If the question title can't make it clear, take me explain here in more detail. Suppose the production jar of one of my Maven applications needs to be used into my other Maven web-application. Adding that jar to my second application Maven dependency doesn't add its transitive dependencies. Also, the jar in itself is an application.
One way is to look at the POM of the first application and add those in the POM of the other application. But then, how do central Maven jars add their own transitive dependencies when added to some project.
In other words, if I add commons-io.jar Maven dependency to my project, it automatically adds its transitive dependencies. But when I add myjar.jar as a Maven dependency (scope->system) then it doesn't automatically adds its transitive dependencies.
I think that I should develop my first application as some other archetype which can be used in such a case. Please advise me how to proceed further.
Sorry for this newbie question. Actually, I'm new to Maven and I've started using Netbeans-embedded-maven to create applications. I really like the way Maven simplifies the job.
edited
Seems like I should explain in more detail. So here is it.
Suppose I wrote a program/application that used A.jar,B.jar,C.jar and my production output was X.jar (which obviously doesn't contain other jars within as per maven default build). The above A,B,C jars are present in maven central repository and were added as dependency to my project. The project build jar is X.jar
Now I write another application in which I added X.jar as a system dependency, now what I want is that A.jar, B.jar, C.jar added automatically to the project since they are transitive dependencies for X.jar
Hope so I've explained it clear this time. Please forgive me for my writing style in case you didn't understand earlier.
One solution is to build X.jar containing all dependencies within it using something like this
<plugin>
<artifactId>maven-assembly-plugin</artifactId>
<configuration>
<archive>
<manifest>
<addClasspath>true</addClasspath>
<mainClass>com.nitinsurana.mlmmaven.Start</mainClass>
</manifest>
</archive>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
</configuration>
<executions>
<execution>
<id>make-my-jar-with-dependencies</id>
<phase>package</phase>
<goals>
<goal>single</goal>
</goals>
</execution>
</executions>
</plugin>
But I'm looking for something that automatically adds transitive dependencies of a system dependency.
The system scope is not supposed to be used for actual jar dependencies that will be packaged with another application. Quoting from the official documentation:
Dependencies with the scope system are always available and are not looked up in repository. They are usually used to tell Maven about dependencies which are provided by the JDK or the VM. Thus, system dependencies are especially useful for resolving dependencies on artifacts which are now provided by the JDK, but where available as separate downloads earlier. Typical example are the JDBC standard extensions or the Java Authentication and Authorization Service (JAAS).
You should use the default compile scope.
As others have suggested, use the (default) compile scope and add <exclusions> for transitive dependencies you don't want / need.
See: Maven > Optional Dependencies and Dependency Exclusions
I had gone through the link provided by #Sean and it seems like what I want is not possible.
Shall I vote to delete this question ?
Although the answer is IT CAN'T BE DONE and heres' why :
Project-A -> Project-B
The diagram above says that Project-A depends on Project-B. When A declares B as an optional dependency in its POM, this relationship remains unchanged. Its just like a normal build where Project-B will be added in its classpath.
Project-X -> Project-A
But when another project(Project-X) declares Project-A as a dependency in its POM, the optional dependency takes effect. You'll notice that Project-B is not included in the classpath of Project-X; you will need to declare it directly in your POM in order for B to be included in X's classpath.
Taken from Official Documentation
So, your X module is mavenized? Then you can install it locally with mvn clean install and then use it in another projects with all transitive dependencies and compile scope. This case is good till you do everything on you own machine. As far as you want to share the code with others or configure CI build you need X with its pom available to others. The best way to do this is to have your own artifactory, accessible from all other machines. You install X there and use it with compile scope as ususal, just need to add new repo to pom.
Related
There are lots of tutorials, which shows how to cope with dependencies of the OSGi project and how should they be converted to the bundle. After more than one day research, I have still not found how to deal with the dependencies with provided scope.
