I am working on a project, when I run maven test, I get all the dependencies as jars, so I can use methods of classes in those jars when editing the code, however I was wondering when running maven deploy to package the code as a jar and put it on a remote repository, how does this jar execute? doesn't it need all the jars mentioned in the pom? because when reading the contents of the jar it only includes the compiled classes of the code which are under src/main/java.
I think there is a point that I have misunderstood. please if there are some basics that I have missed or I should have known refer me with a good guide.
thanks in advance
It's like you said, to run a jar you need each dependency. But to put it on repository you don't need that.
So basically when you want to create runnable jar you need some maven build plugins which will pack every dependency inside your .jar file like maven-shade-plugin.
If you want to pack a jar to upload it to remote repository for other people to use you don't need that because now it is on the side of someone who will use your dependency to download each dependant jar of your created one (maven does it automatically).
Example
It all depends on what you need to do.
Imagine that you have a console application which shows you weather for Chicago, that application uses dependency for getting weather lets call it weather-dep so your application needs a dependency of weather-dep inside.
And now if you want your user to just run it (jar can be run from console "java -jar yourWeatherApp.jar") you need to package it in a way that yourWeatherApp.jar will have inside weather-dep.jar which maven will download on packaging process.
Second option is when you know that someone want's to show weather in Chicago using yourWeatherApp.jar so that person makes his application lets call it usaWeatherApp.jar and he will include your dependency inside his application he will then be able to use classes from yourWeatherApp.jar but also from weather-dep.jar because it's dependency inside your's app.
You just need to know which use case is best suited for you.
Short answer you package your jar including dependencies when someone wan't to just run your application and not include it's functions/classes etc. inside their app.
Related
I am trying to use a number of external libraries in a Java project. The project runs fine from Intelij but I want to package it in a jar, (or something else) so I can distribute it to others. When I package it in a jar it works if I just do hello world, but as soon as I start using my libraries I get the error bellow. I have also tried packaging it as an application but when I run the batch file it just opens and then immediatly closes a command window. I read all the other posts and nothing is fixing my problem. Please help
My error
My build.gradle
The problem is most likely that your classpath does not point to the correct relative location of your 3rd party libraries. You can check the manifest file to verify if the paths are correct.
However, if it is a runnable jar file with a main method (which it looks like it is), you should use the Application plugin and package it with the Distribution plugin. Right now you are using the Java Library Distribution plugin, which is for libraries. If you do this, you can remove most of the stuff under your jar task.
When testing it locally, run gradle run and when ready, use gradle distZip to create a zip of it all. It will create a script used to start the application with the correct classpath.
Alternatively, you could also package it in a fat jar using the Shadow plugin or similar.
I have a Maven-Springboot project setup. After doing a mvn install I can run the jar file in command prompt using java -jar <my-jar-file.jar>
There was a dependency to a jar say as-common-1.0.0.jar that is there in my-jar-file.jar. Now I want to override the version of this dependent jar at run time by giving an external jar. something like:
java -jar my-jar-file.jar using as-common-1.0.1.jar
I went through many SO posts like thisinclude external jar when running java -jar but they didn't help.
is it achievable?
EDIT: The issue we have is many of our applications depend upon one of our internal framework jar which gets updated(version) often.
So every time changing the pom file and re-deploying all the apps doesn't look feasible to us. We want somehow the dependency of this particular jar is given at run time. Any idea regarding best possible way to manage this scenario?
No, this is not sensible. At best, you would load classes twice and this may/may not work.
If you build a complete jar containing everything, you cannot swap content at runtime. You need to rebuild it.
Today at work I came across something interesting. Say i have an old java project that were compiled with an ant build file and we have converted this project into a maven project. So now to build this project, we only need to do a mvn install.
When i do call
mvn install
I get a myproject.jar under the target folder, along with all the dependencies under a lib folder inside the target folder.
To run the executable of this jar I need to do something like :
java -classpath $classpath com.myproject.Mainclass $myArgs
Where $classpath is the path to all of my external libs and where $myArgs is the arguments that is passed to the main function.
I came across this website and I'm really considering to use the spring boot maven plugin to package my executable jar.
Wouldn't it be easier to execute it if all the dependencies are packaged in a single jar file ?
Why would I use the manual configuration vs the Spring Boot Maven Plugin for the executable jar ?
What are the pro and the cons of doing this ?
As the article you had linked covers with pros and cons how to do such single jar file packaging, I'll write out things that you need to consider if you want to use this approach.
Pros:
1. Simplicity of deployment
Users don't have to maintain any dependencies. All they need to do to run the app is get the jar file and execute java -jar file.jar.
2. No easy way to update dependencies by user
If your app uses some external dependencies, you can be sure they are in version that you have chosen. Using "classic" approach user can easily update it by himself to the version that may require some migration steps in your app.
Cons:
1. Size of final package
If your app has large dependencies, every update will require users to download the whole package,
even if dependencies haven't changed.
2. No easy way to update dependencies by user
To change a version of any dependency you will need to update the whole package, where using the old way you could update only the dependency jar.
Summarizing, if your app doesn't have any heavy (in sense of file size) dependencies, I'll personally use single jar file approach. Even if your dependencies changes frequently. It's a lot easier to change a single file, no matter if your app has to be updated or some of its dependency.
