I am facing this unique problem, i have some custom libraries deployed in weblogic lib folder and some of them have same package structure and even some classes have same names. But these libraries are being used in different applications, so applications dont give any compile time error. But in a shared environment, they are causing trouble. Any suggestion on how to fix this with minimum changes. I am using weblogic 11 server and working with EJB 3.0 applications.
The problem is at level of design. A good library or application should have a custom package not reused by other libraries or applications.
The best solution is to refactoring your code changing the package names. Don't limit the changes to the conflicting classes, but change the whole package. It should be simple with modern ide (Eclipse, IntelliJ).
For next projects remember to use always a syntax for packages like the following
com.yourcompany.yourproject.specificpackages
this will guarantee that no class will go in conflict with others.
Related
I want to build a REST API using RestEasy. The generated file should be deployed in a WildFly application server.
I face the issue described in the following SO-question:
AsynchronousDispatcher error
The marked solution tells me, to set the dependency to "provided". Which as far as I understand means, that the library is not included in my war file but taken directly from the app-server...
Isn't that just wrong?
My idea would be to build a self-containing war file which contains all the needed libraries in the version I need.
When provided from the app-server I do get the currently available version from there. I have not really a clue about the version... when someone has the idea to update the RestEasy library on the server, it might break my app.
I'm not sure whether I missed something or did something completely wrong?
One of the big advantages to Java EE is developing towards the API and not having to worry about the implementation. Java EE containers provide the API's and implementations for the API's. If you include implementation dependencies one of two things is likely to happen.
You're dependencies will be ignored making it pointless to include them in your deployment.
You'll get conflicts between the dependencies you included vs what the server is expecting. This could be things like:
ClassCastException because it's finding two of the same class on the class path.
MethodNotFoundException because there is a version mismatch
Various other issues with conflcts
Developing towards the API instead of the implementation also allows you to easily switch between Java EE compliant containers with no to minimal changes to your deployment. The API's are generally backwards compatible as well making version upgrades not as big of an issue.
If you want to use a fat WAR (including implementations) instead of a skinny WAR (not including the implementations) then a servlet container is probably a better solution. WildFly does have a servlet only download. I'd encourage you though to trust container to do the right thing with the implementation dependencies :). Usually the only time there is an issue with upgrading is if you're upgrading Java EE versions. Even then it's usually pretty safe.
I have an ant script that I use to build my J2EE application and create jar files. The problem is the following: Two jar files are necessary for the application to run.
commons-math-2.0.jar
commons-math-1.0.jar
However, I want to only use the 2.0 for a particular package inside the application with the rest of the application using 1.0. How can I build the application to only use the 2.0 version for example with a package name such as com.naurus.eventhandler.risk? Again, I'm using an Ant script, but if there's an easier way to do this sort of thing I'm willing to experiment. Thanks!
If the two jars contain different classes/packages there should be no problem to have all of them in the application classpath. It is then a matter of discipline not to use the classes from the one jar in the other package.
However I guess these two jars contain mostly the same classes/methods? There are many ways of using different versions of the same classes:
Using different ClassLoader instances. I would not qualify it as "easy", far from it means opening the door to a bunch of nasty bugs. (can be helped using a tool like OSGi)
Splitting the application in two processes, these process being launched in the same Ant target and using any mean (CORBA, RMI, REST, etc.) to communicate.
I would not advise using any of these methods though. It would probably be simpler to make all your packages use the same version. Is there any specific difficulty in doing so?
That will be problematic since both JAR files will end up in the same classpath when you deploy your J2EE application. You could achieve what you are trying to attempt with OSGI bundles, which allow each package to have separate dependencies. However, that is a relatively large refactoring of your application.
IMO, it would be best to either:
a) Duplicate the features you need from 2.0 (if the number is small and the license allows it, e.g., package individual classes).
or
b) Spend the time to upgrade the entire application to 2.0
You could use the manisfest in your jar to define the classpath.
http://docs.oracle.com/javase/tutorial/deployment/jar/manifestindex.html
Although honestly it seems a bit convoluted, but it is your requirement.
I have written a common class which I want to use in separate Blackberry applications. This class is not in a separate project but just at a common location and I have linked the path of the common class in Java Build Path. I have added same common path to both of my BB applications and they builds and installs without any problem. When I run one application, it start running but when I run the other application, it gives error message "class xxx multiply defined" error and exits.
Any idea what is going wrong here. Thanks in advance
Regards,
Braj
BlackBerry doesn't work as other Java platforms. In BB Java, you can't have two classes with the same full qualified name, even if they live in different projects.
You'll have to rename one of them (either change the class name or the package name) for it to work.
In fact, the only platform where I have seen this restriction is BB. It is a real pain in the ass since you can't reuse a jar library in different projects without renaming it.
