Jtanium's Notebook » Java

JDK Source on OS X

jtanium — Wed, 07 Nov 2007 04:11:15 +0000

If you’re lookin’ to get your hands on the JDK source on OS X, you’ll find it in the developer documentation. To obtain said documentation, log into the ADC Member Site, go to “Downloads,” then “Java,” and download the “J2SE x.x Release x Developer Documentation.”

Once you’ve downloaded and installed it, you’ll find the src.jar (not src.zip!) in /System/Library/Frameworks/JavaVM.framework/Versions/x.x/Home/src.jar

Java Programmer’s Guide to Ruby Metaclasses

jtanium — Thu, 16 Aug 2007 17:38:28 +0000

I finally got my head wrapped around Ruby metaclasses — what a trip! So if you’re a Java programmer trying to understand metaclasses, maybe this will help.

There are many great resources on Ruby metaclasses, but none of them really quite worked for me. Good or bad, Java is still my “native” language, so when I’m doing new things in other languages it helps for me to “translate” it back into Java — in other words, I think, “how would I do this in Java?” Since there is nothing like metaclasses in Java, we’ll have to use our imagination.

Let’s pretend that for whatever reason, you want to add an instance method to an object, at runtime. How would you do it in Java? This is how I imagine you would do it, if you *could* do it:

// create a method that looks like this:
//   public void sayHello() { System.out.println("Hello!"); }
Method sayHelloMethod = new Method(Method.PUBLIC, Method.VOID, "sayHello", new Class[] {}, "System.out.println(\"Hello!\");");

MyObject myFirstObject = new MyObject();
/*
 * This is where you need your imagination, imagine that java.lang.Object had
 * a method named addMethod()...
 */
myFirstObject.addMethod(sayHelloMethod); // add the sayHello method to our object

// now use it!
myFirstObject.sayHello();  //=> prints "Hello!" to standard out...

MyObject mySecondObject = new MyObject();
mySecondObject.sayHello(); //=> throws a NoSuchMethodError

Quasi-straightforward, right? We told the JVM that we wanted the myFirstObject object to have a new method. But the mySecondObject doesn’t have the sayHellomethod. Once you have a good feel for that, look to see how it’s done in Ruby:

my_first_object = MyObject.new
class << my_first_object
  def say_hello
    puts "Hello!"
  end
end
my_first_object.say_hello #=> "Hello!" printed to standard out
my_second_object = MyObject.new
my_second_object.say_hello #=> undefined method `say_hello' for # (NoMethodError)

Alright, but what if we want all instances of MyObject to have a sayHello method? Let’s imagine how we might do it in Java:

// create a method that looks like this:
//   public void sayHello() { System.out.println("Hello!"); }
Method sayHelloMethod = new Method(Method.PUBLIC, Method.VOID, "sayHello", new Class[] {}, "System.out.println(\"Hello!\");");
Class myObjectClass = Class.forName("MyObject");
myClass.addInstanceMethod(sayHelloMethod);
((MyObject) myObjectClass.newInstance()).sayHello();   //=> prints "Hello!"
((MyObject) myObjectClass.newInstance()).sayHello();   //=> prints "Hello!" again

This time instead of just modifying the single instance of MyObject we changed the class, so all instances have the method. Let’s do the same in Ruby:

MyObject.send :define_method, :say_hello do
  puts "Hello!"
end
MyObject.new.say_hello #=> print "Hello!"
MyObject.new.say_hello #=> print "Hello!"

Good enough. From now on all instances of MyObject (including the ones instantiated before we added this method!) will have a say_hello method. Pretty cool.

Finally we can add static methods as well, once again imagining in Java…

Method sayHelloMethod = new Method(Method.PUBLIC, Method.VOID, "sayHello", new Class[] {}, "System.out.println(\"Hello!\");");
Class myObjectClass = Class.forName("MyObject");
myObjectClass.addStaticMethod(sayHelloMethod);
MyObject.sayHello  //=> prints "Hello!"

And the same thing in Ruby:
class << MyObject
  def say_hello
    puts "Hello!"
  end
end
MyObject.say_hello #=> prints "Hello!"

Custom Fonts and Colors for Netbeans

jtanium — Thu, 28 Jun 2007 20:37:23 +0000

I like TextMate and I like Netbeans. So I created a custom fonts and colors profile for Netbeans which is *similar* to TextMate.

To install, just put this in:

~/.netbeans/6.0m9/config/Editors/FontsColors/TextMate-MacClassic/org-netbeans-modules-editor-settings-CustomFontsColors.xml

java.util.jar.JarException: file:/Developer/Java/Ant/lib/ant.jar has unsigned entries

jtanium — Mon, 07 May 2007 19:13:44 +0000

This occurred while trying to use Ant to run some JUnit tests which test some encryption/decryption stuff (using BouncyCastle). To resolve this issue, add fork="true" to the junit task in your build.xml.

