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Apache Felix HTTP Service

This is an implementation of the HTTP Service Specification as described in chapter 102 of the OSGi Compendium. The goal is to provide a standard and simplified way to register servlets and resources in a Servlet container, and to associate them with URIs. It also implement a non-standard extension for registering servlet filters as well as a whiteboard implementation. Complete set of features:

Installing

The Apache Felix HTTP Service project includes several bundles.

So, in most cases you could just use org.apache.felix.http.bundle and forget about all the other ones. Note that by default, this bundle operates in "bridged mode" and needs explicit configuration to enable or operate in other modes. See this section for more information.

Using the HttpService

The main components provided by the Apache Felix HTTP Service bundle are:

Servlets created for the OSGi HTTP service don't need to have any reference to the OSGi specification (they only need to conform to the Servlet specification), like in the example:

public class HelloWorld extends HttpServlet {
  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    resp.getWriter().write("Hello World");      
  }
}

To register a Servlet and map it to a URI, you need to retrieve the HttpService and call its registerServlet method. For this example, a ServiceTracker is used to ensure that the registration occurs when a HttpService actually is available, and a deregistration occurs when the HttpService becomes unavailable. Alternatively, you can use more high-level dependency management libraries, like Declarative Services, Felix Dependency Manager, or Felix HTTP whiteboard service (see below).

public class Activator implements BundleActivator {
  private ServiceTracker httpTracker;

  public void start(BundleContext context) throws Exception {
    httpTracker = new ServiceTracker(context, HttpService.class.getName(), null) {
      public void removedService(ServiceReference reference, Object service) {
        // HTTP service is no longer available, unregister our servlet...
        try {
           ((HttpService) service).unregister("/hello");
        } catch (IllegalArgumentException exception) {
           // Ignore; servlet registration probably failed earlier on...
        }
      }

      public Object addingService(ServiceReference reference) {
        // HTTP service is available, register our servlet...
        HttpService httpService = (HttpService) this.context.getService(reference);
        try {
          httpService.registerServlet("/hello", new HelloWorld(), null, null);
        } catch (Exception exception) {
          exception.printStackTrace();
        }
        return httpService;
      }
    };
    // start tracking all HTTP services...
    httpTracker.open();
  }

  public void stop(BundleContext context) throws Exception {
    // stop tracking all HTTP services...
    httpTracker.close();
  }
}

In the same way, you can unregister a Servlet (for instance, in the removedMethod method in the former example) by calling the HttpService.unregister method.

As you notice in the example above, the registerServlet method accepts four parameters:

The Servlet alias must begin with a slash and must not end with a slash. When a request is processed, the HTTP Service will try to exact match the requested URI with a registered Servlet. If not existent, it will remove the last '/' in the URI and everything that follows, and try to match the remaining part, and so on.

An additional configuration Map can be optionally specified; if present, all the parameters contained will be copied in the ServletContext object.

Finally, an HttpContext object can be optionally specified to handle authentication, mime type and resource mapping. The HttpContext interface is quite simple:

public interface HttpContext {
  /** Returns the mime type of the specified resource */
  String getMimeType(java.lang.String name);

  /** Returns the URL to retrieve the specified resource */
  URL getResource(java.lang.String name);

  /** Manages security for the specified request */
  boolean handleSecurity(HttpServletRequest request, HttpServletResponse response); 
}

The use of a custom HttpContext is typical when you want to serve static contents with the HTTP Service. Let's first see an example of resource registration without HttpContext:

public class Activator implements BundleActivator {
  private ServiceTracker httpTracker;

  public void start(BundleContext context) throws Exception {
    httpTracker = new ServiceTracker(context, HttpService.class.getName(), null) {
      public void removedService(ServiceReference reference, Object service) {
        // HTTP service is no longer available, unregister our resources...
        try {
           ((HttpService) service).unregister("/static");
        } catch (IllegalArgumentException exception) {
           // Ignore; servlet registration probably failed earlier on...
        }
      }

      public Object addingService(ServiceReference reference) {
        // HTTP service is available, register our resources...
        HttpService httpService = (HttpService) this.context.getService(reference);
        try {
          httpService.registerResources("/static", "/etc/www", null);
        } catch (Exception exception) {
          exception.printStackTrace();
        }
        return httpService;
      }
    };
    // start tracking all HTTP services...
    httpTracker.open();
  }

  public void stop(BundleContext context) throws Exception {
    // stop tracking all HTTP services...
    httpTracker.close();
  }
}

As a result of the httpService.registerResources("/static", "/etc/www", null) code, all the files available under /etc/www will be exposed under /static (e.g. http://localhost:8080/static/001.jpg will render the /etc/www/001.jpg). However, the example above can be simplistic in practice; the HttpContext object is the solution to customize the resource handling.

