Installing and compiling Maven artifacts on Java 8 - maven

Question

I have a project with a pom.xml that has the following <build> declaration:
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.1</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
<encoding>UTF-8</encoding>
</configuration>
</plugin>
</plugins>
</build>
When I run mvn install on this project, it compiles the project, runs unit tests and publishes it to my local repo. I am trying to learn a little more about Maven here, and am having a tough time finding documentation/explanations on the following:
How am I able to run mvn install, if the POM doesn't declare it under build/plugins? Does maven-compiler-plugin include maven-install-plugin, if so, how could I have figured that out?
Most importantly: the value of build/plugins/plugin/configuration/source and .../target are both set to 1.8. If my machine has Java 8 on it, and I run mvn install on this project without any errors, does that guarantee that the project builds with Java 8? I'm looking at the docs for the Compiler Plugin and don't see those source/target configs listed anywhere.

Answer 1

First you should learn what the build life cycle is and how it works and how the plugins are bound to the life cycle by default.
Furthermore you should understand that in Maven every project inherits from the super pom file which is part of the maven distribution (the package you have downloaded). The super pom defines the default folder layout and some versions of plugins.
The question to define the maven-compiler-plugin as you did is to be very accurate simply wrong. You should have defined it like the following:
<build>
<pluginManagement>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>1.8</source>
<target>1.8</target>
<encoding>UTF-8</encoding>
</configuration>
</plugin>
</plugins>
</pluginManagement>
</build>
This would overwrite the definition which is inherited by the super pom and changes it's configuration. In your case i would suggest to change the definition into this:
<project>
...
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<build>
<pluginManagement>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.2</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
</pluginManagement>
</build>
..
</project>
The encoding should be set globally cause there are other plugins which use this definition like the maven-resources-plugin. The usage of the above property simplifies this, cause every plugin which has an option for encoding will use the default as defined in the property.
To be sure using the correct version of Java (your JDK on your machine) you have to use the maven-enforcer-plugin.
Apart from that please take a look onto the plugins page which shows the most up-to-date releases of the plugins.
As a good documentation i can recomment the Books on Maven but be aware they are written with Maven 2 in mind. So if something is not clear ask on users mailing list of here on SO.