Random Password Generator in Java

I needed a random password generator done in Java and while reading a few articles here and there I did not find the solution I was looking for. Piecing a few of them I came up with some code.

One of the requirement that made this a bit more complicated is that I needed to have a special character in the password but from a limited list of possible special characters.
I also needed to make sure that it respected some basic complexity rules.

It has a dependency on the commons-lang 3 library from Apache but since I already had it in my project it was easy to accommodate.

Maven dependency:


Java code:

package com.halogensoftware.hosting.example;

import org.apache.commons.lang3.RandomStringUtils;

public class Random {

	public static void main(String args[]){
		String pwd = "";
		for ( int i = 0; i < 1000; i++ ) {
			do {
				pwd = RandomStringUtils.random(12, "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890%#^*:");
			} while (!valid(pwd));
			System.out.println(i + ".valid pwd: " + pwd);

	private static boolean valid(String pwd){
		return (pwd.matches(".*([0-9]).*") && pwd.matches(".*([a-z]).*") && pwd.matches(".*([A-Z]).*") && pwd.matches(".*([%#^*:]).*"));

Installing the Oracle JDK on Fedora

Had to learn this one from this site.

In my use case I only want to compile and run Hadoop application so I have not completed all the steps for the browser setup.

Short version:

  1. Download the JDK of your choice; I picked 1.7.0_51
  2. sudo rpm -Uvh /tmp/jdk-7u51-linux-x64.rpm
  3. sudo alternatives –install /usr/bin/java java /usr/java/latest/bin/java 200000
  4. sudo alternatives –install /usr/bin/javac javac /usr/java/latest/bin/javac 200000
  5. sudo alternatives –install /usr/bin/jar jar /usr/java/latest/bin/jar 200000
  6. sudo alternatives –config java

The last step was to activate the new installation I added. I selected option 2.

As simple as that and running java -version shows me the Oracle JVM version.

Starting with Hadoop – 2

I created a page for my Hadoop notes and will keep those up to date with what I am experimenting.

I will post short articles on what I have done and where I am facing challenges.

I think that using the OpenJDK is a mistake so I am testing with the Oracle JVM to see if it fixes some of the issues I am facing.

I have also upgraded to Fedora 20 which should not change much in how Hadoop works. The only I have noticed is an error because the temp directory is gone. I will have to investigate why that is preventing the namenode from starting. Might have to move the temp outside of /tmp to avoid this issue.

Starting with Hadoop

Trying to find simple and authorative documentation for Hadoop is harder than I expected. With the many versions out there it is easy to find documentation for the wrong version and not being able to find what really needs to be done.


  • Hadoop 2.2.0
  • OpenJDK 1.7.0_51
  • Fedora 19

I have set my environment variables in my .bash_profile:

export JAVA_HOME=/usr/lib/jvm/java
export HADOOP_HOME=/opt/hadoop-2.2.0

Configuration file:

<!--?xml version="1.0" encoding="UTF-8"?-->

First few Hadoop commands:

hadoop namenode -format
hadoop namenode

Things to resolve:

$HADOOP_HOME/sbin/start-all.sh – does not work at all; throws a lot of errors

A Not acceptable Rest with Spring

Trying to come up with a clever title for a blog post is not easy.

This problem caused me headaches for 2 days and as much as I have resolved it I have no idea why and how it happened.

I have done REST application with Spring many times in the past and it easy. At one point in the process for this one I was creating REST application with STS just to confirm that it was a no brainer, which helped and puzzled me.

The simplest class that worked for me was something like this:

public class Rest {
    @RequestMapping(value="/{something}", method=RequestMethod.GET, produces=MediaType.APPLICATION_JSON_VALUE)
    public String[] firstTry(@PathVariable String something){
        return new String[]{something, "testValue"};

I could quickly package it with Maven and run it on Wildfly and it would work as expected.

When I tried to do the same in IntelliJ I was getting a non working application that returned a 406, Not Acceptable, return code to all REST calls.

I compared the web.xml, the application context xml files, the pom files, everything I could thing of and the STS app would work with nothing special but the IntelliJ app would not.

Most articles I was finding were talking about bugs in some version of Spring and to make sure you had the element in your application context xml. I tried many version and adding the annotation driven did not fix the issue.

I finally found this article that explained that you needed to make sure you specified the jackson-databind library in your pom.xml otherwise you would get 406 answers. Once I added the jackson libraries to my project from IntelliJ I was able to get things to work as expected.

No Jackson libraries are specified in my STS generated project and they work so I am still puzzled as to why this was needed in the IntelliJ project.

JDK7 and JPA

We have to migrate some projects from Java 1.6 to 1.7 and I was looking at what would break. Something I noticed is that a Spring 3.2 project using Java 1.6 does not need to specify the javax.persistence dependency but a similar project using Java 1.7 does need to. I am wondering how many other surprises I will find with these migrations.

