AssertJ Support for Optional, Streams and LocalDate API

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.

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.

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

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.

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

Refactor Java code safely — and automatically — with OpenRewrite.

Refactoring big codebases by hand is slow, risky, and easy to put off. That’s where OpenRewrite comes in. The open-source framework for large-scale, automated code transformations helps teams modernize safely and consistently.

Each month, the creators and maintainers of OpenRewrite at Moderne run live, hands-on training sessions — one for newcomers and one for experienced users. You’ll see how recipes work, how to apply them across projects, and how to modernize code with confidence.

Join the next session, bring your questions, and learn how to automate the kind of work that usually eats your sprint time.

This article is part of a series:

• Introduction to AssertJ
• AssertJ for Guava

• AssertJ Support for Optional, Streams and LocalDate API (current article)

• Custom Assertions with AssertJ

1. Overview

This article focuses on AssertJ‘s Java8-related features and is the third article from the series.

If you’re looking for general information on its main features have a look at the first article in the series Introduction to AssertJ and then at AssertJ for Guava.

2. Maven Dependencies

Java 8’s support is included in the main AssertJ Core module since version 3.5.1. In order to use the module, you will need to include the following section in your pom.xml file:

<dependency>
    <groupId>org.assertj</groupId>
    <artifactId>assertj-core</artifactId>
    <version>3.26.0</version>
    <scope>test</scope>
</dependency>

This dependency covers only the basic Java assertions. If you want to use the advanced assertions, you will need to add additional modules separately.

The latest Core version can be found here.

3. Java 8 Features

AssertJ leverages Java 8 features by providing special helper methods and new assertions for Java 8 types.

**3.1. Optional Assertions**

Let’s create a simple Optional instance:

Optional<String> givenOptional = Optional.of("something");

We can now easily check if an Optional contains some value and what that containing value is:

assertThat(givenOptional)
  .isPresent()
  .hasValue("something");

**3.2. Predicate Assertions**

Let’s create a simple Predicate instance by checking the length of a String:

Predicate<String> predicate = s -> s.length() > 4;

Now you can easily check which Strings are rejected or accepted by the Predicate:

assertThat(predicate)
  .accepts("aaaaa", "bbbbb")
  .rejects("a", "b")
  .acceptsAll(asList("aaaaa", "bbbbb"))
  .rejectsAll(asList("a", "b"));

**3.3. LocalDate Assertions**

Let’s start by defining two LocalDate objects:

LocalDate givenLocalDate = LocalDate.of(2016, 7, 8);
LocalDate todayDate = LocalDate.now();

You can now easily check if a given date is before/after a given date, or today:

assertThat(givenLocalDate)
  .isBefore(LocalDate.of(2020, 7, 8))
  .isAfterOrEqualTo(LocalDate.of(1989, 7, 8));

assertThat(todayDate)
  .isAfter(LocalDate.of(1989, 7, 8))
  .isToday();

**3.4. LocalDateTime Assertions**

The LocalDateTime assertions work similarly to LocalDate‘s, but do not share the isToday method.

Let’s create an example LocalDateTime object:

LocalDateTime givenLocalDate = LocalDateTime.of(2016, 7, 8, 12, 0);

And now you can check:

assertThat(givenLocalDate)
  .isBefore(LocalDateTime.of(2020, 7, 8, 11, 2));

**3.5. LocalTime Assertions**

The LocalTime assertions work similarly to other java.util.time.* assertions, but they do have one exclusive method: hasSameHourAs.

Let’s create an example LocalTime object:

LocalTime givenLocalTime = LocalTime.of(12, 15);

and now you can assert:

assertThat(givenLocalTime)
  .isAfter(LocalTime.of(1, 0))
  .hasSameHourAs(LocalTime.of(12, 0));

**3.6. FlatExtracting Helper Method**

The FlatExtracting is a special utility method that utilizes Java 8’s lambdas in order to extract properties from Iterable elements.

Let’s create a simple List with LocalDate objects:

List<LocalDate> givenList = asList(ofYearDay(2016, 5), ofYearDay(2015, 6));

now we can easily check if this List contains at least one LocalDate object with the year 2015:

assertThat(givenList)
  .flatExtracting(LocalDate::getYear)
  .contains(2015);

the flatExtracting method does not limit us to field extraction. We can always provide it with any function:

assertThat(givenList)
  .flatExtracting(LocalDate::isLeapYear)
  .contains(true);

or even:

assertThat(givenList)
  .flatExtracting(Object::getClass)
  .contains(LocalDate.class);

You can also extract multiple properties at once:

assertThat(givenList)
  .flatExtracting(LocalDate::getYear, LocalDate::getDayOfMonth)
  .contains(2015, 6);

**3.7. Satisfies Helper Method**

The Satisfies method allows you to quickly check if an object satisfies all provided assertions.

Let’s create an example String instance:

String givenString = "someString";

and now we can provide assertions as a lambda body:

assertThat(givenString)
  .satisfies(s -> {
    assertThat(s).isNotEmpty();
    assertThat(s).hasSize(10);
  });

**3.8. HasOnlyOneElementSatisfying Helper Method**

The HasOnlyOneElement helper method allows checking if an Iterable instance contains exactly only one element satisfying provided assertions.

Let’s create an example List:

List<String> givenList = Arrays.asList("");

and now you can assert:

assertThat(givenList)
  .hasOnlyOneElementSatisfying(s -> assertThat(s).isEmpty());

**3.9. Matches Helper Method**

The Matches helper method allows checking if a given object matches the given Predicate function.

Let’s take an empty String:

String emptyString = "";

and now we can check it’s state by providing an adequate Predicate lambda function:

assertThat(emptyString)
  .matches(String::isEmpty);

4. Conclusion

In this last article from the AssertJ series, we explored all advanced AssertJ Java 8’s features, which concludes the series.

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.

Custom Assertions with AssertJ

« Previous

AssertJ for Guava

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.

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

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.

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

Modern Java teams move fast — but codebases don’t always keep up. Frameworks change, dependencies drift, and tech debt builds until it starts to drag on delivery. OpenRewrite was built to fix that: an open-source refactoring engine that automates repetitive code changes while keeping developer intent intact.

The monthly training series, led by the creators and maintainers of OpenRewrite at Moderne, walks through real-world migrations and modernization patterns. Whether you’re new to recipes or ready to write your own, you’ll learn practical ways to refactor safely and at scale.

If you’ve ever wished refactoring felt as natural — and as fast — as writing code, this is a good place to start.

REST with Spring Boot

Learn Spring Security ▼▲

Learn Spring Security Core

Learn Spring Security OAuth

Learn Spring

Learn Spring Data JPA

Learn JUnit

Learn Maven

Learn Hibernate JPA

Learn Mockito

Learn JSON with Jackson

Full Archive

Baeldung Ebooks

About Baeldung

1. Overview

2. Maven Dependencies

3. Java 8 Features

3.1. Optional Assertions

3.2. Predicate Assertions

3.3. LocalDate Assertions

3.4. LocalDateTime Assertions

3.5. LocalTime Assertions

3.6. FlatExtracting Helper Method

3.7. Satisfies Helper Method

3.8. HasOnlyOneElementSatisfying Helper Method

3.9. Matches Helper Method

4. Conclusion

**3.1. Optional Assertions**

**3.2. Predicate Assertions**

**3.3. LocalDate Assertions**

**3.4. LocalDateTime Assertions**

**3.5. LocalTime Assertions**

**3.6. FlatExtracting Helper Method**

**3.7. Satisfies Helper Method**

**3.8. HasOnlyOneElementSatisfying Helper Method**

**3.9. Matches Helper Method**