An Opinionated Guide to Modern Java, Part 2

http://blog.paralleluniverse.co/2014/05/08/modern-java-pt2/

by dafnap • 12 years ago

313 137 12 years ago

blog.paralleluniverse.co

vidar• 12 years ago

This feels like a different universe.

Terr_• 12 years ago

... You mean the name of the blog?

afandian• 12 years ago

To which universe?

anjanb• 12 years ago

cool article. I wish if someone can give a Java update like this once every year!

derengel4• 12 years ago

As someone not very familiar with Java can someone expand on what he means by this: "Every library is usually packaged into its own JAR, and merging all dependencies into a single JAR, might cause collisions, especially with packaged resources (non-class files)."

jacobheric2• 12 years ago

When you merge multiple libraries into a single jar, it is possible that two libraries might have two (unpackaged) resources with the same name that will collide on the JVM's classpath. Or, perhaps more annoying, you might end up with an unexpected version of a (packaged) library defined class than you expected.

saryant• 12 years ago

A common example is with logging config files (e.g., logback.xml). Some libraries ship with their own (or a library's dependency). It's not uncommon in a large project to wind up with several logback.xml files littered around from libraries that included their own. These are called "resources" because they aren't code but they are included with the compiled distributable and are placed on the classpath.

Of course, your project probably includes its own logback.xml in your resources directory.

Libraries are typically distributed as JAR files, so when you include their JAR on your classpath you're also including their logback.xml in that JAR.

Now, when you go to package up an uber-JAR for your project, whatever packaging tool you use has to merge all those files into one classpath. So now it's found collisions: there are multiple, different logback.xml files on your classpath but you can only have one. How does the tool pick?

So now you have to specify a "merge strategy" to make sure that only your logback.xml is merged in and the rest are discarded.

logback.xml is just one example. Typically Java classes themselves merge just fine because the packaging tool can dedup by fully-qualified class name which is almost never shared across projects. So even if two different dependencies have a Utils class, the FQCN is different. com.foo.bar.Utils is not the same as com.bar.baz.Utils, so there's no conflict.

Conflicts can also arise from libraries which include different versions of the same transitive dependency. Generally the fix here is to exclude a transitive dependency from one of your direct dependencies so as to only include one version of that library. A common culprit is Apache Commons since so many Java libraries rely on it.

pivo• 12 years ago

Speaking of Java logging, that's one area that drives me batty. The lack of a good standard Java logging library caused a multitude of logging libraries to be written. Different libraries then of course use different logging libraries, so each logging library generally has a way to wrap all the others, and they all work in different ways. Getting consistent and controllable logging (e.g. ability to turn on or off logging for a given thing) can sometimes be almost impossible to understand.

philbarr5• 12 years ago

Each JAR is just a zip file. It can be convenient to merge all those JAR files into one for deployment so you don't have to have all the JAR files lying around in the system and upgrades are just "replace this one JAR file" (among other reasons).

Since each JAR is just a zip if you have two files in seperate JARs with the same path you'll have a problem when you try to merge them.

jpollock• 12 years ago

Class loaders work in a tree, and there typically isn't sharing between sibling branches. I believe that visibility is up the tree, and never across. So, you can end up with two different versions of a library existing quite happily in the same process space. Collapsing them down into a single [ejsw?]ar file results in the tree being collapsed down too.

All of a sudden all of the log4j.xml files that everyone has sprinkled everywhere end up overwriting each other...

twic7• 12 years ago

FWIW, classloaders don't have to work as a tree. The JDK itself has a simple model with three classloaders in a hierarchy (bootstrap, extension, and system), which is a degenerate tree, and application servers have traditionally had a more general tree, but other topologies are possible. But OSGi and JBoss Modules have directed graphs of classloaders.

benjaminpv2• 12 years ago

"Java application servers are dead" and since there's no alternative to Java application servers here's a solution I cooked up myself.

Like I mentioned last time I appreciate an overview of modern Java practices but boy howdy I can't discern if this is clever trolling or a cheap way to make me read Part 3.

UK-AL• 12 years ago

I'm guessing tomcat.

philbarr5• 12 years ago

I skimmed through Part 3 and it's basically saying that app servers are hard to deploy, maintain and dev against and you should be using Spring Boot or Dropwizard instead to create applications with the services you require.

twic7• 12 years ago

I used Spring Boot the other day. It was really easy! Up until things just didn't work for no apparent reason, and neither the error messages nor documentation gave me any clues as to how to fix it.

