8274771: Map, FlatMap and OrElse fluent bindings for ObservableValue

modules/javafx.base/src/main/java/com/sun/javafx/binding/Subscription.java

@@ -0,0 +1,111 @@
+/*
+ * Copyright (c) 2022 Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package com.sun.javafx.binding;
+
+import java.util.Objects;
+import java.util.function.Consumer;
+
+import javafx.beans.InvalidationListener;
+import javafx.beans.value.ChangeListener;
+import javafx.beans.value.ObservableValue;
+
+/**
+ * A subscription encapsulates how to cancel it without having
+ * to keep track of how it was created.<p>
+ *
+ * For example:<p>
+ * <pre>Subscription s = property.subscribe(System.out::println)</pre>
+ * The function passed in to {@code subscribe} does not need to be stored
+ * in order to clean up the subscription later.
+ */
+@FunctionalInterface
+public interface Subscription {
+
+    /**
+     * An empty subscription. Does nothing when cancelled.
+     */
+    static final Subscription EMPTY = () -> {};
+
+    /**
+     * Cancels this subscription.
+     */
+    void unsubscribe();
+
+    /**
+     * Combines this {@link Subscription} with the given {@code Subscription}
+     * and returns a new {@code Subscription} which will cancel both when
+     * cancelled.
+     *
+     * @param other another {@link Subscription}, cannot be null
+     * @return a combined {@link Subscription} which will cancel both when
+     *     cancelled, never null
+     */
+    default Subscription and(Subscription other) {
+        Objects.requireNonNull(other);
+
+        return () -> {
+            unsubscribe();
+            other.unsubscribe();
+        };
+    }
+
+    /**
+     * Creates a {@link Subscription} on this {@link ObservableValue} which
+     * immediately provides its current value to the given {@code subscriber},
+     * followed by any subsequent changes in value.
+     *
+     * @param subscriber a {@link Consumer} to supply with the values of this
+     *     {@link ObservableValue}, cannot be null
+     * @return a {@link Subscription} which can be used to cancel this
+     *     subscription, never null
+     */
+    static <T> Subscription subscribe(ObservableValue<T> observableValue, Consumer<? super T> subscriber) {
+        ChangeListener<T> listener = (obs, old, current) -> subscriber.accept(current);
+
+        subscriber.accept(observableValue.getValue());  // eagerly send current value
+        observableValue.addListener(listener);
+
+        return () -> observableValue.removeListener(listener);
+    }
+
+    /**
+     * Creates a {@link Subscription} on this {@link ObservableValue} which
+     * calls the given {@code runnable} whenever this {@code ObservableValue}
+     * becomes invalid.
+     *
+     * @param runnable a {@link Runnable} to call whenever this
+     *     {@link ObservableValue} becomes invalid, cannot be null
+     * @return a {@link Subscription} which can be used to cancel this
+     *     subscription, never null
+     */
+    static Subscription subscribeInvalidations(ObservableValue<?> observableValue, Runnable runnable) {
+        InvalidationListener listener = obs -> runnable.run();
+
+        observableValue.addListener(listener);
+
+        return () -> observableValue.removeListener(listener);
+    }
+}

modules/javafx.base/src/main/java/javafx/beans/binding/ObjectBinding.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2010, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2010, 2022, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -154,7 +154,13 @@ public ObservableList<?> getDependencies() {
     @Override
     public final T get() {
         if (!valid) {
-            value = computeValue();
+            T computed = computeValue();
+
+            if (!allowValidation()) {
+                return computed;
+            }
+
+            value = computed;
             valid = true;
         }
         return value;
@@ -174,6 +180,7 @@ public final void invalidate() {
             valid = false;
             onInvalidating();
             ExpressionHelper.fireValueChangedEvent(helper);
+            value = null;  // clear cached value to avoid hard reference to stale data
         }
     }
 
@@ -182,6 +189,33 @@ public final boolean isValid() {
         return valid;
     }
 
+    /**
+     * Checks if the binding has at least one listener registered on it. This
+     * is useful for subclasses which want to conserve resources when not observed.
+     *
+     * @return {@code true} if this binding currently has one or more
+     *     listeners registered on it, otherwise {@code false}
+     */
+    protected final boolean isObserved() {
+        return helper != null;
+    }
+
+    /**
+     * Checks if the binding is allowed to become valid. Overriding classes can
+     * prevent a binding from becoming valid. This is useful in subclasses which
+     * do not always listen for invalidations of their dependencies and prefer to
+     * recompute the current value instead. This can also be useful if caching of
+     * the current computed value is not desirable.
+     * <p>
+     * The default implementation always allows bindings to become valid.
+     *
+     * @return {@code true} if this binding is allowed to become valid, otherwise
+     *     {@code false}
+     */
+    protected boolean allowValidation() {
+        return true;
+    }
+
     /**
      * Calculates the current value of this binding.
      * <p>

