Create a WFS 1.1 service in java

I wanted to create an OGC Web Feature Service (version 1.1) from scratch in java. When I tried to use jdk6 xjc with the OpenGIS schemas I had lots of errors so I had to create a bindings file to resolve them. It all works fine now, here are the results of my labours:

Ant fragment:

 <exec executable="${xjc}"
              failonerror="true"
              outputproperty="xjc.output"
              errorproperty="xjc.error"
              logerror="true">
            <arg value="-extension">
            <arg value="-verbose">
            <arg value="-httpproxy">
            <arg value="proxy:8080">
            <arg value="-b">
            <arg value="${opengis}/wfs/1.1.0/wfs-bindings.xml">
            <arg value="-d">
            <arg value="${generated}">
            <arg value="${opengis}/wfs/1.1.0/wfs.xsd">
            <arg value="${opengis}/cts/craft-feature.xsd">
            <arg value="${opengis}/ows/1.0.0/owsExceptionReport.xsd">
        </exec>

wfs-bindings.xml:

<bindings xmlns="http://java.sun.com/xml/ns/jaxb" version="1.0" xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <bindings schemaLocation="wfs.xsd" node="/xs:schema">
   <globalBindings
       underscoreBinding="asCharInWord"
       />
    <schemaBindings>
      <package name="net.opengis.schema.wfs"/>
    </schemaBindings>
  </bindings>
  <bindings schemaLocation="../../gml/3.1.1/base/gml.xsd" node="/xs:schema">
    <schemaBindings>
      <package name="net.opengis.schema.gml"/>
    </schemaBindings>
    <bindings schemaLocation="../../gml/3.1.1/base/defaultStyle.xsd" node="/xs:schema/xs:element[@name='topologyStyle']">
    <class name="topologyStyleLowerCase"/>
  </bindings> 
  <bindings schemaLocation="../../gml/3.1.1/base/defaultStyle.xsd" node="/xs:schema/xs:element[@name='geometryStyle']">
    <class name="geometryStyleLowerCase"/>
  </bindings> 
  <bindings schemaLocation="../../gml/3.1.1/base/defaultStyle.xsd" node="/xs:schema/xs:element[@name='graphStyle']">
    <class name="graphStyleLowerCase"/>
  </bindings> 
  <bindings schemaLocation="../../gml/3.1.1/base/defaultStyle.xsd" node="/xs:schema/xs:element[@name='featureStyle']">
    <class name="featureStyleLowerCase"/>
  </bindings>
  <bindings schemaLocation="../../gml/3.1.1/base/defaultStyle.xsd" node="/xs:schema/xs:element[@name='labelStyle']">
    <class name="labelStyleLowerCase"/>
  </bindings>
  </bindings>
  <bindings schemaLocation="../../filter/1.1.0/filter.xsd" node="/xs:schema">
    <schemaBindings >
      <package name="net.opengis.schema.filter" />
    </schemaBindings>
  </bindings>
  <bindings schemaLocation="../../ows/1.0.0/owsAll.xsd" node="/xs:schema">
    <schemaBindings>
      <package name="net.opengis.schema.ows"/>
    </schemaBindings>
  </bindings>
</bindings>

Starting a background thread in Tomcat

I have long running processes that repeatedly do something (like check a directory for new files or a database table for new records) then sleep for a while. These processes are deployed to Tomcat (giving me jsp interfaces for monitoring and any other requests).

Ideally the Tomcat container should manage this long running thread. i.e Tomcat should be aware of the background thread particularly for stopping a web application completely (stopping the background thread) but also for metrics gathering.

I implement long running threads as HttpServlets and start them in my ant build via the task which does an http get to the servlet url. We want the to return control to the build process and not wait for the long running thread to finish. The trick is to simply close the response output stream and continue. i.e.

    public abstract class RunnableServlet extends HttpServlet {

        private Runnable runnable;

        public RunnableServlet(Runnable runnable) {
            this.runnable = runnable;
        }

        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
            String command = req.getParameter("command");

            // continue with the task but with the container aware of this thread
            if ("start".equals(command)) {
                response.getOutputStream().write("started");
                response.getOutputStream().close();
                runnable.run();
            }
        }
    }

By the way to use the above servlet extend it!

