Agile India.

If you have your web application running on one tomcat instance and want to add another tomcat instance (ideally on a different machine), following steps will guide you.

Step 1: Independently deploy your web application (WAR file) on each instance and make sure they can work independently.

Step 2: Stop tomcat

Step 3: Update the <Cluster> element under the <Engine> element in the Server.xml file (under the conf dir in tomcat installation dir) on both your servers with:

<Engine name="<meaningful_unique_name>" defaultHost="localhost">      
     <Cluster className="org.apache.catalina.ha.tcp.SimpleTcpCluster"
              channelSendOptions="8">
          <Manager className="org.apache.catalina.ha.session.DeltaManager"
                   expireSessionsOnShutdown="false"
                   notifyListenersOnReplication="true"/>
          <Channel className="org.apache.catalina.tribes.group.GroupChannel">
               <Membership className="org.apache.catalina.tribes.membership.McastService"
                           address="228.0.0.4"
                           port="45564"
                           frequency="500"
                           dropTime="3000"/>
               <Receiver className="org.apache.catalina.tribes.transport.nio.NioReceiver"
                         address="auto"
                         port="4000"
                         autoBind="100"
                         selectorTimeout="5000"
                         maxThreads="6"/>
               <Sender className="org.apache.catalina.tribes.transport.ReplicationTransmitter">
                   <Transport className="org.apache.catalina.tribes.transport.nio.PooledParallelSender"/>
               </Sender>
               <Interceptor className="org.apache.catalina.tribes.group.interceptors.TcpFailureDetector"/>
               <Interceptor className="org.apache.catalina.tribes.group.interceptors.MessageDispatch15Interceptor"/>
          </Channel>
          <Valve className="org.apache.catalina.ha.tcp.ReplicationValve"
                 filter=".*\.gif;.*\.js;.*\.jpg;.*\.png;.*\.css;.*\.txt;"/>
          <ClusterListener className="org.apache.catalina.ha.session.ClusterSessionListener"/>
     </Cluster>
     ...
</Engine>

For more details on these parameters, check https://sec1.woopra.com/docs/cluster-howto.html

Step 4: Start tomcat and make sure it starts up correctly. You should be able to access http://locahost:8080. Most default tomcat installations come with an examples web app. Try access http://localhost:8080/examples/jsp/ You should see a list of JSP files.

Step 4.a: Also if you see catalina.out log file, you should see:

INFO: Initializing Coyote HTTP/1.1 on http-8080
Nov 9, 2009 9:29:43 AM org.apache.catalina.startup.Catalina load
INFO: Initialization processed in 762 ms
Nov 9, 2009 9:29:43 AM org.apache.catalina.core.StandardService start
INFO: Starting service <server_name>
Nov 9, 2009 9:29:43 AM org.apache.catalina.core.StandardEngine start
INFO: Starting Servlet Engine: Apache Tomcat/6.0.16
Nov 9, 2009 9:29:43 AM org.apache.catalina.ha.tcp.SimpleTcpCluster start
INFO: Cluster is about to start
Nov 9, 2009 9:29:43 AM org.apache.catalina.tribes.transport.ReceiverBase bind
INFO: Receiver Server Socket bound to:/<server_ip>:4000
Nov 9, 2009 9:29:43 AM org.apache.catalina.tribes.membership.McastServiceImpl setupSocket
INFO: Setting cluster mcast soTimeout to 500
Nov 9, 2009 9:29:43 AM org.apache.catalina.tribes.membership.McastServiceImpl waitForMembers
INFO: Sleeping for 1000 milliseconds to establish cluster membership, start level:4

Step 5: Stop tomcat.

Step 6: We’ll use the examples web app to test if our session replication is working as expected.

Step 6.a: Open the Web.xml file of the “examples” web app in your webapps. Mark this web app distributable, by adding a <distributable/> element at the end of the Web.xml file (just before the </web-app> element)

Step 6.b: Add the session JSP file. This JSP prints the contents of the session and also adds/increments a counter stored in the session.

