Finding out what MySQL is doing

I was recently updating our production system when I noticed that our main MySQL database was going unusually hard. On a quad-core processor system, it was using up three processors simaltaneously. This prompted me to find out what MySQL is doing, and after being unable to read the logs, I did a Google search and ran across this useful little command :

show processlist

This runs a query (can be run from either the command line or the query browser) and shows you a summary of all the processes that MySQL is currently using.

Migrating from Spring Webflow 1 to Webflow 2

...was relatively painless. At least in the very small app that I'm currently working on as a helper application for dealing with one of our partners' systems. The flow definition migration assistant that comes with Webflow 2 is a huge help. There are, however, a few things to take note of when it comes to differences between Webflow 1 and Webflow 2. They are significantly different beasts to say the least :

• 
  

  
  My configuration went from this (in Webflow 1) :
  

  
  

  
   <flow:registry id="flowRegistry">
    <flow:location path="/WEB-INF/flows/**/*-flow.xml"/>
   </flow:registry>
  
   <flow:executor id="flowExecutor" registry-ref="flowRegistry">
    <!--flow:execution-listeners>
     <flow:listener ref="webflowDebugListener"/>
    </flow:execution-listeners-->
   </flow:executor>
   
   <!--bean id="webflowDebugListener" class="org.springframework.webflow.execution.DebuggingListener"/-->
   
   <bean name="flowController" class="org.springframework.webflow.executor.mvc.FlowController">
    <property name="flowExecutor" ref="flowExecutor" />
    <property name="argumentHandler">
     <bean class="org.springframework.webflow.executor.support.RequestParameterFlowExecutorArgumentHandler" />
    </property>
   </bean>
    

  
  

  
  To this (in Webflow 2) :
  

  
  

  
   <webflow:flow-registry id="flowRegistry" flow-builder-services="flowBuilderServices">
    <webflow:flow-location-pattern value="/WEB-INF/flows/**/*-flow.xml"/>
   </webflow:flow-registry>
  
   <webflow:flow-executor id="flowExecutor" flow-registry="flowRegistry">
    <webflow:flow-execution-listeners>
     <!-- webflow:listener ref="webflowDebugListener"/ -->
     <webflow:listener ref="securityFlowExecutionListener"/>
    </webflow:flow-execution-listeners>
   </webflow:flow-executor>
   
   <bean id="securityFlowExecutionListener" class="org.springframework.webflow.security.SecurityFlowExecutionListener" />
   
   <webflow:flow-builder-services id="flowBuilderServices" view-factory-creator="viewFactoryCreator" conversion-service="webflowConversionService"/>
   
   <bean id="webflowConversionService" class="com.mypackage.modules.springframework.webflow2.ConversionServiceFactoryBean">
    <property name="editorMappings">
     <map>
      <entry key="java.util.Calendar"><idref bean="sqlDateCalendarEditor"/></entry>
     </map>
    </property>
   </bean>
  
   <bean id="viewFactoryCreator" class="org.springframework.webflow.mvc.builder.MvcViewFactoryCreator">
    <property name="viewResolvers">
     <list>
      <ref local="xmlViewResolver"/>
      <ref local="decoratedJstlViewResolver"/>
      <ref local="urlBasedViewResolver"/>
     </list>
    </property>
   </bean>
  
   <bean id="webflowDebugListener" class="org.springframework.webflow.execution.DebuggingListener"/>
   
   <bean name="flowController" class="org.springframework.webflow.mvc.servlet.FlowController">
    <property name="flowExecutor" ref="flowExecutor" />
    <property name="flowUrlHandler">
     <bean class="org.springframework.webflow.context.servlet.DefaultFlowUrlHandler" />
    </property>
   </bean>
    

  
  

  
  Now, you may be asking yourself, "Why would there be more configuration in Spring Webflow 2 ? Doesn't Spring generally improve on things like configuration syntax between major versions ? The answer is, of course, yes. However, there are a number of new features that come with Webflow 2 that need to be configured, hence the extra beans for configuration. Note also, that the syntax has changed. I direct your attention to the added 'flow-' prefixes on element names of the previously existing Webflow elements.
  