For instance, you can set the define more complex URI to file mappings overriding the HttpContext.getResource method, or the correct MIME type implementing the method HttpContext.getMimeType like in the example:

//....
public String getMimeType(String file) {
  if (file.endsWith(".jpg") {
    return "image/jpeg";  
  } else if (file.endsWith(".png")) {
    return "image/png";  
  } else {  
    return "text/html";  
  }
}
//....

If you implement a customised HttpContext object, don't forget to specify it as third parameter of the registerResources method invocation:

// ....
      public Object addingService(ServiceReference reference) {
        // HTTP service is available, register our resources...
        HttpService httpService = (HttpService) this.context.getService(reference);
        try {
          // explicitly use our own context as 3rd parameter...
          httpService.registerResources("/static", "/etc/www", new MyHttpContext());
        } catch (Exception exception) {
          exception.printStackTrace();
        }
        return httpService;
      }
// ....

Using the ExtHttpService

To be able to register filters, it is possible to get hold of org.apache.felix.http.api.ExtHttpService. This is exported by both Jetty and the bridged implementation. Let's see an example of a filter registration:

public class Activator implements BundleActivator {
  private ServiceTracker httpTracker;

  public void start(BundleContext context) throws Exception {
    httpTracker = new ServiceTracker(context, ExtHttpService.class.getName(), null) {
      public void removedService(ServiceReference reference, Object service) {
        // HTTP service is no longer available, unregister our resources...
        try {
           ((ExtHttpService) service).unregister("/static");
        } catch (IllegalArgumentException exception) {
           // Ignore; servlet registration probably failed earlier on...
        }
      }

      public Object addingService(ServiceReference reference) {
        // HTTP service is available, register our resources...
        ExtHttpService httpService = (ExtHttpService) this.context.getService(reference);
        try {
          httpService.registerFilter(new HelloWorldFilter(), "/hello/.*", null, 0, null);
        } catch (Exception exception) {
          exception.printStackTrace();
        }
        return httpService;
      }
    };
    // start tracking all HTTP services...
    httpTracker.open();
  }

  public void stop(BundleContext context) throws Exception {
    // stop tracking all HTTP services...
    httpTracker.close();
  }
}

Using the Whiteboard

The whiteboard implementation simplifies the task of registering servlets and filters. A servlet (or filter) can be registered by exporting it as a service, making it no longer necessary to track and use the HttpService directly. The whiteboard implementation detects all javax.servlet.Servlet, javax.servlet.Filter and org.osgi.service.http.HttpContext services with the right service properties. Let us illustrate the usage by registering a servlet:

public class Activator implements BundleActivator {
  private ServiceRegistration registration;

  public void start(BundleContext context) throws Exception {
    Hashtable props = new Hashtable();
    props.put("alias", "/hello");
    props.put("init.message", "Hello World!");

    this.registration = context.registerService(Servlet.class.getName(), new HelloWorldServlet(), props);
  }

  public void stop(BundleContext context) throws Exception {
    this.registration.unregister();
  }
}

Servlet service properties:

Filter service properties:

HttpContext service properties:

Using the Servlet Bridge

The servlet bridge is used if you want to use the HTTP service inside a WAR deployed on a 3rd part applicaiton server. A little setup is needed for this to work:

A detailed example can be found here.

Using the all-in-one bundle

The all-in-one bundle combines the the Jetty server, the whiteboard implementation, the servlet bridge and the CometD functionality in a single, easy to use bundle. By default its functionality is equivalent to the Servlet Bridge, meaning that the Jetty, Whiteboard and CometD features are disabled. To enable these features, you need to supply one or more configuration properties as described in the next section.