Step 6.c: Start tomcat on both machines

Step 6.d: You should see the following log in catalina.out

Nov 9, 2009 9:29:44 AM org.apache.catalina.ha.tcp.SimpleTcpCluster memberAdded
INFO: Replication member added:org.apache.catalina.tribes.membership.MemberImpl[tcp://{-64, -88, 0, 101}:4000,{-64, -88, 0, 101},4000, alive=10035,id={68 106 92 39 -110 -8 73 124 -116 -122 -15 -3 11 117 56 105 }, payload={}, command={}, domain={}, ] 
 
Nov 9, 2009 9:29:49 AM org.apache.catalina.ha.session.DeltaManager start
INFO: Register manager /examples to cluster element Engine with name <server_name>
Nov 9, 2009 9:29:49 AM org.apache.catalina.ha.session.DeltaManager start
INFO: Starting clustering manager at /examples
Nov 9, 2009 9:29:49 AM org.apache.catalina.ha.session.DeltaManager getAllClusterSessions
WARNING: Manager [localhost#/examples], requesting session state from org.apache.catalina.tribes.membership.MemberImpl[tcp://{-64, -88, 0, 101}:4000,{-64, -88, 0, 101},4000, alive=15538,id={68 106 92 39 -110 -8 73 124 -116 -122 -15 -3 11 117 56 105 }, payload={}, command={}, domain={}, ]. This operation will timeout if no session state has been received within 60 seconds.
Nov 9, 2009 9:29:49 AM org.apache.catalina.ha.session.DeltaManager waitForSendAllSessions
INFO: Manager [localhost#/examples]; session state send at 11/9/09 9:29 AM received in 101 ms.
 
Nov 9, 2009 9:29:49 AM org.apache.catalina.core.ApplicationContext log
INFO: ContextListener: contextInitialized()
Nov 9, 2009 9:29:49 AM org.apache.catalina.core.ApplicationContext log
INFO: SessionListener: contextInitialized()
Nov 9, 2009 9:29:50 AM org.apache.coyote.http11.Http11Protocol start
INFO: Starting Coyote HTTP/1.1 on http-8080
Nov 9, 2009 9:29:50 AM org.apache.jk.common.ChannelSocket init
INFO: JK: ajp13 listening on /0.0.0.0:8009
Nov 9, 2009 9:29:50 AM org.apache.jk.server.JkMain start
INFO: Jk running ID=0 time=0/49  config=null
Nov 9, 2009 9:29:50 AM org.apache.catalina.startup.Catalina start
INFO: Server startup in 6331 ms

Step 6.e: Try to access http://localhost:8080/examples/jsp/session.jsp Try refreshing the page a few times, you should see the counter getting updated.

Step 6.f: You should see the same behavior when you try to access the other tomcat server. Open another tab in your browser and hit http://<other_server_ip>:8080/examples/jsp/session.jsp

Step 6.g: At this point we know the app works fine and the session is working correctly. Now we want to check if the tomcat cluster is replicating the session info. To check this, we want to pass the session from server 1 to session 2 and see if it increments the counter from where we left.

Step 6.h: Before accessing the page, make sure you copy the j_session_id from server 1 (displayed on the http://localhost:8080/examples/jsp/session.jsp). Also make sure to clear all cookies from server 2. (All browsers give you a facility to clear cookies from a specific host/ip).

Step 6.i: Now hit http://<server_2_ip>:8080/examples/jsp/session.jsp;jsessionid=<jsession_id_from_server1>

Step 6.j: If you see the counter incrementing from where ever you had left, congrats! You have session replication working.