Let me give an example. I am currently using Dropbox (dropbox-core-sdk 3.0) and it has two dependencies (com.google.android and javax.servlet) with provided scope. When I use the techniques such as maven-bundle-plugin or bnd, it only downloads the artifacts and its transitive dependencies. However, I need also provided dependencies in order to be able to import my project to the OSGi container.
I am using maven-bundle-plugin and my pom.xml looks like:
<build>
<plugins>
<plugin>
<groupId>org.apache.felix</groupId>
<artifactId>maven-bundle-plugin</artifactId>
<extensions>true</extensions>
<configuration>
<instructions>
<Bundle-SymbolicName>${project.artifactId};singleton:=true</Bundle-SymbolicName>
<Bundle-Version>${project.version}</Bundle-Version>
<Export-Package>*</Export-Package>
<Embed-Transitive>true</Embed-Transitive>
<Embed-Dependency>*</Embed-Dependency>
</instructions>
</configuration>
</plugin>
</plugins>
</build>
even if Embed-Dependency says include everything, only the dependencies + transitive dependencies are in the jar. However, I want the provided-scoped jars are also in the jar.
Is there any way to download dependencies with provided scope. If not, how to deal with this situation?
I would have to defer to the Maven BND experts out there, but I don't think you can include provided dependencies through a Maven build. Since it is unlikely you will be using the Android components outside of your bundle, couldn't you just manually download the needed Jars and place them in your bundle (Bundle-Classpath)?
I think you can specify the scopes of the dependencies you want to embed. Be careful though that some dependencies like the OSGi spec jars should never be deployed.
In general you may only embed dependencies that are hidden inside the bundle. Any packages that are needed to talk to other bundles should better not deployed.
For example the servlet api is typically provided by the httpservice bundle you use.
Try this option:
<Embed-Dependency>*;scope=compile|provided</Embed-Dependency>
I'm using a MySQL connector JAR to make JDBC connections. My understanding is that I just have this JAR in the classpath, and it'll be dynamically loaded when I specify mysql: in the connection string.
I declare this dependency in my POM using <scope>runtime</scope>. When I run mvn dependency:analyze, it reports this artifact as "unused". I guess it can't determine that I'll need it through simple static analysis, fine, but surely that's going to be true of just about any runtime-scoped artifact, right? How can I convince Maven that this artifact really needs to be there?
dependency:tree will list all artifacts that are referenced by your pom files if that is what you are looking for. Otherwise you are likely out of luck. Maven openly declares that their dependency analyzer works at the bytecode level and will falsely report dependencies as unused in some scenarios.
A runtime-scoped dependency may or may not be used, it is impossible to tell with bytecode analysis (in fact, impossible to tell with most analysis I could think of). Maven has to decide to either assume they are used or assume they are unused and they went with the latter figuring the user could figure it out.
There is no option to tell Maven to treat runtime-scoped dependencies as used but you can manually add specific artifacts to the usedDependencies array in the configuration. Maven will simply assume those dependencies are used. You could also write your own dependency analyzer or find a 3rd party dependency analyzer that can handle this scenario.
==Update for comments==
You're right, it is quite new. The issue was fixed in version 2.6 which was released Nov, 25, 2012. It isn't yet in many of the public mirror repositories. You can find it here.
Since it is so new there are no examples of its usage however Maven follows some conventions. I would expect it to be declared as:
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-dependency-plugin</artifactId>
<version>2.6</version>
<configuration>
<usedDependencies>
<usedDependency>org.foo.bar:baz-tron</usedDependency>
<usedDependency>org.foo:whatsit</usedDependency>
</usedDependencies>
</configuration>
</plugin>
</plugins>
</build>
I have a Maven repository where I load Jena TDB 0.9.3 (which depends on Jena ARQ 2.9.3), Jersey 1.8 and RMOnto 1.0. The point is, as you expected, to do some analysis on semantic datasets.
It looks like RMOnto has ARQ 2.8.7 built in, as in "hardwired". There isn't any explicit dependency in its pom file, yet the jar file contains a ARQ.class. It's very tricky because you won't notice it with Maven Enforcer Plugin and the like.
