I'm developing on an java application that consists on a main-application that is loading extensions (jars) at runtime. Each extension is a java project.
all jars have the main application in class path and other libraries. The manifest of the main application also has dependencies in the manifest classpath, e.g. sqldriver, poi,log4j etc.
Everytime I change on of the lib, i have to set all classpaths of the projects. Also if i want to build all the jars, i have to export each project once.
So I thought maybe is Maven a good solution for me. So I've installed m2eclipse and converted the projects to maven projects.
But for now i have for each projekt an own pom.xml and i also have to build all projects once.
I'm new to Maven and searching for best practises for my problem. So I'll thank you for your help and advice
Make all your projects modules of one parent pom project. This way you can build them all at the same time.
You can use a hierarchy for your pom files. Here's an older question (similar to yours) that has a great example in the answers:
Maven: POM modules and submodules hierarchy
Basically this structure:
<project>
<parent>...
</parent>
<artifactId>module</artifactId>
<packaging>pom</packaging>
<name>Module</name>
<modules>
<module>submodule</module>
</modules>
(...)
</project>
in a 'root' pom.xml file, besides the actual submodule pom.xml files.
Unless you really, really need OSGi , Maven is great. If you're doing OSGi maven is less great.
M2eclipse however is less helpful, and in my experience only leads to confusing headaches.
How you should build your projects depends on a few things. I agree that the submodule approach described in the other answers is best-practice, and if all your sub-module candidates are related (for instance, each represents a tier in a n-tiered application), in the same SCM repository, and the interfaces change often, and the versions are co-dependant then by all means, you should do that.
If however your submodules are stand-alone and don't have a lot of transitive dependencies, particularly if they are in separate SCM repositories, they are independently versioned, and you have a little spare hardware for a build server (like say Hudson) and a Maven2 artifactory (like Sonatype Nexus), you could just keep them as seperate projects, and let maven handle the rest. This way you avoid having to re-build everything because you made a small change in one of the submodules. You can just build that one.
Related
I have been battling dependencies on a Java Maven multi-module project for a couple of days.
With too little oversight developers managed to create a situation where modules each can be compiled on their own but not as a single whole together. This results in all kinds of errors. Classes that cannot be found, casting errors etc etc. The cause of these problems seems impossible to determine.
My suspicion is that Maven puts conflicting dependencies on the class path. I think we made a mess of the Maven dependencies but regardless I don't understand how Maven can be such a poor performing framework for multi-module projects.
Now I can understand that Maven tries to do very smart useful things when compiling multiple modules as a whole but shouldn't there be an option in Maven to just configure a module to be isolated from other modules? Is there such an option? To avoid this dependency hell?
Or is the Maven best practice to create other scripts, bash scripts for example to be able to compile multiple modules in isolation, with one command?
But that is also poort workaround some tools for example SonarQube require ability to run Maven on the whole code base in order to create a single project in SonarQube.
This results in all kinds of errors. Classes that cannot be found, casting errors etc etc. The cause of these problems seems impossible to determine.
Could you post the error messages? it would make analyzing your issues easier. This may be caused by dependency conflicts, but it is hard to say without more information.
Now I can understand that Maven tries to do very smart useful things when compiling multiple modules as a whole but shouldn't there be an option in Maven to just configure a module to be isolated from other modules? Is there such an option? To avoid this dependency hell?
I do not get this. If two modules do not depend on each other, their builds will be independent. If one module depends on another module and its build fails because of version conflicts, this build will fail regardless of whether it is built together with the other modules or in isolation.
Or is the Maven best practice to create other scripts, bash scripts for example to be able to compile multiple modules in isolation, with one command?
Maven follows the philosophy "convention over configuration", meaning the more you follow the convention, the less configuration you will have and the less maintenance work. Creating all kinds of scripts goes against this philosophy and is not Maven's best practice.
To manage dependency conflicts in a multi module project, you would typically have a parent module with a pom.xml that looks like
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>...</groupId>
<artifactId>...</artifactId>
<version>...</version>
<packaging>pom</packaging>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>javax</groupId>
<artifactId>javaee-web-api</artifactId>
<version>6.0</version>
<scope>provided</scope>
</dependency>
...
</dependencies>
</dependencyManagement>
<modules>
...
</modules>
</project>
In the dependendencyManagement element you define the version of libraries used. This way you force each module to use the same version of libraries.
For Maven, I often recommend the Java EE NetBeans IDE, because among other things it has a good visualisation tool for dependencies, which is useful in detecting and removing version conflicts. (I am not aware of a similar tool in Eclipse or IntelliJ). If you open a Maven project in NetBeans, click on the pom.xml (in the Projects window) and then select Graph > Show Graph.
I use this tool for 2 things:
remove the transitive dependencies in Maven, otherwise you have to manage more dependencies than required. To remove transitive dependencies, right click in the graph and select the Hierarchical layout. Every dependency that is not on the first line is a transitive dependency and can be removed from the pom.xml.
identifying conflicts between transitive dependencies. (Conflicts are coloured red in the graph.) I resolve these conflicts by explicitly setting the version for the dependencies in the dependencyManagement element in the root pom.xml
I have 3 projects, A->B->C in that dependency order. Currently everytime I make a change to B or C I have to go to the directory and do a mvn clean install in order to install it into the local repository. It is troublesome if I have to do this every time the projects updates.