Step 6.k: Also catalina.out log file should have:

Nov 9, 2009 9:42:03 AM org.apache.catalina.core.ApplicationContext log
INFO: SessionListener: sessionCreated('CDC57B8C5CFDFDDC2C8572E7D14C0D28')
Nov 9, 2009 9:42:03 AM org.apache.catalina.core.ApplicationContext log
INFO: SessionListener: attributeAdded('CDC57B8C5CFDFDDC2C8572E7D14C0D28', 'counter', '1')
Nov 9, 2009 9:42:05 AM org.apache.catalina.core.ApplicationContext log
INFO: SessionListener: attributeReplaced('CDC57B8C5CFDFDDC2C8572E7D14C0D28', 'counter', '2')

While this might like smooth, I ran into lot of issues when getting to this point. Following are some trap routes I ran into:

1) java.sql.SQLException: No suitable driver tomcat cluster
Make sure your DB Driver jar (in our case mysql-connector-java-x.x.xx-bin.jar) is in tomcat/lib folder

2) In catalina.org if you see the following exception:

Nov 7, 2009 3:48:53 PM org.apache.catalina.ha.session.DeltaManager requestCompleted
SEVERE: Unable to serialize delta request for sessionid [1F43C3926FF3CC231574EF248896DCA6]
java.io.NotSerializableException: com.company.product.Class
	at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1156)
	at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:326)
	at java.util.ArrayList.writeObject(ArrayList.java:570)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)

This means that you are storing com.company.product.Class object (or some other object that holds a reference to this Object) in your session. And you’ll need to make com.company.product.Class implement Serializable interface.

3) In your catalina.out log if you see

INFO: Register manager /<your_app_name> to cluster element Engine with name <tomcat_engine_name>
Nov 7, 2009 11:56:20 AM org.apache.catalina.ha.session.DeltaManager start
INFO: Starting clustering manager at /<your_app_name>
Nov 7, 2009 11:56:20 AM org.apache.catalina.ha.session.DeltaManager getAllClusterSessions
INFO: Manager [localhost#/<your_app_name>]: <strong>skipping state transfer. No members active in cluster group</strong>.

If both your tomcat instance are up and running, then check if your tomcat servers can communicate with each other using Multicast with the following commands:

$ ping -t 1 -c 2 228.0.0.4
PING 228.0.0.4 (228.0.0.4): 56 data bytes
64 bytes from <server_1_ip>: icmp_seq=0 ttl=64 time=0.076 ms
64 bytes from <server_2_ip>: icmp_seq=0 ttl=64 time=0.645 ms

— 228.0.0.4 ping statistics —
1 packets transmitted, 1 packets received, +1 duplicates, 0.0% packet loss

or

$ sudo tcpdump -ni en0 host 228.0.0.4
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on en0, link-type EN10MB (Ethernet), capture size 65535 bytes
22:11:50.016147 IP <server_1_ip>.45564 > 228.0.0.4.45564: UDP, length 69
22:11:50.033336 IP <server_2_ip>.45564 > 228.0.0.4.45564: UDP, length 69
22:11:50.516746 IP <server_1_ip>.45564 > 228.0.0.4.45564: UDP, length 69
22:11:50.533613 IP <server_2_ip>.45564 > 228.0.0.4.45564: UDP, length 69
…

If you don’t see the results as described above, you might want to read my blog on Enabling Multicast.

On one of the projects we are using Cargo Maven Plugin to run an embedded Jetty server for our builds. Out of the blue, today, I started getting the following error when I was running my Selenium Tests after deploying the application.

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WARN:  Nested in org.apache.jasper.JasperException: org.apache.jasper.JasperException: Unable to initialize TldLocationsCache: null:
org.apache.jasper.JasperException: Unable to initialize TldLocationsCache: null
at org.apache.jasper.compiler.TldLocationsCache.init (TldLocationsCache.java:253)
at org.apache.jasper.compiler.TldLocationsCache.getLocation (TldLocationsCache.java:224)
at org.apache.jasper.JspCompilationContext.getTldLocation (JspCompilationContext.java:526)
at org.apache.jasper.compiler.Parser.parseTaglibDirective (Parser.java:422)
...

No clue why this is happening. Surprising this is, this issue cannot be reproduced on a Windows box. Only on my Mac with JDK 1.6 and Maven 2.0, I’m getting this issue.

On goolging for this issue, I make across this bug report which kind of indicated that this might be an issue with the Cargo Maven Plugin. On upgrading the plugin to version 1.0, the issue was solved.

Need to find out what caused the problem in the first place.