It looks like this causes Jersey to use RMOnto's ARQ version instead of the one defined in pom.xml. Here is a minimal example. When you run the test (checks whether or not ARQ.VERSION equals 2.9.3), it succeeds. When you build the project and deploy it on a Tomcat 7, you should see 2.8.7 as output.
Is this behaviour expected and why?
How could one force Jersey to use ARQ 2.9.3?
In case it's not possible, could one isolate RMOnto to use 2.8.7 while the rest of the source uses 2.9.3?
Thanks in advance!
You should define the ARQ 2.9.3 first in the dependencies list. By doing that you force your build to use that specific version. The dependency order is relevant when choosing what artifact to use.
Update
OK, I understand what the problem is.
The RMOnto jar is obviously shaded according to the pom: http://semantic.cs.put.poznan.pl/maven/put/semantic/RMOnto/1.0/RMOnto-1.0.pom.
Tomcat 7 loads the jars in WEB-INF/lib in an undefined order. This means that even if you define ARQ 2.9.3 to be first in your dependencies it will not be the case when the application is run in Tomcat. http://tomcat.apache.org/tomcat-7.0-doc/class-loader-howto.html
Good thing is that Tomcat always look in WEB-INF/classes before WEB-INF/lib for dependencies.
So what you can do as a work around is to make sure that the ARQ 2.9.3 version is added to the WEB-INF/classes folder. This can be done using the maven-dependency-plugin:
<build>
<plugins>
<plugin>
<artifactId>maven-dependency-plugin</artifactId>
<executions>
<execution>
<phase>prepare-package</phase>
<goals>
<goal>unpack</goal>
</goals>
<configuration>
<artifactItems>
<artifactItem>
<groupId>org.apache.jena</groupId>
<artifactId>jena-arq</artifactId>
<version>2.9.3</version>
<outputDirectory>${project.build.directory}/classes</outputDirectory>
<excludes>**/META-INF/</excludes>
</artifactItem>
</artifactItems>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
Your war as well as your exploded war will now contain all the classes from ARQ 2.9.3 in the WEB-INF/classes folder. They will be loaded before any jar-file that is in WEB-INF/lib folder.
NB: I have not tested this on Tomcat but I cannot see that it would not work.
NB2: This is a hack. Best thing would be to remove the ARQ packages out of the RMOnto jar.
You should file a defect report against RMOnto. Hard-wiring library code into a jar, instead of including it as a dependency you can manage in the POM, is definitely a bad idea that the code maintainer should fix.
If the files have been copied directly to the RMOnto .jar, the behaviour is expected.
In that case, I'd say the best bet is to hardcode it away, aka remove the ARQ files directly from the package. Opening up the RMOnto-1.0.jar package one can see arq files in the arq folder. What you'd need to do is open up the jar file (it's just a .zip), remove the ARQ files from there, store the edited RMOnto package in your version control / repository and refer to the edited package from there. Also, you'd need to add excludes statement to your pom for the old version of ARC and keep the dependency to the new version.
If you feel like it, it would be also good practice to remove the other dependencies that haven't been mentioned in the RMOnto's pom file, then add them in the RMOnto pom file (and rebuild, if you have the source code). This way Maven mechanism would be aware of them. The file seems to contain a lot of dependencies like this, which will cause headaches in the future.
Created project with Spring, Hibernate & Maven. My question is what is the logic behind plugin versus dependency ?
Both plugins and dependencies are Jar files.
But the difference between them is, most of the work in maven is done using plugins; whereas dependency is just a Jar file which will be added to the classpath while executing the tasks.
For example, you use a compiler-plugin to compile the java files. You can't use compiler-plugin as a dependency since that will only add the plugin to the classpath, and will not trigger any compilation. The Jar files to be added to the classpath while compiling the file, will be specified as a dependency.
Same goes with your scenario. You have to use spring-plugin to execute some spring executables [ I'm not sure what spring-plugins are used for. I'm just taking a guess here ]. But you need dependencies to execute those executables. And Junit is tagged under dependency since it is used by surefire-plugin for executing unit-tests.