Upgrading Groovy and Grails

I have started to learn what Groovy and Grails can do for web application development and I already faced a fun problem.

After I installed GGTS (from Spring.io), I started a simple application and then wanted to upgrade the Groovy and Grails version to the latest.

Not as straight forward as I would have taught but I got everything working again.

First thing learned is that GVM is a useful tool to use to install Groovy and Grails and manage multiple versions. Doing it manually does not make sense.

I also learned from a stackoverflow article that you need to erase the .metadata directory in the GGTS workspace after upgrading. This will force you to re-import your projects but that is the only way I have found to recover the projects so it is a small inconvenience.

Back to learning!

Learning Groovy and GRails – 1 of X

I want to learn Groovy and Grails because I want to deliver applications faster and with better quality.

I am unsure if this is the right strategy but it is going to be a fun experiment. Learning is always fun.

I will start with a few videos and go from there:

I will also have to look at the documentation on the spring site to figure out all the static variables and built-in methods that can be used.

Quartz Scheduler Errors

We learned this week what this error message meant for us:

org.quartz.impl.jdbcjobstore.JobStoreTX.recoverMisfiredJobs [] Handling 1 trigger(s) that missed their scheduled fire-time.

This was happening because we had more jobs configured to run at certain time than we had threads configured to run.

We changed the spring servlet configuration file to specify more threads and more datasource connections.

<bean class="org.springframework.scheduling.quartz.SchedulerFactoryBean">
 <property name="triggers">
 <ref bean="somethingTrigger" />
 <ref bean="something2Trigger" />
 <ref bean="something3Trigger" />
<property name="applicationContextSchedulerContextKey"><value>applicationContext</value></property>
 <property name="overwriteExistingJobs"><value>true</value></property>
 <property name="quartzProperties">
 <prop key="org.quartz.scheduler.instanceName">InstanceNameX</prop>
 <prop key="org.quartz.scheduler.instanceId">AUTO</prop>
 <prop key="org.quartz.threadPool.class">org.quartz.simpl.SimpleThreadPool</prop>
 <prop key="org.quartz.threadPool.threadCount">20</prop>
 <prop key="org.quartz.threadPool.threadPriority">5</prop>
 <prop key="org.quartz.jobStore.misfireThreshold">60000</prop>
 <prop key="org.quartz.jobStore.class">org.quartz.impl.jdbcjobstore.JobStoreTX</prop>
 <prop key="org.quartz.jobStore.driverDelegateClass">org.quartz.impl.jdbcjobstore.PostgreSQLDelegate</prop>
 <prop key="org.quartz.jobStore.useProperties">false</prop>
 <prop key="org.quartz.jobStore.dataSource">myDS</prop>
 <prop key="org.quartz.jobStore.tablePrefix">QRTZ_</prop>
 <prop key="org.quartz.jobStore.isClustered">true</prop>
 <prop key="org.quartz.jobStore.clusterCheckinInterval">20000</prop>
 <prop key="org.quartz.dataSource.myDS.driver">${db.driver}</prop>
 <prop key="org.quartz.dataSource.myDS.URL">${db.url}</prop>
 <prop key="org.quartz.dataSource.myDS.user">${db.username}</prop>
 <prop key="org.quartz.dataSource.myDS.password">${db.password}</prop>
 <prop key="org.quartz.dataSource.myDS.maxConnections">23</prop>
 <prop key="org.quartz.dataSource.myDS.validationQuery">select 1</prop>

We have not seen the error since we have made these changes.

It also means that we will have to increase the number of thread as we have more bean scheduled with Quartz.

JSON API with Spring 3.1.2 and Jackson 2.2.0

It took me a few hours to get everything working but I am quite happy at how simple it really is.

I read this blog post that had most of the instructions on how to do it: Spring MVC with JSON via Jackson 2.0

Norris mentions that you need to make sure that you have the jackson-databind dependency otherwise you will get a 406 error. I was getting a 406 error even with the jackson databind because I did not have the mvc:annotation-driven specified. I assumed I had it and was surprised that it was not there (lost an hour to something so trivial).

I was also not sure how to submit a JSON post to the API that I was creating to validate that it worked. I found a few example but the one that worked for me was this answer on stackoverflow: Parsing JSON into Java objects in spring-mvc.

The other testing I needed to do was what the JSON message format was to send to Spring. I tried something like:

{ objectName: [ {“field1”: “value”, “field2”: “value”} ] }

But that was giving me 400 errors.

The JSON message format that works is:

{ “field1”: “value1”, “field2”: “value2” }

Note that I am submitting only 1 object at a time to the API.

The last error that I encountered is that I had an internal class for the status (return object on submission) that was private. I got a 500 error when the spring bean was trying to access it so I switched to a protected class and everything is working.

I like the short code that Spring allows me to write to get this to work. Should make it quite easy to maintain.