So I'm fairly new to Java and especially Eclipse, so please excuse my ignorance. I took a project from a server and copied it locally to my machine. When I opened the workspace, I had many errors due to it not being able to find the jars. This makes sense because I don't have the same dir structure as the server I copied from. So if I copy the same external jar's to my machine and get it to compile into a jar and copy it back to the server, will it work? Or will it fail because now the external jar's are in a different place than it is expecting?
Also, down the road should I put the external jars into regular jars to avoid this problem?
You should be OK. Java is using what is called classpath to locate dependencies. The classpath may be different on the development machines, but as long as all the dependencies are on the classpath in the production everything should work.
To avoid issues with the synchronisation of directory structures the most common way is to use Maven - it will manage all the dependencies for you (but you have to manage the pom.xml - the Maven's project descriptor). A little clumsier way is to have the dependencies in the project, however you may end up with many projects having to include same jars, and then there will be version conflicts and so on.
For small projects you can manage dependencies yourself, however larger projects will need a more thought through strategy (like Maven).
In regard to the executable jars, make sure the Class-Path entry in <jarfile>:\META-INF\MANIFEST.MF is correct, e.g. where it references other jars, those jars are going to be there in the production. For example, assume we have ourjar.jar and assume this is a snippet from its MANIFEST.MF:
Class-Path: lib/myteamjar.jar
It will then be expected that a following directory structure is in place:
lib/myteamjar.jar
ourjar.jar
No, the location of the external jars does not mater. What you want to do is put the external jars on your classpath. How you do it depends on how you are running your java code. If you are running it from the CLI using the java command, it takes the classpath as an argument. If you want your code to build/run in Eclipse, you need to right click on your project, select "Build Path" > "Configure Build Path..." Use the "Add JARs..." button to add jars that are part of a project you have open and "Add External JARs..." to add jars that reside outside of the project. See specific documentation for your tool for more details about classpaths.
I would not recommend Maven to somebody who is fairly new to Java and Eclipse. I would forget about Eclipse, too.
You have a packaging and CLASSPATH issue. Focus on that.
What kind of project are you talking about? The answer you get will depend on what type of app you're creating. Is it an executable JAR? Then the right way to do it is to package everything into a ZIP file that's laid out exactly as the CLASSPATH in the JAR manifest expects.
If it's a web app, the right thing is a WAR file, with all the JARs your app needs in the WEB-INF/lib directory.
If you package things properly, you should end up with a single package that has everything laid out the right way. You should be able to deploy it to the server and make it all work.
So I've been pigeon-holed into writing some Jython code. I've been using the latest version of Eclipse IDE with the PyDev plugin for development. Up until now, things have been moderately tolerable. I've gotten all my Python scripts working and I'm successfully including a couple of JAR files and the class directory of another Java project as external dependencies. Everything seems to run fine through the Eclipse IDE.
Now I need to package everything up and deploy it. From what I can gather, the best way to do this would be to package everything up in a JAR file. The Jython documentation suggests starting out with the jython.jar file and adding to it. OK. So I modify my main python module and start adding all my python source to the JAR.
It executes but of course can't find all the external dependencies.
How is one supposed to add the external JAR files so that they are correctly seen by the Jython interpreter? How is one supposed to manage more complex dependencies in a setup like this?
Is there a plugin for Eclipse or maybe something like Ant or Maven that can handle all of these steps for me with the push of a button?
I can't be the first person that has needed to deploy Jython code with complex dependencies can I?
I've made some headway on getting this all working so I thought I would put some notes here in case they help anyone else out. I'd still like to hear from others on their experiences trying to put together something like this.
It turns out that Eclipse as of 3.5 has a project export option for Java -> Runnable JAR File. If you use this option, you can point to a Java main class in the export wizard. You also have the option to have it repackage all the JARs that you are dependent on in your new JAR file. Make sure to check the box to save the export as an ANT build so that you can repeat the process quickly. NOTE that the first time you do this through the interface, it may fail, but it will still have created a JAR file.
Now here's where it gets strange. To track all the dependencies, I am still using a mostly incomplete Maven build in my project. I create the Maven .POM file. And I told Maven what my external JAR dependency was. I then told Maven to do a dependency update for me. It pulled everything into my Maven repository as expected.
Now when I do my ANT build, it appears that it is getting its list of JARs to include in the final build from Maven. I'm not really sure if it is supposed to work that way. I'm also not 100% sure that it is working. I guess I'll find out when I have to add another external JAR to the project.
Anyways, if you follow this question you'll see that you can take the latest builds of Jython and pull the org.python.util.JarRunner.java file out and use it in your own project. This is you Java.main class that you will need to point your ANT build at. From there, convert your main Python/Jython script to be the run script that was talked about in that question.
Next, build up another copy of the Jython JAR file in your Jython directory. This one should have the /Lib directory pulled into the JAR. Save that off and then point your Eclipse IDE Jave Build option for your PyDev project at that JAR as an external dependency. Your JarRunner will now work and execute the run.py file under Jython.
If all that works, you should then be able to rerun the ANT exported build from earlier and you will end up with a single JAR file that you can execute on the command line as:
java -jar {yourjar} args
And distribute to your customers without any additional dependencies.
If that all seems a little bit convoluted, it is. If anyone has a better way of setting this all up using Eclipse, please let me know.
Make your life easier and just use Maven and the mavenjython compile plugin.
See my answer of this question: Using Jython with Maven
You get full automation of the build and deploy process, and the result is a jar that includes jython and all other dependencies.