

On top of what was built in second article (adding Mina transport to KIE Server), we need to add KIE Server Client extension that allow to use Mina transport with unified KIE Server Client API.

Before you start create empty maven project (packaging jar) with following dependencies:

<properties>
    <version.org.kie>6.4.0-SNAPSHOT</version.org.kie>
  </properties>

  <dependencies>
    <dependency>
      <groupId>org.kie.server</groupId>
      <artifactId>kie-server-api</artifactId>
      <version>${version.org.kie}</version>
    </dependency>

    <dependency>
      <groupId>org.kie.server</groupId>
      <artifactId>kie-server-client</artifactId>
      <version>${version.org.kie}</version>
    </dependency>
    
    <dependency>
      <groupId>org.drools</groupId>
      <artifactId>drools-compiler</artifactId>
      <version>${version.org.kie}</version>
    </dependency>
  </dependencies>

Design ServicesClient API interface

First thing we need to do is to decide what API we should have to be exposed to the callers of our Client API. Since the Mina extension is an extension on top of Drools one so let's provide same capabilities as RulesServicesClient:

public interface RulesMinaServicesClient extends RuleServicesClient {

}

As you can notice it simply extends the default RulesServiceClient interface and thus provide same capabilities. 

Why we need to have additional interface for it? It's because we are going to register client implementations based on their interface and there can be only one implementation for given interface.

Implement RulesMinaServicesClient

Next step is to actually implement the client and here we are going to prepare a socket based communication for simplicity sake. We could use Apache Mina client API though this would introduce additional dependency which we don't need for sample implementation.

Note that this client implementation is very simple and in many cases can be improved, but the point here is to show how it can be implemented rather than provide bullet proof code.

So few aspects to remember when reviewing the implementation:
  • it relies on default configuration from KIE Server client and thus uses serverUrl as place where to provide host and port of Mina server
  • hardcodes JSON as marshaling format
  • decision if the response is success or failure is based on checking if the received message is a JSON object (start with {) - very simple though works for simple cases
  • uses direct socket communication with blocking api while waiting for first line of the response and then reads up all lines that are available
  • does not use "stream mode" meaning it disconnects from the server after invoking command
Here is the implementation
public class RulesMinaServicesClientImpl implements RulesMinaServicesClient {
    
    private String host;
    private Integer port;
    
    private Marshaller marshaller;
    
    public RulesMinaServicesClientImpl(KieServicesConfiguration configuration, ClassLoader classloader) {
        String[] serverDetails = configuration.getServerUrl().split(":");
        
        this.host = serverDetails[0];
        this.port = Integer.parseInt(serverDetails[1]);
        
        this.marshaller = MarshallerFactory.getMarshaller(configuration.getExtraJaxbClasses(), MarshallingFormat.JSON, classloader);
    }

    public ServiceResponse<String> executeCommands(String id, String payload) {
        
        try {
            String response = sendReceive(id, payload);
            if (response.startsWith("{")) {
                return new ServiceResponse<String>(ResponseType.SUCCESS, null, response);
            } else {
                return new ServiceResponse<String>(ResponseType.FAILURE, response);
            }
        } catch (Exception e) {
            throw new KieServicesException("Unable to send request to KIE Server", e);
        }
    }

    public ServiceResponse<String> executeCommands(String id, Command<?> cmd) {
        try {
            String response = sendReceive(id, marshaller.marshall(cmd));
            if (response.startsWith("{")) {
                return new ServiceResponse<String>(ResponseType.SUCCESS, null, response);
            } else {
                return new ServiceResponse<String>(ResponseType.FAILURE, response);
            }
        } catch (Exception e) {
            throw new KieServicesException("Unable to send request to KIE Server", e);
        }
    }

    protected String sendReceive(String containerId, String content) throws Exception {
        
        // content - flatten the content to be single line
        content = content.replaceAll("\\n", "");
        
        Socket minaSocket = null;
        PrintWriter out = null;
        BufferedReader in = null;

        StringBuffer data = new StringBuffer();
        try {
            minaSocket = new Socket(host, port);
            out = new PrintWriter(minaSocket.getOutputStream(), true);
            in = new BufferedReader(new InputStreamReader(minaSocket.getInputStream()));
        
            // prepare and send data
            out.println(containerId + "|" + content);
            // wait for the first line
            data.append(in.readLine());
            // and then continue as long as it's available
            while (in.ready()) {
                data.append(in.readLine());
            }
            
            return data.toString();
        } finally {
            out.close();
            in.close();
            minaSocket.close();
        }
    }
}

Once we have the client interface and client implementation we need to make it available for KIE Service client to find it.

