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Azure Container Apps is a fully managed serverless container service that enables you to build and deploy modern, cloud-native Java applications and microservices at scale. It offers a simplified developer experience while providing the flexibility and portability of containers.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

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You can also ask questions and leave feedback on the Azure Container Apps GitHub page.

Partner – Microsoft – NPI EA (cat= Spring Boot)
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Azure Container Apps is a fully managed serverless container service that enables you to build and deploy modern, cloud-native Java applications and microservices at scale. It offers a simplified developer experience while providing the flexibility and portability of containers.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, you can get started over on the documentation page.

And, you can also ask questions and leave feedback on the Azure Container Apps GitHub page.

Partner – Orkes – NPI EA (cat=Spring)
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Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.

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Partner – Orkes – NPI EA (tag=Microservices)
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Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.

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Since its introduction in Java 8, the Stream API has become a staple of Java development. The basic operations like iterating, filtering, mapping sequences of elements are deceptively simple to use.

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To get a better understanding on how Streams work and how to combine them with other language features, check out our guide to Java Streams:

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Spring Data JPA is a great way to handle the complexity of JPA with the powerful simplicity of Spring Boot.

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End-to-end testing is a very useful method to make sure that your application works as intended. This highlights issues in the overall functionality of the software, that the unit and integration test stages may miss.

Playwright is an easy-to-use, but powerful tool that automates end-to-end testing, and supports all modern browsers and platforms.

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1. Introduction

In this tutorial, we’re going to learn 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.

This article is part of the “Java – Back to Basic” series here on Baeldung.

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.

2. Generate Random Unbounded String With Plain Java

Let’s start simple and generate a random String bounded to 7 characters:

@Test
public void givenUsingPlainJava_whenGeneratingRandomStringUnbounded_thenCorrect() {
    byte[] array = new byte[7]; // length is bounded by 7
    new Random().nextBytes(array);
    String generatedString = new String(array, Charset.forName("UTF-8"));

    System.out.println(generatedString);
}

Keep in mind that the new string will not be anything remotely alphanumeric.

3. 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:

@Test
public void givenUsingPlainJava_whenGeneratingRandomStringBounded_thenCorrect() {
 
    int leftLimit = 97; // letter 'a'
    int rightLimit = 122; // letter 'z'
    int targetStringLength = 10;
    Random random = new Random();
    StringBuilder buffer = new StringBuilder(targetStringLength);
    for (int i = 0; i < targetStringLength; i++) {
        int randomLimitedInt = leftLimit + (int) 
          (random.nextFloat() * (rightLimit - leftLimit + 1));
        buffer.append((char) randomLimitedInt);
    }
    String generatedString = buffer.toString();

    System.out.println(generatedString);
}

4. Generate Random Alphabetic String With Java 8

Now let’s use Random.ints, added in JDK 8, to generate an alphabetic String:

@Test
public void givenUsingJava8_whenGeneratingRandomAlphabeticString_thenCorrect() {
    int leftLimit = 97; // letter 'a'
    int rightLimit = 122; // letter 'z'
    int targetStringLength = 10;
    Random random = new Random();

    String generatedString = random.ints(leftLimit, rightLimit + 1)
      .limit(targetStringLength)
      .collect(StringBuilder::new, StringBuilder::appendCodePoint, StringBuilder::append)
      .toString();

    System.out.println(generatedString);
}

5. Generate Random Alphanumeric String With Java 8

Then we can widen our character set in order to get an alphanumeric String:

@Test
public void givenUsingJava8_whenGeneratingRandomAlphanumericString_thenCorrect() {
    int leftLimit = 48; // numeral '0'
    int rightLimit = 122; // letter 'z'
    int targetStringLength = 10;
    Random random = new Random();

    String generatedString = random.ints(leftLimit, rightLimit + 1)
      .filter(i -> (i <= 57 || i >= 65) && (i <= 90 || i >= 97))
      .limit(targetStringLength)
      .collect(StringBuilder::new, StringBuilder::appendCodePoint, StringBuilder::append)
      .toString();

    System.out.println(generatedString);
}

We used the filter method above to leave out Unicode characters between 65 and 90 in order to avoid out of range characters.

6. 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:

@Test
public void givenUsingApache_whenGeneratingRandomStringBounded_thenCorrect() {
 
    int length = 10;
    boolean useLetters = true;
    boolean useNumbers = false;
    String generatedString = RandomStringUtils.random(length, useLetters, useNumbers);

    System.out.println(generatedString);
}

So instead of all the low-level code in the Java example, this one is done with a simple one-liner.

7. Generate Alphabetic String With Apache Commons Lang

Here is another very simple example, this time a bounded String with only alphabetic characters, but without passing boolean flags into the API:

@Test
public void givenUsingApache_whenGeneratingRandomAlphabeticString_thenCorrect() {
    String generatedString = RandomStringUtils.randomAlphabetic(10);

    System.out.println(generatedString);
}

8. Generate Alphanumeric String With Apache Commons Lang

Finally, we have the same random bounded String, but this time numeric:

@Test
public void givenUsingApache_whenGeneratingRandomAlphanumericString_thenCorrect() {
    String generatedString = RandomStringUtils.randomAlphanumeric(10);

    System.out.println(generatedString);
}

And there we have it, creating bounded and unbounded strings with either plain Java, a Java 8 variant, or the Apache Commons Library.

9. 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.

In these Java examples, we 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 code backing this article is available on GitHub. Once you're logged in as a Baeldung Pro Member, start learning and coding on the project.
Baeldung Pro – NPI EA (cat = Baeldung)
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Baeldung Pro comes with both absolutely No-Ads as well as finally with Dark Mode, for a clean learning experience:

>> Explore a clean Baeldung

Once the early-adopter seats are all used, the price will go up and stay at $33/year.

Partner – Microsoft – NPI EA (cat = Spring Boot)
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Azure Container Apps is a fully managed serverless container service that enables you to build and deploy modern, cloud-native Java applications and microservices at scale. It offers a simplified developer experience while providing the flexibility and portability of containers.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, visit the documentation page.

You can also ask questions and leave feedback on the Azure Container Apps GitHub page.

Partner – Orkes – NPI EA (cat = Spring)
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Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.

Try a 14-Day Free Trial of Orkes Conductor today.

Partner – Orkes – NPI EA (tag = Microservices)
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Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.

Try a 14-Day Free Trial of Orkes Conductor today.

eBook – HTTP Client – NPI EA (cat=HTTP Client-Side)
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The Apache HTTP Client is a very robust library, suitable for both simple and advanced use cases when testing HTTP endpoints. Check out our guide covering basic request and response handling, as well as security, cookies, timeouts, and more:

>> Download the eBook

eBook – Java Concurrency – NPI EA (cat=Java Concurrency)
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Handling concurrency in an application can be a tricky process with many potential pitfalls. A solid grasp of the fundamentals will go a long way to help minimize these issues.

Get started with understanding multi-threaded applications with our Java Concurrency guide:

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eBook – Java Streams – NPI EA (cat=Java Streams)
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Since its introduction in Java 8, the Stream API has become a staple of Java development. The basic operations like iterating, filtering, mapping sequences of elements are deceptively simple to use.

But these can also be overused and fall into some common pitfalls.

To get a better understanding on how Streams work and how to combine them with other language features, check out our guide to Java Streams:

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eBook – Persistence – NPI EA (cat=Persistence)
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Working on getting your persistence layer right with Spring?

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Course – LS – NPI EA (cat=REST)

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eBook Jackson – NPI EA – 3 (cat = Jackson)