In this tutorial, we're going to show how to generate a random string in Java – first using the standard Java libraries, then using a Java 8 variant, and finally using the Apache Commons Lang library.
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This article is part of the “Java – Back to Basic” series here on Baeldung.
1. Generate Random Unbounded String With Plain Java
Let's start simple and generate a random String bounded to 7 characters:
Keep in mind that the new string will not be anything remotely alphanumeric.
Further reading:
Efficient Word Frequency Calculator in Java
Explore various ways of counting words in Java and see how they perform.
Java – Random Long, Float, Integer and Double
Learn how to generate random numbers in Java - both unbounded as well as within a given interval.
Guide to Java String Pool
Learn how the JVM optimizes the amount of memory allocated to String storage in the Java String Pool.
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2. Generate Random Bounded String With Plain Java
Next – let's look at creating a more constrained random string; we're going to generate a random String using lowercase alphabetic letters and a set length:
3. Generate Random Alphabetic String With Java 8
Now, let's use Random.ints – added in JDK 8 – to generate an alphabetic String:
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4. Generate Random Alphanumeric String With Java 8
And then we can widen our character set in order to get an alphanumeric String: Overpicture for safari 1 3 1.
Notice the use of filter Steam lonely mountains downhill. method above to leave out Unicode characters between 65 and 90 – to avoid out of range characters.
5. Generate Bounded Random String With Apache Commons Lang
The Commons Lang library from Apache helps a lot with random string generation. Let's take a look at generating a bounded String using only letters:
So – instead of all the low-level code in the Java example – this one is done with a simple one-liner.
6. Generate Alphabetic String With Apache Commons Lang
Another very simple example – this time a bounded String with only alphabetic characters, but without passing boolean flags into the API:
7. Generate Alphanumeric String With Apache Commons Lang
And finally – the same random bounded String but this time – numeric:
And there we have it – creating bounded and unbounded strings with either plain Java, a Java 8 variant, or the Apache Commons Library.
8. Conclusion
Through different implementation methods we were able to generate bound and unbound strings, using plain Java, a Java 8 variant or the Apache Commons Library.
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In these Java examples, we've used java.util.Random, but one point worth mentioning is that it is not cryptographically secure. Consider using java.security.SecureRandom instead for security-sensitive applications.
The implementation of all of these examples and snippets can be found in the GitHub project. This is a Maven-based project so it should be easy to import and run.
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