Implement KieServicesClientBuilder

org.kie.server.client.helper.KieServicesClientBuilder is the glue interface that allows to provide additional client apis to generic KIE Server Client infrastructure. This interface have two methods:
  • getImplementedCapability - which must much the server capability (extension) is going to use
  • build - which is responsible for providing map of client implementations where key is the interface and value fully initialized implementation
Here is a simple implementation of the client builder for this use case

public class MinaClientBuilderImpl implements KieServicesClientBuilder {

    public String getImplementedCapability() {
        return "BRM-Mina";
    }

    public Map<Class<?>, Object> build(KieServicesConfiguration configuration, ClassLoader classLoader) {
        Map<Class<?>, Object> services = new HashMap<Class<?>, Object>();

        services.put(RulesMinaServicesClient.class, new RulesMinaServicesClientImpl(configuration, classLoader));

        return services;
    }

}

Make it discoverable

Same story as for other extensions ... once we have all that needs to be implemented, it's time to make it discoverable so KIE Server Client can find and register this extension on runtime. Since KIE Server  Client is based on Java SE ServiceLoader mechanism we need to add one file into our extension jar file:

META-INF/services/org.kie.server.client.helper.KieServicesClientBuilder

And the content of this file is a single line that represents fully qualified class name of our custom implementation of  KieServicesClientBuilder.


How to use it

The usage scenario does not much differ from regular KIE Server Client use case:
  • create client configuration
  • create client instance
  • get service client by type
  • invoke client methods
Here is implementation that create KIE Server Client for RulesMinaServiceClient

protected RulesMinaServicesClient buildClient() {
    KieServicesConfiguration configuration = KieServicesFactory.newRestConfiguration("localhost:9123", null, null);
    List<String> capabilities = new ArrayList<String>();
    // we need to add explicitly capabilities as the mina client does not respond to get server info requests.
    capabilities.add("BRM-Mina");
    
    configuration.setCapabilities(capabilities);
    configuration.setMarshallingFormat(MarshallingFormat.JSON);
    
    configuration.addJaxbClasses(extraClasses);
    
    KieServicesClient kieServicesClient =  KieServicesFactory.newKieServicesClient(configuration);
    
    RulesMinaServicesClient rulesClient = kieServicesClient.getServicesClient(RulesMinaServicesClient.class);
    
    return rulesClient;
}
And here is how it is used to invoke operations on KIE Server via Mina transport

RulesMinaServicesClient rulesClient = buildClient();

List<Command<?>> commands = new ArrayList<Command<?>>();
BatchExecutionCommand executionCommand = commandsFactory.newBatchExecution(commands, "defaultKieSession");

Person person = new Person();
person.setName("mary");
commands.add(commandsFactory.newInsert(person, "person"));
commands.add(commandsFactory.newFireAllRules("fired"));

ServiceResponse<String> response = rulesClient.executeCommands(containerId, executionCommand);
Assert.assertNotNull(response);

Assert.assertEquals(ResponseType.SUCCESS, response.getType());

String data = response.getResult();

Marshaller marshaller = MarshallerFactory.getMarshaller(extraClasses, MarshallingFormat.JSON, this.getClass().getClassLoader());

ExecutionResultImpl results = marshaller.unmarshall(data, ExecutionResultImpl.class);
Assert.assertNotNull(results);

Object personResult = results.getValue("person");
Assert.assertTrue(personResult instanceof Person);

Assert.assertEquals("mary", ((Person) personResult).getName());
Assert.assertEquals("JBoss Community", ((Person) personResult).getAddress());
Assert.assertEquals(true, ((Person) personResult).isRegistered());

Complete code of this client extension can be found here.

