KVCAsync.java

package strimillinn.xperimental;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

@Retention( RetentionPolicy.RUNTIME )
public @interface KVCAsync {}

ProductDetailComponent.java

	/**
	 * Stores a list of all keys annotated with @KVCAsync
	 */
	private List<String> _asyncKeys;

	/**
	 * Stores the calculated values of all _asyncKeys, once they've been calculated.
	 */
	private Map<String, Object> _asyncValues;

	public ProductDetailComponent( WOContext context ) {
		super( context );
	}

	/**
	 * Checks if the requested key is annotated with @KVCAsync.
	 * The first time such a method is requested, all keys annotated
	 * with @KVCAsync are calculated simultaneously and the results then cached.
	 */
	@Override
	public Object valueForKey( String key ) {
		if( isAsync( key ) ) {
			if( _asyncValues == null ) {
				populateAsyncValues();
			}

			return _asyncValues.get( key );
		}

		return super.valueForKey( key );
	}

	/**
	 * @return A list of names of methods annotated with @KVCAsync
	 */
	private List<String> asyncKeys() {
		if( _asyncKeys == null ) {
			_asyncKeys = new ArrayList<>();

			for( Method method : getClass().getDeclaredMethods() ) {
				if( method.isAnnotationPresent( KVCAsync.class ) ) {
					_asyncKeys.add( method.getName() );
				}
			}
		}

		return _asyncKeys;
	}

	/**
	 * @return true if the given key references a method annotated with @KVCAsync
	 */
	private boolean isAsync( String key ) {
		return asyncKeys().contains( key );
	}

	/**
	 * Populates the map of cached asynchronous values
	 */
	private void populateAsyncValues() {
		_asyncValues = Collections.synchronizedMap( new HashMap<>() );

		try {
			CompletableFuture<?>[] futures = new CompletableFuture[asyncKeys().size()];

			int i = 0;
			for( String key : asyncKeys() ) {
				futures[i++] = CompletableFuture.runAsync( () -> {
					_asyncValues.put( key, super.valueForKey( key ) );
				} );
			}

			CompletableFuture.allOf( futures ).get();
		}
		catch( InterruptedException | ExecutionException e ) {
			throw new RuntimeException( "Failed to populate async fields", e );
		}
	}

	@KVCAsync
	public BigDecimal basketPenetration() {
		return ReportUtil.basketPenetration( selectedObject() ).multiply( new BigDecimal( "100" ) );
	}

	@KVCAsync
	public BigDecimal averageBasketValue() {
		return ReportUtil.averageBasketValue( selectedObject() );
	}

	@KVCAsync
	public BigDecimal averageBasketSize() {
		return ReportUtil.averageBasketSize( selectedObject() );
	}