  
  


• 
  Webflow 2 has much better, much closer integration with Spring Security, hence the need for SecurityFlowExecutionListener listed above. I haven't had a chance to play around with the new integration between Spring Security 2 and Spring Webflow 2, but I'm quickly getting there.
  


• 
  Thanks to the built in model binding and validation that comes with Spring Webflow 2, there's much less syntax for views that simply bind to a model object on transitions. Instead of having to add in FormActions and adding action elements to the view-state you want them applied to, you can now simply specify a model name for the 'model' attribute of the view state, and Webflow 2 will automatically bind the form object for you (which leads us into our next point). Of course, the Spring developers maintained their usual style of keeping things as configurable as possible, so you can not only choose not to bind the model object for particular state transitions, but you can disable validation as well, using the new 'bind' and 'validate' attributes of Webflow 2 'transition' elements.
  


• 
  Because Webflow 2 can now do binding and validation for us right in the flow definition without having to define FormAction beans in our Spring ApplicationContext, Webflow 2 comes with its own updates to the spring-binding framework, hence the need for the 'webflowConversionService' bean in the configuration above. Now, you're probably saying to yourself right now, "Well what the fuck am I supposed to do with the custom PropertyEditors I wrote for my objects when dealing with Spring / Webflow 1 ?". Don't worry, all is not lost. There's a PropertyEditorConverter class that adapts PropertyEditor implementations to the new Webflow 2 Converter interface. You can use this to interface your editors with Webflow 2, and in fact that's what I did.
  


• 
  Webflow 1 left it up to the Spring framework to resolve and render views. Some people found this inconvenient, so Webflow 2 now allows you to have Webflow directly resolve and render views itself. However, since I'm already using the Spring framework and don't need Webflow's abstraction away from the underlaying framework, I chose to keep the Webflow 1 style of resolution and view rendering, hence the need for the 'viewFactoryCreator' bean above.
  

Once all the new configuration was done and out of the way, it was simply a matter of upgrading my existing flows to the new Webflow 2 syntax, which was almost entirely taken care of by the migrator that comes with Webflow 2. Previously, I used the 'var' element heavily to make use of beans in my Spring ApplicationContext, but the 'var' element has since had its usage completely reworked for Webflow 2, so I'm going to have to refactor a couple of my flows and change my style of design with Webflow 2.

One other feature that I'm learning about as I write this post is the Webflow 2 PersistenceContext. It's a solution for the use case where you want to be able to load objects from a database, and only allow a single user to be able to access them at once, ie you wouldn't want multiple people logging into a database and being able to access data on a particular user at the same time and potentially overwrite each others' changes. I'll post more about that later.

Migrating from Acegi Security to Spring Security 2

In an effort to keep our applications current, I've been looking at upgrading from Acegi Security to Spring Security 2 in one of our smaller applications as a test, to see how well it'd go over for our larger applications. So far, the tests are pretty positive. The main advantage to the migration that I can see is improved Web Service security (which I'll definitely be needing), as well as a considerably simplified configuration syntax. The following is a small migration guide :

0. If you haven't already, update your project to use Spring 2.5.4 or greater. This is necessary because of changes to Spring that Spring Security (as well as other Spring subprojects) requires. If you're using Maven 2, this is dead easy, you need only update the <version> elements of the appropriate dependencies.

1. Change all package references starting with 'org.acegisecurity' to 'org.springframework.security' in your code. If you've architected your system right, this should mean very few changes.