And that's the last extension method to provide more features in KIE Server then given out of the box.

Thanks for reading the entire series of KIE Server extensions and any and all feedback welcome :)

KIE Server: Extend KIE Server with additional transport

There might be some cases where existing transports in KIE Server won't be sufficient, for whatever reason

  • not fast enough
  • difficult to deal with string based data formats (JSON, XML)
  • you name it..so there might be a need to build a custom transport to overcome this limitation.

Use case

Add additional transport to KIE Server that allows to use Drools capabilities. For this example we will use Apache Mina as underlying transport framework and we're going to exchange string based data that will still rely on existing marshaling operations. For simplicity reason we support only JSON format.

Before you start create empty maven project (packaging jar) with following dependencies:

<properties>
    <version.org.kie>6.4.0-SNAPSHOT</version.org.kie>
  </properties>

  <dependencies>
    <dependency>
      <groupId>org.kie</groupId>
      <artifactId>kie-api</artifactId>
      <version>${version.org.kie}</version>
    </dependency>
    <dependency>
      <groupId>org.kie</groupId>
      <artifactId>kie-internal</artifactId>
      <version>${version.org.kie}</version>
    </dependency>

    <dependency>
      <groupId>org.kie.server</groupId>
      <artifactId>kie-server-api</artifactId>
      <version>${version.org.kie}</version>
    </dependency>
    <dependency>
      <groupId>org.kie.server</groupId>
      <artifactId>kie-server-services-common</artifactId>
      <version>${version.org.kie}</version>
    </dependency>
    <dependency>
      <groupId>org.kie.server</groupId>
      <artifactId>kie-server-services-drools</artifactId>
      <version>${version.org.kie}</version>
    </dependency>

    <dependency>
      <groupId>org.drools</groupId>
      <artifactId>drools-core</artifactId>
      <version>${version.org.kie}</version>
    </dependency>
    <dependency>
      <groupId>org.drools</groupId>
      <artifactId>drools-compiler</artifactId>
      <version>${version.org.kie}</version>
    </dependency>
    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-api</artifactId>
      <version>1.7.2</version>
    </dependency>

    <dependency>
      <groupId>org.apache.mina</groupId>
      <artifactId>mina-core</artifactId>
      <version>2.0.9</version>
    </dependency>

  </dependencies>

Implement KieServerExtension

Main part of this implementation is done by implementing org.kie.server.services.api.KieServerExtension which is KIE Server extension main interface. This interface has number of methods which implementation depends on the actual needs:

In our case we don't need to do anything when container is created or disposed as we simply extend the Drools extension and rely on complete setup in that component. For this example we are mostly interested in implementing:
  • init method
  • destroy method
in these two methods we are going to manage life cycle of the Apache Mina server. 
public interface KieServerExtension {

    boolean isActive();

    void init(KieServerImpl kieServer, KieServerRegistry registry);

    void destroy(KieServerImpl kieServer, KieServerRegistry registry);

    void createContainer(String id, KieContainerInstance kieContainerInstance, Map<String, Object> parameters);

    void disposeContainer(String id, KieContainerInstance kieContainerInstance, Map<String, Object> parameters);

    List<Object> getAppComponents(SupportedTransports type);

    <T> T getAppComponents(Class<T> serviceType);

    String getImplementedCapability();

    List<Object> getServices();

    String getExtensionName();

    Integer getStartOrder();
}

Next there are few methods that describe the extension:
  • getImplementedCapability - should instruct what kind of capability is covered by this extension, note that capability should be unique within KIE Server
  • getExtensionName - human readable name of this extension
  • getStartOrder - defined when given extension should be started, important for extensions that have dependencies to other extensions like in this case where it depends on Drools (startup order is set to 0) so our extension should start after drools one - thus set to 20
Remaining methods are left with standard implementation to fulfill interface requirements.