Configuration Properties

The service can both be configured using OSGi environment properties and using Configuration Admin. The service PID for this service is "org.apache.felix.http". If you use both methods, Configuration Admin takes precedence. The following properties can be used (some legacy property names still exist but are not documented here on purpose):

Property Description
org.apache.felix.http.debug Flag to enable debugging for this service implementation. The default is false.
org.apache.felix.http.host Host name or IP Address of the interface to listen on. The default is null causing Jetty to listen on all interfaces.
org.osgi.service.http.port The port used for servlets and resources available via HTTP. The default is 8080. See port settings below for additional information. A negative port number has the same effect as setting org.apache.felix.http.enable to false.
org.osgi.service.http.port.secure The port used for servlets and resources available via HTTPS. The default is 8443. See port settings below for additional information. A negative port number has the same effect as setting org.apache.felix.https.enable to false.
org.apache.felix.http.context_path The Servlet Context Path to use for the Http Service. If this property is not configured it defaults to "/". This must be a valid path starting with a slash and not ending with a slash (unless it is the root context).
org.apache.felix.http.timeout Connection timeout in milliseconds. The default is 60000 (60 seconds).
org.apache.felix.http.session.timeout Allows for the specification of the Session life time as a number of minutes. This property serves the same purpose as the session-timeout element in a Web Application descriptor. The default is 0 (zero) for no timeout at all.
org.apache.felix.http.nio Flag to enable the use of NIO instead of traditional IO for HTTP. One consequence of using NIO with HTTP is that the bundle needs at least a Java 5 runtime. The default is true.
org.apache.felix.https.nio Flag to enable the use of NIO instead of traditional IO for HTTPS. One consequence of using NIO with HTTPS is that the bundle needs at least a Java 5 runtime. If this property is not set the (default) value of the org.apache.felix.http.nio property is used.
org.apache.felix.http.enable Flag to enable the use of HTTP. The default is true.
org.apache.felix.https.enable Flag to enable the user of HTTPS. The default is false.
org.apache.felix.https.keystore The name of the file containing the keystore.
org.apache.felix.https.keystore.password The password for the keystore.
org.apache.felix.https.keystore.key.password The password for the key in the keystore.
org.apache.felix.https.truststore The name of the file containing the truststore.
org.apache.felix.https.truststore.type The type of truststore to use. The default is JKS.
org.apache.felix.https.truststore.password The password for the truststore.
org.apache.felix.https.jetty.ciphersuites.excluded Configures comma-separated list of SSL cipher suites to exclude. Default is null, meaning that no cipher suite is excluded.
org.apache.felix.https.jetty.ciphersuites.included Configures comma-separated list of SSL cipher suites to include. Default is null, meaning that the default cipher suites are used.
org.apache.felix.https.clientcertificate Flag to determine if the HTTPS protocol requires, wants or does not use client certificates. Legal values are needs, wants and none. The default is none.
org.apache.felix.http.jetty.headerBufferSize Size of the buffer for request and response headers. Default is 16 KB.
org.apache.felix.http.jetty.requestBufferSize Size of the buffer for requests not fitting the header buffer. Default is 8 KB.
org.apache.felix.http.jetty.responseBufferSize Size of the buffer for responses. Default is 24 KB.
org.apache.felix.http.jetty.maxFormSize The maximum size accepted for a form post. Defaults to 200 KB.
org.apache.felix.http.mbeans If true, enables the MBean server functionality. The default is false.
org.eclipse.jetty.servlet.SessionCookie Name of the cookie used to transport the Session ID. The default is JSESSIONID.
org.eclipse.jetty.servlet.SessionURL Name of the request parameter to transport the Session ID. The default is jsessionid.
org.eclipse.jetty.servlet.SessionDomain Domain to set on the session cookie. The default is null.
org.eclipse.jetty.servlet.SessionPath The path to set on the session cookie. The default is the configured session context path (/).
org.eclipse.jetty.servlet.MaxAge The maximum age value to set on the cookie. The default is -1.

Additionally, the all-in-one bundle uses the following environment properties:

Property Description
org.apache.felix.http.jettyEnabled If true, the embedded Jetty server is used as HTTP container. The default is false.
org.apache.felix.http.whiteboardEnabled If true, the whiteboard-style registration of servlets and filters is enabled. The default is false.
org.apache.felix.http.cometdEnabled If true the CometD/Ajax Push feature is enabled. The default is false.

The CometD bundle supports the following configuration options:

Property Description
org.apache.felix.http.cometd.path Defines the path for the CometD endpoint. Default is /system/cometd.

HTTP port settings

As of HTTP Jetty version 2.2.2, it is possible to assign a free port for HTTP or HTTPS automatically, based on certain rules, for example, a range between 8000 and 9000. The syntax is based on the version ranges, as described in the OSGi specification. The following forms are supported:

Note that picking a port is not performed atomically and multiple instances can try to bind to the same port at the same time.

