调整集合相关工具类。

src/main/java/xyz/zhouxy/plusone/commons/collection/CollectionTools.java

@@ -0,0 +1,101 @@
+package xyz.zhouxy.plusone.commons.collection;
+
+import java.util.Collection;
+import java.util.Comparator;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.TreeMap;
+import java.util.function.Function;
+
+import javax.annotation.Nullable;
+
+import com.google.common.base.Preconditions;
+
+public class CollectionTools {
+
+    // isEmpty
+
+    public static boolean isEmpty(@Nullable Collection<?> collection) {
+        return collection == null || collection.isEmpty();
+    }
+
+    public static boolean isEmpty(@Nullable Map<?, ?> map) {
+        return map == null || map.isEmpty();
+    }
+
+    // isNotEmpty
+
+    public static boolean isNotEmpty(@Nullable Collection<?> collection) {
+        return collection != null && !collection.isEmpty();
+    }
+
+    public static boolean isNotEmpty(@Nullable Map<?, ?> map) {
+        return map != null && !map.isEmpty();
+    }
+
+    // Collection -> Map
+
+    public static <K, V> HashMap<K, V> toHashMap(
+            Iterable<V> c,
+            Function<? super V, K> keyGenerator,
+            int initialCapacity) {
+        HashMap<K, V> map = new HashMap<>(initialCapacity);
+        fillIntoEmptyMap(map, c, keyGenerator);
+        return map;
+    }
+
+    public static <K, V> HashMap<K, V> toHashMap(
+            Collection<V> c,
+            Function<? super V, K> keyGenerator) {
+        return toHashMap(c, keyGenerator, c.size());
+    }
+
+    public static <K, V> SafeConcurrentHashMap<K, V> toConcurrentHashMap(
+            Iterable<V> c,
+            Function<? super V, K> keyGenerator,
+            int initialCapacity) {
+        SafeConcurrentHashMap<K, V> map = new SafeConcurrentHashMap<>(initialCapacity);
+        fillIntoEmptyMap(map, c, keyGenerator);
+        return map;
+    }
+
+    public static <K, V> SafeConcurrentHashMap<K, V> toConcurrentHashMap(
+            Collection<V> c,
+            Function<? super V, K> keyGenerator) {
+        return toConcurrentHashMap(c, keyGenerator, c.size());
+    }
+
+    public static <K extends Comparable<? super K>, V> TreeMap<K, V> toTreeMap(
+            Iterable<V> c,
+            Function<? super V, K> keyGenerator) {
+        TreeMap<K, V> map = new TreeMap<>();
+        fillIntoEmptyMap(map, c, keyGenerator);
+        return map;
+    }
+
+    public static <K, V> TreeMap<K, V> toTreeMap(
+            Iterable<V> c,
+            Function<? super V, K> keyGenerator,
+            Comparator<? super K> keycComparator) {
+        TreeMap<K, V> map = new TreeMap<>(keycComparator);
+        fillIntoEmptyMap(map, c, keyGenerator);
+        return map;
+    }
+
+    public static <K, V> void fillIntoEmptyMap(
+            Map<K, ? super V> map,
+            Iterable<V> c,
+            Function<? super V, K> keyGenerator) {
+        Preconditions.checkNotNull(map);
+        Preconditions.checkNotNull(c);
+        Preconditions.checkNotNull(keyGenerator);
+        Preconditions.checkArgument(map.isEmpty(), "The map should be empty.");
+        for (V v : c) {
+            map.put(keyGenerator.apply(v), v);
+        }
+    }
+
+    private CollectionTools() {
+        throw new IllegalStateException("Utility class");
+    }
+}