Here is the implementation of the KIE Server extension based on Apache Mina:

public class MinaDroolsKieServerExtension implements KieServerExtension {

    private static final Logger logger = LoggerFactory.getLogger(MinaDroolsKieServerExtension.class);

    public static final String EXTENSION_NAME = "Drools-Mina";

    private static final Boolean disabled = Boolean.parseBoolean(System.getProperty("org.kie.server.drools-mina.ext.disabled", "false"));
    private static final String MINA_HOST = System.getProperty("org.kie.server.drools-mina.ext.port", "localhost");
    private static final int MINA_PORT = Integer.parseInt(System.getProperty("org.kie.server.drools-mina.ext.port", "9123"));
    
    // taken from dependency - Drools extension
    private KieContainerCommandService batchCommandService;
    
    // mina specific 
    private IoAcceptor acceptor;
    
    public boolean isActive() {
        return disabled == false;
    }

    public void init(KieServerImpl kieServer, KieServerRegistry registry) {
        
        KieServerExtension droolsExtension = registry.getServerExtension("Drools");
        if (droolsExtension == null) {
            logger.warn("No Drools extension available, quiting...");
            return;
        }
        
        List<Object> droolsServices = droolsExtension.getServices();
        for( Object object : droolsServices ) {
            // in case given service is null (meaning was not configured) continue with next one
            if (object == null) {
                continue;
            }
            if( KieContainerCommandService.class.isAssignableFrom(object.getClass()) ) {
                batchCommandService = (KieContainerCommandService) object;
                continue;
            } 
        }
        if (batchCommandService != null) {
            acceptor = new NioSocketAcceptor();
            acceptor.getFilterChain().addLast( "codec", new ProtocolCodecFilter( new TextLineCodecFactory( Charset.forName( "UTF-8" ))));
    
            acceptor.setHandler( new TextBasedIoHandlerAdapter(batchCommandService) );
            acceptor.getSessionConfig().setReadBufferSize( 2048 );
            acceptor.getSessionConfig().setIdleTime( IdleStatus.BOTH_IDLE, 10 );
            try {
                acceptor.bind( new InetSocketAddress(MINA_HOST, MINA_PORT) );
                
                logger.info("{} -- Mina server started at {} and port {}", toString(), MINA_HOST, MINA_PORT);
            } catch (IOException e) {
                logger.error("Unable to start Mina acceptor due to {}", e.getMessage(), e);
            }
    
        }
    }

    public void destroy(KieServerImpl kieServer, KieServerRegistry registry) {
        if (acceptor != null) {
            acceptor.dispose();
            acceptor = null;
        }
        logger.info("{} -- Mina server stopped", toString());
    }

    public void createContainer(String id, KieContainerInstance kieContainerInstance, Map<String, Object> parameters) {
        // no op - it's already handled by Drools extension

    }

    public void disposeContainer(String id, KieContainerInstance kieContainerInstance, Map<String, Object> parameters) {
        // no op - it's already handled by Drools extension

    }

    public List<Object> getAppComponents(SupportedTransports type) {
        // nothing for supported transports (REST or JMS)
        return Collections.emptyList();
    }

    public <T> T getAppComponents(Class<T> serviceType) {

        return null;
    }

    public String getImplementedCapability() {
        return "BRM-Mina";
    }

    public List<Object> getServices() {
        return Collections.emptyList();
    }

    public String getExtensionName() { 
        return EXTENSION_NAME;
    }

    public Integer getStartOrder() {
        return 20;
    }

    @Override
    public String toString() {
        return EXTENSION_NAME + " KIE Server extension";
    }
}
As can be noticed main part of implementation is in the init method that is responsible for collecting services from Drools extensions and bootstrapping Apache Mina server.
Worth noticing is the TextBaseIOHandlerAdapter class that is used as handler on Mina server that in essence will react to incoming requests.