So, we can say, plugin is a Jar file which executes the task, and dependency is a Jar which provides the class files to execute the task.
Hope that answers your question!
Maven itself can be described as food processor which has many different units that can be used to accomplish different tasks. Those units are called plugins. For example, to compile your project maven uses maven-compiler-plugin, to run tests - maven-surefire-plugin and so on.
Dependency in terms of maven is a packaged piece of classes that your project depends on. It can be jar, war etc. For example, if you want to be able to write JUnit test, you'll have to use JUnit annotations and classes thus you have to declare that your project depends on JUnit.
Plugins and dependencies are very different things and these are complementary.
What plugins are ?
Plugins perform tasks for a Maven build. These are not packaged in the application.
These are the heart of Maven.
Any task executed by Maven is performed by plugins.
There are two categories of plugins : the build and the reporting plugins :
Build plugins will be executed during the build and they should be configured in the <build/> element from the POM.
Reporting plugins will be executed during the site generation and they should be configured in the <reporting/> element from the POM.
According to the maven goal specified in the command line (for example mvn clean, mvn clean package or mvn site) , a specific lifecyle will be used and a specific set of plugins goals will be executed.
There are three built-in build lifecycles: default, clean and site. The default lifecycle handles your project deployment, the clean lifecycle handles project cleaning, while the site lifecycle handles the creation of your project's site documentation.
A plugin goal may be bound to a specific phase of a specific lifecyle.
For example the maven-compiler-plugin binds by default the compile goal to the lifecycle phase: compile.
Most of maven plugins (both core plugins and third party plugins) favor convention over configuration. So these generally bound a plugin goal to a specific phase to make their usage simpler.
That is neater and less error prone :
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.7.0</version>
</plugin>
than :
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.7.0</version>
<executions>
<execution>
<phase>compile</phase>
<goals>
<goal>compile</goal>
</goals>
</execution>
</executions>
</plugin>
What dependencies are ?
Dependencies are Maven artifacts/components required for the project.
Concretely most of dependencies are jar (that is libraries) but these may also be other kinds of archives : war, ear, test-jar, ejb-client ... or still POM or BOM.
In a pom.xml, dependencies may be specified at multiple places : the <build><dependencies> part , the dependencies management part or still in a plugin declaration ! Indeed some plugins may need to have some dependencies in the classpath during their execution. That is not common but that may happen.
Here is an example from the documentation that shows that plugin and dependency may work together :
For instance, the Maven Antrun Plugin version 1.2 uses Ant version
1.6.5, if you want to use the latest Ant version when running this plugin, you need to add <dependencies> element like the following:
<project>
...
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-antrun-plugin</artifactId>
<version>1.2</version>
...
<dependencies>
<dependency>
<groupId>org.apache.ant</groupId>
<artifactId>ant</artifactId>
<version>1.7.1</version>
</dependency>
<dependency>
<groupId>org.apache.ant</groupId>
<artifactId>ant-launcher</artifactId>
<version>1.7.1</version>
</dependency>
</dependencies>
</plugin>
</plugins>
</build>
...
</project>
In Maven, dependencies are referenced in a specific format :
groupId:artifactId:packaging:classifier:version.
The classifier (that is optional) and the packaging (JAR by default) are not commonly specified. So the common format in the dependency declaration is rather : groupId:artifactId:version.
Here is an example of dependency declared in the <build><dependencies> part :
<build>
<dependencies>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-core</artifactId>
<version>5.2.14.Final</version>
</dependency>
<dependencies>
</build>
Dependency doesn't have a phase binding as plugins to address the "when" question.
But it has a counterpart : the scope.
Indeed declared dependencies are usable by the application at a specific time according to the scope we defined for these.
The scope is a central concept about how a dependency will be visible for the project.
The default scope is compile. That is the most commonly needed scope (convention over configuration again).
The compile scope means that the dependency is available in all classpaths of a project.
The scope defines in which classpaths the dependency should be added.
For example do we need it at compile and runtime, or only for tests compilation and execution ?
