I have many questions about scala. I have done a bit of reading and googling and SO'ing and not found any solid answers readily available. I'm not at the experimentation/prototyping stage yet, so I thought I might as well just ask my questions and get some expert knowledge for everyone to share. Thanks in advance!
What is scala.exe really for? Can someone give a rundown about what scala.exe does differently than java.exe? Is there runtime black magic in scala.exe other than providing for an interpreter shell?
(UPDATE: There is no such thing as a scala.exe. Scala ships with a simple batch script launcher, scala.bat (or scala on *nix). The Scala runtime is java.exe with Scala's standard library jars in the CLASSPATH.)
Can I link in scala code to an existing java program if I launched the process with java.exe? If so, does my CLASSPATH need to change to link in the scala standard library jars? Also if I am launching with java.exe, are any new -javaagent parameters required to link in scala code? Is there a way to include scala code in jars in my existing web application .war file (or in WEB-INF/classes) and have it run?
Conversely, if scala.exe is required in my Java EE app server launcher to execute scala+java code, can scala.exe take all my esoteric -XX:InsertYourCrazySunPerfSwitchHere JVM command line parameters?
Finally, is incorporating new Scala code into an existing Spring Framework + JSF2 web application like trying to fit a round peg into a square hole? I see long lists of web frameworks designed for Scala that are available, but I wondered how smooth or how awkward Scala would be playing with commodity tools like JSF2. Are these Scala-based web frameworks the byproduct of non-Java developers migrating to the Scala community and wanting to recreate their framework du jour in the Scala language? Or, is there something intrinsic about the way JSF2 is designed such that, once I became an expert at Scala, I would see it's a sloppy mess trying to mix the two and I had wasted my time?
You have asked many questions. I will try to address them all, one at a time.
Question:
What is scala.exe really for? Can someone give a rundown about what
scala.exe does differently than java.exe? Is there runtime black magic
in scala.exe other than providing for an interpreter shell?
scala.bat can do several things depending on the arguments:
it can launch an interpreter shell
it can execute a Scala script file
it can execute a compiled Scala binary from a classpath
it can execute a jar file
When launching binaries, scala.bat will simply call java.exe with scala-library.jar added to the classpath. There is no magic of any kind.
Question:
Can I link in scala code to an existing java program if I launched the
process with java.exe? If so, does my CLASSPATH need to change to link
in the scala standard library jars? Also if I am launching with
java.exe, are any new -javaagent parameters required to link in scala
code?
All the Scala binaries are simple jars. The only difference is that they require the scala runtime library (scala-library.jar). So when launching with java.exe you simply follow the steps you would when launching a jar with dependencies. Again, there is no magic and no extra switches.
Question:
Is there a way to include scala code in jars in my existing web
application .war file (or in WEB-INF/classes) and have it run?
Scala jars are just like java jars, so you can treat them as such.
Question:
Finally, is incorporating new Scala code into an existing Spring
Framework + JSF2 web application like trying to fit a round peg into a
square hole? I see long lists of web frameworks designed for Scala
that are available, but I wondered how smooth or how awkward Scala
would be playing with commodity tools like JSF2. Are these Scala-based
web frameworks the byproduct of non-Java developers migrating to the
Scala community and wanting to recreate their framework du jour in the
Scala language? Or, is there something intrinsic about the way JSF2 is
designed such that, once I became an expert at Scala, I would see it's
a sloppy mess trying to mix the two and I had wasted my time?
Using Java libraries from Scala is at least as easy as using them from Java and often much smoother. On the other hand Scala is much richer that Java. So you will feel that Java libraries are lacking as soon as you start getting used to Scala.
Related
I am thinking about writing a Java application where the user can write some modules in Java and add them to a library in this application. The modules will be some calculations that use data from the main app. Maybe a bit like VBA in Office.
I would appreciate if someone would give me some hints where to start as I couldn't find something useful on the net.
Thanks in advance!
You can try to develop a module framework from scratch, if you wish.
However, if you are developing anything serious you should consider using OSGi.
Theoretically it is possible. You can allow user to write java classes, then you can compile the class using java compiler, generate .class files. you can load them using your custom class loader (probably URLClassLoader or its subclass, etc.
BUT
It is very serious application. Actually it is a kind of IDE. So, of you really want this check out a possibility to create Eclipse based application, i.e. implement several eclipse plugins.
