Downloading: http://repo1.maven.org/maven2/org/geotools/gt2/2.3.1/gt2-2.3.1.jar
[WARNING] An error occurred during dependency resolution.
    Failed to retrieve org.geotools:gt2-2.3.1
Caused by: Unable to download the artifact from any repository

Try downloading the file manually from the project website.

Then, install it using the command: 
    mvn install:install-file -DgroupId=org.geotools -DartifactId=gt2 \
        -Dversion=2.3.1 -Dpackaging=jar -Dfile=/path/to/file