2. In your POM, remove all mention of Acegi security and replace it with the following :

<dependency>
    <groupId>org.springframework.security</groupId>
    <artifactId>spring-security-core-tiger</artifactId>
    <version>${spring.security.version}</version>

    <exclusions>
        <exclusion>
            <groupId>org.springframework</groupId>
            <artifactId>spring-core</artifactId>
        </exclusion>

        <exclusion>
            <groupId>org.springframework</groupId>
            <artifactId>spring-support</artifactId>
        </exclusion>
    </exclusions>

</dependency>
...
<dependency>
    <groupId>org.springframework.security</groupId>
    <artifactId>spring-security-taglibs</artifactId>
    <version>${spring.security.version}</version>

    <exclusions>
        <exclusion>
            <groupId>org.springframework</groupId>
            <artifactId>spring-web</artifactId>
        </exclusion>

    </exclusions>
</dependency>

The exclusions are necessary to prevent Spring 2.0.x dependencies from being unnecessarily pulled in.

3. Go through your JSPs and remove all xmlns:authz="..." declarations and replace them with :

    xmlns:security="http://www.springframework.org/security/tags"

4. Go through your applicationContext*.xml files and replace any constants you may have referring to Acegi security with their proper Spring Security 2 counterparts. This means replacing the package prefixes 'org.acegisecurity' with 'org.springframework.security' and in some cases replacing ACEGI with SPRING_SECURITY in some static constant names.

This migration guide was based on (and expanded from) the one provided by Matt Raible. If you get the time, I recommend you check out his site, he has a lot of good wisdom and examples to share.

On Hibernate UserTypes

Hibernate UserTypes are a great way for persisting complex classes which may require more than one column in a table in order to be properly represented in a database. Many people have used them successfully in order to be able to simplify storage of complex objects and thus simplify their applications at the same time. One simpler use case of them was to create Enum types before support for Java 5+ enums came along.
Now, you'd think that once you've got Java 5 support with Hibernate, you'd never have to use such a simple use case again because you've got the Enums themselves, along with the @Enumerated annotation you can place on fields and properties, right ? Wrong. I've recently started migrating my projects to Spring Security from Acegi Security, and I've found that in the process, they've made the GrantedAuthority interface extend Comparable. This conflicts with the fact that Java 5+ Enums already implemented the Comparable interface with a generic parameter, and as such your code won't compile if you have an Enum that also implements GrantedAuthority, such as the following :

public enum Role implements GrantedAuthority, ConfigAttribute
{
 ROLE_ADMINISTRATOR;

 public String getAuthority() {
  return name();
 }

 public String getAttribute() {
  return name();
 }

 public String getMessageKey() {
  return "enum.Role.".concat(name());
 }
}

In order to remedy the conflict, I've had to convert my nice, pretty, simple Enum into a class, and simulate Java 5+'s enum behaviour, like so :

public final class Role implements GrantedAuthority, ConfigAttribute, Serializable, Cloneable {

 private static final long serialVersionUID = 1L;

 public static final Role ROLE_ADMINISTRATOR = new Role(0, "ROLE_ADMINISTRATOR");

 private static final Role[] VALUES = new Role[] {
  ROLE_ADMINISTRATOR
 };
 
 private static final Map NAME_MAPPINGS = new HashMap();
 
 static {
  Arrays.sort(VALUES, new Comparator() {
   public int compare(Role o1, Role o2) { 
    return o1.ordinal - o2.ordinal;
   }
  });
  
  for (Role r : VALUES) {
   NAME_MAPPINGS.put (r.getName(), r);
  }
 }
 
 private int ordinal;
 private String name;

 //Constructors

 /*
  * DO NOT EVER USE THIS! It exists only for serialization purposes.
  */
 public Role() {
  super();
 }
 
 private Role(Role r) {
  this(r.ordinal, r.name);
 }

 private Role(int ordinal, String name) {
  super();
  this.ordinal = ordinal;
  this.name = name;
 }

