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All rights reserved. 2015 © ZeroTurnaround Inc.
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Yes it has
JAVA FOREVER CHANGED
By Arnel Pällo

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CLAIM YOUR FREE JREBEL TRIAL TODAY!
Use the links below for instructions on adding JRebel to your IDE:
JRebel for:
Or visit ZeroTurnaround.com/JRebel to learn more about
eliminating Java redeploys with JRebel
For those with only few minutes to spare, this paper addresses the ways
in which JRebel, Java’s famed redeploy killer, has made an impact on how
developers spend their day coding. With JRebel, developers get to reload
code changes instantly, fine-tune their code with incremental changes,
debug, explore their code with ease (both locally and remotely), and
ultimately spend more time learning and communicating with colleagues
instead of waiting for the dreaded application redeploy to finish.
ZeroTurnaround is transforming how software is created, enabling
development teams to build better software faster. Powered by award-
winning Hotpatching Technology, JRebel and XRebel are revolutionizing
the way development teams work with Java. Thousands of engineers
use JRebel to turn the laborious build/test/deploy phase of application
development into a light-speed cycle as fast and iterative as Python or PHP,
while XRebel, the lightweight Java profiler, helps developers get insight into
their application’s performance.
Abstract
Click and continue
being awesome

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Introduction
Java’s bane has always been a reliance on tools. If all I had for writing
code was Notepad and a command line compiler, I would have gladly
considered a worthwhile career in street-cleansing, fruit-picking or
subway-guitar playing industries.
But we have a handful of modern IDEs. We also have a huge ecosystem
that provides us with amazing OSS libraries and application servers. And
since we have JRebel, gone are the days of reading through the whole
series of Harry Potter novels in one week while waiting for the application
to redeploy itself after fixing that spelling typo, only to discover there’s
one more.
This post reviews some of the great advantages of using JRebel in Java
development, and how eradicating the daily, time-consuming process of
redeploying your application to see your changes has long-lasting effects
on the way that you will write code in the future.

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Java changed forever #1
Does your code smell? Find out really quickly and run your own
mini-tests throughout the day. Remove bad code before it goes
to QA and they make fun of you.
With JRebel, you get to reload the your changes immediately
after compiling them. When the IDE builds classes automatically,
the process is as fast as using a scripting language or testing
your latest HTML changes. In fact, I urge you to try compiling
the following code snippet, start it up with JRebel enabled,
and change the “Hello World” part to something else while the
program is running.
For me, the console output following the JRebel banner was
(yes, I write fast):
This opens up a world of possibilities that have never before been
available for developers. It combines the power of Java with the
fast turnaround of dynamic scripting languages. You don’t have to
queue up a gazillion changes before redeploying. You can code by
making small incremental changes and alt-tabbing to your browser
to verify the results.
SEE ALL CHANGES IMMEDIATELY

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This works best when you have to implement some
logic that is tricky to get just right. Imagine you have
to add validation to your form. With JRebel, you can
add the rules field by field and play around with
the way errors should be displayed until satisfied
by the results. You can even add some new fields
to your controller or validator with JRebel as well.
By the way, JRebel preserves all application state,
which means it does not matter how you reached
the page you’re modifying.
JRebel actually goes way beyond “simple” class
reloading. Applications today take advantage of
frameworks and Java EE technologies, such as EJBs,
Hibernate, Spring Framework, JSF, Seam, Struts,
etc. The thing with frameworks and technology
implementations is that they initialize themselves
when the application starts up and generate lots of
metadata. It is usually a good thing since nobody
wants Hibernate to re- initialize itself for every HTTP
request (that’s what PHP programs have to do, by
the way, even with opcode caching enabled).
JRebel has addressed this by having explicit support
for almost 90+ popular frameworks and application
containers. This means when you make a change
to a “special” resource such as adding a new EJB,
changing JPA mappings (either via xml or
annotations), or add new Spring Beans (again,
either via xml or annotations), JRebel updates the
metadata to reflect those changes. Your job is to
press F5 in the browser.
FINE-TUNING THROUGH INCREMENTAL CHANGES

