I'm thinking about start using (not playing with) Clojure. Are there any useful guides? I'm not asking about lein, javac or any other 'small' manual tools. I need to know how to have Java and Clojure sources in eclipse in the same project. How to make them calling each other without compilation errors? How to configure maven? How to set up fully productive development environment? Is it even possible at the moment? What plugins may be useful? Where to start?
I have a fully working production setup with Eclipse, Maven and Clojure that is working very nicely at the moment. Hopefully it is helpful as an example of a good polyglot setup within a Java IDE.
I don't use leiningen - Nothing against lein at all - it's very nice and ideal in a pure Clojure/CLI world. But I've found that pure Maven is nicer to work with in a polyglot Java+Clojure environment with an IDE since the tool integration is so much better. Also from an ecosystem / audience / community perspective if you want people from the Java world to be able to build your source you are going to cause a lot less confusion if you just use Maven directly.
Here is my setup:
Eclipse 4.2 as main IDE
Counterclockwise Eclipse plugin - very good, takes care of REPL, Clojure editing etc.
Maven used to manage all projects (I use the built in Eclipse Maven integration mostly, but occasionally use the CLI version as well)
cljunit used to enable JUnit tests to run on Clojure parts of the project
Github / Travis CI used for SCM and Continuous integration, accessed using the built-in EGit team provider in Eclipse
In terms of actually how I manage / set up the project itself:
I configure everything with Maven, using standard Maven directory layout. Polyglot Java+Clojure Projects typically have both src/main/java and src/main/clojure
Clojure is just a Maven dependency, like any other Java library.
I make the Clojure source directories into resource directories in the Maven setup. This means that the .clj files get bundled in any jars and can be loaded / run dynamically at runtime.
I usually make the entry point on the Java side with a public static void main(...) as usual, but call quite quickly into the Clojure code. See this blog post on calling Clojure from Java.
Finally some coding tips for polyglot Java+Clojure
I find that Java is better for low level data structures, libraries and algorithms, while Clojure is better for integrating things together and "glue" code.
Clojure calling Java is usually easier / more elegant than the other way round. Also it makes sense since you generally want the dependencies to flow that way (higher level code calling lower level code)
If you make all your Java classes immutable, they play very nicely in a Clojure world with minimal effort.
Sometimes it is worth making one or more of your Java classes implement some of the Clojure interfaces, particularly clojure.lang.IFn for example. This way your Java objects can act as first class functions in Clojure code.
Here's an example project that mixes Java and Clojure source:
https://github.com/mikera/enlight
I also wrote a small library (clojure-utils) that includes some example code for calling Clojure from Java, which you may find useful.
Despite your tone about leiningen, I recommend looking at it. Leiningen supports Java compilation, so combining java and clojure sources in one project isn't a problem.
The Counterclockwise plugin, the clojure plugin for Eclipse, can work with leiningen project files (project.clj). So within Eclipse you have dependency management and java compilation all handled for you by defining the right things in project.clj, without the need to install leiningen separately or execute commands from the command line.
In the project.clj set :java-source-paths, like for example:
:java-source-paths ["src/main/java"]
In package src/main/java put a class Foo:
package main.java;
public class Foo {
public static final String value = "Michiel";
}
Somewhere in a clojure source file define this function and "Michiel" will be printed when it is called:
(defn foo
"I don't do a whole lot."
[]
(println (main.Foo/value)))
Further reading:
http://leiningen.org/
http://code.google.com/p/counterclockwise/
You could also try the framework "Funky". It will completly seperate you Clojure and Java code . Just have a look at https://github.com/windler/Funky
Related
I am trying to make the HelloWorldImage example from Beginning Java Development with Libgdx but I can't get the project to read the image.
This is what the project directory and first class looks like:
And this is the error I get when I try to run the program:
I also used "Beginning Java Game Development with LibGDX" to learn LibGDX, so I know you are using BlueJ because that's what the book does. You definitely can build LibGDX games with BlueJ: the author uses it to develop dozens of games in the book. That said, the other commenters are correct: BlueJ is an "educational IDE" arguably suitable for learning Java. You could consider using a different IDE, especially if you already know Java.
