When.java
When.java is a Java implementation of the CommonJS Promises/A specification.
It is a port of cujojs/when v3.2.3 by Brian Cavalier and John Hann.
Getting started
Add a maven dependency to when.java
<dependency>
<groupId>com.englishtown</groupId>
<artifactId>when.java</artifactId>
<version>3.1.1</version>
</dependency>
Examples
1. The most basic scenario
The following demonstrates registering a resolution handler that is triggered in the future.
// Create the when and deferred objects
When when = WhenFactory.createAsync();
Deferred<Integer> d = when.defer();
// Register on fulfilled callback
Promise<Integer> p = d.getPromise();
p.then(value -> {
// Do something
return null;
});
// Use the resolver to trigger the callback registered above.
// The callback value will be 10
d.resolve(10);
2. Chaining callbacks
The following demonstrates chaining resolution handlers and how the value can be modified.
// Create the when and deferred objects
When when = WhenFactory.createAsync();
CountDownLatch latch = new CountDownLatch(1);
Deferred<Integer> d = when.defer();
Promise<Integer> p = d.getPromise();
p.then(value -> {
return when.resolve(2 * value);
}).then(value2 -> {
// Do something
assertEquals(20, value2.intValue());
return when.resolve(String.valueOf(value2));
}).then(value3 -> {
assertEquals("20", value3);
latch.countDown();
return null;
});
// Use the resolver to trigger the callbacks registered above.
// The first callback value will be Integer 10
// The second callback value will be Integer 20
// The third callback value will be String "20"
d.resolve(10);