At some point every developer reaches the point where they need larger amounts of data. One open-source library I like to use is Mockneat.

The Mockneat library offers an easy-to-read API to generate JSON, XML, CSV, SQL and whole POJOs. The nice thing about it is that you can generate valid data with little effort.

Just a foretaste of what Mockneat can generate without much effort:

mockneat dataset

If something is still missing, I can fall back on a regular expression:

mock.regex("([LO]){2}\\\d{6}\$")

You can use a Regular expression to generate a value that fits into the regex.

There are plenty of code examples — have a look at the tutorial or visit the project on GitHub directly.