App servers have historically been hard to deploy, maintain and dev against. There has been a huge amount of progress in the last few years. Based on my experience, Java EE / Wildfly is actually easier to develop with than Spring Boot.

john-waterwood2• 12 years ago

App servers like TomEE, JBoss and GlassFish are not hard to install at all, and certainly not to dev against. What's the author smoking?

These servers are just unzip == fully installed things. We have them checked in and just deploy them automatically whenever there's a need for an update, pretty much as every other library out there.

I wonder are we missing something or do people just wrongly think there's "something" difficult, where there's no need at all for things to be difficult?

Patient0• 12 years ago

Where did you find part 3?

jacobheric2• 12 years ago

I'd not go so far as to say it's trolling. Perhaps overly-dramatic hyperbole. As a Java developer, I do see a shift away from packaging up wars and deploying them to application servers. See Dropwizard or Spring Boot for examples of frameworks that prefer to run fat jars that serve http requests via embedded containers.

curun1r4• 12 years ago

Why is the Java community so enamored with creating Java-only solutions when general-purpose solutions work just as well (and often better)?

There's no need to bundle everything up into an executable jar or war. It's much easier to write a Chef recipe to copy all the right files to the right places. And it's even easier to create a Docker container with the exploded war in its correct place. Both of those solutions don't rely on the clunky put-everything-inside-a-jar and the resulting need to write your own ClassLoader.

bubbleRefuge• 12 years ago

play framework as well ( with no jsp dependency)

bad_user3• 12 years ago

"Java application servers are dead" and since there's no alternative to Java application servers here's a solution I cooked up myself.

The alternative are servlet containers, like Jetty or Tomcat. Jetty for example is very popular and really good and can be easily embedded inside an app for single JAR deployments, which is an awesome way to deploy an app btw.

benjaminpv2• 12 years ago

Fair enough, it's a matter of terminology then, I guess?

Generally I think of Tomcat as being as much of an application server as something like JBoss is.

Granted, JBoss/Wildfly has a lot more enterprise-y features, but they both 'serve' web 'applications.'

jebblue4• 12 years ago

I'm a fan of simplifying the server side, one I'd recommend for the latter part of the slideshow he referenced:

http://www.sparkjava.com/

microtonal• 12 years ago

...or just use JAX-RS, which is simple, standardised, and has good implementations (such as RESTEasy and Jersey).

jebblue4• 12 years ago

I suppose but SparkJava has as its core philosophy, build as a runnable jar from the start which is in line with what the article was discussing in its referential prohibition of conventional app server approaches.

edit: Further to the point of getting Java server technology to a simpler to understand, design, debug and maintain place, SparkJava makes it insanely easy to do REST services eliminating both Annotations and heavy configuration. I've also speed tested my side projects on SparkJava and they are unreal fast.

cmicali2• 12 years ago

Nice article - Many of the suggestions (single-jar deployment, metrics, slf4j logging, etc) are all wrapped up for you in Dropwizard http://dropwizard.io, which we use and love.

asdf1234• 12 years ago

Do you just use it for producing a REST API or do you use it to render HTML, handle session management etc.?

zodvik• 12 years ago

I happen to use Dropwizard as well and purely for REST APIs that serve as internal micro services.

badlogic2• 12 years ago

We use it for both REST APIs on top our services and rendering templated HTML. We had to bastardize the asset bundle extension considerably for that though. Once we got things working we didn't want to go back.

cmicali2• 12 years ago

We use dropwizard only for rest APIs currently. Our HTML and JS are served up with an in-house framework that has plugins for less, minimization, svg inlining, etc. We have open tasks to both publish it and make it hostable in dropwizard directly.

ytsejammer• 12 years ago

Sharing a lot of the Dropwizard philosophy, there is Spring Boot (http://projects.spring.io/spring-boot/), which we use and love as well.

jebblue4• 12 years ago

I'm not clear, just did a ton of Googling and I think maybe spring.io is related to the Spring Framework at VMware. That would mean it's dependency injection.

pron19• 12 years ago

We'll discuss Dropwizard in part 3, but the single-jar deployment is not really solved by Dropwizard. To launch the server you still need to configure the JVM at the command line.

pan69• 12 years ago

An off topic question; Would it be possible to have an RSS feed on your blog? I see you have Twitter but personally I don't really use that.

derengel4• 12 years ago

is that really a big issue? passing the arguments to java to configure the jvm.

eshvk3• 12 years ago

While I personally prefer Gradle’s nice DSL and the ability to use imperative code for non-common build operations, I can understand the preference for the fully declarative Maven, even if it requires lots of plugins. The modern Java developer, then, might prefer Maven to Gradle.