The book's source code is available for download on GitHub. Download and extract the "978-1-4842-1501-2_Ch01_code.zip" archive and see how the project files are supposed to be arranged. If you compare your project to the source, it looks like you're missing the "+libs" folder which should contain gdx.jar, gdx-backend-lwjgl.jar, gdx-backend-lwjgl-natives.jar, and gdx-natives.jar. I know the author described several ways these dependencies could be installed, so perhaps you have used an alternative method, but I recommend you use the structure you find on GitHub to ensure it's working.
(If you want to use a different IDE like Netbeans or Eclipse but don't want to use LibGDX's Gradle build tool, I wrote a short Maven pom file that can be used to build the LibGDX games in the book.)
You don't have libGDX's dependencies (i.e. libGDX libraries etc.) included in your program's classpath.
I don't think BlueJ even has an option to use dependencies. Use Eclipse, NetBeans or IntelliJ, the only 3 officially supported IDEs for libGDX (and the most commonly used).
Edit: You can add your libraries in a folder called +libs in the BlueJ project directory.
I would not recommend using BlueJ - BlueJ is, IMO, often used for teaching Java concepts (because of its object visualizer etc.) but has an extremely limited feature set.
Also, BlueJ Gradle integration doesn't exist (a useful tool for development in general.)
Instructions for setting up libGDX with these 3 IDEs are available here.
I want to program in Java or other JVM languages like Scala, Kotlin, or Groovy. When I am programming on my projects, I only want to have import statements in my Java/Scala/Kotlin source files without the need to state the packages a second time in a Gradle/Maven build script. Instead I want to work as I would do in Python, i.e. have my import statements at the beginning of my source files and I am done.
The packages should then automatically included when I am compiling if all packages are installed in a central local package management system or otherwise get an error message telling me that I have to install a missing package. It should essentially work the same as for Python and PIP respectively.
Is a workflow like this possible preferably with Groovy or Maven?
Thanks in advance!
The closest I can think is Grape:
Grape is a JAR dependency manager embedded into Groovy. Grape lets you quickly add maven repository dependencies to your classpath, making scripting even easier. The simplest use is as simple as adding an annotation to your script:
#Grab(group='org.springframework', module='spring-orm', version='3.2.5.RELEASE')
import org.springframework.jdbc.core.JdbcTemplate
Like in this example:
#Grab('net.sourceforge.nekohtml:nekohtml:1.9.16')
def parser = new org.cyberneko.html.parsers.SAXParser()
def page = new XmlParser(parser).parse('https://news.google.com/nwshp?hl=zh-TW&tab=wn')
page.depthFirst().DIV.grep{ it.'#class'=='title' }.each {
println it.A.SPAN.text()
}
I can't judge the Groovy landscape since I don't have any experience there, but for developing Java or Scala applications this exact workflow is not possible as far as I know.
Regarding "I only want to have import statements..." I think the closest you can get is good Maven/Gradle/sbt integration in an IDE, like IntelliJ that automatically adds the desired library to your build system's configuration file when using the correct shortcut. It (at least) works for some Java libraries when you're dealing with a Maven project in IntelliJ.
And regarding your other wish to have packages automatically included when compiling: On the JVM there is the concept of the fat JAR (also called uber JAR), which is basically a JAR (Java archive) that contains all dependencies and is thus self-contained. Usually you can start the application contained in it with a single java command.
To build fat JARs you need to have the approriate plugin for your build system:
For Maven that would be the maven shade plugin, see https://maven.apache.org/plugins/maven-shade-plugin/
For sbt you can use the assembly plugin, see https://github.com/sbt/sbt-assembly
Gradle probably has something similar
A lot of Java frameworks also come with their own build plugins that make building such self-contained applications relatively simple (Spring Boot is one example, but only suitable for applications that on top of an HTTP server)
Hope this helps, althought it's not an accurate answer to your question. :)
I'm trying to learn project automation and I'm using the book Pragmatic Project Automation as a guide. It's examples are in Java so I find it easier to follow it along in Java. I don't have any experience using Java or any of its IDEs. However, I've learned some C# using Visual Studio (although I'm still a beginner).