Servlet API Events

The Servlet API defines a number of EventListener interfaces to catch Servlet API related events. As of HTTP Service 2.1.0 most events generated by the servlet container are forwarded to interested service. To be registered to receive events services must be registered with the respective EventListener interface:

Interface Description
javax.servlet.ServletContextAttributeListener Events on servlet context attribute addition, change and removal.
javax.servlet.ServletRequestAttributeListener Events on request attribute addition, change and removal.
javax.servlet.ServletRequestListener Events on request start and end.
javax.servlet.http.HttpSessionAttributeListener Events on session attribute addition, change and removal. To receive such events in a bridged environment, the ProxyLister must be registered with the servlet container. See the Using the Servlet Bridge section above.
javax.servlet.http.HttpSessionListener Events on session creation and destroyal. To receive such events in a bridged environment, the ProxyLister must be registered with the servlet container. See the Using the Servlet Bridge section above.

Of the defined EventListener interfaces in the Servlet API, the javax.servlet.ServletContextListener events are actually not support. For one thing they do not make much sense in an OSGi environment. On the other hand they are hard to capture and propagate. For example in a bridged environment the contextInitialized event may be sent before the framework and any of the contained bundles are actually ready to act. Likewise the contextDestroyed event may come to late.

Servlet Context Notes

ServletContext instances are managed internally by the Http Service implementation. For each HttpContext instance used to register one or more servlets and/or resources a corresponding ServletContext instance is created. These ServletContext instances is partly based on the single ServletContext instance received from the Servlet Container --- either embedded Jetty or some external Servlet Container when using the Http Service Bridge --- and partly based on the provided HttpContext instance:

Method(s) Based on ...
getContextPath, getContext, getMajorVersion, getMinorVersion, getServerInfo Servlet Containers ServletContext
getResourcePaths Bundle.getEntryPaths of the bundle using the Http Service
getResource, getResourceAsStream HttpContext.getResource
getMimeType HttpContext.getMimeType
getRequestDispatcher, getNamedDispatcher, getInitParameter, getServlet, getRealPath Always return null
getInitParameterNames, getServlets, getServletNames Always returns empty Enumeration
getAttribute, getAttributeNames, setAttribute, removeAttribute By default maintained for each ServletContext managed by the Http Service. If the org.apache.felix.http.shared*servlet*context_attributes framework property is set to true these methods are actually based on the ServletContext provided by the servlet container and thus attributes are shared amongst all ServlectContext instances, incl. the ServletContext provided by the servlet container

Examples

A set of simple examples illustrating the various features are available.

Maven Artifacts

<dependency>
  <groupId>org.apache.felix</groupId>
  <artifactId>org.apache.felix.http.api</artifactId>
  <version>2.2.2</version>
</dependency>
<dependency>
  <groupId>org.apache.felix</groupId>
  <artifactId>org.apache.felix.http.base</artifactId>
  <version>2.2.2</version>
</dependency>
<dependency>
  <groupId>org.apache.felix</groupId>
  <artifactId>org.apache.felix.http.bridge</artifactId>
  <version>2.2.2</version>
</dependency>
<dependency>
  <groupId>org.apache.felix</groupId>
  <artifactId>org.apache.felix.http.bundle</artifactId>
  <version>2.2.2</version>
</dependency>
<dependency>
  <groupId>org.apache.felix</groupId>
  <artifactId>org.apache.felix.http.cometd</artifactId>
  <version>2.2.2</version>
</dependency>
<dependency>
  <groupId>org.apache.felix</groupId>
  <artifactId>org.apache.felix.http.jetty</artifactId>
  <version>2.2.2</version>
</dependency>
<dependency>
  <groupId>org.apache.felix</groupId>
  <artifactId>org.apache.felix.http.proxy</artifactId>
  <version>2.2.2</version>
</dependency>
<dependency>
  <groupId>org.apache.felix</groupId>
  <artifactId>org.apache.felix.http.whiteboard</artifactId>
  <version>2.2.2</version>
</dependency>
<dependency>
  <groupId>org.apache.felix</groupId>
  <artifactId>org.apache.felix.http.sslfilter</artifactId>
  <version>0.0.1</version>
</dependency>
Rev. 1575969 by jawi on Mon, 10 Mar 2014 15:26:06 +0000
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