Regex in java to get version number

I need regex expert with preferred java skills. Need this regex to be used with Java Pattern class.
Requirements:
1. Must start with a number and end with a number.
2. Must have at least one decimal in version number. Example valid: 2.0, 2.2, 17.5, 18.254, etc. Can't start or end with decimal.
3. Can have up to 3 decimal points in version number. Examples valid: 2.1, 2.1.5, 2.1.5.12

Invalid examples:
.2.5
2.5.
2
2.
2.a
2.4.5.z
3.5.2.
2.6.8.3.

Valid examples:
2.5
2.5.1
2.5.1.7
2.5.1.7\0 ((This is valid it should get only 2.5.1.7 and ignore any characters after number).
2.5.1a (This is valid it should get only 2.5.1 and ignore any characters after number).