Recently Brett Schuchert from Object Mentor has started posting code snippets on his blog and inviting people to refactor it. Similar to the Daily Refactoring Teaser that I’m conducting at Directi. (I’m planning to make it public soon).

Following is my refactored solution (take 1) to the poorly written code.

Wrote some Acceptance Test to understand how the RpnCalculator works:

Then I updated the perform method to

@Deprecated
public void perform(final String operatorName) {
  perform(operators.get(operatorName));
}
 
public void perform(final Operator operator) {
  operator.eval(stack);
  currentMode = Mode.inserting;
}

Notice I’ve deprecated the old method which takes String. I want to kill primitive obsession at its root.

Had to temporarily add the following map (this should go away once our deprecated method is knocked off).

private static Map operators = new HashMap() {
  {
    put("+", Operator.ADD);
    put("-", Operator.SUBTRACT);
    put("!", Operator.FACTORIAL);
  }
 
  @Override
  public Operator get(final Object key) {
    if (!super.containsKey(key)) {
      throw new MathOperatorNotFoundException();
    }
    return super.get(key);
  }
};

Defined various Operators

private static abstract class Operator {
  private static final Operator ADD = new BinaryOperator() {
    @Override
    protected int eval(final int op1, final int op2) {
      return op1 + op2;
    }
  };
 
  private static final Operator SUBTRACT = new BinaryOperator() {
    @Override
    protected int eval(final int op1, final int op2) {
      return op2 - op1;
    }
  };
 
  private static final Operator FACTORIAL = new UnaryOperator() {
    @Override
    protected int eval(final int op1) {
      int result = 1;
      int currentOperandValue = op1;
      while (currentOperandValue > 1) {
        result *= currentOperandValue;
        --currentOperandValue;
      }
      return result;
    }
  };
 
  public abstract void eval(final OperandStack stack);
}

Declared two types of Operators (BinaryOperator and UnaryOperator) to avoid duplication and to make it easy for adding new operators.

public static abstract class BinaryOperator extends Operator {
  @Override
  public void eval(final OperandStack s) {
    s.push(eval(s.pop(), s.pop()));
  }
 
  protected abstract int eval(int op1, int op2);
}

and

public static abstract class UnaryOperator extends Operator {
  @Override
  public void eval(final OperandStack s) {
    s.push(eval(s.pop()));
  }
 
  protected abstract int eval(int op1);
}

Today I spent a good 3 hours trouble shooting issues with code coverage on a legacy project. I’ve been using Cobertura for a good 3 years now. Hence I decided to use Cobertura to help a team working on a legacy project. What looked like a simple 10 mins job, ended up taking forever.

To start off, the team did not have an automated build. So I quickly put an Ant script together. Last 2 days I had helped them write some acceptance tests using FitNesse. I set up the build file to run the FitNesse tests as part of the build. Once I had the testing in place, I wanted to see what kind of code coverage we had. So we started adding Cobertura Ant tasks to the build. This was a fairly trivial task. But surprisingly cobertura-report kept displaying N/A for Line and Branch coverage. Clearly there was something wrong.

After spending a good amount of time, I realized that we need to compile the source code with debug=true option, else Cobertura does not generate any coverage numbers. What’s amazing is, it does not complain (in the normal mode) about this nor does cobertura’s documentation talks about this. When I ran the ant build in verbose mode, it showed the following warning

[cobertura-instrument] WARN visitEnd, No line number information found for class

That’s when it occurred to me that I need to compile my source code with debug=true option.

Once I solved this problem I hit the next roadblock. Even thought I fixed the debug=true option issue, cobertura-report was still displaying N/A for Line and Branch coverage. I quickly wrote a dummy unit tests and that seemed to work. Cobertura report started showing some numbers. But I was not able to generate any coverage numbers from the main Java application (server) that I was trying to test.

I knew there was some problem with the Shutdown hook not been executed correctly to flush the coverage numbers to the ser file. It turned out that if you have a server which is started as a daemon process in a forked JVM in the build, it needs to have a way to shutdown the server gracefully. So I ended up writing a shutdown command for the server which would basically do a System.exit(0). One need to explicitly call the shutdown script before calling the cobertura report target.