 //Behaviour Methods

 public int compareTo(Object o) {

  if (o == null || o.getClass() != Role.class) {
   throw new IllegalArgumentException(
     "Comparison object may not be null, and must be a Role");
  }

  return this.ordinal - ((Role) o).ordinal;
 }
 
 public String getAuthority() {
  return getName();
 }

 public String getAttribute() {
  return getName();
 }

 //Pseudo-properties

 public String getMessageKey() {
  return "enum.Role.".concat(getName());
 }
 
 //Property Accessors

 public final int getOrdinal() {
  return this.ordinal;
 }

 public final String getName() {
  return this.name;
 }

 //Helper Methods
 
 public static final int hashCode(Role r) {
  return r == null ? 0 : r.hashCode();
 }
 
 public static final boolean equals(Role x, Role y) {
  return x == null ? (y == null) : x.equals(y);
 }
 
 public static final Role clone(Role r) {
  return r == null ? null : r.clone();
 }
 
 public static final Role[] values() {
  return VALUES;
 }
 
 public static final Role valueOf(String s) throws IllegalArgumentException {
  
  String key = defaultString(s).toUpperCase();
  
  if (NAME_MAPPINGS.containsKey(key)) {
   return NAME_MAPPINGS.get(key);
  } else {
   throw new IllegalArgumentException("No role by the name ["+s+"] exists");
  }
 }
 
 //Object Overrides
 
 @Override
 public String toString() {
  return new StringBuffer().append(this.name)
   .append("(").append(this.ordinal).append(")")
   .toString();
 }

 @Override
 public Role clone() {
  return new Role(this);
 }

 @Override
 public int hashCode() {
  final int prime = 31;
  int result = 1;
  result = prime * result + ((this.name == null) ? 0 : this.name.hashCode());
  result = prime * result + this.ordinal;
  return result;
 }

 @Override
 public boolean equals(Object obj) {
  if (this == obj)
   return true;
  if (obj == null)
   return false;
  if (getClass() != obj.getClass())
   return false;
  final Role other = (Role) obj;
  if (this.name == null) {
   if (other.name != null)
    return false;
  } else if (!this.name.equals(other.name))
   return false;
  if (this.ordinal != other.ordinal)
   return false;
  return true;
 }

}

Once this was done, I created a Hibernate UserType implementation for Role, so that Hibernate could persist Roles as Integers, just as was already being done for the Enum version of Role:

public class RoleUserType implements UserType {

 private static final int[] SQL_TYPES = new int[] { Types.INTEGER };
 
 public static final String HIBERNATE_TYPE_NAME = "RoleUserType";

 public Object deepCopy(Object value) throws HibernateException {
  return value;
 }

 public Object assemble(Serializable cached, Object owner) throws HibernateException {
  return (Role)cached;
 }

 public Serializable disassemble(Object value) throws HibernateException {
  return (Role)value;
 }

 public boolean equals(Object x, Object y) throws HibernateException {
  return Role.equals((Role)x, (Role)y);
 }

 public int hashCode(Object x) throws HibernateException {
  return Role.hashCode((Role)x);
 }

 public boolean isMutable() {
  return false;
 }

 public Object nullSafeGet(ResultSet resultSet, String[] names, Object owner) throws HibernateException, SQLException {
  int roleOrdinal = resultSet.getInt(names[0]);
  
  return resultSet.wasNull() ? null : Role.values()[roleOrdinal]; 
 }

 public void nullSafeSet(PreparedStatement statement, Object value, int index)
   throws HibernateException, SQLException {
  if (value == null) {
   statement.setNull(index, Types.INTEGER);
  } else {
   statement.setInt(index, ((Role)value).getOrdinal());
  }
 }

 public Object replace(Object original, Object target, Object owner) throws HibernateException {
  return original;
 }

 @SuppressWarnings("unchecked")
 public Class returnedClass() {
  return Role.class;
 }

 public int[] sqlTypes() {
  return SQL_TYPES;
 }

}

Once the Hibernate UserType implementation was written, it was just a matter of adding my model package to Hibernate's list of annotated packages (using Java 5 after all) :

@TypeDef(name = RoleUserType.HIBERNATE_TYPE_NAME, typeClass = RoleUserType.class)
package com.mypackage.model;

import org.hibernate.annotations.TypeDef;
import eu.alenislimited.acshelper.support.hibernate.RoleUserType;

After defining the Hibernate UserType type, it was then just a matter of going around to all my fields that used Role, and replacing ...

