Craig Pardey

List.clear() throws UnsupportedOperationException

Posted on September 16, 2013 | Craig Pardey

Consider the following code

String[] s = new String[]{""};  
List<String> list = Arrays.asList(s);  
list.clear();

All looks good, right? When you run it you get:

java.lang.UnsupportedOperationException  
	at java.util.AbstractList.remove(AbstractList.java:144)  
	at java.util.AbstractList$Itr.remove(AbstractList.java:360)  
	at java.util.AbstractList.removeRange(AbstractList.java:559)  
	at java.util.AbstractList.clear(AbstractList.java:217)

This is because Arrays.asList(array) returns a fixed-size list backed by the specified array. Fixed-size being the operative word.

Java

Arrays.asList() gives a list with wrong size

Posted on July 8, 2013 | Craig Pardey

Try this out for fun. int[] i = new int[]{1, 2, 3}; System.out.println(Arrays.asList(i).size()); Integer[] ii = new Integer[]{1, 2, 3}; System.out.println(Arrays.asList(ii).size()); Output: 1 3 What the hell, Java? This is totally unexpected behaviour! In this case Java is being a bit pedantic. See, Collections can contain only contain Objects, and an int is not an Object but int[] is an Object, so that’s why you get a list with only 1 element. [Read More]

Java

How to set JMSXUserID in Websphere MQ using Spring JMS

Posted on July 5, 2013 | Craig Pardey

Every time I work with MQ and Spring JMS I want to poke my eyes out with a dull instrument. It’s always a pain in the neck. My most recent challenge was trying to get the JMSXUserID field to flow through to the application on the other side of MQ. First, I created a MessagePostProcessor to add the JMS header public class MyMessagePostProcessor implements MessagePostProcessor { private String userId; @Override public Message postProcessMessage(Message msg) throws JMSException { msg. [Read More]

Websphere MQ

Big Data and HR

Posted on April 29, 2013 | Craig Pardey

This piece from the New York Times touches on a subject that I’m passionate about - the challenges of hiring good people. Deep into it, it mentions that: “…the most proven method, Dr. Lewin said, is a referral from someone already working there. Current employees know the culture, he said, and have their reputations and their work environment on the line.” The big data thing is a cool, tech solution, but really it’s referrals that matter. [Read More]

Recruiting

Can not execute Sonar: Missing column: period in ALERTS

Posted on March 27, 2013 | Craig Pardey

I recently encountered the following error in Sonar 3.5 [ERROR] Failed to execute goal org.codehaus.mojo:sonar-maven-plugin:2.0:sonar (default-cli) on project smartfx: Can not execute Sonar: Missing column:period in DB.ALERTS -> [Help 1] org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.codehaus.mojo:sonar-maven-plugin:2.0:sonar (default-cli) on project myproject: Can not execute Sonar at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java: 203) at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java: 148) at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java: 140) at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:84) A quick check of the database revealed that the ALERTS table does indeed contain a column named ‘period’. [Read More]

Sonar

hg clone fails with 255 error

Posted on March 26, 2013 | Craig Pardey

I recently encountered an issue with cloning a Mercurial repository where it would fail with an obtuse error stating that “[command returned code 255 Mon Mar 25 11:39:55 2013]”. My initial Googling implied that this was caused by a server timeout but the problem persisted even after increasing the timeout on our Apache web server. The clone was always failing on one particular file - a 600Mb binary. (Don’t ask…) [Read More]

Mercurial

The Guild

Posted on March 20, 2013 | Craig Pardey

Troy Hunt’s Ghost Who Codes ignited something inside me. Initially I was a little insulted because I don’t have much of an online presence apart from my blog and my Twitter account. There are many reasons for this but in the end it doesn’t matter. You see, as much as I respect Troy, I think he’s missing the point. The best developers rarely apply for advertised jobs. They’re hired through their network and are never on the market. [Read More]

Recruiting Inner Circle

Apache commons for readability

Posted on February 20, 2013 | Craig Pardey

There are many short methods in the Apache Commons libraries that seem like overkill at first glance, however, their purpose becomes more apparent when you examine the effect that these methods have on the readability of the caller. I see a lot of code that does stuff like this: if( s == null || "".equals(s.trim())) { // Do something } which could be re-written as if( StringUtils.isBlank(s)) { // Do something } Personally, I find it much easier to understand the intent of the second version. [Read More]

Java Apache Commons

SonarException: The project is already been analysing.

Posted on February 12, 2013 | Craig Pardey

I was getting this error when running a Sonar analysis recently.

This was caused by the Jenkins/Sonar process getting killed while the project analysis is underway. Sonar now uses a database semaphore to prevent multiple builds running at the same time, but if the job gets terminated then the semaphores don’t get cleaned up.

To fix the problem: Log into the database and delete any rows in the ‘semaphores’ table.

Sonar

How to show which .hgrc Mercurial is using

Posted on November 22, 2012 | Craig Pardey

Mercurial loads a bunch of different configuration files and overlays their values on top of each other. The hgrc man page shows the order in which these files are loaded. I encountered an issue recently where I knew that hg was using an erroneous setting but I had no idea where the setting was coming from. The magic answer is hg --debug showconfig This will output all the current settings, along with the name of the file that it got each setting from. [Read More]

Mercurial