I got some exposure to custom Java 5 Annotations today and came across a noobie mistake.

Here’s my annotation:

public @interface Annotated {
}

Pretty simple, right?

Here’s a test class that uses the annotation:

import java.lang.annotation.Annotation;

@Annotated
public class Main {
    public static void main(String[] args) throws Exception {
        for(Annotation ann: Main.class.getAnnotations()) {
            System.out.println(ann);
        }
    }
}

What does this print?
…
Nothing!

Well, WTF?

Turns out Annotations are not run-time accessible unless you declaratively specific it via @Retention. The updated annotation looks like this:

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

@Retention(RetentionPolicy.RUNTIME)
public @interface Annotated {

}

By default, the Retention is specified with RetentionPolicy.CLASS which, per the javadocs, “Annotations are to be recorded in the class file by the compiler but need not be retained by the VM at run time.”

RetentionPolicy.RUNTIME allows the annotation “to be recorded in the class file by the compiler and retained by the VM at run time, so they may be read reflectively.”

File this one under, RTFM.

I’ve been doing some date math at work and I came across something I thought was wack.

Check this out:

Calendar cal1 = Calendar.getInstance();
Thread.sleep(500);
Calendar cal2 = Calendar.getInstance();
Thread.sleep(500);
Date now = new Date();

System.out.println(cal1.before(cal2));
System.out.println(cal1.before(now));

What do you think this snippet prints (It compiles, I promise!)?

Looking at the code, it shows that we are getting three snapshots in time, waiting half a second between snapshots, and assigning those values to cal1,cal2, and now, respectively. I put in the Thread.sleep() to illustrate the point more clearly. The first print statement compares the first and second snapshots in time, returning true if the first is before the second. The second print statement returns true if the first is before the third snapshot.

Logically, we would expect both print statements to prints true. However, this outputs:

true
false

But, how could the first snapshot be before the second snapshot but not the third?

Putting up the javadocs, gives us our answer. The Calendar before and after methods always returns false if you don’t pass it a Calendar object. Why? I have no idea. Why not just have the method signature take a Calendar object? I mean, I guess this allows you to extend Calendar to be able to call after/before on whatever kind of classes you want to support…but does it really make sense to compare a Calendar to a Monkey class? This is what I call a Java WTF.

In the previous post, I described how to get your Java SDK installed on your machine. In this piece, I’ll lay out how to get your tomcat instance up and running.

Let’s setup our JAVA_HOME. While you can set this setting in many places, I decide to stick it in bash.bashrc.

My Java installation from apt-get put Java under /usr/lib/jvm/java-6-sun.

sudo vi /etc/bash.bashrc

Enter in:

# set JAVA_HOME environment variable
JAVA_HOME=/usr/lib/jvm/java-6-sun

Save and quit vi. Log out and log back into your console and you should be able to do

 >>echo $JAVA_HOME
/usr/lib/jvm/java-6-sun

I went through the initial attempt of installing tomcat from apt-get. This resulted in a successfully download of all the files, but I wasn’t able to get tomcat to start up. Not only that, it installed tomcat and created symbolic links everywhere and there were permission issues galore. Thanks to the beauty of slicehost, I just rebuilt my machine from my previous snapshot (luckily I made a snapshot after the previous post).

So, I decided to just download and install tomcat manually. I decided on apache-tomcat-5.5.25.

To get started, download the tarball and extract it somewhere.

wget http://apache.cs.utah.edu/tomcat/tomcat-5/v5.5.25/bin/apache-tomcat-5.5.25.tar.gz
tar xzvf apache-tomcat-5.5.25.tar.gz
cp -R apache-tomcat-5.5.5 <PATH_TO_TOMCAT_INSTALL>

You will need to go to the bin directory and set some file permissions so you can execute some of the files.

cd <PATH_TO_TOMCAT_INSTALL>/bin
sudo chmod a+x *.sh

It’s a probably good time to see if things are looking good. So try,

 >> ./version.sh
Using CATALINA_BASE:   /usr/share/tomcat
Using CATALINA_HOME:   /usr/share/tomcat
Using CATALINA_TMPDIR: /usr/share/tomcat/temp
Using JRE_HOME:       /usr/lib/jvm/java-6-sun
Server version: Apache Tomcat/5.5.25
Server built:   Aug 24 2007 05:33:50
Server number:  5.5.25.0
OS Name:        Linux
OS Version:     2.6.16.29-xen
Architecture:   amd64
JVM Version:    1.6.0-b105
JVM Vendor:     Sun Microsystems Inc.

Sexy. Let’s go ahead and try to startup tomcat.

./startup.sh

By default, tomcat should be running on port 8080. (If you tried to install from apt-get, it’s setup on port 8180)

Setting up the tomcat manager

sudo vi conf/tomcat-users.xml

We need to setup a manager role to see the tomcat status page:

<tomcat-users>
  ...
  <role rolename="manager">
  ...
  <user username="admin" password="mysecretpassword" roles="tomcat,manager">
</tomcat-users>

Restart tomcat and confirm you can log into the Tomcat status page and we’re done!

TODOS:

• I need to setup the system to run tomcat on startup
• I need to write an init.d script
• I need to get tomcat to proxy through apache via mod_jk

When I first got my slice, I had it setup with java and tomcat. Apparently, I updated or rebuilt my slice and forgot to install those two again. Too bad I didn’t take good notes because I totally forgot how to do it.

So this time, I’m going to document it via this post.

I am currently running Ubuntu Feisty (v. 7.04). You can find out what version you’re running by running the following command:

cat /etc/issue

The usual apt-get command allows me to install sun-j2re1.4. That’s not very helpful if I want to compile java code off of my slice or set it up to be a continuous build server. I remember that I had to add a specific repository in order to be able to install the Java SDK via apt-get. After some digging around, I came up with the following:

sudo vi /etc/apt/sources.list

Paste the following into the file:

deb http://archive.ubuntu.com/ubuntu feisty universe multiverse
deb-src http://archive.ubuntu.com/ubuntu feisty universe multiverse

The Ubuntu docs recommend enabling the universe/multiverse security/updates repositories to prevent version mismatches during installs or upgrades but I didn’t run into any issues proceding without them.

Save and exit out of vi.

Next, run

sudo apt-get update

apt-get should be pulling down an updated list of installable packages. So if you type

sudo apt-get install sun-j

and then hit TAB, you should get a list of installable sun packages.

I decided to install Java 6.0 SDK.

sudo apt-get install sun-java6-sdk

It will begin to download and install the SDK. You will have to accept a license. Just hit TAB to get select “OK” and hit enter.

Once it completes, you should be able to confirm the JDK was installed successfully.

  >> javac -version
javac 1.6.0

The next post will lay out steps to install Apache Tomcat.

Here’s an interesting talk at Google by Josh Bloch, author of Java Puzzlers and special guest Bill Pugh.

I definitely learned a few things about Java from it.