HTTP Whiteboard - OSGI Compendium 6.0

State of the Art

• Current Java webapps are generally uninspiring
• There is little to no definition of modularity in Java webapps
• Webapps easily become monoliths
• A weak webapp lifecycle of has been badly abused
• Cross platform support is incredibly complex due to what remains unspecified

Http Whiteboard

• Started as RFC 189 - Http Service Updates
• Evolved into OSGi Enterprise Section 140 - Http Whiteboard Specification ** .. an addition which left the original Http Service untouched
• Added whiteboard style programming model

Design Goals

• Bring support for Servlet 3.0 (minimally)
• Enhancements which were long missing ** multiple url patterns ** servlet filters ** event listeners ** error pages
• Clarify relationship between contexts in OSGi and Servlet spec
• Introspection of current state of http services
• Define a capability namespace

From Monoliths to … Anything, Please!

• Every modern software engineering discussion spews buckets of descriptive buzzwords all describing in every way anything that is monolith.

  See The Reactive Manifesto for details.

ServletContextHelper

@Component(
	property = {
		HttpWhiteboardConstants.HTTP_WHITEBOARD_CONTEXT_NAME + "=default",
		HttpWhiteboardConstants.HTTP_WHITEBOARD_CONTEXT_PATH + "=/"
	}
)
public class SampleServletContextHelper extends ServletContextHelper {
}

Servlets

@Component(
	property = {
		HttpWhiteboardConstants.HTTP_WHITEBOARD_SERVLET_PATTERN + "=/"
	},
	service = Servlet.class
)
public class SampleServlet extends HttpServlet {
	@Override
	protected void service(
			HttpServletRequest request, HttpServletResponse response)
		throws ServletException, IOException {

		PrintWriter writer = response.getWriter();

		writer.write("Hello World!");
	}
}

Resources

@Component(
	property = {
		HttpWhiteboardConstants.HTTP_WHITEBOARD_RESOURCE_PREFIX + "=/META-INF/resources",
		HttpWhiteboardConstants.HTTP_WHITEBOARD_RESOURCE_PATTERN + "=/resources/*"
	}
)
public class SampleResources {
}

Filters

@Component(
	property = {
		HttpWhiteboardConstants.HTTP_WHITEBOARD_FILTER_PATTERN + "=/*"
	}
)
public class SampleFilter implements Filter {
	@Override
	public void doFilter(
			ServletRequest request, ServletResponse response,
			FilterChain filterChain)
		throws IOException, ServletException {

		filterChain.doFilter(request, response);
	}
}

Event Listeners

@Component
public class SampleServletContextListener implements ServletContextListener {

	@Override
	public void contextDestroyed(ServletContextEvent arg0) {
	}

	@Override
	public void contextInitialized(ServletContextEvent arg0) {
	}

}

Error Pages

@Component(
	property={
		HttpWhiteboardConstants.HTTP_WHITEBOARD_SERVLET_ERROR_PAGE + "=java.io.IOException",
		HttpWhiteboardConstants.HTTP_WHITEBOARD_SERVLET_ERROR_PAGE + "=5xx"
	},
	service = Servlet.class
)
public class SampleErrorPage extends HttpServlet {

	@Override
	protected void service(
			HttpServletRequest request, HttpServletResponse response)
		throws IOException, ServletException {

		//
	}

}

DTOs

@Component(
	immediate  = true,
	property = {
		HttpWhiteboardConstants.HTTP_WHITEBOARD_SERVLET_PATTERN + "=/dto"
	},
	service = Servlet.class
)
public class SampleDTOReportServlet extends HttpServlet {

	@Override
	protected void service(
			HttpServletRequest request, HttpServletResponse response)
		throws IOException, ServletException {

		final HttpServiceRuntime httpServiceRuntime = _httpServiceRuntime;

		if (httpServiceRuntime == null) {
			response.sendError(
				HttpServletResponse.SC_INTERNAL_SERVER_ERROR,
				"Something went terribly wrong...");

			return;
		}

		response.setContentType("application/json");
		response.setCharacterEncoding("UTF-8");

		PrintWriter writer = response.getWriter();

		writer.write(httpServiceRuntime.getRuntimeDTO().toString());

		writer.close();
	}

	@Reference(unbind = "-")
	protected void setHttpServiceRuntime(
		HttpServiceRuntime httpServiceRuntime) {

		_httpServiceRuntime = httpServiceRuntime;
	}

	private volatile HttpServiceRuntime _httpServiceRuntime;

}

Verdict

• I’m excited with the result of the Http Whiteboard specification
• http://www.osgi.org/Specifications/Drafts[OSGi R6 Early Draft] (Since has released Http Whiteboard Specification)
• Eclipse Project 4.5 M3 - New and Noteworthy - Friday
• There’s very little time left to get your feedback in. But, if you have any, please contact myself or any member of the EEG