Maven dependencies basics

Source: https://maven.apache.org/pom.html

Always required in a POM:

• groupId
• artifactId
• version

Dependency hierarchy:

• All POMs inherit from Maven's Super POM.
  This is why some properties you specify but not use have effect. For example you can set the compiler version with these properties:
  

  <maven.compiler.source>1.7</maven.compiler.source>
  <maven.compiler.target>1.7</maven.compiler.target>

• To set up a POM hierarchy within your project, all POMs that are specified as <parent> in other POMs or that have <modules> (aggregation aka. multi-module projects) must use <packaging>pom</packaging>.
  
• Note:  A POM project may be inherited from - but does not necessarily have any modules that it aggregates. Conversely, a POM project may aggregate projects that do not inherit from it.
  

Dependency scope:

• compile - this is the default scope, used if none is specified. Compile dependencies are available in all classpaths. Furthermore, those dependencies are propagated to dependent projects.
• provided - this is much like compile, but indicates you expect the JDK or a container to provide it at runtime. It is only available on the compilation and test classpath, and is not transitive.
• runtime - this scope indicates that the dependency is not required for compilation, but is for execution. It is in the runtime and test classpaths, but not the compile classpath.
• test - this scope indicates that the dependency is not required for normal use of the application, and is only available for the test compilation and execution phases. It is not transitive.
• system - this scope is similar to provided except that you have to provide the JAR which contains it explicitly. The artifact is always available and is not looked up in a repository.

Exclusion of transitive dependencies:

• One by one: specify them one by one
• All: use the * wildcard for both the groupId and artifactId