Implement Apache Mina handler

Here is the implementation of the handler class that receives text message and executes it on drools service. 

public class TextBasedIoHandlerAdapter extends IoHandlerAdapter {
    
    private static final Logger logger = LoggerFactory.getLogger(TextBasedIoHandlerAdapter.class);

    private KieContainerCommandService batchCommandService;
    
    public TextBasedIoHandlerAdapter(KieContainerCommandService batchCommandService) {
        this.batchCommandService = batchCommandService;
    }

    @Override
    public void messageReceived( IoSession session, Object message ) throws Exception {
        String completeMessage = message.toString();
        logger.debug("Received message '{}'", completeMessage);
        if( completeMessage.trim().equalsIgnoreCase("quit") || completeMessage.trim().equalsIgnoreCase("exit") ) {
            session.close(false);
            return;
        }

        String[] elements = completeMessage.split("\\|");
        logger.debug("Container id {}", elements[0]);
        try {
            ServiceResponse<String> result = batchCommandService.callContainer(elements[0], elements[1], MarshallingFormat.JSON, null);
            
            if (result.getType().equals(ServiceResponse.ResponseType.SUCCESS)) {
                session.write(result.getResult());
                logger.debug("Successful message written with content '{}'", result.getResult());
            } else {
                session.write(result.getMsg());
                logger.debug("Failure message written with content '{}'", result.getMsg()); 
            }
        } catch (Exception e) {
            
        }
    }
}

Few details about the handler implementation:
  • each incoming request is single line, so make sure before submitting anything to it make sure it's single line
  • there is a need to pass container id in this single line so this handler expects following format:
    • containerID|payload
  • response is set the way it is produced by marshaller and that can be multiple lines
  • handlers allows "stream mode" that allows to send commands without disconnecting from KIE Server session. to be able to quit the stream mode - send either exit or quit

Make it discoverable

Same story as for REST extension ... once we have all that needs to be implemented, it's time to make it discoverable so KIE Server can find and register this extension on runtime. Since KIE Server is based on Java SE ServiceLoader mechanism we need to add one file into our extension jar file:

META-INF/services/org.kie.server.services.api.KieServerExtension

And the content of this file is a single line that represents fully qualified class name of our custom implementation of  KieServerExtension.


Last step is to build this project (which will result in jar file) and copy the result into:
 kie-server.war/WEB-INF/lib

Since this extension depends on Apache Mina we need to copy mina-core-2.0.9.jar into  kie-server.war/WEB-INF/lib as well.

Usage example

Clone this repository and build the kie-server-demo project. Once you build it you will be able to deploy it to KIE Server (either directly using KIE Server management REST api) or via KIE workbench controller.

Once deployed and KIE Server started you should find in logs that new KIE Server extension started:
Drools-Mina KIE Server extension -- Mina server started at localhost and port 9123
Drools-Mina KIE Server extension has been successfully registered as server extension

That means we are now interact with our Apache Mina based transport in KIE Server. So let's give it a go... we could write a code to interact with Mina server but to avoid another coding exercise let's use... wait for it .... telnet :)

Start telnet and connect to KIE Server on port 9123:
telnet 127.0.0.1 9123

once connected you can easily interact with alive and kicking KIE Server:
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
demo|{"lookup":"defaultKieSession","commands":[{"insert":{"object":{"org.jbpm.test.Person":{"name":"john","age":25}}}},{"fire-all-rules":""}]}
{
  "results" : [ {
    "key" : "",
    "value" : 1
  } ],
  "facts" : [ ]
}
demo|{"lookup":"defaultKieSession","commands":[{"insert":{"object":{"org.jbpm.test.Person":{"name":"john","age":25}}}},{"fire-all-rules":""}]}
{
  "results" : [ {
    "key" : "",
    "value" : 1
  } ],
  "facts" : [ ]
}
demo|{"lookup":"defaultKieSession","commands":[{"insert":{"object":{"org.jbpm.test.Person":{"name":"maciek","age":25}}}},{"fire-all-rules":""}]}
{
  "results" : [ {
    "key" : "",
    "value" : 1
  } ],
  "facts" : [ ]
}
exit
Connection closed by foreign host.

where:

  • green is request message
  • blue is response
  • orange is exit message


in the server side logs you will see something like this:
16:33:40,206 INFO  [stdout] (NioProcessor-2) Hello john
16:34:03,877 INFO  [stdout] (NioProcessor-2) Hello john
16:34:19,800 INFO  [stdout] (NioProcessor-2) Hello maciek

This illustrated the stream mode where we simply type in commands after command without disconnecting from the KIE Server.