Finally after 3 hrs, there was some ray of hope in my life when I saw a good 86% code coverage. This meant I could now go and refactor the code till I dropped dead.

Returns a string representation of the object. In general, the 

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toString

 method returns a string that “textually represents” this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

Being out of touch with Java coding and moving between Java 5 and 6 can be a great way to assume yourself. Couple of days back I stumbled upon a fairly well know Java 5 feature, @Override annotation. Annotations were introduced in Java 5. According to the JavaDoc

public @interface Override

Indicates that a method declaration is intended to override a method declaration in a superclass. If a method is annotated with this annotation type but does not override a superclass method, compilers are required to generate an error message.

One would read this and think the following code should work perfectly fine:

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interface I {
  void m1();
}

1

class C implements I {

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  @Override
  public void m1() {
  }
}

But guess what? In Java 5, the compiler gives the following error: “The method m1() of type C must override a superclass method”

Currently I’m working on adding Revision Control support to FitNesse. In the process, I’m creating a SVN adapter using svnkit library.

Once I’ve added a file, if I try to commit the file using

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protected void commit(File file) throws SVNException {
final SVNClientManager manager = SVNClientManager.newInstance();
final SVNCommitClient commitClient = manager.getCommitClient();
final File[] filesToCommit = new File[] { file };
commitClient.doCommit(filesToCommit, false, "Auto Commit", false, false);
}

I get the following exception:

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svn: Unable to open an ra_local session to URL
at org.tmatesoft.svn.core.internal.wc.SVNErrorManager.error(SVNErrorManager.java:55)
at org.tmatesoft.svn.core.internal.wc.SVNErrorManager.error(SVNErrorManager.java:40)
at org.tmatesoft.svn.core.wc.SVNCommitClient.doCommit(SVNCommitClient.java:582)
at org.tmatesoft.svn.core.wc.SVNCommitClient.doCommit(SVNCommitClient.java:549)

Trying to Google for this, did not take me anywhere. Finally after debugging thru svnkit’s code, I stumbled upon the following line which throws the exception:

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SVNRepository repository = SVNRepositoryFactory.create(SVNURL.parseURIDecoded(url));

Basically, they have SVNRepositoryFactory class which expects the client to register an appropriate driver to handle the given protocol. Their javadocs says:

Depending on what protocol a user exactly would like to use to access the repository he should first of all set up an appropriate extension of this factory. So, if the user is going to work with the repository via the custom svn-protocol (or svn+xxx) he initially calls

1	SVNRepositoryFactoryImpl.setup();

More details: http://svnkit.com/kb/javadoc/org/tmatesoft/svn/core/io/SVNRepositoryFactory.html

Solution: Since I’m using File System (file://) protocol, I had to add the following line in a static block of my adapter class:

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FSRepositoryFactory.setup();

Few months back I moved to JDK 5. After this move, recently, I tried running some Acceptance tests using an old fitnesse.jar, which was compiled using JDK 1.4. And guess what? I get the following exception :

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javax.xml.parsers.FactoryConfigurationError:
Provider com.sun.org.apache.xerces.internal.jaxp.
DocumentBuilderFactoryImpl could not be instantiated: java.lang.NullPointerException
[java] at javax.xml.parsers.DocumentBuilderFactory.newInstance
(DocumentBuilderFactory.java:104)
[java] at fitnesse.util.XmlUtil.<clinit>
[java] at fitnesse.wiki.WikiPageProperties.loadFromXmlStream
[java] at fitnesse.wiki.FileSystemPage.attemptToReadPropertiesFile
[java] at fitnesse.wiki.FileSystemPage.loadAttributes
[java] at fitnesse.wiki.FileSystemPage.makePageData
[java] at fitnesse.wiki.CachingPage.getData
[java] at fitnesse.responders.run.FitClientResponder.readyToSend
[java] at fitnesse.responders.run.PuppetResponse.readyToSend
[java] at fitnesse.FitNesseExpediter.sendResponse
[java] at fitnesse.FitNesseExpediter.start
[java] at fitnesse.FitNesseServer.serve
[java] at fitnesse.FitNesseServer.serve
[java] at fitnesse.socketservice.SocketService$ServerRunner.run
[java] at java.lang.Thread.run(Thread.java:595)

If I use JDK 1.4, everything works fine. But there seems to be some backward compatibility issues with JDK 1.5.

