reactor.fn.Suppliers Maven / Gradle / Ivy
/*
* Copyright (c) 2011-2014 Pivotal Software, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package reactor.fn;
import java.util.*;
import java.util.concurrent.atomic.AtomicInteger;
/**
* Helper class for working tying {@link Supplier Suppliers} to {@link Iterable Iterables} and other types of
* collections.
*
* @author Jon Brisbin
*/
public abstract class Suppliers {
private Suppliers() {
}
/**
* Wrap the given object that will supply the given object every time {@link Supplier#get()} is
* called.
*
* @param obj
* the object to supply
* @param
* type of the supplied object
*
* @return the new {@link Supplier}
*/
public static Supplier supply(final T obj) {
return new Supplier() {
@Override
public T get() {
return obj;
}
};
}
/**
* Supply the given object only once, the first time {@link Supplier#get()} is invoked.
*
* @param obj
* the object to supply
* @param
* type of the supplied object
*
* @return the new {@link Supplier}
*/
@SuppressWarnings("unchecked")
public static Supplier supplyOnce(final T obj) {
return drain(Arrays.asList(obj));
}
/**
* Supply the given object to callers only as long as the given {@link Predicate} returns true.
*
* @param obj
* the object to supply
* @param predicate
* the predicate to check to determine whether or not to supply the given value
* @param
* type of the supplied object
*
* @return the new {@link Supplier}
*/
public static Supplier supplyWhile(final T obj, final Predicate predicate) {
return new Supplier() {
@Override
public T get() {
if(predicate.test(obj)) {
return obj;
} else {
return null;
}
}
};
}
/**
* Create a {@link Supplier} that continually round-robin load balances each call to {@link
* Supplier#get()} by iterating over the objects. When the end is reached, it wraps around to the first object and
* keeps providing objects to callers.
*
* @param objs
* the objects to load-balance
* @param
* type of the supplied object
*
* @return the new {@link Supplier}
*/
public static Supplier roundRobin(final T... objs) {
final AtomicInteger count = new AtomicInteger();
final int len = objs.length;
return new Supplier() {
@Override public T get() {
return objs[count.getAndIncrement() % len];
}
};
}
/**
* Filter the given {@link Iterable} using the given {@link Predicate} so that calls to the return {@link
* Supplier#get()} will provide only items from the original collection which pass the predicate
* test.
*
* @param src
* the source of objects to filter
* @param predicate
* the {@link Predicate} to test items against
* @param
* type of the source
*
* @return the new {@link Supplier}
*/
public static Supplier filter(final Iterable src, final Predicate predicate) {
return new Supplier() {
Iterator iter = src.iterator();
@Override
public T get() {
if(!iter.hasNext()) {
return null;
}
T obj;
do {
obj = iter.next();
} while(!predicate.test(obj));
return obj;
}
};
}
/**
* Create a {@link Supplier} which drains the contents of the given {@link java.lang.Iterable} by
* internally creating an {@link java.util.Iterator} and delegating each call of {@link
* Supplier#get()} to {@link java.util.Iterator#next()}.
*
* @param c
* the collection to consume
* @param
* type of the source
*
* @return the new {@link Supplier}
*/
public static Supplier drain(Iterable c) {
final Iterator iter = c.iterator();
return new Supplier() {
@Override
public T get() {
return (iter.hasNext() ? iter.next() : null);
}
};
}
/**
* Create a {@link Supplier} which drains all of the given {@link java.lang.Iterable Iterables}.
*
* @param iters
* the collections to consume
* @param
* type of the source
*
* @return the new {@link Supplier}
*
* @see #drain(Iterable)
*/
public static Supplier drainAll(Iterable> iters) {
List> ls = new ArrayList>();
for(Iterable iter : iters) {
ls.add(drain(iter));
}
return collect(ls);
}
/**
* Create a {@link Supplier} that aggregates the given list of suppliers by calling each one, in
* turn, until the supplier returns {@code null}. The aggregator then goes on to the next supplier in the list and
* delegates calls to that supplier, and so on, until the end of the list is reached.
*
* @param suppliers
* the list of suppliers to delegate to
* @param
* type of the source
*
* @return the new {@link Supplier}
*/
public static Supplier collect(List> suppliers) {
final ListIterator> iter = suppliers.listIterator();
return new Supplier() {
@Override
public synchronized T get() {
if(iter.hasNext()) {
T obj = iter.next().get();
if(null != obj) {
return obj;
}
} else if(iter.hasPrevious()) {
// rewind
while(iter.hasPrevious()) {
iter.previous();
}
return get();
}
return null;
}
};
}
}