I'm having trouble understanding some parts of setting up a Java project. I'm using Netbeans IDE 7.0 on Windows 7. With Visual Studio, I have a solution with projects underneath. With Netbeans, I appear to just have a project with directories determining the rest of the structure (and the IDE to some degree)? The equivalent to Add Reference appears to be adding a source to the Classpath. There also seems to be a degree of separation between the compiler and the IDE. I'm currently in a situation where I can compile my project just fine while the IDE tells me I still have errors (and I assume this is because I have the project set up incorrectly).
I'm basically looking for analogies that will help me better understand Java project structure.
Lots of similarities between the two languages and IDEs. I spent many years in both. For starters the equivalent to 'add reference' in VS is adding a library or jar in netbeans. In respect to a reference - a jar is pretty much the same thing as a module or .dll in VS. A jar is a compiled reference. To add a reference just go to the project menu and then properties then to the libraries menu from there you can add either pre-assembled netbeans libraries, which are collections of .jar's, or a single .jar, or even a project. Once you add a reference you can import them into your class just like you would in C#.
Netbeans doesn't really have a 'solution' as VS does. You deal with individual projects. It does however have the capability to add a project as a reference so you don't have to continually re-build the references when you change something between multiple projects. It also has project groups to group similar projects.
Lastly Apache ANT is responsible for tying everything together in the background. Netbeans creates a build.xml and build-impl.xml file in the background to tell ANT how to assemble the project into a .jar.
There are my other things to cover but I thing this answers most of your questions. Does this help?
I can't speak for NetBeans, as I use Eclipse, but you are on the right track with classpath being roughly equivalent to references in the Visual Studio world. Libraries (usually .jar files) are placed on the classpath and must be there both at compile time and runtime (you specify the classpath to the compiler at compile time, and to the JVM at runtime). The classpath can contain many different entries, and they can be anywhere in the project structure (or outside of it entirely).
Java itself doesn't impose many restrictions on your project structure, although various IDEs and build tools do. The one thing that is a universal restriction in all Java environments is that source files (and class files) are placed in a directory named after the package name. So if your package name is com.test.something, then your source files will be in SRC_DIR/com/test/something, and your class files in OUT_DIR/com/test/something (note: SRC_DIR and OUT_DIR are not special variables; each IDE will have a different way to specify those directories).
Java libraires tend to heavily build-on one-another, so at some point, you'll find that the classpath entries are too many to manage manually. Before you get there, you'll want to take a look at Apache Maven or Apache Ivy which are dependency management tools. You'll need to understand how they work (either one, not both) and how to integrate them with your IDE. If you use Eclipse and Maven, m2eclipse offers fairly complete integration between the IDE and the dependency management tool.
With Netbeans, I appear to just have a
project with directories determining
the rest of the structure (and the IDE
to some degree)?
Visual Studio dictates a particular project layout and since the compiler is so tightly integrated into the IDE there's no real concept of a build script. In contrast, Java has no such structure (although certain 'best practices' have emerged such as having a 'src' directory for source files, 'lib' for libraries, 'test' for test source, etc.) and a build script is usually required to tell the compiler were to find source files and libraries, what artefacts to produce and a miscellany of other chores (running tests, deployment, creating code metrics and so forth).
In simple cases, the IDE will take care of this for you (if you follow the convention for that particular IDE) but ultimately you will probably want to take a look at a build tool to understand what's going on behind the scenes. Apache Ant and Apache Maven are both prominent offerings. Ant is very flexible whereas Maven attempts to dictate a common layout. I suggest you investigate both and see which suits.
There also seems to be a degree of
separation between the compiler and
the IDE. I'm currently in a situation
where I can compile my project just
fine while the IDE tells me I still
have errors
If your code compiles, it is correct. The IDE is simply acting in an advisory capacity (and will highlight issues beyond compiler errors, such as warning you of potential code mistakes or bad practice).
and I assume this is because I have
the project set up incorrectly
This is a possibility although, as stated above, there are many other explanations.
