Here's a quick Dockerfile to install Oracle's Java 7 and Maven.

FROM dockerfile/java

# Install maven
RUN apt-get update
RUN apt-get install -y maven

This uses the the trusted java build base image to install Java and then just installs the default maven version delivered with Ubuntu 12.04 (which seems to be 3.0.4-2).

Anyways, real simple Dockerfile - but it helps out when building Java code.