After trying different things for a while, I came across a site that stated that “The J2SE 1.4 platform included the ‘Crimson‘ reference implementation for JAXP 1.1. The J2SE 5 platform includes a reference implementation for JAXP 1.3 based on the Apache ‘Xerces‘ library.”

In JDK 1.4, xerces and xalan are embedded in the JDK. In JDK 1.5 too, but the packages are under com/sun (so com.sun.org.apache….).

So you would think all this should be transparent to developers. But no.

To verify the above statement, I opened up the DocumentBuilderFactory in JDK 1.5 and I found

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public static DocumentBuilderFactory newInstance() {
try {
return (DocumentBuilderFactory) FactoryFinder.find(
/* The default property name according to the JAXP spec */
"javax.xml.parsers.DocumentBuilderFactory",
/* The fallback implementation class name */
"com.sun.org.apache.xerces.internal.jaxp.
DocumentBuilderFactoryImpl");
} catch (FactoryFinder.ConfigurationError e) {
throw new FactoryConfigurationError(e.getException(),
e.getMessage());
}

}
while the JDK 1.4‘s DocumentBuilderFactory class had:

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public static DocumentBuilderFactory newInstance()
throws FactoryConfigurationError
{
try {
return (DocumentBuilderFactory) FactoryFinder.find(
/* The default property name according to the JAXP spec */
"javax.xml.parsers.DocumentBuilderFactory",
/* The fallback implementation class name */
"org.apache.crimson.jaxp.
DocumentBuilderFactoryImpl");
} catch (FactoryFinder.ConfigurationError e) {
throw new FactoryConfigurationError (e.getException(),
e.getMessage());
}
}

After all this research I still don‘t know what is the exact problem. But I have a solution.

Solution: Luckily adding the xerces.jar to the classpath solved the problem.

Would appreciate if someone would let me know the answer.

I just released the first beta version of Lattu.

Lattu is a framework for testing Eclipse RCP Applications. It can run both Unit and Functional tests. Essentially, it is an Eclipse Plugin which provides Fitnesse extension to run unit and acceptance tests. It uses JUnit for unit testing and Abbot for GUI tests.

More details: http://lattu.sourceforge.net

Having problems parsing Dates in your fit/fitnesse tests?

Here is a simple way to fix date parsing problem using FitLibrary.

Fit Page

|set date format as|MM/dd/yyyy|

|date|
|11/23/2006|

|set date format as|dd-MMM-yyyy|

|date|
|23-Nov-2006|

Fixture Class

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<br />
public void setDateFormatAs(String format) {<br />
ValueAdapter.registerParseDelegate(java.sql.Date.class, new SimpleDateFormat(format));<br />
ValueAdapter.registerParseDelegate(java.util.Date.class, new SimpleDateFormat(format));<br />
}</p>
	<p>

How this works?
The ValueAdapter class holds a static HashMap called PARSE_DELEGATES which contains all the ParseDelegators. The ParseDelegator‘s job is to implement a parse method which take a String and returns the Object of your Data Type. You can register the Data Type and its respective ParseDelegator using the registerParseDelegate() method.

In this case, my ParseDelegator is SimpleDateFormat which has the following method

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<br />
public Date parse(String source) throws ParseException{<br />
ParsePosition pos = new ParsePosition(0);<br />
Date result = parse(source, pos);<br />
if (pos.index == 0)<br />
throw new ParseException("Unparseable date: " + source ,<br />
pos.errorIndex);<br />
return result;<br />
}</p>
	<p>

All that matters is the following method signature:
public Date parse(String source){

You can use the same mechanism to parse any object of choice.