I find Maven's abstractions surprisingly hard to understand. It is a major part of my annoyance with Java as a dev setup. I miss Make/Ant. Not sure if Gradle will be a good replacement or not but would be curious to try.

krschultz2• 12 years ago

I really enjoy Gradle. I have done significant work with Ant, Maven, and a host of tool chains in the C/C++ world. Gradle seems to have the cleanest DSL. Not every single thing under the sun is supported (Maven seems to be the most comprehensive tool I have used), but Gradle is nice to work with.

Groxx• 12 years ago

I've been struggling to find out what's even available in Gradle. How does one debug it, or print available methods, or really anything?

My woes are mostly around Android's gradle integration, which appears poorly documented at best. There are tons of magic commands that appear out of nowhere and with no explanation beyond "use this.". And Gradle's massive guide covers things that barely see the light after being seemingly wrapped in several layers by Android's plugin.

I want to give it a real try, but the Android projects I deal with are reasonably complex, would use code generation (`scopes.PROVIDED.plus += configurations.provided }`? wtf does that even do and how in the world would I have discovered I could use it?), and need multiple products. I would have to know what and why before considering switching over for real, but there seem to be some huge walls preventing me from finding out.

lmm5• 12 years ago

What abstractions? You have a project which has a name and some other metadata and it has a bunch of dependencies. If your build does something weird then it also has plugins, but you should try to avoid those as much as possible. I guess profiles could be confusing, but again, try to avoid them. Maven is the simplest build tool I've used, in any language.

mike_hearn• 12 years ago

Maven has a lot of jargon. I also found it confusing when I started. POMS, artifacts, plugins, reactors etc ... heck I still find Maven confusing and unintuitive sometimes. Their docs are awful: typical failure mode for software that's in love with the idea of plugins.

zmmmmm• 12 years ago

I find all of them hard to work with, because they are all aiming for the modern day "zero configuration" nirvana that Ruby on Rails achieved, and thus enormous amounts of implicit knowledge is required to understand them.

Part of the problem is that the initial steps are so easy that you're actually never forced to learn the mechanics of what is happening. Hence you get away with a lot until you need to do something there isn't a magic command for. This is also why you see blithe statements that you "don't need to know Groovy to use Gradle", etc. However these are only said after the fact when you've learned Gradle, understood enough Groovy to intuit what it's doing and then retrospectively realised there is a theoretical path from ignorance to enlightenment that didn't involve learning Groovy.

What you would probably like is Gant, which is Ant entirely converted to Groovy. It's missing all the higher level project stuff from Maven / Gradle, but it works a treat when you just want the simplest possible thing that could work.

eshvk3• 12 years ago

I find all of them hard to work with, because they are all aiming for the modern day "zero configuration" nirvana that Ruby on Rails achieved, and thus enormous amounts of implicit knowledge is required to understand them.
... realised there is a theoretical path from ignorance to enlightenment that didn't involve learning Groovy.

Yes! Learning is so non-linear that sure there are in theory fine lines that minimize the amount of new stuff to learn. Yet, it never is that simple. Bad design, indeed.

What you would probably like is Gant, which is Ant entirely converted to Groovy. It's missing all the higher level project stuff from Maven / Gradle, but it works a treat when you just want the simplest possible thing that could work.

I will check it out; thank you!

thejdude3• 12 years ago

At least with Maven you have a standardized build process in every project. Checkout the code and be productive right away. It structures dependencies and project layout.

Currently I'm in a large enterprise project where the build department decided it was a good idea to reimplement a whole complex build in gradle (basically all that maven does by default). It didn't help that they didn't realize Gradle uses Maven conventions by default, ignored that and ran their own dependency system. The build is REALLY slow and really complex and nobody has any idea exactly what it does.