This concludes this exercise and complete code for this can be found here.

KIE Server: Extend existing server capability with extra REST endpoint

First and most likely the most frequently required extension to KIE Server is to extend REST api of already available extension - Drools or jBPM. There are few simple steps that needs to be done to provide extra endpoints in KIE Server.

Our use case

We are going to extend Drools extension with additional endpoint that will do very simple thing - expose single endpoint that will accept list of facts to be inserted and automatically call fire all rules and retrieve all objects from ksession.
Endpoint will be bound to following path:
server/containers/instances/{id}/ksession/{ksessionId}

where:
  • id is container identifier
  • ksessionId is name of the ksession within container to be used

Before you start create empty maven project (packaging jar) with following dependencies:

 
 <properties>
    <version.org.kie>6.4.0-SNAPSHOT</version.org.kie>
  </properties>

  <dependencies>
    <dependency>
      <groupId>org.kie</groupId>
      <artifactId>kie-api</artifactId>
      <version>${version.org.kie}</version>
    </dependency>
    <dependency>
      <groupId>org.kie</groupId>
      <artifactId>kie-internal</artifactId>
      <version>${version.org.kie}</version>
    </dependency>

    <dependency>
      <groupId>org.kie.server</groupId>
      <artifactId>kie-server-api</artifactId>
      <version>${version.org.kie}</version>
    </dependency>
    <dependency>
      <groupId>org.kie.server</groupId>
      <artifactId>kie-server-services-common</artifactId>
      <version>${version.org.kie}</version>
    </dependency>
    <dependency>
      <groupId>org.kie.server</groupId>
      <artifactId>kie-server-services-drools</artifactId>
      <version>${version.org.kie}</version>
    </dependency>
    
    <dependency>
      <groupId>org.kie.server</groupId>
      <artifactId>kie-server-rest-common</artifactId>
      <version>${version.org.kie}</version>
    </dependency>

    <dependency>
      <groupId>org.drools</groupId>
      <artifactId>drools-core</artifactId>
      <version>${version.org.kie}</version>
    </dependency>
    <dependency>
      <groupId>org.drools</groupId>
      <artifactId>drools-compiler</artifactId>
      <version>${version.org.kie}</version>
    </dependency>
    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-api</artifactId>
      <version>1.7.2</version>
    </dependency>

  </dependencies>

Implement KieServerApplicationComponentsService

First step is to implement org.kie.server.services.api.KieServerApplicationComponentsService that is responsible for delivering REST endpoints (aka resources) to the KIE Server infrastructure that will be then deployed on application start. This interface is very simple and has only one method:

Collection<Object> getAppComponents(String extension, 
                                    SupportedTransports type, Object... services)

this method is then invoked by KIE Server when booting up and should return all resources that REST container should deploy.

This method implementation should take into consideration following:

  • it is called by all extensions and thus it provides extension name so custom implementations can decide if this extension is for it or not
  • supported type - either REST or JMS - in our case it will be REST only
  • services - dedicated services to given extensions that can be then used as part of custom extension - usually these are engine services
Here is a sample implementation that uses Drools extension as base (and by that its services)

 
public class CusomtDroolsKieServerApplicationComponentsService implements KieServerApplicationComponentsService {

    private static final String OWNER_EXTENSION = "Drools";
    
    public Collection<Object> getAppComponents(String extension, SupportedTransports type, Object... services) {
        // skip calls from other than owning extension
        if ( !OWNER_EXTENSION.equals(extension) ) {
            return Collections.emptyList();
        }
        
        RulesExecutionService rulesExecutionService = null;
        KieServerRegistry context = null;
       
        for( Object object : services ) { 
            if( RulesExecutionService.class.isAssignableFrom(object.getClass()) ) { 
                rulesExecutionService = (RulesExecutionService) object;
                continue;
            } else if( KieServerRegistry.class.isAssignableFrom(object.getClass()) ) {
                context = (KieServerRegistry) object;
                continue;
            }
        }
        
        List<Object> components = new ArrayList<Object>(1);
        if( SupportedTransports.REST.equals(type) ) {
            components.add(new CustomResource(rulesExecutionService, context));
        }
        
        return components;
    }

}


So what can be seen here is that it only reacts to Drools extension services and others are ignored. Next it will select RulesExecutionService and KieServerRegistry from available services. Last will create new CustomResource (implemented in next step) and returns it as part of the components list.