Java/Daylight Savings Time Fun!

jtanium — Wed, 03 Jan 2007 17:14:41 +0000

Last week I finally figured out this little date problem that has been plaguing some of my applications at work. Basically the symptom was under some circumstances credit card expiration dates would be sent to the processor one month earlier than it was supposed to be. While digging through logs I noticed the expiration date was serialized to ’2010-11-01T06:00:00.000Z’. The reason this is interesting is because the servers are in the Mountain time zone, so the date should have been serialized to ’2010-11-01T07:00:00.000Z’. So I wrote a this little example program:

    public static void main(String[] args) throws ParseException
    {
        SimpleDateFormat dateFormat = new SimpleDateFormat("MM/yyyy");
        TimeZone mst = TimeZone.getTimeZone("MST");
        TimeZone gmt = TimeZone.getTimeZone("GMT");

        dateFormat.setTimeZone(mst);

        Date date = dateFormat.parse("11/2010");
        System.out.println("date: " + date);

        Calendar cal = Calendar.getInstance();
        cal.setTime(date);
        cal.set(Calendar.HOUR_OF_DAY, 6);
        cal.setTimeZone(gmt);
        System.out.println("cal: " + cal.getTime());
        System.out.println("cal.formatted: " + dateFormat.format(cal.getTime()));
        System.out.println("cal.month: " + cal.get(Calendar.MONTH));
        System.out.println("cal.year: " + cal.get(Calendar.YEAR));
    }

This is the output I got when I ran it on my Mac, using Java 1.4 (j2sdk 1.4.2_09):

date: Mon Nov 01 00:00:00 MST 2010
cal: Sun Oct 31 23:00:00 MST 2010
cal.formatted: 10/2010
cal.month: 10
cal.year: 2010
ERROR!!! Expected inputDate: 11/2010, received: 10/2010

No matter what I did, Java would always localize the date to my current time zone. I happen to know a Java Champion (besides the one that has commented on my blog), and his first solution was to switch all our machines to UTC — which is easier said than done. I then sent him the program, and he said it worked. I asked him to send me the output, and this is what he sent me:

date: Mon Nov 01 00:00:00 MDT 2010
cal: Mon Nov 01 00:00:00 MDT 2010
cal.formatted: 11/2010
cal.month: 10
cal.year: 2010
SUCCESS!!!

He had run it on Java 1.5. I didn’t realize it at the time, but the MDT is the clue. Some bit of Googling about Java and Daylight Savings Time turned up an article on java.sun.com called U.S. Daylight Saving Time Changes in 2007. Mystery solved.

The machine parsing and creating the date, running on j2sdk1.4.2_11, properly parsed the date, and recognized it as being in Daylight Savings Time (GMT-6). However the web service receiving that date was running on j2sdk1.4.2_05, treats the date as GMT-7, thus effectively pushing the month back by one.

Lessons Learned:

Don’t use a java.util.Date object when all you need is the month and year components
Use new versions of Java (which is tough on a Mac since Apple has only released j2sdk 1.4.2_09)

Using Commons Logging SimpleLog

jtanium — Sat, 07 Oct 2006 21:44:17 +0000

I always seem to forget how to do this:
-Dorg.apache.commons.logging.Log=org.apache.commons.logging.impl.SimpleLog -Dorg.apache.commons.logging.simplelog.defaultlog=debug

Other options are ‘trace’, ‘info’, ‘warn’, ‘error’, and ‘fatal’.

Alternating Row Color in JSP/JSTL

jtanium — Tue, 12 Sep 2006 16:00:13 +0000

Here’s the simplest way I’ve found for alternating the background color of rows in JSP/JSTL:

"> ...

Things IDEA Could Learn From NetBeans

jtanium — Mon, 21 Aug 2006 20:35:12 +0000

After using NetBeans 5.5 for a few days now, I’ve found a few really neat features I really wish I had in IntelliJ IDEA:

Code generation – The ability to generate “Entity Classes from Database” and “JSF Pages from Entity Classes” (a la Ruby on Rails scaffold generator) is a good way to jump start development.
Built in HTTP monitor – I know there’s a plugin (maybe several), but it really should be integrated.
Having a seperate classpath for test cases – This is the one thing that has always driven me nuts about IntelliJ.
Collapse regular block comments – This seems so natural, I’ve never understood why Idea didn’t do this
It’s open source – Is this really a feature? I like not feeling guilty when I write code…
C/C++ pack – I haven’t tried it out, but the thought of finally having basic refactoring support for C/C++ is really appealing.

All that said, I’m not sure if I can stay away from IDEA for too long, it still has features unlike any other IDE, e.g. recognition for camel hump words and hyperlinking from any file type (XML -> Java), and advanced refactoring support just for starters. Despite the significant speed improvement with NB5.5, IDEA is still faster (though it’s becoming bloated).

NetBeans 5.5 (Beta 2)

jtanium — Sat, 19 Aug 2006 05:23:03 +0000

So I downloaded NetBeans 5.5beta2 today — I’m pretty impressed. There were two major hangups with it before, but they have been remedied: it’s noticeably faster than NB 5.0 and it has Subversion support. It also did a good job of importing the project I’m currently working on.

[java.lang.UnsupportedClassVersionError: ... (Unsupported major.minor version 49.0)]

jtanium — Thu, 02 Mar 2006 12:49:14 +0000

[java.lang.UnsupportedClassVersionError: ... (Unsupported major.minor version 49.0)]

Why can I not remember that an ‘Unsupported major.minor version 49.0′ means ‘you can’t run a class compiled with JDK 1.5 in JRE 1.4?’ Yesterday, jad was complaining about it, but it still didn’t occur to me until put the class files in a jar file.