@Enumerated(EnumType.ORDINAL)

... with ...

@Type(type = RoleUserType.HIBERNATE_TYPE_NAME)

Fortunately, doing the conversion was just extra work, and didn't require any special changes to any of my Spring configuration, or even my Hibernate configuration (beyond adding the @TypeDef to my model package and adding it to my Hibernate SessionFactory's list of annotatedPackages).

A first time gem creator's addendum

I recently started researching how to create Ruby Gems because I was working on on a Ruby application that is a reference application for accessing our production system at work, and I wanted to make the specific access code for our production system a Gem in Ruby so that I could just hand it off to future clients who want to integrate with Ruby. Further to that end, I read about the Newgem gem, and so I decided to use it, since it had recently hit 1.0.1. You can read the documentation there, so I won't repeat it here, but there's a couple of things you should do, prior to following their instructions.

1. Set a 'HOME' environment variable if you're using Windows (as I am)


2. gem install cucumber newgem


3. rake config_hoe

The first step is to install newgem, but to also ensure that cucumber is installed as well because it's an unlisted dependency. The second step is to ensure that there's a basic .hoerc file created in your home directory that's ready to go whenever you want to run any tasks on your gem while testing / packaging it. I'm guessing it's automatically created in Linux, but I had to manually set the 'HOME' environment variable and run the configuration task myself in order to have the proper configuration file generated for me to run the tasks for creating and testing my gem.

A quick note on ActiveResource in Ruby on Rails

I've learned a bunch of new things about Ruby on Rails in the past few days, specifically when it comes to RESTful web services.

• ActiveResource uses the built in Ruby XML::Mapping library for its OXM (Object to XML mapping) layer


• Apparently, no Ruby library out there properly handles namespaces. Not a one : REXML, ROXML, XML::Mapping


• ActiveResource can be highly customized to adjust to other RESTful web service schemes, just not when it comes to the generated XML.

Unfortunately this makes it very hard to integrate (in ruby) with the RESTful web service that I've written for our company's production web site. Ironically, I wanted to make the service very Ruby friendly. I really wish there was more in depth documentation out there for Ruby APIs. It would have made things so much easier when I was designing our API, which runs in Java, using JAXB.

A quick note on Maven plugins

I've recently had to go abroad to various other countries for work, and I've found that porting my projects around to various workspaces hasn't been as easy as it otherwise should have been, and here's why : I use Maven, especially the plugins. I've used others, and I've even written my own. I've also learned that one should specify versions of all plugins used, because the behaviour of a plugin may change between versions and if you're unaware of that and you start getting strange behaviour from your project build, this can lead to hours of wasted time trying to figure out what the hell is going on. I'm referring specifically to the maven-war-plugin for building web application WAR files. I had previously left the version unspecified, and when I ported my workspace to my laptop, Maven chose to use a different version of the plugin than that of my desktop, and as a result was including files I didn't want in my WAR file. This led to classpath errors, and me spending several hours trying to find out where the problem was. So in short, always specify versions of the plugins you use to ensure consistent behaviour in your build, wherever you may be working on your project.

Reflection in Ruby

I've recently gotten started going on a Ruby on Rails project for my company, that's meant to be a simple app that we'll throw up and let run for any prospective customers. But I ran into a problem with copying property values between objects, since I'm not as familiar with the language as I'd like to be. The Object type defines a method called 'send' which lets you invoke a method with given arguments. However, I wanted to be able to assign property values via this method, and just sending the name of the property as the name of the method to invoke wasn't working. (Works just fine if you want to get the property). As it turns out, the method for invoking the setter of a property is brain-dead simple : use the name of the method as you'd define it if you were overriding the setter for the property. For example, if you have a property called 'name', you'd define the setter for it as follows :

def name= (name)
  @name = name
end

So if you wanted to set the value of this property reflectively, you'd do something like :