For example we previously defined Hibernate as a compile dependency as we need it everywhere : source compilation, test compilation, runtime and so for....
But we don't want that testing libraries may be packaged in the application or referenced in the source code. So we specify the test scope for them :
<build>
<dependencies>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-engine</artifactId>
<version>5.1.0</version>
<scope>test</scope>
</dependency>
<dependencies>
</build>
One line answer - basic understanding
Plugin is a tool you use at the execution of your maven build
Dependency means kind of any library which you will use in your code
If you're coming from a front-end background like me, and are familiar with Grunt and npm, think of it like this:
First you would run, say, npm install grunt-contrib-copy --save-dev. This is like maven's <dependency></dependency>. It downloads the files needed to execute a build task.
Then you would configure the task in Gruntfile.js
copy: {
main: {
src: 'src/*',
dest: 'dest/',
},
}
This is like maven's <plugin>/<plugin>. You are telling the build tool what to do with the code downloaded by npm/<dependency></dependency>.
Of course this is not an exact analogy, but close enough to help wrap your head around it.
Plug-ins are used for adding functionalities to Maven itself (like adding eclipse support or SpringBoot support to Maven etc.). Dependencies are needed by your source code to pass any Maven phase (compile or test for example). In case of JUnit since the test code is basically part of your code base and you call JUnit specific commands inside test suites and those commands are not provided by Java SDK therefore JUnit must be present at the time Maven is in the test phase and this is handled by mentioning JUnit as a dependency in your pom.xml file.
In simple words:
Plugins are used to add some additonal features to the software/tools(like Maven). Maven will use the added plugins at the time of building when we use the build command.
Dependecies are used to add some addtional code to your source code, so a dependency will make some extra code (like Classes in Java) in the form of library available for your source code.
Maven at its heart is a plugin execution framework -- as per formal and standard compact definition. To make it more clear, the commands you use like maven-install/clean/compile/build etc for creating/executing jars, which we sometimes manually run too. So, the things which you want to run (or configure or execute) you basically put them in dependency tag of mavens pom and the answer so as to who will run these dependencies (required for environment setup) be the plugins.
javac (compiler) dependency.java (dependency)
A plugin is an extension to Maven, something used to produce your artifact (maven-jar-plugin for an example, is used to, you guess it, make a jar out of your compiled classes and resources).
A dependency is a library that is needed by the application you are building, at compile and/or test and/or runtime time.
I'm trying to convert a project from ant to maven.
The unit tests depend on a third party binary jar, which is not available in any public maven repositories.
How do I make maven handle this situation? I have found two solutions, neither of which are acceptable. First is to use a system dependency; this doesn't work because a) the dependency should only be for the tests, and b) the dependency is not found by eclipse after generating an eclipse project.
Second is to manually install the dependency in a local repository. This seems to be the recommended way. I don't want to do this because I want users to be able to build and test with a simple 'mvn test'. If users have to read a document and copy/paste some shell commands to be able to build and test, then something's wrong.
I suppose it would be OK if maven itself installed the dependency in the local repository as part of the build - is this possible, and if so, how?
Aled.
You may want to look at install:install-file. You can make it execute in the early phase of your project (validate or initialize) via standard means.
On the second thought, if it fails because of missing dependency in the same project, there are couple more options. One is to call ant script via antrun plugin to install artifact.
Or create additional module not dependent on your artifact to be executed prior to main module and have that module install artifact as described earlier.
First of all my way would be using a repository manager such as nexus and installing this dependency to there.
However there is another solution. You can include this 3rd party jar to your project and with test plugin you can configure to include it in classpath such this:
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.10</version>
<configuration>
<additionalClasspathElements>
<additionalClasspathElement>path/to/additional/resources</additionalClasspathElement>
<additionalClasspathElement>path/to/additional/jar</additionalClasspathElement>
</additionalClasspathElements>
</configuration>
</plugin>
By the way, I hope that you are aware of that maven is executing surefire plugin in order to run tests by default lifecycle.