Homemade Digital TV Antenna

living in O'Connor, Canberra I should get good reception from Black Mtn tower but I haven't been able to suss it for a couple of years. Reception was very patchy and for my favourite station SBS was terrible. I just couldn't get my rabbit ears to work well so I made my own antenna. I used that strip tv antenna cable that costs about a dollar per metre from Bunnings and soldered it to a coaxial end.

In detail I cut a 1.8m piece of tv antenna cable and joined the paired wires on the cable together at the ends (so I end up still a 1.8m strip but it has little u turns at the ends). Then I broke one side of the strip and twisted in a bit of copper to then solder the two ends to the coax connector (one end to the centre prong and the other to the outer ring).

Worked ok but was still having some reception problems. Luckily I stumbled upon an article that suggested you make sure there are no sharp curves in your coax cable. When I smoothed that I had flawless reception!

So the deal is you can probably make your own antenna for maybe $10 including a length of coax.

If you have rabbit ears already smooth out the run of coax, no small radius curves. Worked for me.

Start Tomcat using an Ant target

I like using a direct call to the tomcat startup class so I can avoid shell scripts:

    <!-- start tomcat -->
    <target name="tomcat.start">
        <mkdir dir="${tomcat}/temp" />
        <mkdir dir="${tomcat}/logs" />
        <echo message="starting tomcat" level="info" />
        <java classname="org.apache.catalina.startup.Bootstrap"
              fork="true"
              failonError="false"
              dir="${tomcat}/bin"
              spawn="true">
            <classpath location="${env.JAVA_HOME}/lib/tools.jar" />
            <classpath location="${tomcat}/bin/bootstrap.jar" />
            <classpath location="${tomcat}/bin/commons-logging.api.jar" />
            <jvmarg value="-Dprocess.name=tomcat" />
            <jvmarg value="-Xmx800m" />
            <jvmarg value="-XX:MaxPermSize=350m" />
            <jvmarg value="-Dcom.sun.management.jmxremote.port=9003" />
            <jvmarg value="-Dcom.sun.management.jmxremote.ssl=false" />
            <jvmarg value="-Dcom.sun.management.jmxremote.authenticate=false" />
            <jvmarg value="-Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager" />
            <jvmarg value="-Djava.util.logging.config.file=${tomcat}/conf/logging.properties" />
            <jvmarg value="-Djava.endorsed.dirs=${tomcat}/endorsed" />
            <jvmarg value="-Dcatalina.base=${tomcat}" />
            <jvmarg value="-Dcatalina.home=${tomcat}" />
            <jvmarg value="-Djava.io.tmpdir=${tomcat}/temp" />
            <arg value="start" />
        </java>
    </target>

How to deploy a Web Service to Tomcat 5.5 or 6.0

This example uses JDK6.

Adapted from http://saloon.javaranch.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic&f=51&t=004355:

Download the latest JAXWS Release Implementation (RI) from https://jax-ws.dev.java.net/ri-download.html. Unpack its jars as per instructions.

Tomcat 5.5

• copy the jaxws jars to the shared/lib directory in tomcat.
• move the jaxb-api.jar in shared/lib to common/endorsed.
• start tomcat

Tomcat 6.0

• create a shared directory in tomcat.
• copy the jaxws jars to that directory.
• create an endorsed directory in tomcat. If you are running tomcat using an ant task make sure you include the option

-Djava.endorsed.dirs=${catalina}/endorsed

• Move jaxb-api.jar from shared to endorsed.
• Edit conf/catalina.properties and set the shared.loader property as follows:

shared.loader=${catalina.home}/shared/*.jar

War

In the war, we update the web.xml to use a special listener that enables the web service. The web.xml should look like this:

    <listener>  
      <listener-class>com.sun.xml.ws.transport.http.servlet.WSServletContextListener</listener-class>
    </listener>
    <servlet>
      <servlet-name>MyExampleService</servlet-name>
      <servlet-class>com.sun.xml.ws.transport.http.servlet.WSServlet</servlet-class>
      <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
      <servlet-name>MyExampleService</servlet-name>
      <url-pattern>/example</url-pattern>
    </servlet-mapping>

Create a sun-jaxws.xml file in WEB-INF directory which the listener uses to configure itself with the web service you want to expose:

    <endpoints xmlns="http://java.sun.com/xml/ns/jax-ws/ri/runtime" version="2.0">
        <endpoint name="MyExampleService" implementation="moten.david.example.ws.MyExample" pattern="/example"/>
    </endpoints>

After starting tomcat you can access the service by:

http://localhost:8080/{war-name}/example