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Date: Tue, 16 Apr 2013 11:45:51 +0100
Subject: Using the Servlet component in a Blueprint container
From: Andreas Gies <andreas@wayofquality.de>
To: <users@camel.apache.org>
Message-ID: <CD92EA6F.26448%andreas@wayofquality.de>
Thread-Topic: Using the Servlet component in a Blueprint container
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Hello Community,=20

I apologize for the long post upon list entry, but I thought this might be
interesting.=20

I was working on a use case that involves running Camel inside an OSGi
Container and for configuration I am using Apache Aries 1.0.0.
As i have a HTTP Service already running and need to support HTTP posts, I
figured using the servlet component would make sense.

This having said, trying to use the configuration found here
(http://camel.apache.org/servlet.html) doesn't work out of the box.
The main reason seems to be that CamelServlet is a class rather than an
interface, so it can't be registered as an OSGi service
easily. Googling around indicated that using the attribute "ext:classes" on
the blueprint reference should do the trick, but I got
errors from Blueprint not being able to create the service proxy.

I stepped back and tried to understand what *should* happen and came up wit=
h
a solution / workaround that I thought was worth sharing.

1. I need to gain access to the CamelServlet by OSGI means.
2. I need to stick a HTTP Registry into that servlet.
3. I need to define an endpoint that wires the Registry and the Servlet
together.=20

First, I have defined an Interface CamelServletProvider that has merely one
method:

public interface CamelServletProvider {

  public CamelServlet getCamelServlet();
}

with an associated implementation:

public class CamelServletProviderImpl implements CamelServletProvider {

  private CamelServlet camelServlet =3D null;

  public void setCamelServlet(CamelServlet camelServlet) {
    this.camelServlet =3D camelServlet;
  }

  @Override
  public CamelServlet getCamelServlet() {
    return camelServlet;
  }
}

The idea for this class is, that it lives alongside the CamelServlet and a
CamelServletProvider is registered as an OSGi Service like this:

<?xml version=3D"1.0" encoding=3D"UTF-8" standalone=3D"no"?>

<blueprint
  xmlns=3D"http://www.osgi.org/xmlns/blueprint/v1.0.0"
  xmlns:xsi=3D"http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation=3D"
">

  <bean id=3D"camelServlet"
class=3D"org.apache.camel.component.servlet.CamelHttpTransportServlet" />

  <bean id=3D"servletProvider"
class=3D"de.woq.camel.sib.servlet.internal.CamelServletProviderImpl">
    <property name=3D"camelServlet" ref=3D"camelServlet" />
  </bean>

  <service ref=3D"camelServlet" interface=3D"javax.servlet.Servlet" >
    <service-properties>
      <entry key=3D"alias"                value=3D"/camel/services" />
      <entry key=3D"matchOnUriPrefix"     value=3D"true" />
      <entry key=3D"servlet-name"         value=3D"CamelServlet"/>
      <entry key=3D"osgi.web.contextpath" value=3D"/camel/services" />
    </service-properties>
  </service>

  <service ref=3D"servletProvider"
interface=3D"de.woq.camel.sib.servlet.CamelServletProvider">
    <service-properties>
      <entry key=3D"servlet-name"         value=3D"CamelServlet"/>
    </service-properties>
  </service>

</blueprint>

Now we have a bundle that exposes a Camel Servlet as HTTP transport which I
can use in endpoints to come in another bundle.


To make this work I need a HTTP Registry, that I can stick into Blueprint
and that reacts to CamelServletProviders coming and going.
The DefaultHTTPRegistry in Camel reacts to javax.servlet.Servlet.

I have simply cloned the DefaultHTTPRegistry and made it react to
CamelServletProviders:

public class  CamelServletHTTPRegistry implements HttpRegistry {
  private static final transient Logger LOG =3D LoggerFactory.getLogger(
CamelServletHTTPRegistry.class);

  private static HttpRegistry singleton;

  private final Set<HttpConsumer> consumers;
  private final Set<CamelServlet> providers;

  public  CamelServletHTTPRegistry() {
    consumers =3D new HashSet<HttpConsumer>();
    providers =3D new HashSet<CamelServlet>();
  }

  /**
   * Lookup or create a HttpRegistry
   */
  public static synchronized HttpRegistry getSingletonHttpRegistry() {
    if (singleton =3D=3D null) {
      singleton =3D new  CamelServletHTTPRegistry();
    }
    return singleton;
  }

