This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
DataOutputStream writes primitive Java types in a platform-portable way. It is not intended to be human-readable. If you want to write human-readable data, you'll have to format the data on the way out and parse the data on the way back in. Have a look at the Java Tutorial chapter on IO for how to correctly use Java classes to perform IO.