I want to checkout sonar, so I added the following snippet to my pom.xml the dependency part was taken from http://maven.apache.org/general.html#tools-jar-dependency
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Are you running this in eclipse? If the answer is yes, this is an annoying and very misunderstood problem. Take a look at my answer here
You may not be pointing eclipse to the right jre/jdk when you're starting up (this is something you didn't necessarily configure rather was Windows)