You'd just have to apply all three rules:. One of the practices that Maven encourages is don't repeat yourself. However, there are circumstances where you will need to use the same value in several different locations.
To assist in ensuring the value is only specified once, Maven allows you to use both your own and pre-defined variables in the POM. For example, to access the project. One factor to note is that these variables are processed after inheritance as outlined above. This means that if a parent project uses a variable, then its definition in the child, not the parent, will be the one eventually used. Any field of the model that is a single value element can be referenced as a variable.
Refer to the POM reference to see a full list of properties. These variables are all referenced by the prefix " project. You may also see references with pom. The format of the build timestamp can be customized by declaring the property maven. If the property is not present, the format defaults to the value already given in the example.
You are also able to reference any properties defined in the project as a variable. Consider the following example:. The directory that the current project resides in, represented as an URI. Since Maven 2. The timestamp that denotes the start of the build UTC. Using them will allow for example to put all dynamic values that can be used in multiple places in a unique place inside the pom.
What this means is that, is possible to access user properties, system properties, environment variable properties,…. It is possible and there is a convention in Maven to access predefined properties system properties, environment variables,….
One of, if not the main capability of Maven is to be able to organize the library dependencies for our project. Basically a library is another Java project that is present in a accessible central repository. From there, Maven is able to download and add the same to our project. For example, in our Maven pom example, if we want to create unit tests, we want to use JUnit Java library.
The way to bring the same to our project, is add a dependency entry like the one below. Or, If we want to use an external library to create logs, we can add another entry green below. In the above maven pom example, two artifacts are being imported to our project: Junit and Log4j.
There are complex projects with many entries in the dependencies element and possibly with exclusions. Exclusions means that, dependency libraries are Java projects that can bring other libraries as dependencies. This is particularly handy and important If they are with different versions. What we saw up to now, is inside the basics of a Maven project configuration.
Building a project means to run a set of Maven instructions that will produce a final result. In Maven there is the concept of building lifecycle. This means that a build runs in a set of phases called by Maven commands.
There are 3 types of lifecycles in Maven: default, clean and site. Each of those lifecycles will call a set of phases. When building a project, it will be inside the default lifecycle and a subset phases of the same are called. These subset phases are :. All these rules can be defined inside the build section of a pom. Inside a pom. Below, in our Maven pom example, in green, you can find the structure of the two above points inside a pom.
A profile is an element that can be referenced when the build is triggered. That way, the rules that are defined inside that element will apply to the build process.
Different profiles can be created with different rules. That way, different build behavior and results can be achieved. So what is the difference between put the build section inside the profiles element or outside more global?
The main difference between each other are:. There are many elements that can be used inside these sections. Environment settings are different elements that will define environment rules.
Below, you can find all the above elements defined in a real pom. The goal for this article is only to show the structure. Although configurations can be overridden easily. An easy way to look at the default configurations of the super POM is by running the following command: mvn help:effective-pom.
Create a pom. Use the content of above mentioned example pom. Now open command console, go the folder containing pom. Effective POM displayed as result in console, after inheritance, interpolation, and profiles are applied. In above pom. Maven pom. Maven provides numerous archetype plugins to create projects, which in order, create the project structure and pom. Karthikeya T. Quaatso Learning. Maven - POM Advertisements. Previous Page.
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