Implement REST resource

Next step is to implement custom REST resource that will be used by KIE Server to provide additional functionality. Here we do a simple, single method resource that:
  • uses POST http method
  • expects following data to be given:
    • container id as path argument
    • ksession id as path argument
    • list of facts as message payload 
  • supports all KIE Server data formats:
    • XML - JAXB
    • JSON
    • XML - Xstream
It will then unmarshal the payload into actual List<?> and create for each item in the list new InsertCommand. These inserts will be then followed by FireAllRules and GetObject commands. All will be then added as commands of BatchExecutionCommand and used to call rule engine. As simple as that. It is already available on KIE Server out of the box but requires complete setup of BatchExecutionCommand to be done on client side. Not that it's not possible but this extension is tailored one for simple pattern :
insert -> evaluate -> return

Here is how the simple implementation could look like:
 
@Path("server/containers/instances/{id}/ksession")
public class CustomResource {

    private static final Logger logger = LoggerFactory.getLogger(CustomResource.class);
    
    private KieCommands commandsFactory = KieServices.Factory.get().getCommands();

    private RulesExecutionService rulesExecutionService;
    private KieServerRegistry registry;

    public CustomResource() {

    }

    public CustomResource(RulesExecutionService rulesExecutionService, KieServerRegistry registry) {
        this.rulesExecutionService = rulesExecutionService;
        this.registry = registry;
    }
    
    @POST
    @Path("/{ksessionId}")
    @Consumes({MediaType.APPLICATION_XML, MediaType.APPLICATION_JSON})
    @Produces({MediaType.APPLICATION_XML, MediaType.APPLICATION_JSON})
    public Response insertFireReturn(@Context HttpHeaders headers, 
            @PathParam("id") String id, 
            @PathParam("ksessionId") String ksessionId, 
            String cmdPayload) {

        Variant v = getVariant(headers);
        String contentType = getContentType(headers);
        
        MarshallingFormat format = MarshallingFormat.fromType(contentType);
        if (format == null) {
            format = MarshallingFormat.valueOf(contentType);
        }
        try {    
            KieContainerInstance kci = registry.getContainer(id);
            
            Marshaller marshaller = kci.getMarshaller(format);
            
            List<?> listOfFacts = marshaller.unmarshall(cmdPayload, List.class);
            
            List<Command<?>> commands = new ArrayList<Command<?>>();
            BatchExecutionCommand executionCommand = commandsFactory.newBatchExecution(commands, ksessionId);
            
            for (Object fact : listOfFacts) {
                commands.add(commandsFactory.newInsert(fact, fact.toString()));
            }
            commands.add(commandsFactory.newFireAllRules());
            commands.add(commandsFactory.newGetObjects());
                
            ExecutionResults results = rulesExecutionService.call(kci, executionCommand);
                    
            String result = marshaller.marshall(results);
            
            
            logger.debug("Returning OK response with content '{}'", result);
            return createResponse(result, v, Response.Status.OK);
        } catch (Exception e) {
            // in case marshalling failed return the call container response to keep backward compatibility
            String response = "Execution failed with error : " + e.getMessage();
            logger.debug("Returning Failure response with content '{}'", response);
            return createResponse(response, v, Response.Status.INTERNAL_SERVER_ERROR);
        }

    }
}


Make it discoverable

Once we have all that needs to be implemented, it's time to make it discoverable so KIE Server can find and register this extension on runtime. Since KIE Server is based on Java SE ServiceLoader mechanism we need to add one file into our extension jar file:

META-INF/services/org.kie.server.services.api.KieServerApplicationComponentsService

And the content of this file is a single line that represents fully qualified class name of our custom implementation of  KieServerApplicationComponentsService.


Last step is to build this project (which will result in jar file) and copy the result into:
 kie-server.war/WEB-INF/lib

And that's all that is needed. Start KIE Server and then you can start interacting with your new REST endpoint that relies on Drools extension.

