Tuesday, August 26, 2014

Why Jython when you can microservice with Flask

Over the last little while I have been working on Sibbly it's my little pet project to try summarize, group, filter and target software development information on the web. All 'n all a rather ambitious task, but the worst thing that could happen is that I learn something, so there is really no risk. It is still currently in a very closed beta, only occasionally showing it to fellow work colleagues and getting some input.

After initially starting development for Sibbly on Ubuntu, as I was always planning on deploying on Ubuntu, I had migrated back to windows, and after a couple weeks of work when finally deploying to Ubuntu... Surprise! it obviously did work right off the bat.

The issue I ended up with was, there seems to be a classpath issue between Spring Boot, it's embedded Tomcat instance and Jython. The reason I use Jython is for an awesome library called Pygments.

So after much dismay and checking all the Java alternatives and attempted Pygment ports (jygments, jgments), I started thinking of alternate solutions.
Having recently read: Microservices I decided to look at a way of interacting with Python more indirectly.
This lead me to: Flask
Within a couple minutes thanks to: Awesome Flask Example
I had the following up and running:

What this little bit of Python does is wrap and expose the highlight and guess functionality from Pygments via a RESTful service accepting and producing JSON.

I deploy Sibbly on DigitalOcean
To install Python on my droplet, I followed the process below:

sudo apt-get install python-dev build-essential  
sudo apt-get install zlib1g-dev
sudo apt-get install libssl-dev openssl
sudo apt-get install python-pip
sudo pip install virtualenv
sudo pip install virtualenvwrapper

export WORKON_HOME="$HOME/.virtualenvs"
source /usr/local/bin/virtualenvwrapper.sh

sudo mkdir /opt/python3.4.1
wget http://python.org/ftp/python/3.4.1/Python-3.4.1.tgz
tar xvfz Python-3.4.1.tgz
cd Python-3.4.1
./configure --prefix=/opt/python3.4.1
sudo make install

mkvirtualenv --python /opt/python3.4.1/bin/python3 py-3.4.1

workon py-3.4.1

pip install flask
pip install pygments

Once that was done to run the Flask app:
python app.py & disown

Sunday, August 10, 2014

Upgrading Spring 3.x and Hibernate 3.x to Spring Platform 1.0.1 (Spring + hibernate 4.x)

I recent volunteered to upgrade our newest project to the latest version of Spring Platform. What Spring Platform gives you is dependency & plugin management across the whole Spring framework's set of libraries.

Since we had fallen behind a little the upgrade did raise some funnies. Here are the things I ran into:

Our pom files were still referencing:
These artefacts don't exit on the latest version, so replaced those with
hibernate-core.jar  and ehcache-core.jar

We also still use the hibernate tools + maven run plugin to reverse engineer our db object.
This I needed to update to a release candidate:

The code: "Hibernate.createBlob"... no longer exists

replaced with:

On the HibernateTemplate
return types are now List; not element...So needed to add casts for the lists being returned.

import org.hibernate.classic.Session;
replaced with:
import org.hibernate.Session;

Reverse engineer works a little differently...
Assigns Long to numeric...

Possible Errors:

  • Caused by: org.hibernate.service.UnknownUnwrapTypeException: Cannot unwrap to requested type [javax.sql.DataSource]
Add a dependency for c3p0:

And configure the settings in the cfg.xml for it:
  • Caused by: java.lang.ClassNotFoundException: org.hibernate.engine.FilterDefinition

Probably still using a reference to hibernate3 factory / bean somewhere, change to hibernate4:

  • Caused by: java.lang.ClassNotFoundException: Could not load requested class : org.hibernate.hql.classic.ClassicQueryTranslatorFactory There is minor change in new APIs, so this can be resolved by replacing property value with:


Amazingly some of our application context files still referenced the Spring DTD ... replaced with XSD

In Spring configs added for c3p0:

Spring removed the "local"=: so needed to just change that to "ref"=

Spring HibernateDaoSupport no longer has: "releaseSession(session);", which is a good thing so was forced to update the code to work within a transaction.

Possible Errors:

  • getFlushMode is not valid without active transaction; nested exception is org.hibernate.HibernateException: getFlushMode is not valid without active transaction

Removed from hibernate properties:
     <prop key="hibernate.current_session_context_class">thread</prop>

Supply a custom strategy for the scoping of the "current"Session. See Section 2.5, “Contextual sessions” for more information about the built-in strategies

  • org.springframework.dao.InvalidDataAccessApiUsageException: Write operations are not allowed in read-only mode (FlushMode.MANUAL): Turn your Session into FlushMode.COMMIT/AUTO or remove 'readOnly' marker from transaction definition.

Another option is :
<bean id ="productHibernateTemplate" class="org.springframework.orm.hibernate4.HibernateTemplate">
<property name="sessionFactory" ref="productSessionFactory"/>
<property name="checkWriteOperations" value="false"/>

  • java.lang.NoClassDefFoundError: javax/servlet/SessionCookieConfig
Servlet version update:

  • Then deploying on weblogic javassist: $$_javassist_  cannot be cast to javassist.util.proxy.Proxy

The issue here was that there were different versions of javassist being brought into the ear. I all references removed from all our poms, so that the correct version gets pulled in from from Spring/Hibernate...

and then configured weblogic to prefer our version:

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