OK so I have a couple of jars that I need for my JBoss application to run. Under normal circumstances, I would just copy these jars into my apps WEB-INF/lib folder and rock on.
However, these jars are part of a third party library and they have dependencies on a whole host of .dlls and other stuff in the directory where they live. So I can't just copy the jars because the copies won't work because they don't have all of the stuff surrounding them like the originals do.
What I want to do, then, is tell JBoss where to look to find these jars, which will be in C:/Program Files/SomeDirectory/Common. I tried just adding these jars to my ClassPath, but that doesn't work because JBoss's classloader won't use that for user apps (right?).
Is there a way I can tell JBoss's Class loader "Hey, look over here! These are the jars you want!"?
Related
I'm doing some clean-ups in a GWT (no maven) project. It has a lot of jars added in WEB-INF/lib. I know the purpose of those jars (for example for REST service - luckily it's documented) so I wanted to put them in appropriate subfolders for nicer look.
After re-adding them to build path (as now they are in subfolders) I tried to run SuperDevMode and got multiple warnings:
Server class 'X' could not be found in the web app, but was found on the system classpath
and some errors like:
Cannot find a default implementation of the HK2 ServiceLocatorGenerator
When I put those jars back in WEB-INF/lib (without subfolders) and re-add to build path everything runs just fine.
My question is: can't/should't I use subfolders in WEB-INF/lib? If so, why?
Server class loader is programmed to look only into WEB-INF/lib, not other folder nor subfolders.
I strongly suggest to get into the maven world, it has a steep learning curve but it will assure to your project a solid foundation to grow on. Another big plus of Maven is that it can automatically pick up the latest security patch of your libraries (Equifax, anyone?).
Extract from the Apache Tomcat 7 Docs:
WebappX — A class loader is created for each web application that is deployed in a single Tomcat instance. All unpacked classes and resources in the /WEB-INF/classes directory of your web application, plus classes and resources in JAR files under the /WEB-INF/lib directory of your web application, are made visible to this web application, but not to other ones.
I have an Eclipse project running on Tomcat, with my dependency jars sitting in the WEB-INF/lib directory. Everything is great. But the war file created on export is huge, and I'm going to need to send it back and forth to the test server, which will be time consuming. It seems like a waste.
So I put all my dependency jars in a folder, dependency_jars, in my file system, and configured the build to point there. The build works, but when I run it (still on my local machine) the app is throwing runtime errors.
Reading around, I went to the project properties and added the jars to the Web Deployment Assembly. Now the runtime works, but the exported war once again has all the jars packaged with it.
So how do I have my dependencies available for the runtime environment, without having Eclipse package them inside the war?
OK I'm not sure this is the most elegant solution but what I did is configure Tomcat to use an external library, put the dependency jars there, and then let eclipse create the war with everything in it, explode it from the command line, remove the dependency jars, repackage the war, and finally send it out.
Well, definitely not an elegant solution. But it works. Here are the steps:
Configure Tomcat to use an external resources library. Go to tomcat_home/conf/catalina.properties and add your directory under the comment that starts with "List of comma-separated paths defining the contents of the "common" classloader..."
Export war through Eclipse.
Explode the war (pun probably merited here:) jar -xvf MyWar.war
Remove your dependency jars (which are now in the external directory from step 1 above.)
Repackage the war: jar cvf MyWar.war WEB-INF
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 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.
I have a jruby rails app that has some jar dependencies in rails lib/java. I prefer this to just putting them straight in lib as it separates my java libs from ruby libs. Works locally using jruby. Problem is, on deploy, tomcat is looking for a bunch of these jars (such as jruby) in WEB-INF/lib, not WEB-INF/lib/java.
I think i need to put some config in the web.xml that tells tomcat to also look in lib/java, but i can't find ANY docs on the matter.
I don't want to modify tomcat's system wide classpath, I just want to tell its class loader to check a directory other than WEB-INF/lib for this particular app only
Can anyone enlighten me on how to do this?
you can't change this directory, j2ee spec says that all libs go in WEB-INF/lib. That is where they are supposed to go.
Just stay with your two directories in your project folder, but join them, when creating your .war file. This should be pretty easy with apache ant and other build tools.