Usage example

Clone this repository and build the kie-server-demo project. Once you build it you will be able to deploy it to KIE Server (either directly using KIE Server management REST api) or via KIE workbench controller.

Once deployed you can use following to invoke new endpoint:
URL: 
http://localhost:8080/kie-server/services/rest/server/containers/instances/demo/ksession/defaultKieSession

HTTP Method: POST
Headers:
Content-Type: application/json
Accept: application/json

Message payload:
[
{
  "org.jbpm.test.Person":{
     "name":"john",
     "age":25}
   },
  {
    "org.jbpm.test.Person":{
       "name":"mary",
       "age":22}
   }
]

A simple list with two items representing people, execute it and you should see following in server log:
13:37:20,347 INFO  [stdout] (default task-24) Hello mary
13:37:20,348 INFO  [stdout] (default task-24) Hello john

And the response should contain objects retrieved after rule evaluation where each Person object has:
  • address set to 'JBoss Community'
  • registered flag set to true

With this sample use case we illustrated how easy it is to extend REST api of KIE Server. Complete code for this extension can be found here.

Extending KIE Server capabilities

As a follow up of previous articles about  KIE Server, I'd like to present the extensibility support provided by KIE Server. Let's quickly look at KIE Server architecture...

Extensions overview

KIE Server is built around extensions, every piece of functionality is actually provided by extension. Out of the box we have following:

  • KIE Server extension - this is the default extension that provides management capabilities of the KIE Server - like creating or disposing containers etc
  • Drools extension - this extension provides rules (BRMS) capabilities, e.g. allows to inserting facts and firing rules (among others)
  • jBPM extension - this extensions provides process (BPMS) capabilities e.g. business process execution, user tasks, async jobs
  • jBPM UI extension - added in 6.4 additional extension that depends on jBPM extension and provides UI related capabilities - forms and process images
With just these out of the box capabilities KIE Server provides quite a bit of coverage. But that not all... extensions provide the capabilities but these capabilities must be somehow exposed to the users. And here KIE Server comes with two transports by default:
  • REST
  • JMS
Due to a need to be able to effectively manage extensions in runtime these are packaged in different jar files. So looking at the out of the box extensions we have following modules:
  • Drools extension
    • kie-server-services-drools
    • kie-server-rest-drools
  • jBPM extension
    • kie-server-services-jbpm
    • kie-server-rest-jbpm
  • jBPM UI extension
    • kie-server-services-jbpm-ui
    • kie-server-rest-jbpm-ui
All above modules are automatically discovered on runtime and registered in KIE Server if the are enabled (which by default they are). Extensions can be disabled using system properties
  • Drools extension
    • org.drools.server.ext.disabled = true
  • jBPM extension
    • org.jbpm.server.ext.disabled = true
  • jBPM UI extension
    • org.jbpm.ui.server.ext.disabled = true
But this is not all... if someone does not like the client api a client api can also be extended by implementing custom interfaces. This is why there is an extra step needed to get remote client:

kieServerClient.getServicesClient(Interface.class)

Why extensions are needed?

Let's not look at why would someone consider extending KIE server?

  • First and foremost is there might be missing functionality which is not yet implemented in KIE Server but exists in engines (process or rule engine). 
    • REST extension
  • Another use case is that something should be done differently than it is done out of the box - different parameters and so on..
    • client extension
  • Last but not least, it should be possible to extend the transport coverage meaning allow users to add other transports next to REST and JMS.
    • server extension
With this users can first of all, cover their requirements even if the out of the box KIE Server implementation does not provide required functionality. Next such extensions cane contributed to be included in the project or can be shipped as custom extensions available for other users.

This benefits both project and users so I'd like to encourage every one to look into details and think if there is anything missing and if so try to solve it by building extensions.

Let's extend KIE Server capabilities

Following three articles will provide details on how to build KIE Server extensions:

Important note: While most of the work could be achieved already with 6.3.0.Final I'd strongly recommend to give it a go with 6.4.0 (and thus all dependencies refer to 6.4.0-SNAPSHOT) as the extensions have been simplified a lot.