[New] add CollectionsHelper.singletonCollector(Supplier)
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@ -3,11 +3,30 @@ package li.strolch.utils.collections;
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import java.util.ArrayList;
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import java.util.Comparator;
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import java.util.List;
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import java.util.function.Supplier;
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import java.util.stream.Collector;
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import java.util.stream.Collectors;
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/**
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* A helper class to handle collections
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*/
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public class CollectionsHelper {
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/**
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* Returns true if the elements in the two given lists are equal according to the given comparator regardless of the
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* sequence
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*
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* @param one
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* the first list
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* @param two
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* the second list
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* @param comparator
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* the comparator
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* @param <T>
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* the type of elements being compared
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*
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* @return true if the lists have the same elements, regardless of their order in the given lists
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*/
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public static <T> boolean equalsUnordered(List<T> one, List<T> two, Comparator<T> comparator) {
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if (one == null && two == null)
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return true;
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@ -24,17 +43,63 @@ public class CollectionsHelper {
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return one.equals(two);
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}
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public static <T> Collector<T, List<T>, T> singletonCollector() {
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return singletonCollector(null);
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/**
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* Returns a collector which returns exactly one element from a stream, and throws an exception if not exactly one
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* element is in the stream
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*
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* @param <T>
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* the type of element to return
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*
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* @return the singleton collector
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*
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* @throws IllegalStateException
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* if not 1 and only 1 element is in the stream
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*/
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public static <T> Collector<T, List<T>, T> singletonCollector() throws IllegalStateException {
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return singletonCollector(() -> null);
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}
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public static <T> Collector<T, List<T>, T> singletonCollector(String errorMsg) {
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/**
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* Returns a collector which returns exactly one element from a stream, and throws an exception if not exactly one
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* element is in the stream
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*
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* @param errorMsg
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* the error message to use if not 1 and only 1 element is in the collection
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* @param <T>
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* the type of element to return
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*
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* @return the singleton collector
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*
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* @throws IllegalStateException
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* if not 1 and only 1 element is in the stream
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*/
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public static <T> Collector<T, List<T>, T> singletonCollector(String errorMsg) throws IllegalStateException {
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return singletonCollector(() -> errorMsg);
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}
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/**
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* Returns a collector which returns exactly one element from a stream, and throws an exception if not exactly one
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* element is in the stream
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*
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* @param errorMsgSupplier
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* the supplier for an error message to use if not 1 and only 1 element is in the collection
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* @param <T>
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* the type of element to return
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*
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* @return the singleton collector
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*
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* @throws IllegalStateException
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* if not 1 and only 1 element is in the stream
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*/
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public static <T> Collector<T, List<T>, T> singletonCollector(Supplier<String> errorMsgSupplier)
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throws IllegalStateException {
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return Collector.of(ArrayList::new, List::add, (left, right) -> {
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left.addAll(right);
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return left;
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}, list -> {
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if (list.isEmpty()) {
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String errorMsg = errorMsgSupplier.get();
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if (errorMsg == null) {
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throw new IllegalStateException("Expect one element, but received no elements");
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} else
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@ -43,6 +108,7 @@ public class CollectionsHelper {
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if (list.size() != 1) {
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String listS = list.stream().map(Object::toString).collect(Collectors.joining(", "));
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String errorMsg = errorMsgSupplier.get();
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if (errorMsg == null) {
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throw new IllegalStateException(
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"Expect one element, but received " + list.size() + " in list " + listS);
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