In ant having a non-standard project layout was ok, but then at least the build was FAST and didn't take half a minute just to START the build system.

I'm not yet sure if gradle actually IS better if you use it right, or if it's just a very very slow solution to a problem you shouldn't have it the first place if you do it right with something like maven.

badlogic2• 12 years ago

I'm glad someone took the time to write this, it's actually a very nice resource to get new coworkers up to speed. Shouldn't be tought as dogma of course (e.g. Gradle vs. Maven).

Also, thanks for mentioning Packr even though noone has used it in production yet. It's only a week old.

Assuming OP is the original author: are you by any chance following JGO? I see Quasar is actually using Matthias Mann's green thread lib which i don't think was advertised anywhere outside JGO.

pron19• 12 years ago

Yep. JGO. And Quasar now uses a heavily modified fork of Matthias Mann's code.

pjmlp4• 12 years ago

I like the overview given to JVM tooling, many developers are fully unaware of what JVMs (not only the official one from Oracle) offer in terms of monitoring.

If you want to go really low level, a few of them even show the generated assembly code by the JIT.

sehugg• 12 years ago

You can do this from the JVM command line with "-XX:+UnlockDiagnosticVMOptions -XX:+PrintAssembly". (it's kind of a mess, though)

pjmlp4• 12 years ago

Yes, it still requires the plugins which aren't delivered with the JDKs and each JVM does it a bit differently, but is possible.

As complement of it, check JIT Watch

https://skillsmatter.com/skillscasts/5243-chris-newland-hots...

dave3773• 12 years ago

Very nice article. Capsule looks promising in regards to packaging. I'm going to have give 'er a try. One could also use the fatjar[1] or application[2] plugins (within the context of gradle).

[1] https://github.com/musketyr/gradle-fatjar-plugin [2] http://www.gradle.org/docs/current/userguide/application_plu...

eeperson6• 12 years ago

As a Java developer, I thought this article had some interesting information about logging and monitoring. However, the deployment section had my scratching my head a little.

I've never totally understood why people want to make fat jars. It seems like a process full of headaches since you can't have jars in jars. Wouldn't it be much easier to create a regular zip file with a small script to set the classpath and and run the project?

I'm not sure I understand the motivation for embedded instead of standalone servlet container. The article linked to some slides but they mostly seemed be demonstrating that you can function using an embedded container rather than providing clear benefits. Maybe it would have made more sense with the associated talk.

Can anyone provide more insight to these?

pron19• 12 years ago

Author here. A capsule is not necessarily a fat jar. It can point to Maven dependencies that are downloaded on the first launch, and can later be shared by other capsules. A zip with startup scripts is OK, but it requires installation.

As to full blown app servers vs embedded servers, I think it's the other way around. It's the big app servers that require justification, as they are a lot more cumbersome to set up and deploy.

derengel4• 12 years ago

unzipping a folder and running a <10 line bash script requires installation? is that what you mean by installation?

eeperson6• 12 years ago

Looks like I should have read the Capsule Github page. I didn't realize Capsule was caching the project dependencies. I could certainly see that making projects much faster to deploy.

Aren't the app servers and the embedded servers the same servers just configured differently? Standalone it is configured with XML and and embedded it is configured with Java code. It doesn't seem to me like there is much of a set up difference.

As far as I can tell, it comes down who cares more about the settings for the server, the people who maintain the machines or the people who maintain the code. If those people are the same then it sounds like it really doesn't matter.

twic7• 12 years ago

It can point to Maven dependencies that are downloaded on the first launch

You wouldn't do this for a production deployment, right? Application starup that may or may not require access to the artifact repository to complete successfully. When that idea bounces around my developer neocortex, my sysadmin hindbrain starts reaching forward to strangle it.

And if you're not going to do it in production, doing it in development means having a gratuitous difference between development and production, which, again, is something i have learned to fear.

A zip with startup scripts is OK, but it requires installation.

'gradle installApp' works out of the box, and 'installs' the jars and scripts in your build directory, which is all you need to run locally. It's work of minutes to write an fpm [1] invocation that packages the output of installApp as an operating system package, which you can then send down the pipe towards production. This is simple, easy, standard, and fully integrated with a world of existing package management tools. Why would i use Capsule instead of doing this?

