org.httprpc.util.Collections Maven / Gradle / Ivy
/*
* 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 org.httprpc.util;
import java.util.AbstractMap;
import java.util.Arrays;
import java.util.LinkedHashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
/**
* Class that provides static utility methods for working with collections.
*/
public class Collections {
private Collections() {
}
/**
* Creates an immutable list of elements.
*
* @param elements
* The list elements.
*
* @param
* The element type.
*
* @return
* An immutable list containing the provided elements.
*/
@SafeVarargs
public static List listOf(E... elements) {
return java.util.Collections.unmodifiableList(Arrays.asList(elements));
}
/**
* Creates an immutable map of entries.
*
* @param entries
* The map entries.
*
* @param
* The key type.
*
* @param
* The value type.
*
* @return
* An immutable map containing the provided entries.
*/
@SafeVarargs
public static Map mapOf(Map.Entry... entries) {
Map map = new LinkedHashMap<>();
for (Map.Entry entry : entries) {
map.put(entry.getKey(), entry.getValue());
}
return java.util.Collections.unmodifiableMap(map);
}
/**
* Creates an immutable map entry.
*
* @param key
* The entry key.
*
* @param value
* The entry value.
*
* @param
* The key type.
*
* @param
* The value type.
*
* @return
* An immutable map entry containing the provided key/value pair.
*/
public static Map.Entry entry(K key, V value) {
return new AbstractMap.SimpleImmutableEntry<>(key, value);
}
/**
* Returns an empty list.
*
* @param elementType
* The element type.
*
* @param
* The element type.
*
* @return
* An empty list.
*/
public static List emptyListOf(Class elementType) {
if (elementType == null) {
throw new IllegalArgumentException();
}
return java.util.Collections.emptyList();
}
/**
* Returns an empty map.
*
* @param keyType
* The key type.
*
* @param valueType
* The value type.
*
* @param
* The key type.
*
* @param
* The value type.
*
* @return
* An empty map.
*/
public static Map emptyMapOf(Class keyType, Class valueType) {
if (keyType == null || valueType == null) {
throw new IllegalArgumentException();
}
return java.util.Collections.emptyMap();
}
/**
* Returns the value at a given path.
*
* @param
* The type of the value to return.
*
* @param root
* The root object.
*
* @param path
* The path to the value.
*
* @return
* The value at the given path, or null if the value does not exist.
*/
public static T valueAt(Object root, Object... path) {
return valueAt(root, new LinkedList<>(Arrays.asList(path)));
}
@SuppressWarnings("unchecked")
private static T valueAt(Object root, List path) {
if (root == null) {
return null;
} else if (path.isEmpty()) {
return (T)root;
} else {
Object component = path.remove(0);
Object value;
if (root instanceof List && component instanceof Number) {
value = ((List)root).get(((Number)component).intValue());
} else if (root instanceof Map) {
value = ((Map)root).get(component);
} else {
throw new IllegalArgumentException();
}
return valueAt(value, path);
}
}
}