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JRebel makes remote debugging more useful than ever. Imagine you are using it to hunt down some difficult bug. Now you can hit
a breakpoint, investigate what’s going on, make a change, resume execution, and see the result almost immediately! The new code kicks in
right after compiling, next time when the affected method is invoked. You can use this approach to fix discovered bugs immediately or to
quickly add some debugging statements in the code (just remember to avoid committing them). You can even drop to
a parent frame and check the effect immediately!
One of the benefits of small turnaround is
that you can test the framework features
interactively. You can write a small method to
test some functionality of a new framework
and learn hands on how it works. Python and
Scala even have interactive shells.
The problem here is the applicability in real
world. While exploring the API of Java libraries
is easy (even if they lack documentation), it
can be ridiculously tedious in some other
languages, especially when they are dynamic
in nature, lack documentation and/or miss
out on good IDE support.
Even if you can indeed enjoy the fast
turnaround with PHP and the like, it has little
net value when you have to dig into some big
and obscure framework (like Joomla CMS,
which I actually tried that a few years ago,
and it wasn’t pleasant) to see how it works.
The ability to ctrl-click and dive into the code,
as well as enjoy the auto- completion would
be great, if only they were there. Granted,
there is some support for it in modern
IDE’s, but it is nowhere nearly as useful. The
difference is in the order of magnitudes.
Java, on the other hand, suffers from the
fact that while the 3rd-party code is easily
navigable, writing the stubs and running
them can be tedious or time consuming.
Writing stand alone tests requires effort to
set up and are not exactly a substitute for a
real-world use case.
Embedding a test code into an existing
application is simple and easy, but restarting
the server or redeploying the app to see
the changes takes time...unless you’re using
JRebel to eliminate the need to restart.
DEBUG REMOTELY FOR FUN AND PROFIT
EXPLORE THE CODE WITH EASE

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It’s great when a developer can check out a code from
a repository, compile it, and deploy the thing in his own
machine. Sometimes this is not possible.
It can be due to performance reasons, or the whole system
is simply too complex. Sometimes the system has to run in
a different network than the developer’s, which cannot be
easily simulated. Some developers may be using low-powered
laptops. Whatever the reason, sometimes running the app in
the same machine is not an option.
I can almost hear developers cry (myself included) when that
is the case. JRebel can help even in this case and the capability
to make a system deployable on a developer’s machine is not
crucial anymore.
JRebel Remoting was introduced in version 4.6, which lets
you push changes from a developer’s machine to a remote
server. It works over HTTP on the same port as the server is
serving the application itself, therefore needs close to zero
configuration to set up and no changes to firewall settings.
We have examples on our website where we show JRebel
Remoting in action when deploying to Amazon EC2, so if it can
work well in the cloud far away, it will definitely work in your
LAN or on the other side of the city.
You can even let multiple developers loose on a single
application instance on a remote machine. By default, JRebel
Remoting reverts back to the initial codebase when the
app server is restarted. You can set up an application on
the remote machine, have a developer have his way with it,
restart it (ok, there’s one redeploy, sorry), and allow another
developer do his magic on the app. This is the case when
both developers are making changes to the same application.
When there are several apps deployed to the remote server,
developers can bombard them without stepping on each
other’s toes.
DEPLOYING CODE LOCALLY OR REMOTELY

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No restarts means no forced interruptions, which means devs have more time for doing
better things. Sometimes it’s hard to maintain concentration on a single task for more than
a few minutes, and that’s when the level of focus is totally up to the devs themselves. If
there was a circus clown jumping out from behind a door every 6 minutes to frighten me, I
couldn’t imagine working properly throughout the day.
With JRebel, you get more time to meet your deadlines, research & learn and *gasp*
communicate with people. According to a recent report on Developer Stress, it came out
that developers really do care about making deadlines and their level of expertise, wishing
they had more time to spend on education.
In a related post, we also discovered that for every 1 hour developers spend writing
code, they spend 30 minutes dealing with communication overhead (i.e. meetings, chats,
reporting/timesheets, etc). JRebel’s instantly class reloading magic simply frees up more
time for doing the things that developers are already spending time on.
NO RESTARTS = MORE TIME FOR BETTER STUFF

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Final words
JRebel will give you the best of both worlds – the performance, scalability and robustness of Java, as well as the
FTL-turnaround and the feeling of lightness, which are typically associated with 100 line guestbook applications,
not with big mature systems. JRebel behaves as if it’s in Rome – you don’t have to make changes to your code,
architecture or sysops. It adapts to your environment and requirements. All you have to do is start using it.
You get to keep all the effort and investments already made to your infrastructure.
We’ve heard from thousands of developers directly about how JRebel has forever changed not only how
productive they work – saving more than 5 full work weeks of time otherwise lost to Java restarts each year – but
the way in which they actually write the code, how they discover faults and test iteratively in order to minimize
service requests and bugs.
The joy we provide is achieved in a sensible way, not via some dark magic of something “on rails”. Nothing in your
entire app (frameworks included) is vague, ambiguous or hidden from you. All we do is some good engineering
with JVMs and popular OSS frameworks. And only within the walls of Hogwarts (i.e. during development). The
delivered software has no runtime penalties or lingering dependencies.
Arnel Pällo is a Java engineer at ZeroTurnaround.
He works on adding support for web-service frameworks
into JRebel and is a major fanboy of pretty code. He plays
Bioware games and hacks his Android phone on weekends.
He also likes salsa dancing and can make a great Mojito.
You can connect with Arnel on Facebook. Thanks for reading

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Contact Us
Twitter: @zeroturnaround
Web: http://zeroturnaround.com
Email: info@zeroturnaround.com
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Phone: 1(857)277-1199
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170 00 Prague 7, Czech Republic
Phone:+420 227 020 130

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