[1] https://github.com/jordansissel/fpm

objectified• 12 years ago

It can point to Maven dependencies that are downloaded on the first launch

Please don't. Never assume that production machines have access to the internet or even an internal Maven repository. If they do, they're a security risk. There are plenty of scenarios I can think of where an attacker could possibly make your application download something from the internet, or has your application server functioning as an anonymous proxy by exploiting your application.

einrealist• 12 years ago

Actually, you can have Jars in Jars. Of course, you need to do the lifting yourself. It is actually very nice to have a simple unpack / installation application inside a Jar and to unpack the actual application from this Jar. In this way, the only requirement for unpack / installation is the JVM, which you already require to run the application itself. This is much more elegant than a platform dependent unpack / installation (installer binary or ZIP plus Windows Batch or a Shell script).

depsypher• 12 years ago

spring boot has done the lifting: http://docs.spring.io/spring-boot/docs/current-SNAPSHOT/refe...

Yeroc• 12 years ago

Huh, jars within jars... sounds a lot like .war files!

lmm5• 12 years ago

Having moved from Tomcat to embedded Jetty, it avoids a bunch of problems - no two linux distributions can agree on where to put Tomcat particularly when you need multiple instances, and they have an unfortunate tendency to run out of PermGen space and need restarting after you've done a few redeploys. But it's mainly just faster, and much easier to use in development; you can just run the same java class either way, so running it with a debugger is easy, hot code replace just works, etc. As a bonus you can avoid having an XML config file. It's not a huge difference but it makes life slightly easier.

Fully agreed with the zip and script though, that's what we do (using the appassembler maven plugin, so it just happens as part of the build).

eeperson6• 12 years ago

These arguments don't make sense to me.

I'm not sure why it matters that different distros put Tomcat in different locations. Embedding Jetty just means that now you have to restart every time. You could just do the same thing with standalone Tomcat instance. The only reason you are running out PermGen space on the redeploys is because your application is not cleaning up its threads on shutdown.

Why is it difficult to do any of those development things without having the server embedded in your application? Pretty much every Java build tool (Maven, SBT, Gradle, Lein) makes those things easy to do without specifying an XML file for your server. Also, they will frequently let you reload your application, which is faster.

gsmethells• 12 years ago

As far as packaging and deployment of a native executable goes, I thought it odd to not mention Excelsior JET (http://www.excelsiorjet.com) as I believe that's the only Java compiler that can handle all of the JDK (gcj isn't there yet).

pron19• 12 years ago

Native executables are not always what you want. For example, they don't get security patches.

Pacabel• 12 years ago

That's total nonsense. Binaries (or shared libraries they depend on) can be and are updated, on all sorts of systems. In many cases it's as simple as overwriting the existing binary with the updated version.

Heck, the runtimes you're advocating are generally installed as binaries. If they can get updated, then so can any other binary.

And if a user doesn't bother to update a given application's binary when a critical flaw of some sort is found, then there's a very good chance they wouldn't bother to update any runtimes that are installed, either. This is true even when some sort of update notification and installation process is offered. The end result is the same in either case: the update is not applied.

Runtimes shouldn't be portrayed as any better in this case, when they're generally no different than any other binary.

pjmlp4• 12 years ago

gcj is dead since 2009.

The only alternatives, besides Excelsior, is the new RoboVM, Websphere Realtime JVM, Aicas, Aonix among a few other ones.

And if Graal eventually replaces Hotspot on the reference JVM, it might be that Truffle comes along as well.

12345678123• 12 years ago

This article does not mention OSGI or Jigsaw with one word but claims to guide to modern Java development. Seems they never run any large scale EE projects yet :)

twic7• 12 years ago

Ah, OSGI. OSGI is a bit of an enigma. People who use it think it's great, and, by the sound of it, assume everyone else is using it. People who don't use it think it's some weird thing from the turn of the century that nobody actually uses.

I do think a well-rounded Java developer should know about OSGI (i have to confess that i don't). But it would be mistaken to think that it's mainstream.

pswenson• 12 years ago

I've found OSGi to be an absolute nightmare. Classloader hacks is not the way to solve Java's dependency problem, it needs to be baked in the language IMO.

I think it's one of those ideas that sounds great in theory, but in reality it all falls apart.