 @person_instance.send "name=", "John Smith"

A moment of developer clarity and zen

I had a moment today where I was just letting my mind wander. It was one of those moments where you have a brilliant idea that just seems so common sense that you can only ask yourself "Why the hell didn't I think of that before ?" This moment of clarity happened to be concerning my horribly slow laptop, with it's horribly old ATA 100, 5400 rpm hard drive. Then it occurred to me : just like with video encoding that I had setup months ago, I could setup a RAM disk to speed up Eclipse by storing my workspace on the RAM disk to speed up access to all the (ridiculous number of) temp files that Eclipse uses. On Ubuntu Linux, it turns out this was ridiculously easy : http://ubuntuforums.org/showthread.php?t=182764

The really amazing part was just how much this sped things up : it took my project build time from 6 mins, 30 seconds down to 35 seconds. And those are real numbers (plus or minus a couple seconds, due to slight variations in repeated builds.)

More JAXB quirks

Today I ran across yet more quirks of JAXB 2.0. I'm getting really tired of running across stupid errors that are difficult to debug because the programmers who wrote JAXB are lazy. Today, I was receiving a java.lang.InternalError when I tried to compile a schema from beans I'd recently refactored. The error I received was something along the lines of "could not escape schema namespace". As it turns out, it was caused by the lack of an @XmlType annotation on the enums I had added to one of my XML serializable beans. I hope this helps anybody who has the same problem.

A quick note about JAXB

JAXB (the Java API for XML Binding) is a great piece of technology (2.x, not 1.x). However, if you're starting an application and your JAXBContext is throwing an exception saying that it's unaware of a given class, there's a quick fix. At this point, I'm guessing you've configured your JAXB context to use a package, and the class that the JAXBContext is unaware of is in the given package, and you're scratching your head as to why it can't seem to find a class that's in the proper package. Well, here's the most probable answer : if you're using package-configured JAXBContexts, you need to have factory methods for all top level elements, similar to the following :

    /**
     * Create an instance of {@link PurchaseOrder }
     * 
     */
    public PurchaseOrder createPurchaseOrder() {
        return new PurchaseOrder();
    }

... assuming that mypackage.PurchaseOrder is the class the JAXBContext is complaining that it's unaware of. This little quirk took me a couple hours to debug because I had just regenerated some web services code using Apache CXF 2.1.1 from an updated WSDL document for an updated Web Service that our company uses. Little did I know, that in comparing the two ObjectFactory files in Eclipse, I had missed copying over certain important functions. Hopefully this helps you.

Pure FTP on Ubuntu

Pure FTP is a great FTP server and I love it because it's ridiculously fast, reliable and works well for our company. The only problem is that it's tricky to configure on Ubuntu because just like with numerous other programs, the people at Ubuntu, in their infinite wisdom, felt the need to fuck with the program's default way of doing things. Specifically, in Ubuntu, command line arguments for starting the FTP service are done through individual files for each command line option you want the service to be started with, with values for the options placed inside each of the files. This is a stupid way of doing things, but that's not the topic of this post.

The problem I've been having lately is that I recently deployed new projects within our production network, and these new projects required access to the FTP server, and aren't on the same box as the server, as is the sole other project that has been using the FTP server. I'd been getting problems trying to connect to the server from any LAN box, but not any external boxes nor the machine itself (localhost). The error I got back was "421 Service not available". I googled around for hours and found nothing useful, until I started realizing that other people were getting 421 errors when their PureFTP instance was misconfigured, but with different messages, and then it got me thinking that maybe my instance was somehow misconfigured.

I re-read the documentation for PureFTP and after an hour or so, it hit me that the server does reverse lookups to resolve fully qualified names, and such resolution doesn't work properly on our network (for good reasons that I'm not going to go into). After disabling reverse DNS resolution with the -H startup option (`echo "yes" >> DontResolve` in the configuration directory in Ubuntu), the problem went away.