UPDATE:
This is the official article on the topic:
http://supportforums.blackberry.com/t5/Java-Development/Application-throws-quot-multiply-defined-quot-error-at-start-up/ta-p/501498
All applications in RIM OS run under one instance of Java Virtual Machine. And therefore it is allowed only one class with particular full qualified name. Adding another class with the same name will lead to failure upon running both of these classes.
There is a library thing, supported in RIM OS, but I do not recommend to use libraries in your project, unless it is very necessary.
It is because if you have several apps with the same library, but with different versions of libraries you may get the same error you reported in your question. And it is hard to manage libraries when you have many applications which use these libraries.
I recommend to copy source code of your library to the project you are working on. Copy via refactoring, to change all full qualified names of classes included in that library.
Thanks guys for replying. I have created a common library and put common code in that. Now I can use this library in different applications without any problem.
However, when I install my applications using BB desktop Manager, the library appears as part of first application but not in second application. I assume it is because, second application realizes that the library is already been included so doesn't need to include it again.
I am developing a WebSphere portlet in IDEA 11. The portlet is using some methods defined on portal. I don't have the production environment compiled classes or jars on my PC but I have the source code.
Can I somehow "attach" the .java files to my projects in order to build a war file that will be deployed into the production environment? Or do I have to build the production sources first (this seems to be harder since there are lots of dependencies)?
If this is just to test something while you await the JARs/compiled classes, you can likely do this by only bringing over the API (e.g., referenced interfaces that hopefully don't have external dependencies). Then, open up the compiled WAR and remove those .class files manually to avoid collisions with the real code on the server.
The biggest problem is that you will definitely run into issues trying to limit the exposure to the real code, unless the rest of the code was setup nicely to expose an API that has very limited dependencies.
I have recently joined a project that is using multiple different projects. A lot of these projects are depending on each other, using JAR files of the other project included in a library, so anytime you change one project, you have to then know which other projest use it and update them too. I would like to make this much easier, and was thinking about merging all this java code into one project in seperate packages. Is it possible to do this and then deploy only some of the packages in a jar. I would like to not deploy only part of it but have been sassked if this is possible.
Is there a better way to handle this?
Approach 1: Using Hudson
If you use a continuous integration server like Hudson, then you can configure upstream/downstream projects (see Terminology).
A project can have one or several downstream projcets. The downstream projects are added to the build queue if the current project is built successfully. It is possible to setup that it should add the downstream project to the call queue even if the current project is unstable (default is off).
What this means is, if someone checks in some code into one project, at least you would get early warning if it broke other builds.
Approach 2: Using Maven
If the projects are not too complex, then perhaps you could create a main project, and make these sub-projects child modules of this project. However, mangling a project into a form that Maven likes can be quite tricky.
If you use Eclipse (or any decent IDE) you can just make one project depend on another, and supply that configuration aspect in your SVN, and assume checkouts in your build scripts.
Note that if one project depends on a certain version of another project, the Jar file is a far simpler way to manage this. A major refactoring could immediately means lots of work in all the other projects to fix things, whereas you could just drop the new jar in to each project as required and do the migration work then.
I guess it probably all depends on the specific project, but I think I would keep all the projects separate. This help keep the whole system loosely coupled. You can use a tool such as maven to help manage all the dependencies between the projects. Managing dependencies like this is one of maven's main strengths.
Using Ant as your build tool, you can package your project any way that you want. However, leaving parts of your code out of the distribution seems like it would be error prone; you might accidentally leave out necessary classes (presumably, all of your classes are necessary).
In relation to keeping your code in different projects, I have a loose guideline. Keep the code that changes together in the same project and package it in its own jar file. This works best when some of your code can be broken out into utility libraries that change less frequently than your main application.
For example, you might have an application where you've generated web service client classes from a web service WSDL (using something like the Axis library). The web service interface will likely change infrequently, so you don't want to have the regeneration step reoccurring all the time in your main application build. Create a separate project for this piece so that you only have to recreate the web service client classes when the WSDL changes. Create a separate jar and use it in your main application. This style also allows other projects to reuse these utility modules.
When following this style, you should place a version number in the jar manifest so that you can keep track of which applications are using which versions of your module. Depending on how far you want to take this, you could also keep a text file in the jar that details the changes that have occurred for each revision (much like an open source library).
It's all possible (we had the same situation some years ago). How hard or easy it'll be depends on your IDE (refactoring, merging, organizing new project) and you build tool (deploying). We used IDEA as IDE and Ant as build tool and it wasn't too hard. One sunday (nobody working+committing), 2 people on one computer.
I'm not sure what you mean by
"deploy only some of the packages in a jar"
I think you will need all of them at runtime, won't you? As I understood they depend on each other.