My Head Hurts

Rod Johnson on standardization and design by committee

2010-05-07T13:23:00.003-04:00

This is an extremely interesting presentation. Highly recommended.

http://www.infoq.com/presentations/Lessons-Learned-from-Java-EE

Multiple JUnit 4.4 @RunWith annotations

2010-04-29T15:55:00.000-04:00

Anybody know how to do this? JUnit 4.4?


@RunWith(MockitoJUnitRunner.class)
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = {"mocked_spring_tests.xml"})
public class MyTests
...

Eclipse complains "Duplicate annotation @RunWith"

The G1 garbage collector is buggy...

2010-02-03T12:03:00.000-05:00

We're seeing lots of these using the new G1 garbage collector on 1.6.0_16:

# A fatal error has been detected by the Java Runtime Environment:
#
#  SIGSEGV (0xb) at pc=0x00002b55ba46eeb4, pid=17580, tid=1090718016
#
# JRE version: 6.0_16-b01
# Java VM: Java HotSpot(TM) 64-Bit Server VM (14.2-b01 mixed mode linux-amd64 )
# Problematic frame:
# V  [libjvm.so+0x57feb4]
#

Admittedly we're not on the very latest JDK, which at this time is _18.  And wow, look at the release notes for Java SE 6 Update 18!  I count 45 bug fixes tagged with G1...  I guess they're serious when it's unlocked with "-XX:+UnlockExperimentalVMOption".

The Java 1.6 compiler is smarter about generics than 1.5

2009-11-10T17:45:00.000-05:00

Try compiling this code against a Java 1.5 and then a 1.6 compiler. It will compile against 1.6 but not 1.5. Weird... The 1.6 compiler can apparently recognize that a generic class satisfies a method's arguments while 1.5 can not.

import java.util.*;
import java.util.concurrent.*;

public class CompilesOnJava6Not5
{
   public static void main(String args[]) throws Exception
   {
      List tasks = new ArrayList();
      ExecutorService executor = Executors.newCachedThreadPool();
      executor.invokeAll(tasks);
   }
   
   public static class WorkerTask implements Callable
   {
      public String call()
      {
         return "some work";
      }
   }
}

getDeclaredFields vs getFields

2009-11-10T16:43:00.000-05:00

getDeclaredFields will return all fields declared in the current object including private fields, but not fields in any parent objects. getFields returns all public fields visible on the object, including parents... So what if you want all fields (public, protected, and private) on the object? I guess you have use getDeclaredFields and getSuperClass to recurse through the object heirarchy.

Spring autowiring of private fields with no set method

2009-11-10T11:30:00.000-05:00

To autowire a private field with no setter method I always assumed Spring would manipulate the byte code using AspjectJ or something similar and create an "artificial" setter method, but it actually just uses reflection to change the access to the field using "setAccessible". Take a look at the makeAccessible method in the internal spring class org.springframework.util.ReflectionUtils. This likely won't work with a security manager in place so I wonder what happens in that case.

Interestingly also, I found that even if there is a setter for a public field annotated with @Autowired, Spring doesn't call the setter to set the value. It set the value directly on the field. It only appears to call the setter if the setter method is annotated...