I am using a third-party java software which is based on install4j to be executed as a Windows service. The classpath in the .vmoptions file is quite big (almost 8k characters). When I am adding new jars to this classpath, I come up with some ClassNotFoundException, so it seems the newly added jars are not loaded by the JVM.
Is there any limitation on the length of the classpath in the .vmoptions file used by install4j?
Related
I recently started learning more about JBoss Application sever. After installation I was looking inside all directories created by JBoss installation. (I'm using JBoss AS version - jboss-5.0.1.GA)
I referred documentation available at this link
It says 'client' directory contains Jar files needed by remote clients.
client: The JARs that are required for clients that run outside of JBoss are located in the client directory.
When I looked inside 'client' directory after installation, it contains 90 jar files overall. Does that mean If I create a remote ejb client I would need to include all the 90 jars in my remote application classpath?
With JBoss AS 5.x things got complicated.
Placing all of the client jar files on classpath will certainly work.
In JBoss 4.x there was an option to use jbossall-client.jar which integrated other numerous client libs into single file. If you'll look into same named jar in JBoss 5.x you'll find out that it's reduced to manifest referencing other jars. Placing this single jar in your classpath will work as long as all of the jars referenced by manifest are present in the same directory.
If accessing remote EJB is all you need then only a subset of jars is required, unfortunatelly it's hard to tell which ones is it.
Following this coderanch link (I've found it here on SO) you'll find such subset prepared for JBoss 5.1.0.GA.
Be warned though, list of jars published on coderanch has abbreviated names, some misquotations and at least two jars are not present in server version 5.0.1. If reducing number of dependencies is your priority, use this list wisely and enhance/extend it by trials and errors.
Is the Eclipse project Properties > Java Build Path > Libraries tab the analog of the java -classpath definitions? What is the difference between a "build path" and a "classpath"?
The classpath is a Java thing. It's a list of either folders or jar files to consider (in order) when resolving classes to be loaded. It's used by the Java JVM. It can be specified by the CLASSPATH environment variable or java -classpath. It's a list of either Jar files or folders separated by a ":" on Linux/OSX systems or ";" on Windows.
The Eclipse build path is a means to construct this Java classpath from artifacts in the Eclipse environment. The Configure Build Path dialog is used to manipulate a file in your project called .classpath (normally hidden). This dialog allows you to form the Java classpath from Jar files, files you have built, folders, external Jar files and other things. It also controls where the Java Development Tooling (JDT) will locate your compiled files, and other things related to class files. The Eclipse help has pretty good documentation on this.
The classpath is the place in memory where your Class files and other resources (*.properties, *.xml, among many other types of resources) are made available to the programs running within the JVM.
Eclipse's build path is simply a folder where Eclipse will put the result of whatever 'build' process is set up: this process typically includes the compilation of classes, but it could also include other steps, like code generation, depending on plug-ins that might be installed.
Because you might be running your program from within Eclipse, the build path and the Classpath could possibly contain the same resources. However, keep in mind that the 'build path' is a view of your resources from the Operating System file system perspective, the Classpath is a view of your resources from the Java Virtual Machine perspective.
So I'm relatively new to Java EE and I am having a tough time understanding when, where and why Java deployment files are packaged with their dependencies.
Say I build my project into myapp.jar, and it depends on fizz.jar, buzz.jar and JODA (joda-time-2.0.jar).
I've heard that the default classloader doesn't package jars inside of other jars, so I have to assume that if I called a jar task from Ant, then the default classloader would get invoked and myapp.jar would be created without those 3 dependencies in it.
Is this because the mentality is to deploy main-less jars in containers or other systems that will provide its requirements at runtime? If not, then how does myapp.jar ever run correctly?
What about executable jars? To met, these must be different than main-less jars, because they are meant to be standalone units, right? That means they would need all of their dependencies packaged with them, right?
Last but not least, what about jars that depend on jars that depend on jars...etc. (i.e., dependencygraphs that are huge)?
I guess all of these questions can be summed up as follows:
Is the idea behind a non-executable jar that it will be ran in such a way that it will know what classpath(s) to look on for its dependencies at runtime? (And thus doesn't need to be packaged with its dependencies)?
Is the idea behind an executable jar that it is a standalone unit and should be pacakged with its dependencies?
If my assertion to Question #1 above is correct, how does such classpath configuration take place? Are these settings that are stored inside the jar (such as in the manifest)? Else, how would a JRE know where to search for a particular jars dependencies at runtime?
Answers to these questions will actually clarify quite a lot of hangups I have with Java fundamentals, and so any input/help here will be appreciated enormously! Thanks
Jars do not know about other jars (unless assisted by some tools like Maven). The inter dependency of the jars is purely resolved by the Classloaders. I strongly recommend to have some idea about classloaders.