How can I do it such that every time I do a mvn clean package on A, it will automatically build and install my dependent projects B and C into the local repository?
Create a parent project for all your projects A,B,C and then add all your child project on the parent pom.xml file something like this
<modules>
<module>A</module>
<module>B</module>
<module>C</module>
</modules>
Its called maven multi module project mentioned by #khmarbaise
Here are some example for this
How do I create a multi-module project in Eclipse?
Maven Multi module tutorial
Guide to Working with Multiple Modules
By use of multi module project you will get plenty of benefits like
Anytime you can add any new project with all of the current project
Separation of project is good for code cleanup
You can build Single project or You can build all project in one go.
Duplicacy of jar can be easily ignore .
Maven take care of the build order for you.
One single Jenkins job to build everything.
Plenty of other benefits.But remember if there will some pros then cons also there,its totally now what you want to use .
You can follow the solution I provided to the question Maven 2 Projects, since it is the pattern I usually use when building project with a certain complexity.
Summarizing you would have to create a main Maven project which has three submodules, say master, platform and parent.
The main project has simply the order in which the other projects will be evaluated by Maven
The master pom contains the list of project to be built and their order (aka Reactor order)
The platform pom contains all information about your platform, like JDK version, maven plugin versions, encoding and so on.
The parent pom has the platform pom as a parent and contains all global GAV information about the dependencies you are going to use in your project (Spring, CXF, junit, log4j etc.)
I am still fairly new to Maven, I finally have it how I want but now I need to break it all over again.
Here is my scenario:
I need to write two different server applications, which use identical core functionality; just, what is done with that framework is very different. One server application is very easy/simple - it's already done - whereas the other is a lot more complicated.
The code is written in a dependency injection style (using Guice, if it matters), so it should be extremely easy to break apart.
My question is this: how would you structure the projects in Eclipse, using Maven? Would you set up three different projects, something like:
server-core
server-appEasy
server-appComplicated
where each server would have it's own pom. Or, would you keep it all in one project? I need to be able to easily recompile appEasy in, say, a month from now, while I work on appComplicated. The classes for appEasy are already in a subpackage. Note: core would not work by itself without at least a mock dependency injection. It doesn't have a main class.
All thoughts appreciated, even on things I haven't thought of.
I would have a structure like this:
/server
/server-core
pom.xml
/server-appeasy
pom.xml
/server-appcomplicated
pom.xml
pom.xml
So each project has its own pom.xml that allows you to build that project in isolation.
However the parent folder also has a pom.xml, which will build all the projects if run. You can do this by including the projects as modules in the parent pom.
E.g. In the parent pom.xml
<modules>
<module>server-core</module>
<module>server-appeasy</module>
<module>server-appcomplicated</module>
</modules>
You can also use managed dependencies in the parent pom tio allow you to centralise external dependency and plugin version numbers.
I would suggest to structure all as a Maven Multi Module project.
The parent project, would have the three projects as modules, the 3th party dependency versions, and the version of your project as a property.
Then, in the server-appComplicated and server-appEasy I would add a dependecy to the server-core.
In this way you will gain:
1- A root project to compile (the parent), that it will generate the two servers and the core-lib.
2- A point where to handle the version numbers and the common dependencies.
I hope it helps
Im not a maven expert but here is my 2 cents.
Each project needs its own pom.
Do you need to build all the projects together? In that case it might make sense to have a parent pom , which has all the common dependencies.
EDIT: In that case, I feel just have three separate 3 pom files for each project.
There are multiple ways to do this, depending on how you need it when it comes to deployment. Assuming that 'server-core' is a shared artifacts among your 'server-appEasy' and 'server-appComplicated' artifacts, I would suggest something as below
Create a Maven Project 'server-core'
Add two module projects
by name 'server-appEasy' and 'server-appComplicated'
Make sure the module projects have their parent set as the 'server-core'
In the end you should have three projects (each has separate pom.xml), where
a. Building 'server-core' will also build the modules
b. Building either of the 'easy' and 'complicated' modules independently on need basis will also build the server-core.
Hope this helps!
I have a java project that is composed of 3 sub projects that generate a .jar artifact each (and have sub-dependencies among them).
In addition there is a web projects that depends on the first 3 projects and generate a war file. The war file is my final artifact, i.e. what I ship my customers.
Additionally I have a parent module that encompasses all the other projects:
<modules>
<module>../core</module>
<module>../commons</module>
<module>../api</module>
<module>../web</module>
</modules>
I generate eclipse files (mvn eclipse:eclipse) and work with eclipse. The problem is if I modify one of the non-web projects I must manually install it before deploying the web project to my web container. How can I make that the web project depends directly on the source code of the others and not on the version installed in the repository.
In your web application properties (right clic on the project in the Package explorer, then "properties"), add the three modules (core, commons and api) in the "J2EE Module Dependencies" (the others modules must be opened in the Eclipse workspace).
Do you want to add a dependency on the source jars deployed to the repository?