Is it possible to easily manage and compile native Java classes alongside Clojure in a project using leiningen?
I am working at a pretty low level (with netty nio) and thinking that some of the plumbing classes would actually be easier to handle as raw java both in terms of constructing the code as well as performance.
As of Leiningen 2.x, :java-source-path has been replaced with :java-source-paths, whose value is now specified as a vector rather than a string.
A good place to find a full (up-to-date) documentation of Leiningen features is to peruse the sample project file. In this case, you will see:
:java-source-paths ["src/main/java"]
In Leiningen tutorial there is following statement
For projects that include some Java code, you can set the :java-source-path key in project.clj to a directory containing Java files. Then the javac compiler will run before your Clojure code is AOT-compiled, or you can run it manually with the javac task.
so it should work out of box if :java-source-paths option is set
Use Vinyasa - I wrote it especially to deal with this problem
Here is a blog post Dynamic reloading of java code in emacs/nrepl
I am looking for an lightweight Java build tool. As light as possible. Even at the expense of features. Any recommendations?
As light as possible? That must be javac running from within a batch file or shell script.
But why?
There are only really two choices: Ant or Maven.
Ant is essentially a scripting tool that you can do anything with but you have to write everything yourself.
Maven comes with a lot of predefined project types. It will dictate a directory structure to you (which some people don't like) but will also handle dependencies (which Ant can sorta do with Ivy).
Personally I prefer Maven. A few lines of XML will get you the tasks to run unit tests, stop and start a Web container (eg Jetty or Tomcat), etc.
As said elsewhere, your real choice is between maven or ant. To echo other sentiments, I find there is more configuration to do with ant, so I prefer maven. That said, a lot of people tend to criticise maven in that although you need less configuration, it downloads a lot of dependencies (and dependencies/ dependencies), so it all depends on what you mean by "light" - do you mean light in configuration or light in dependency jar downloads/installation size?
If you want something light in terms of config and downloads, you are better off with a shell script, but that will only be as feature-rich as you have time to make it!
I'd again recommend Maven2 - it is very feature rich through the use of plugins, but it can also be very "light" (depending on what that means):
it doesn't need hard installation (just unzip directory + add the path to it to the environment variables (depending on OS))
it doesn't require configuration - just copy-paste a simple POM file and your build is ready. You will just have to follow the directory structure conventions of maven
it has a plugin for every IDE, so using it with GUI makes it even easier.
Of course, an alternative is ant, but I find it less "light". And I find it less light, because ant scripts grow ugly and unpredictable, and become hard to manage, while maven scripts stay simple, because of the rich functionality provided with the tool.
It really depends on your definition of 'light'. Do you want a tool that requires very little work to use (light on code)? If so, Maven or Gradle might be a good option. Maven has been around for a while. If you are doing something that follows their conventions, then you will need to write very little in your pom.xml files. If you start deviating from the norm it can get difficult to make it do what you need (making things less light). Gradle is also an option. It hasn't be around as long as Maven, but allows you to deviate from the convention easier.
If you are looking for something that is light in terms of the tools itself being lightweight, Apache ant may be a better option. It doesn't have the conventions built in like Maven. If you have a non-standard build that is pretty simple it might be possible to create a very light ant script to do your build.
Maven is simplest if you follow its directory structure. If you are on linux or unix system, I would use shell script. Or you could consider IDEs eclipse or netbeans, they will do the job for you, and dependencies are very easy to configure.
Have you tried BlueJ (http://www.bluej.org/) ?. I used it a few years ago to teach students. It is simple in the sense you can just copy/paste code and run it. It was created to teach students, hence is very simple and good for java starters. Note that it is is a full IDE, not a command line tool like maven or ant.
If you are going to stick with standards, Maven is the best bet.
If you want flexibility consider Groovy AntBuilder. terse syntax, and full power of ant and groovy scripting.