Other approach may be to allow user wring code in one of popular scripting languages. For example groovy that has java-like syntax but can be run without compilation and does not require creating classes etc. Javascript is an option too. Javascript interpreter is a part of JDK, so you even do not need external dependencies.
you might be better off incorporating some form of jvm scripting language. Something like groovy, jruby or jython. Those don't need actual compilation and can be stored in your system as source. Plus they can be quite nice to write code in too. Groovy has the advantage of being a superset of java. (For the most part) you could just degrade to java code, and run it in the groovy interpreter.
As I've recently started using JRuby, more specifically building Java applications using Ruby code, I've started using Java Libraries such as LWJGL and Slick.
I know JRuby changes Java method names to a more ruby-esque structure, my question is, is there any current way to generate Ruby documentation, either from source or by conversion of current documentation or even based on what JRuby exposes the methods themselves as?
At some point when JRuby 1.6.7 is out I plan on cleaning this really rough project for just such a thing:
https://github.com/enebo/noridoc
The intention is it will weave both Java and Ruby syntax together and give reasonable documentation for a Rubyist wanting to know all Ruby methods. In it's current form you should be able to generate a reasonable set of HTML docs of Java code showing you all ruby aliased methods. You will need to screw around with the javadoc comment.
Oh and we plan on making this tool available out of the box in JRuby once it is good enough to merge.
We have huge stack of xml files (around 5000+ files) possibly about 80 MB when not compressed) all of them are device configurations used for read & write data & build user interfaces without any language dependencies. These XML files can be ported to any technologies like Android and Apple world. Not all the 5000+ are loaded at one shot to memory, we might load 200 files into memory based on 1 device connected. We have a .NET/WPF based application which is using those XML files to build the UI and access the device information through protocols like Modbus & Hart (Don't bother protocols now). Anywhere we need custom logic, we have written them in DLL's (in .NET) and we use the reflection & IoC to load those DLLs, create object and access them through interfaces at runtime to complete the XML configuration. On desktop, then we build UI and load configuration
Now We need to develop Android app which runs on Phone and tablet as well. I have 1 year experience working lightly in Java. We could write a core modules which can be used for both phone and tablet and UI layer which is just to render our XML as a UI elements. We know to use Java's Class Loader to create instance so that instead of DLL's we could build .jar file in Android world and load them (if possible?) and access via interfaces. When we load our XML, it will consume nearly 80 to 100 MB of RAM (in WPF & .NET).
When looking into Android world, I could not decide whether to go with Scala or Java. We do not have any Java expert to advise us. Having worked on Python, I feel like Scala is modern & good choice. Also I read that Android apps compiled using Scala is fat(big), take long time to boot up.
But coming from Visual Studio background, we are much sophisticated development team expect everything to run through IDE. Also team has to learn Java/Scala whatever our choice from start.
If we choose to work on Scala on Android, do we except the memory efficiency is near to Java? Also do we have sufficient IDE support (Eclipse or NetBeans or IdeaJ) for Scala?
I am specifically looking for Memory footprint (internals) and IDE support for building Android application. No discussion on performance or productivity..
My Scala IDE is Maven in one terminal window and Vim in another. The browser serves up help documentation. If you can base your build process on Maven, then any IDE should do fine. And since you are working a lot with XML files, I suggest that you do base your build process on Maven rather than SBT.
Of course, there is Eclipse support for Scala, Intellij supports it, there is a Netbeans plugin for Scala, even a Komodo language extension for Scala. Lots of IDE choices to try out. Only the developer knows what works for them.
Make half a dozen identical VMs. Install one IDE on each one of them. Get the developers (end users of the IDE) to test them and choose the one that they want. Do all of the build and continuous integration with SVN and Maven. Make that the boundary between the developers'personal toolset (the IDE or Emacs or Vim) and the supported development tools.
If you're coming from C#, I'd advice choosing Scala. That way you could actually preserve some of your business logic, because good C# code might probably look a bit like things are done in Scala, too. E. g. LINQ in C# and Scala's collection classes (v.s Java collections).
The syntax is a bit different compared to Java/C#, but syntax is hardly a real problem these days.
Java's IDE support is pretty good, but if you're coming from Visual Studio, Intellij (or Eclipse) + Scala plugin might be good enough for you.
If you program the same code in Java and Scala, memory consumption should be pretty the same.
You should keep in mind that you should use ProGuard to keep the size of the Android application manageable.
Now, don't get me wrong, I am a very competent programmer, but when I program, I typically develop things for the web using scripting languages like JavaScript, PHP, Python, SQL, etc. If I want to develop Java software (I am relatively experienced in Java), how do I distribute it?