I hope this helps anybody else who runs into the same problem.

More Tomcat quirks

I recently ran across a problem with receiving a LinkageError in one of my web applications. The problem occurred when Acegi security tried to use libraries that were not yet loaded and tried to load them itself. Strangely, the error only occurred while using my RESTful API with a Spring Framework controller. If I logged in through my web interface which uses Acegi and Spring MVC, then the linkage error didn't occur.

After numerous hours of Googling around, I found a small company's JIRA issue tracker that reported the same bug, but also that it only occurred when using the security manager. After disabling the security manager on my own Tomcat instance, I found that the problem went away. I'd very much like to have a better resolution, but it's going to have to do for the time being.

Tomcat quirks

In recent weeks, we've had problems with our company's servers going down because of power problems at our colocation provider. As a result, the fact that Tomcat hadn't been properly configured to boot at startup had really burned us. Consequentially, I've been spending the past few days troubleshooting why the servers wouldn't startup, and ensuring that they do come up properly at boot time in future. The following are some of the things I've run across.

• 
  The JAVA_HOME and JRE_HOME variables must be set. If they're not, then Tomcat won't start, at least on Ubuntu Gutsy Gibbon Server. This is a problem I encountered with the default installation of JIRA on one of our production servers.
  


• 
  When using EhCache with Hibernate, the tmp directories don't get deleted, regardless of whether or not Tomcat is shutdown properly. This will block the container from starting up again, so these temp files must be deleted. I encountered this problem with my own applications.
  

Finally! The trick to proper Java Date and Calendar formatting

It's well documented in the Java API as well as numerous forums and blogs, that the Java API is not properly implemented, and in some respects flat out broken, hence why Java 7 is going to have a brand spanking new Date/Time API based on the Joda Time library hosted at sourceforge.net. In implementing Dates / TimeZones in Java, the developers of Java saw fit to separate time zones from date implementations because, really, a date is just a number of milliseconds from Jan 1, 1970 at 00:00:00.000 GMT in the morning. This is a noble goal which I whole heartedly agree with : dates should be represented separately from their timezones because the printed representation of a date will change depending on time zone, whereas no matter where you are in the world, the number of milliseconds from the Epoch has not changed. However, the Java developers implemented this concept poorly. They chose to attach TimeZones to Calendars and then not have them affect any of the time fields, which is fine. But the TimeZone attached to a calendar is not used when using a DateFormat directly. Here's the key : the DateFormat object uses its own internal TimeZone during formatting (which it takes from the currently running JVM) by default. In order to format using the TimeZone attached to a Calendar, you have to explicitly set the TimeZone of the DateFormat to that of the Calendar instance you want to format.

An interesting 'accesskey's quirk

Since I learned about accesskey support in HTML, I've been including them where appropriate in my web applications to speed up my access and usage of said applications. However, when trying to use the accesskey for a password field, P, I ran across an interesting quirk. The accesskey modifier is different for various browsers. In order to use access keys in IE, the modifier is Alt, for Firefox it's Alt+Shift, for Opera you press Shift+Esc, then the accesskey. I primarily use Firefox (go open source), so when I pressed Alt+Shift+P to access a password field, it opened Windows Media Player. As it turns out, this is the hotkey for accessing WMP from the toolbar (ie the miniplayer). To prevent this hotkey combination from opening WMP, you'll have to disable the toolbar by going to the taskbar, Right-Click -> Toolbars and uncheck Windows Media Player (I don't like the mini-player toolbar that much anyway).

Spring Framework URL mapping quirks

My recent foray into developing using RESTful principles and resources has lead me to an interesting quirk in the Spring Framework, which I use for our company's primary application. As it turns out, the URL mapping scheme requires that you set 'alwaysUseFullPath' to true so that the entire path of a URL that gets submitted to the framework gets inspected to determine the proper controller mapping. Otherwise, it can lead to some quirks, like not submitting the request to the proper controller. I had to learn this the hard way through several hours of debugging.