modules/javafx.base/src/main/java/javafx/beans/value/FlatMappedBinding.java

@@ -0,0 +1,68 @@
+/*
+ * Copyright (c) 2021 Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package javafx.beans.value;
+
+import java.util.Objects;
+import java.util.function.Function;
+
+import com.sun.javafx.binding.Subscription;
+
+class FlatMappedBinding<S, T> extends LazyObjectBinding<T> {
+
+    private final ObservableValue<S> source;
+    private final Function<? super S, ? extends ObservableValue<? extends T>> mapper;
+
+    private Subscription mappedSubscription = Subscription.EMPTY;
+
+    public FlatMappedBinding(ObservableValue<S> source, Function<? super S, ? extends ObservableValue<? extends T>> mapper) {
+        this.source = Objects.requireNonNull(source, "source cannot be null");
+        this.mapper = Objects.requireNonNull(mapper, "mapper cannot be null");
+    }
+
+    @Override
+    protected T computeValue() {
+        S value = source.getValue();
+        ObservableValue<? extends T> mapped = value == null ? null : mapper.apply(value);
+
+        if (isObserved()) {
+            mappedSubscription.unsubscribe();
+            mappedSubscription = mapped == null ? Subscription.EMPTY : Subscription.subscribeInvalidations(mapped, this::invalidate);
+        }
+
+        return mapped == null ? null : mapped.getValue();
+    }
+
+    @Override
+    protected Subscription observeInputs() {
+        Subscription subscription = Subscription.subscribeInvalidations(source, this::invalidate);
+
+        return () -> {
+            subscription.unsubscribe();
+            mappedSubscription.unsubscribe();
+            mappedSubscription = Subscription.EMPTY;
+        };
+    }
+}

modules/javafx.base/src/main/java/javafx/beans/value/LazyObjectBinding.java

@@ -0,0 +1,119 @@
+/*
+ * Copyright (c) 2022 Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package javafx.beans.value;
+
+import com.sun.javafx.binding.Subscription;
+
+import javafx.beans.InvalidationListener;
+import javafx.beans.binding.ObjectBinding;
+
+/**
+ * Extends {@link ObjectBinding} with the ability to lazily register and eagerly unregister listeners on its
+ * dependencies.
+ *
+ * @param <T> the type of the wrapped {@code Object}
+ */
+abstract class LazyObjectBinding<T> extends ObjectBinding<T> {
+
+    private Subscription subscription;
+    private boolean wasObserved;
+
+    @Override
+    public void addListener(ChangeListener<? super T> listener) {
+        super.addListener(listener);
+
+        updateSubcriptionAfterAdd();
+    }
+
+    @Override
+    public void removeListener(ChangeListener<? super T> listener) {
+        super.removeListener(listener);
+
+        updateSubcriptionAfterRemove();
+    }
+
+    @Override
+    public void addListener(InvalidationListener listener) {
+        super.addListener(listener);
+
+        updateSubcriptionAfterAdd();
+    }
+
+    @Override
+    public void removeListener(InvalidationListener listener) {
+        super.removeListener(listener);
+
+        updateSubcriptionAfterRemove();
+    }
+
+    @Override
+    protected boolean allowValidation() {
+        return isObserved();
+    }
+
+    /**
+     * Called after a listener was added to start observing inputs if they're not observed already.
+     */
+    private void updateSubcriptionAfterAdd() {
+        if (!wasObserved) { // was first observer registered?
+            subscription = observeInputs(); // start observing source
+
+            /*
+             * Although the act of registering a listener already attempts to make
+             * this binding valid, allowValidation won't allow it as the binding is
+             * not observed yet. This is because isObserved will not yet return true
+             * when the process of registering the listener hasn't completed yet.
+             *
+             * As the binding must be valid after it becomes observed the first time
+             * 'get' is called again.
+             */
+
+            get(); // make binding valid as source wasn't tracked until now
+            wasObserved = true;
+        }
+    }
+
+    /**
+     * Called after a listener was removed to stop observing inputs if this was the last listener
+     * observing this binding.
+     */
+    private void updateSubcriptionAfterRemove() {
+        if (wasObserved && !isObserved()) { // was last observer unregistered?
+            subscription.unsubscribe();
+            subscription = null;
+            invalidate(); // make binding invalid as source is no longer tracked
+            wasObserved = false;
+        }
+    }
+
+    /**
+     * Called when this binding was previously not observed and a new observer was added. Implementors must return a
+     * {@link Subscription} which will be cancelled when this binding no longer has any observers.
+     *
+     * @return a {@link Subscription} which will be cancelled when this binding no longer has any observers, never null
+     */
+    protected abstract Subscription observeInputs();
+}