Java on Evan Hoffman

Java Wrapper does whatever it wants

Tue, 13 Aug 2013 08:58:41 +0000

Yesterday I set out to increase the memory settings for a bunch of our ActiveMQ machines. Most of the time these queues work pretty efficiently and their steady-state memory usage is just a few MB, but with some upcoming maintenance we expect these queues to get considerably fuller, so I was growing them preemptively. Anyway, our ActiveMQ installation gets bootstrapped using Java Service Wrapper and the JVM settings for ActiveMQ are managed in some wrapper.conf file. What I wanted to do was pretty straightforward: I increased the VM’s ‘physical’ memory to 16 GB and intended to increase Java’s MaxHeap from its current setting (1536MB aka 1.5GB) to 8192MB (8 GB). In wrapper.conf, I found the “wrapper.java.maxmemory” setting (which was set to 1536), set it to 8192, and restarted ActiveMQ. Here’s where it got weird.

Installing Sun (Oracle) JDK 1.5 on an EC2 instance

Wed, 16 Nov 2011 11:52:55 +0000

I’m currently working on moving a Tomcat-based application into EC2. The code was written for Java 5.0. While Java 6 would probably work, I’d like to keep everything as “same” as possible, since EC2 presents its own challenges. I spun up a couple of t1.micro instances and copied everything over, including the Java 5 JDK, jdk-1_5_0_22-linux-amd64.rpm. Installing from RPM was easy, but the EC2 instance defaults to using OpenJDK 1.6:

[root@ec2 ~]# java -version
java version "1.6.0_20"
OpenJDK Runtime Environment (IcedTea6 1.9.10) (amazon-52.1.9.10.40.amzn1-x86_64)
OpenJDK 64-Bit Server VM (build 19.0-b09, mixed mode)

There were a couple of things I had to do to get the system to accept the Sun JDK as its “real” java.

Benchmarking DNS servers with Java

Mon, 26 Sep 2011 12:33:28 +0000

I’m currently in the process of moving our DNS over to another provider and I was curious as to whether the old or new provider offers faster lookups. dig shows query times, but I didn’t want to just run that over and over. I decided to write something to do this, in Java since I like Java. I found this post, which has the meat of the work done already. I also read some of Sun’s JNDI/DNS lookup info, which was pretty dense. All I want to do is specify the name server’s IP and do the lookup. I don’t even really care about the result, just how long the query takes.

Calculating SHA-1 sums in Java

Wed, 25 May 2011 18:19:27 +0000

Java code for calculating SHA-1 sums from arbitrary InputStreams, files, or Strings and printing them as strings.

Java Code: searching a Binary Search Tree for the largest value strictly less than X

Sun, 09 May 2010 13:43:17 +0000

Java code for creating and searching a Binary Search Tree of any element implementing the Comparable interface.

Code to flatten a list in Java, with and without recursion

Sat, 17 Apr 2010 23:42:16 +0000

Recently had someone ask me to solve this problem: assume you have a list of objects, some of which may be lists of arbitrary depths. Write a function to return the list “flattened,” so sublists are all in the “main” list. I solved it recursively pretty easily, but it took some thought to do it without recursion. My solutions are below.

package com.evanhoffman.listflattener;

import java.util.LinkedList; import java.util.List; import java.util.ListIterator;

import org.apache.log4j.BasicConfigurator; import org.apache.log4j.Logger;

How to install the 64-bit Sun Java plugin on 64-bit firefox on 64-bit Fedora Core 11 Linux (which happens to use 64 bits)

Wed, 21 Oct 2009 17:45:09 +0000

I’m giddy! I found this post on mozdev.org which was magical.

[evan@ehoffman ~]$ java -version
java version "1.6.0_17"
Java(TM) SE Runtime Environment (build 1.6.0_17-b04)
Java HotSpot(TM) 64-Bit Server VM (build 14.3-b01, mixed mode)

[root@ehoffman plugins]# uname -a
Linux ehoffman 2.6.30.8-64.fc11.x86_64 #1 SMP Fri Sep 25 04:43:32 EDT 2009 x86_64 x86_64 x86_64 GNU/Linux
[root@ehoffman plugins]# pwd
/usr/lib64/mozilla/plugins
[root@ehoffman plugins]# ln -s /usr/java/jdk1.6.0_16/jre/lib/amd64/libnpjp2.so

The main thing I was missing was that the plugin isn’t libpluginjava_oji.so, or whatever I thought it was, but libnpjp2.so. Once I created the symlink into /usr/lib64/mozilla/plugins it worked (as verified on http://www.java.com/en/download/help/testvm.xml and http://www.java.com/en/download/installed.jsp).

Java compound interest calculator

Thu, 10 Jan 2008 00:00:08 +0000

I wrote a thing to calculate compound interest and print out how much you’ve accrued after each period. It’s pretty basic but I was bored and didn’t want to do it via calculator. The code is in InterestCalculator.java, sample output is below:

Initial principal: 5000.00
Interest rate: 0.05 (4.93%)
# of ann. periods: 4
Total years: 5
Annual Addition: 500.0
Starting year 1 with $5000.00
Year 1, period 1, accrued $61.62, value is now: $5061.62
Year 1, period 2, accrued $62.38, value is now: $5124.01
Year 1, period 3, accrued $63.15, value is now: $5187.16
Year 1, period 4, accrued $63.93, value is now: $5251.09
Added $500.00 for the end of year 1, total is now: 5751.09
Starting year 2 with $5751.09
Year 2, period 1, accrued $70.88, value is now: $5821.98
Year 2, period 2, accrued $71.76, value is now: $5893.73
Year 2, period 3, accrued $72.64, value is now: $5966.37
Year 2, period 4, accrued $73.54, value is now: $6039.91
Added $500.00 for the end of year 2, total is now: 6539.91
Starting year 3 with $6539.91
Year 3, period 1, accrued $80.60, value is now: $6620.51
Year 3, period 2, accrued $81.60, value is now: $6702.11
Year 3, period 3, accrued $82.60, value is now: $6784.71
Year 3, period 4, accrued $83.62, value is now: $6868.34
Added $500.00 for the end of year 3, total is now: 7368.34
Starting year 4 with $7368.34
Year 4, period 1, accrued $90.81, value is now: $7459.15
Year 4, period 2, accrued $91.93, value is now: $7551.08
Year 4, period 3, accrued $93.07, value is now: $7644.15
Year 4, period 4, accrued $94.21, value is now: $7738.37
Added $500.00 for the end of year 4, total is now: 8238.37
Starting year 5 with $8238.37
Year 5, period 1, accrued $101.54, value is now: $8339.90
Year 5, period 2, accrued $102.79, value is now: $8442.69
Year 5, period 3, accrued $104.06, value is now: $8546.75
Year 5, period 4, accrued $105.34, value is now: $8652.09
Added $500.00 for the end of year 5, total is now: 9152.09
Final value: $9152.09

Java utility to reorganize photos by date taken (via EXIF metadata)

Wed, 28 Mar 2007 00:00:37 +0000

I wrote a little utility to reorganize my digital camera pics based on the EXIF date-taken data stored in the pic. It’s pretty simple, I hacked it together in about an hour, but I thought it might be worth sharing for anyone else looking to do something similar. My camera organizes stuff as it sees fit sometimes, I am particular about my directory structure. This is probably a job best left to perl, but I don’t feel like getting Perl running on my Windows box where all the pics are. Now I can finally burn all my images to DVD.