If so you can do it by adding the sources classifier to the dependency. See this answer for more details.
If not, can you clarify further please.
I think your problem is that you are just building just the war project. If you are building it from the command line, then what you have to build is the parent module. "mvn package" in the directory that contains the parent module should be enough. Of course this means that you have to build all the packages every time, but that is the way maven works.
The dependency:tree goal by itself will look things up in the repository rather than the reactor. You can work around this by mvn installing, as previously suggested, or doing something less onerous that invokes the reactor, such as
mvn compile dependency:tree
Works for me.
Edit: D'oh! Posted this answer to the wrong question. Was meant to be answering this
Our software is written in Java and comprise many (7) projects.
These projects are Netbeans ant projects.
I'm considering to converting them to maven2.
Where can I find some hints for doing such thing?
Don't read that book. It will only make you confused. Read this book instead: "Maven - The definitive guide" http://www.sonatype.com/books/maven-book/reference/ .
Also, the maven site has a lot of information, but the structure is terrible so you'll need to use google to navigate in it.
Here is my suggestion:
Do this by hand, not with "automagic" "help" from the IDE. Maven integration doesn't work that good yet, not in any IDE.
Make sure you program project is divided into modules under a common umbrella module, so that each module produces a single binary artifact (jar, war,...) possibly accompanied by the javadoc of the source code behind that artifact, a zip with the source code etc. The basic principle is that each module produces a single artifact, containing all the non-test-code under that module. You can do this while the project is still built by ant.
Each module should conform to the standard maven directory layout. The build destination is under [module]/target/[output-type, e.g. "classes"]. The source code is under [module]/src/main/[src-type e.g. "java"] and [module]/test/[src-type]. The artifact consists of all the code under src/main, and none of the code under src/test, as it built to the target directories. You can do this while the is still built by ant.
Start by transforming the sub-module that has no dependencies on other modules in the project.
Now you can create the parent maven module pom.xml with artifact type "pom", consisting of one of the modules below. Make a child module for the first submodule (the one with only external dependencies), using the umbrella module as "parent". Remember that you need to specify version for the parent. Remember to add the child module as a "module" in the parent too. Always use ${project.version} as version in the child modules when you create multi-module projects like this. All modules under a parent must be released simultaneously in a single operation, and if you use this setting maven will make sure the version fields stay the same across all modules and gets updated everywhere during the release. This may make it difficult to re-use the existing numbering scheme, but that doesn't matter. You are never going to run out of version numbers anyway.
Add the necessary dependencies, and make sure you can build the parent and the child module together using the command "mvn clean install" from the parent module.
Proceed with the rest of the modules the same way. Dependencies to other modules under the same parent project should also use ${project.version} as the "version" they are depending on, meaning "the same version as this". NOTE THAT in order to build, the module you are depending on must be built using "mvn install", so that it gets deployed to you local (computer) repository. Otherwise the depending module will not be able to find the classes. There are NO source-code dependencies between modules in maven, only dependencies to built and packed versions installed in local and remote repositories. This can be very confusing if you come from ant-projects. Build from the root module until you get comfortable with this. It takes two days.
Don't use maven integration in IDEs. It is a bad idea. Use "mvn idea:idea" or "mvn eclipse:eclipse" to set up your workspace as a non-maven ordinary IDE project. The inter-module dependencies mechanisms in maven and the IDE aren't identical and will never be. Also, if you have several mavenized projects with dependencies in between, you want to have several of these in your workspace with dependencies set up between. You can do this with mvn idea:idea / eclipse:eclipse if you create a separate maven project file called "workspace.xml" (or whatever) in the same directory as parent module, set up as a multi-module project containing modules "." and "../otherproject" (only one-way reference here, no parent ref back). If you run "mvn idea:idea / eclipse:eclipse -f workspace.xml" you get a workspace with all these modules linked together. No IDE integration lets you do that. This sound like a lot of extra work, but the workspace.xml-file is really small. It doesn't have to contain all that dependency stuff and all that, only the reference to the modules you want to bind together in your IDE.
I did a succeful migration of NetBeans Ant project to Maven project using the instruccions by Joseph Mocker here: http://forums.netbeans.org/ptopic55953.html
I cite the important part:
close the project
rename the build.xml, nbproject files/folders to something so NB won't recognize them.
close and restart NB (so any memory cache knowledge of the project is gone)
copy in an empty pom from some other project.
open the project back up in NB (NB should now identify it as a maven project)
rearrange the files to follow the maven way (™)
This won't be an easy task since Maven2 expects the files to be organized in a specific way. Anyway Better Builds with Maven is a free book that should get you started. It will help you understand Maven and it also has a chapter on migration.
I discovered that the migration is not necessary. The real requirements that I need was automatic download of dependencies (libraries).
This is also achieved by Ivy which nonetheless uses maven repositories.
I solved converting project from ant to ant+ivy with IvyBeans.
I have built a script to migrate Ant builds to Maven. You can find more information here:
https://github.com/ewhauser/ant2maven
It won't help you with fixing your directory structure and or any additional Ant tasks, but it removes a lot of the tedious steps to get started.