nonulls

A collection of libraries to support a null-avoidance coding style in Java.

NoNulls consists of the following modules:

Validator

A recursive validator that checks objects for null values, letting you know where they are located.

Usage

List<String> nullPaths = NullValidator.findNullPaths(myObject);
if (!nullPaths.isEmpty()) {
    System.out.println("Nulls found: " + nullPaths);
}

// Or throw an exception if nulls are found
MyObject validated = NullValidator.assertNoNulls(myObject);

It supports POJOs, Records, Collections, Maps, Arrays, and Optional.

Available from Maven Central as

<dependency>
    <groupId>net.vanfleteren.nonulls</groupId>
    <artifactId>validator</artifactId>
    <version><!-- latest-version --></version>
</dependency>

Jackson Modules

Available for both Jackson 2 and 3. These modules help handle nulls during deserialization, allowing you to avoid having nulls in your deserialized objects. To allow a null in json to be deserialized, you have to declare it as Optional<T> instead of T in your model.

<dependency>
    <groupId>net.vanfleteren.nonulls</groupId>
    <!-- or jackson2 -->
    <artifactId>jackson3</artifactId>
    <version><!-- latest-version --></version>
</dependency>

Features

• Treat null collections as empty: Automatically converts null in JSON to empty lists, sets, or maps.
• Filter nulls in collections/maps: Automatically removes null elements from lists/sets and null values from maps.
• Empty-aware Optional: Treats empty strings in JSON as Optional.empty().
• Fail on nulls: Can be configured to throw an exception if any null values are encountered during deserialization.
• Result type: Returns a Result<T> instead of throwing an exception when deserializing.
• Customizable: Allows you to register additional type handlers. This is how the Vavr support is implemented.

Usage

// jackson 2 (3 also supported)
ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(new NoNullsModule());

// Or with specific configuration
NoNullsModule module = NoNullsModule.builder()
    .failOnNulls(true)
    .treatNullCollectionsAsEmpty(true)
    .build();
mapper.registerModule(module);

Result Type

The library provides a Result<T> type that can be used to safely handle deserialization outcomes:

Result<MyData> result = mapper.readValue(json, new TypeReference<Result<MyData>>() {});

if (result instanceof Result.Success<MyData> success) {
    process(success.value());
} else if (result instanceof Result.NullsFound<MyData> failure) {
    System.out.println("Nulls found at: " + failure.exception().getNullPaths());
}

Vavr Validator

A Vavr-friendly wrapper for the validator that returns Vavr types instead of throwing exceptions. It also knows about types like Either and Option when checking graphs for nulls.

<dependency>
    <groupId>net.vanfleteren.nonulls</groupId>
    <artifactId>validator-vavr</artifactId>
    <version><!-- latest-version --></version>
</dependency>

Try<MyObject> result = NullValidator.assertNoNulls(myObject);
Either<List<String>, MyObject> either = NullValidator.assertNoNullsEither(myObject);
Validation<List<String>, MyObject> validation = NullValidator.validate(myObject);