To address your questions,
Is the idea behind a non-executable jar that it will be ran in such a way that it will know what classpath(s) to look on for its dependencies at runtime? (And thus doesn't need to be packaged with its dependencies)?
NO. As mentioned, it's the classloader which looks the classpath and the jars mentioned therein. The jars do not have any information about other jars.
Is the idea behind an executable jar that it is a standalone unit and should be packaged with its dependencies?
NO. A classloader loads the standalone executable jars at the start of execution. If it needs other dependency jars it'll look into the classpath for those jars.
If my assertion to Question #1 above is correct, how does such classpath configuration take place? Are these settings that are stored inside the jar (such as in the manifest)? Else, how would a JRE know where to search for a particular jars dependencies at runtime?
For standalone jar (executable jar), the classloader looks for the classpath variable OR classpath passed while invoking the application.
For other type of application (WAR, EAR), There are predefined places/folders where the dependencies should be placed in order to get picked up. This is standardized by specs.
In a nutshell, it's the classloader which is pulling all the threads. There is standard places where it looks for all the dependent jars. This link nicely describes how the classloaders in standalone application and in a deployed (in some container) works.
JAR files are a way to package togher complex java application. Jar application are easy to move between diffrent machines and operating system.
I think the right way to use Jars is not tu put everything (every dependencies) into a single jar.
For example if your application uses a jar libryra (for example jdbc) to access a database you should not put the jdbc jar into your jar.
You had better to build a jar file with only your .class file.
Of course your code needs the jdbc jar to work properly. Here comes to explain how the virtual machine searches for extarnal classes:
-it first searches in the directories that contain the classes that come standard with J2SE (the path depends on your installation)
-it searches in the directories specified by the classpath (a classpath is either an environment variable or an option of the java command)
for example:
java -jar -c /your/path/ yourApp.jar
will run your application and will search th classes your application refers to in the directory /your/path/ so if you have external jars you can put them in that directory.
For detailed documentation: http://download.oracle.com/javase/tutorial/deployment/jar/index.html
I'm trying to package a small application (still learning Scala!) in a "clean way". The goal is to have an executable JAR file. I've done the following:
packaged a JAR using sbt -> will work with
scala -cp myjarfile.jar MyClass
or
java -classpath path\to\scala-library.jar;myjarfile.jar MyClass
but won't work with
java -jar myjarfile.jar
because then scala/ScalaObject cannot be found. And no use adding a classpath on this last one, since the -jar option will ignore the -classpath option. Note that I have added the scala libs in my system CLASSPATH variable, but it seems to be ignored too when -jar is used.
added the scala library contents (by unzipping them first) to the jar created by sbt. This then works (the jar can be double-clicked and launched), but the manipulation is somewhat lengthy, and the resulting file is several megabytes big. Not ideal.
After hours of googling, I can see no way to create a small jar file that will launch when double-clicked and that doesn't involve a painful manipulation. What am I missing? I'm guessing there should be some way to define where the scala libraries are at system level. How do you deal with small applications that you want to be compiled and ready-to-run for efficiency?
Note that while I'm using sbt, I don't have a jar tool at hand (I'm relying on a JRE, not a JDK).
Thanks!
Pierric.
The following setup works for me:
have scala-library.jar in the same folder as the executable jar (and call java from there)
put this into your manifest:
Class-Path: scala-library.jar
Another option is to merge the contents of scala-library.jar into your application jar. The drawback is that this will increase its size. But you can use Proguard to strip unused classes from your final jar. I think there is an easy way of using sbt to package an executable jar using proguard.
Regarding the shrinking using Proguard, you can have a look at this page. It's about Android development; just ignore this part and have a look at the tables of the shrinking results. Some example applications shrink to less than 100kB.
Edit
Maybe you need to refine your question a bit. What are you trying to achieve? Do you want to install the program only on your system or do you want to distribute it?
If all you want is quickly launching a Java application without much impact of the JVM start-up time you can have a look at nailgun.
I have a workspace with nearly fifty web projects in it. In an effort to streamline classpath entries, I have created a user library variable and added all required jars to it. Next, I removed the individual classpath (build) entries from each of the fifty projects and replaced them with my single user library variable. Everything was going great until I deployed one of my projects from Eclipse to Tomcat and discovered the list of jars on the user library variable were not being copied to the WEB-INF/lib folder.
Does anyone know of a way to specify that these libraries get copied to the deployment source? I experimented with the Java EE Module Dependency tab, but the jars were not copied even after selecting the name of the user library set.
Try FatJar
From my experience, Eclipse is not good at packaging all external Jars for you, but FatJar will do the trick.