Even if it worked as advertised, fact is many 3rd party libraries have all sorts of issues with OSGi. For example, my company is stuck on Jersey 1.x because 2.x doesn't work properly with OSGi.

Testing is much slower and harder to write. Testing seems to be an afterthought....

I think you can get most of the benefits of OSGi simply by using proper dependency management (Gradle). Use the Single Responsibility Principle and IoC and you'll get good modular code. These are much easer to do, have low risk, and are easy to test.

JMO

vorg• 12 years ago

I personally prefer Gradle’s nice DSL [...] in order to use Gradle one does not need to know Groovy, even if one wishes to do some non-standard stuff [...] I just learned a few useful Groovy expressions that I found in Gradle examples online

The DSL is Groovy syntax from Groovy's antiquated Antlr 2.7 grammar, so simply by using Gradle you're using Groovy along with all its warts. Underneath, Gradle isn't so much a DSL as an API shipping with a programming language. You could just as easily write the first Gradle example from the article in most other JVM languages. If it was in Clojure...

  (require gradle :as g)

  (g/apply :plugin "java")
  (g/apply :plugin "application")

  (g/source-compatibility "1.8")

  (g/main-class-name "jmodern.Main")

  (g/repositories
    (g/maven-central))

  (g/configurations
    g/quasar)

  (g/dependencies
    (g/compile "co.paralleluniverse:quasar-core:0.5.0:jdk8")
    (g/compile "co.paralleluniverse:quasar-actors:0.5.0")
    (g/quasar "co.paralleluniverse:quasar-core:0.5.0:jdk8")
    (g/test-compile "junit:junit:4.11"))

  (g/run
    (g/jvm-args (str "-javaagent:" (-> (configurations.quasar.iterator) next))))

lmm5• 12 years ago

Does anyone actually swap out their log backend? To me slf4j felt like an overcomplicated, enterprisey step with no clear advantage over log4j.

paukiatwee• 12 years ago

Think slf4j as API, and logj4 as implementation. slf4j has multiple implementations, e.g. logj4, logback, apache common logging bridge, so you can swap implementation easily without change your code(except configuration)

agibsonccc3• 12 years ago

SLF4j is already the standard wrt logging. I think one thing to think of here is libraries.

If there is one logging engine to depend on that libs can use, this means less dependency hell.

Fighting it is a losing battle with how much traction it has among all the different libs.

EdwardDiego• 12 years ago

Yes, we did, from log4j to logback. Due to using slf4j, no code changes were required.

ddeck• 12 years ago

I just switched from Logback to Log4j2 for an application and since I was using SLF4J, there were no code changes required.

Also consider the case of third-party libraries. I have dependencies in my application that are hard coded to log to about three different logging implementations. If they instead used SLF4J, the end user could choose whichever implementation they were already using in their app, instead of having multiple implementations or needing to redirect the output via an SLF4J bridging module.

digaozao2• 12 years ago

slf4j was useful for me in a switch from log4j to logback.

Other useful tool for logging, that integrate with logback or log4j is sentry: https://github.com/getsentry/sentry

And to use it with java: https://github.com/kencochrane/raven-java

thejdude3• 12 years ago

It's great because you can use whatever backend you're comfortable with in your setup. Are you a JUL guy? Great, configure JUL then.

I took a totally baroque project setup (they just don't know WTH they're doing) with some JUL and some log4j, piped everything into SLF via the bridges, then configured a log4j backend (which I'm confortable with) and now I'm the only person in the project that actually has control over their logging and configures it to log into nicely separated files for application output, SQL statements and so on :-)

In an ideal world we'd all just use one log system, but Sun screwed that when they created the very unnecessary JUL back in the day. SLF solves the logging mess nicely.

skybrian• 12 years ago

The article mentions a tool called Flight Recorder for profiling, but it appears this is commercial and not available in the openjdk?

kbcv• 12 years ago

How does profiling Java applications work with JIT. Should you wait until the code has been optimized before profiling, or these tools smart enough to realize that the performance of code changes as the application runs?

thejdude3• 12 years ago

I think as soon as any method takes up a noticeable part of execution time, it has been optimized all the way by the Hotspot or whatever your JVM uses.

After all, you want to profile your app's hot spots ;-)

An Opinionated Guide to Modern Java, Part 2

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