A Result type for the Java programming language.
Wrap a value of any type:
Result.ok(1)
.map(value -> value 2)
.map(String::valueOf)
.flatMap(value -> Result.ok(value "3"))
.ifOk(value -> { /* Do something with the value */ });Propagate errors safely:
Result.error(new IllegalArgumentException("Error message"))
.mapError(IllegalStateException::new)
.ifError(error -> { /* Do something with the error */ });Unwrap the value:
final Result<String> result = Result.ok("Value");
if(result.isOk()) {
final String value = result.get();
/* Do something with the value */
}Unwrap the error:
final Result<String> result = Result.error(new IllegalStateException("Error message"));
if(result.isError()) {
final Throwable error = result.getError();
/* Do something with the error */
}Wrap a value safely by supplying a fallback error:
// If `someVariable` is null, the default error is a NullPointerException.
Result.ofNullable(someVariable);
// Use a custom error supplier.
Result.ofNullable(someVariable, IllegalStateException::new);Or migrate an Optional<T> type to a Result<T>:
final Optional<String> optional = Optional.of("Value");
final Result<String> result = Result.of(optional);Unwrap safely by supplying a fallback value:
final Result<Integer> result = Result.error(new IllegalStateException("Error message"));
final Integer value = result.getOrElse(() -> 7);Wrap a legacy method that may throw an exception to gracefully integrate it to your railway flow:
public Result<User> findUser(final Id id) {
return Result
.of(() -> legacyService.findUser(id))
.map(user -> legacyService.transform(user));
}Try to recover from an error using a fallback method:
public Result<User> findUser(final Id id) {
return Result
.of(() -> legacyService.findUser(id))
.switchIfError(error -> fallbackSearch(id))
.map(user -> legacyService.transform(user));
}
private Result<User> fallbackSearch(final Id id) {
return Result.of(() -> cacheService.findUser(id));
}For Java 8 compatibility, use the latest supported version.
Gradle:
allprojects {
repositories {
...
maven { url 'https://jitpack.io' }
}
}
dependencies {
implementation 'com.github.MrKloan:result-type:2.0.0'
}Maven:
<repositories>
<repository>
<id>jitpack.io</id>
<url>https://jitpack.io</url>
</repository>
</repositories>
<dependencies>
<dependency>
<groupId>com.github.MrKloan</groupId>
<artifactId>result-type</artifactId>
<version>2.0.0</version>
</dependency>
</dependencies>