I have just started working with Maven in Eclipse.
I tried running a sample program in it, and I encountered some problems. The errors were in my pom.xml file. What is the significance of the pom.xml file in Maven?
In short the pom.xml will have all information to build your project.
For example you want to build a project and you have only the pom.xml sent to you via mail. If there are enough entries in the pom.xml then that is all you need! You can import it to Eclipse, Maven will download your source code from CVS, download various dependency jars (like Spring, Apache Commons), run your test cases, build the jar/war, deploy to your jboss/app server, generate a report of your code quality (using Sonar, maybe). Each task you want to do will be mentioned as a goal.
The links already provided are good enough for reference.
POM is an XML file that contains the project configuration details used by Maven. It provides all the configurations required for a project.
POM means Project Object Model, and, as the name suggests, it defines the model of the project as well.
In the normal project development you will add JAR files and libraries as required. In Maven-based development, those JAR files, libraries are added to the project using this pom.xml. In the pom context we call those JAR files, libraries as dependencies.
Maven is a build tool and pom.xml is the main file for the project.
The POM
The pom.xml file is the core of a project's configuration in Maven. It is a single configuration file that contains the majority of the information required to build a project in just the way you want. The POM is huge and can be daunting in its complexity, but it is not necessary to understand all of the intricacies just yet to use it effectively.
For more reference, check Maven in 5 Minutes.
POM stands for project object model. It's the fundamental unit of work in Maven. It is an XML file that contains information about the project and configuration details used to build the project. It downloads required libraries easily using POM XML tags.
When there is no Maven, it needs to add all the library JAR files one by one to the project. But when there is Pom.xml there is no need to add library JAR files one by one.
Simply add the dependency to the Pom.xml, and it will automatically add the library JAR files to the project.
pom.xml is a file which describes the project, configures plugins, and declares dependencies. The POM names the project, provides a set of unique identifiers (called coordinates) for a project, and defines the relationships between this project and others through dependencies, parents, and prerequisites.
A POM file can include a modules section, which tells Maven which directories have POM files which need to be built.
In the build section you can define plugins for which you need to build the artifacts in your project.
Pom.xml is part of your maven project, using pom.xml, maven life cycle you can achieve it.
The pom.xml is a project object model which tells everything 3rd party tool dependencies and library's and required plugins it will give everything to your project like project means any java based web content like itself. once you create the maven project you will get the pom.xml blog which is everything to handle your project
If you want to test your project, you need to add testing dependencies which is the maven community it will provide you once added it will have everything tested.
I would like to use Maven to download a "fat" jar- one that includes all of its dependencies. (The same sort of jar that is built using the jar-with-dependencies descriptor Ref in the maven-assembly-plugin)
The default behavior of mvn dependency:copy is to download the jar and all of its dependencies in separate files. This is not what I want. I want the dependencies to be included in the jar itself.
How do I achieve this using Maven? If it's not possible, is there some sort of manual way of assembling the fat jar myself given all its dependency JARs?
I was reading about how to create a jar file with Maven, but I saw some pom.xml files using Maven Source Plugin and others using Maven Jar Plugin.
In the Apache Maven Project page I found these descriptions:
Apache Maven JAR Plugin
This plugin provides the capability to build jars. If you like to sign jars please use the Maven Jarsigner Plugin.
Apache Maven Source Plugin
The Source Plugin creates a jar archive of the source files of the current project. The jar file is, by default, created in the project's target directory.
Reading these descriptions, I stayed in doubt about when use one or other plugin, and what are the differences or benefits, because I understood that both make the same thing.
The Apache Maven JAR Plugin is used to build jar files containing .class files in order to distribute applications or libraries in bytecode format.
The Apache Maven Source Plugin is used to build jar files containing source files (.java files) in order to allow IDE to show the source code when debugging. This jar file is used in combination with the jar file containing .class files.
maven jar plugin
The jar plugin creates a JAR file from your Maven project. The jar goal of the jar plugin is bound to the package phase of the Maven default lifecycle. When you type mvn clean install, Maven will execute all the phases in the default lifecycle up to and including the install phase, which also includes the package phase.
maven source plugin
The source plugin creates a JAR file with the project source code. It defines five goals: aggregate, jar, test-jar, jar-no-fork, and test-jar-no-fork. All these five goals of the source plugin will run under the package phase of the default lifecycle.
Unlike any of the plugins we discussed before, if you want to execute the source plugin with the Maven default lifecycle, it has to be defined in the project POM file, shown as follows. The super POM file does not define the source plugin; it has to be within your Maven project itself
What is the Difference
Both create JAR files; however, the jar plugin creates a JAR file from the binary artifact, while the source plugin creates a JAR file from the source code. Small-scale open source projects use this approach to distribute the corresponding source code along with the binary artifacts.
Could somebody explain me the exactly differences between these two Maven plugins and when it is useful to work with one of these plugins?
Maven jar plugin simply creates a jar files with all SOURCE files [.class files compiled from .java files] packed in it. However, a jar itself cannot be deployed as it generally has dependencies on 3rd party jar files or other library jar files which are needed to execute SOURCE jar file.
This is where Maven assembly plugin comes into picture. It creates a package of an extension of your choice like .zip, .tar, .gz which is a fully deployable package with all dependencies packed in it. You can also specify directory structure in assembly plugin which should be created when package is deployed on server.
So a assembly plugin is always used in combination with jar plugin.
Maven Jar plugin provides the capability to build and sign jars.The plugin use Maven Archiver to handle jar content and manifest configuration.
Maven Assembly Plugin is used to create all assemblies.
For More Info visit- http://maven.apache.org/plugins/maven-jar-plugin/
http://maven.apache.org/plugins/maven-assembly-plugin/
I am in the middle of an Ant -> Maven migration project and I have a question (I'm not really a Maven expert), since I'm stuck at a particular point:
Within one of my pom.xml files I have to use the maven-antrun-plugin to call an external ANT file, which builds a jar file and puts it in a temporary folder. There is no alternative to this call. Everything is working fine - the ant script works as it should, but how can I "package" this jar in the usual Maven workflow?
I know that I could manually call the mvn install:install-file, but isn't there a possibility to configure my pom.xml in a way that the above generated jar file IS actually the artifact of that pom.xml?
you use the build helper maven plugin's attach artifact goal to attach your extra *.jar to the maven module that triggered its creation.
since having a single maven module produce more than one artifact is generally a bad idea it would be best if you isolate this in a maven module of type pom so that this would be its only artifact