  @Override
  public void register(HttpConsumer consumer) {
    LOG.debug("Registering consumer for path {} providers present: {}",
     consumer.getPath(), providers.size());
    consumers.add(consumer);
    for (CamelServlet provider : providers) {
      provider.connect(consumer);
    }
  }

  @Override
  public void unregister(HttpConsumer consumer) {
    LOG.debug("Unregistering consumer for path {} ", consumer.getPath());
    consumers.remove(consumer);
    for (CamelServlet provider : providers) {
      provider.disconnect(consumer);
    }
  }

  @SuppressWarnings("rawtypes")
  public void register(CamelServletProvider provider, Map properties) {
    LOG.info("Registering provider through OSGi service listener {}",
properties);
    try {
      CamelServlet camelServlet =3D provider.getCamelServlet();
      camelServlet.setServletName((String) properties.get("servlet-name"));
      register(camelServlet);
    } catch (ClassCastException cce) {
      LOG.info("Provider is not a Camel Servlet");
    }
  }

  public void unregister(CamelServletProvider provider, Map<String, Object>
properties) {
    LOG.info("Deregistering provider through OSGi service listener {}",
properties);
    try {
      CamelServlet camelServlet =3D provider.getCamelServlet();
      unregister((CamelServlet)provider);
    } catch (ClassCastException cce) {
      LOG.info("Provider is not a Camel Servlet");
    }
  }

  @Override
  public void register(CamelServlet provider) {
    LOG.debug("Registering CamelServlet with name {} consumers present: {}"=
,
     provider.getServletName(), consumers.size());
    providers.add(provider);
    for (HttpConsumer consumer : consumers) {
      provider.connect(consumer);
    }
  }

  @Override
  public void unregister(CamelServlet provider) {
    providers.remove(provider);
  }

  public void setServlets(List<Servlet> servlets) {
    providers.clear();
    for (Servlet servlet : servlets) {
      if (servlet instanceof CamelServlet) {
        providers.add((CamelServlet) servlet);
      }
    }
  }
}

The trick here is in the register / unregister method reacting to the
CamelServletProvider interface.

Now I was able to stick all of that together in a bundle configuration:

<?xml version=3D"1.0" encoding=3D"UTF-8" standalone=3D"no"?>

<blueprint
  xmlns=3D"http://www.osgi.org/xmlns/blueprint/v1.0.0"
  xmlns:camel=3D"http://camel.apache.org/schema/blueprint"
  xmlns:xsi=3D"http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation=3D"
  http://camel.apache.org/schema/blueprint
http://camel.apache.org/schema/blueprint/camel-blueprint-2.10.3.xsd
">

  <!-- Get an instance of the registry -->
  <bean id=3D"httpRegistry"
class=3D"de.woq.camel.sib.http.CamelServletHTTPRegistry" />

  <!-- Get hold of the Servlet Provider by its interface and servlet name
-->
  <reference
    interface=3D"de.woq.camel.sib.servlet.CamelServletProvider"
    filter=3D"(servlet-name=3DCamelServlet)"
    timeout=3D"1000">
    <reference-listener ref=3D"httpRegistry" bind-method=3D"register"
unbind-method=3D"unregister" />
  </reference>

  <!-- Create the servlet component -->
  <bean id=3D"servlet"
class=3D"org.apache.camel.component.servlet.ServletComponent">
    <property name=3D"httpRegistry" ref=3D"httpRegistry" />
  </bean>

  <camel:camelContext>

    <!-- Just convenience to stick file into a directory and have them
posted to a URL. -->
    <!-- /camel/services was the root context of my transport service above
-->
    <camel:route>
      <camel:from uri=3D"file:///tmp/woq-in" />
      <camel:to uri=3D"http://localhost:8080/camel/services/test" />
    </camel:route>

    <!-- The actual route -->
    <camel:route>
      <!-- Three /// are important, otherwise the endpoint will be
registered with path "/" -->
      <camel:from uri=3D"servlet:///test" />
      <camel:to uri=3D"file:///tmp/woq-out" />
    </camel:route>

  </camel:camelContext>

</blueprint>


If you think this is usefull, I am happy to stick it in the wiki rather tha=
n
in the user's list.


Best regards
Andreas
Andreas Gies

WoQ =AD Way of Quality UG


Gesch=E4ftsf=FChrer & CTO

eMail: andreas@wayofquality.de

Tel DE: +49 151 23470823

Tel UK: +44 755 1381918

Fax: +49 1805 006534 2114


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