Why you should always export your sources with your Java projects

With the advent of popular and widespread Maven 2 adoption, there's no reason you shouldn't be using it to build your open-source or closed source Java projects. With that in mind, it's dead easy to use Maven's 'source' plugin to automatically generate a separate JAR with your project's sources in it when you package and deploy your project. Posting the sources with your project not only allows other people to easily debug their code while using your project, but also serves as a backup in the event of a catastrophic failure of a computer hosting your code for which you did not have proper backup procedures already in place. In the event that you couldn't tell, that happened to me tonight.

JAXB schemagen - Finally got it working

For those not in the know, schemagen is a program that comes as part of the Java Web Services Developer Pack and it's used to generated XML schemas from JAXB annotations on Java beans. It so happens that the creators of the JAXB reference implementation also made a Maven 2 plugin for this program. I had previously attempted to use it to generate schemas in my initial attempts with JAXB, but had been presented with a slough of unfriendly exceptions being thrown at me whenever I ran the plugin. Not having the time back then to really play around with it and being considerably less experienced with JAXB, I had to shelve it and find other, less satisfying solutions to my problems with generating documentation.

Recently, I've had to come back to using JAXB because I'm making a RESTful Web Services API that leverages the power of both JAXB and Hibernate to do all my heavy lifting for me. This time around, I wasn't willing to tolerate a lack of schema to give to our users of the API, because it would mean a lot more work for them, and a lot more work for me. This time, I decided to be persistent and dig around the jaxb-schemagen plugin to make sure I could get it working. I'm proud to say that my perseverance paid off, and I now have my RESTful API schema being automatically generated for my application. Here are the problems and the solutions I ran into when I was trying to get going on this:

NullPointerException

I came across persistent NullPointerExceptions while trying to run the plugin at first. The stack trace indicated that the problem was with apt, the Java annotation processing tool. I later discovered that in order to properly map your classes into XSD schema types, you must specify an @XmlType annotation on *all* of the classes you wish to map (at least with JAXB 2.0, which is the version I'm currently using)

ClassCastException

After I resolved the first problem, I came across another pesky exception that likewise did not provide any useful debugging information. The plugin output indicated that it was finding annotations that it didn't know how to deal with, specifically the Java Persistence API annotations that I was using for Hibernate. After much digging around on Google and some detective work, I discovered that any annotations encountered by the jaxb-schemagen plugin had to be on the Maven runtime classpath. I double checked my POM to find that I had specified the scope of the JPA / Hibernate annotations as 'provided', which instructs Maven not to load them into either the compile or runtime classpaths. The initial reason I had for specifying the dependency scope as 'provided' was so that they would not needlessly get included with my project WAR files. I changed their scope to 'compile' (which also includes 'runtime') and voila, apt could now properly detect the unknown annotations, and get past them to deal with the JAXB annotations it needs to create the XML schema.

If anybody else encounters similar errors with JAXB-schemagen, I hope they find this page and find it useful.

Fixing package retrieval quirks in Ubuntu Gutsy Gibbon Server

In the default installation of Ubuntu Server (Gutsy Gibbon), the default source of packages is the CD-ROM drive. That's fine if you make the assumption that there will always be somebody physically present in order to maintain the servers, but for most server's these days, that's a fallacious assumption. The really bad part about this default, is that there's no way I know of at the time of this writing to override this on the update command. In our company, we have our servers hosted off-site like so many other companies, so everything must be done remotely. Therefore, the CD-ROM as a source for Ubuntu packages is a bad idea. To remedy this, you have to go into the apt-get configuration stored at

/etc/apt/sources.list

, and you'll have to find a line similar to :

deb cdrom:[Ubuntu-Server 7.10 _Gutsy Gibbon_ - Release i386 (20071016)]/ gutsy main restricted

Comment out this line, try your update again and you should be good to go.