Is there any good way to package up Java software in a nice little executable, send it out, and have it run? Alternatively, is there any good way to package up Java in some sort of installer, and send it out to be installed and run?
I'm using Launch4J http://launch4j.sourceforge.net/ it will generate an .exe executable for Windows, if the targeted system don't have JVM, it will tell user to download and get JVM.
You can package Java applications in so called jar-files using the jar tool or any competent Java IDE. These jar-files are self-contained and seldom need any installer.
These .jar files can easily be distributed and executed.
If you're used to web-development, you may also be interested in the Java Webstart technology.
Some links to get you started.
Export to a .jar-file in Eclipse
Lesson: Java Webstart
I have found two approaches to work well, depending on the needs of the end user.
1) Java WebStart - allows for central distribution and easy maintenance, but works best for online users. Require you to have a web site to locate the files - these days this is easy to do on the Google Application Engine.
2) Wrapping up the Java program in a single jar using one-jar, and then using jsmooth to generate an .EXE file which ensures Java is available, extracts the jar-file and invokes Java on it. This works well for users not always on the net, where you want the launch process to be transparent, but is less easy to upgrade than the webstart approach.
I use Maven to handle all the dependencies of my projects and that way when you utilise Maven to build your projects they will compile into one nice executable jar that contains everything so you dont need to worry about getting all your third-party jars in the right place etc.
There are a couple of ways: one is to create an installer that allows your user to install and run it. For this you can take a look at NSIS.... or you can just use Java Web Start where your user can just click the link and launch your application.
Here you will find a large set of options: Open Source Installers Generators in JavaIt is very useful for the "naive" customer or user of your application, to make the installation process as painless as possible. Let them install whatever is needed, DBMS, JVM, JMF and additional options via one installer.
You can also consider use one of the rich client platforms available for Java. The learning curve is probably a lot higher than just creating a jar file and ship it, but you will get a lot for free when it comes to distribution. (Think Eclipse with auto update through an update site).
Do a search for "Eclipse RCP" and "Netbeans RCP" and you'll find the two biggest contenders here. I also performed a serach for "eclipse RCP installer" and one of the hits seems interesting:
http://download.instantiations.com/RCPPackagerDoc/integration/latest/docs/html/gettingstarted/GenInstaller.html
I personally like izpack. It generates a jar file installer that you could wrap up in launch4j, supports things like windows specific shortcuts, is highly customisable through XML and hooks directly into ant.
OneJar is great for smaller stuff, but for larger programs or applications it's nowhere near as flexible and in my experience is rather slow.
Hello you can make an installer for your application.
In the link below you will find a nice help about izpack installer.
http://www.imrantariq.com/blog/?p=89
Link below contains a detailed pdf to make installer with izpack.
http://www.imrantariq.com/blog/?attachment_id=112
cheers
I'd rather not "reinvent the wheel" and I've found a Ruby project that provides functionality I need in my Java app (there is no preexisting Java project that does what I need - trust me, I've looked). So, best case scenario, I am able to run the Ruby code from my Java code (ala JSR223).
However, this Ruby project depends on having several gems installed. I'm not at all interested in converting the entire Java app into a JRuby app, but I'd like to be able to leverage this project. Is there an easy way to load the code from a gem into a ScriptEngine, or am I just asking for headaches?
JRuby is a solid platform and integrates well with Java. But Rubygems do not integrate so well with Java build tools.
If any of the gems include native C code, then forget it, you can't use them from JRuby.
If all the gems (and all their dependencies) are pure Ruby, it is technically possible to use them from JRuby, but you will have headaches getting them packaged in JARs so that the JRuby runtime can find them.
Mostly I'd say no because of complexity. Although it's subjective, I'd personally rather take the time to re-write it anyway--you can make improvements and when you're done, you'll understand it better.
One option you might consider is splitting your application into two pieces, which interact using either something like pipes/files (or simply stdin and stdout) or some sort of an RPC mechanism. Whether an approach like this makes sense really depends on what the Ruby library does - creating the interface between the two applications might be more complex than actually reimplementing the stuff in Java.
I've reused Java code from JRuby, I don't see why this can't go both ways.
Another thought, can you run the Ruby code and then just tack on a web service or set of web services to call from the Java app? Sinatra makes it ridiculously simple to write a web service wrapper for ruby code. And Java has no shortage of tools to call Web Services.