Java tutorial
/* * Copyright 2002-2019 the original author or authors. * * 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 * * https://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.springframework.beans.propertyeditors; import java.beans.PropertyEditorSupport; import java.util.LinkedHashMap; import java.util.Map; import java.util.SortedMap; import java.util.TreeMap; import org.springframework.lang.Nullable; import org.springframework.util.Assert; import org.springframework.util.ReflectionUtils; /** * Property editor for Maps, converting any source Map * to a given target Map type. * * @author Juergen Hoeller * @since 2.0.1 * @see java.util.Map * @see java.util.SortedMap */ public class CustomMapEditor extends PropertyEditorSupport { @SuppressWarnings("rawtypes") private final Class<? extends Map> mapType; private final boolean nullAsEmptyMap; /** * Create a new CustomMapEditor for the given target type, * keeping an incoming {@code null} as-is. * @param mapType the target type, which needs to be a * sub-interface of Map or a concrete Map class * @see java.util.Map * @see java.util.HashMap * @see java.util.TreeMap * @see java.util.LinkedHashMap */ @SuppressWarnings("rawtypes") public CustomMapEditor(Class<? extends Map> mapType) { this(mapType, false); } /** * Create a new CustomMapEditor for the given target type. * <p>If the incoming value is of the given type, it will be used as-is. * If it is a different Map type or an array, it will be converted * to a default implementation of the given Map type. * If the value is anything else, a target Map with that single * value will be created. * <p>The default Map implementations are: TreeMap for SortedMap, * and LinkedHashMap for Map. * @param mapType the target type, which needs to be a * sub-interface of Map or a concrete Map class * @param nullAsEmptyMap ap whether to convert an incoming {@code null} * value to an empty Map (of the appropriate type) * @see java.util.Map * @see java.util.TreeMap * @see java.util.LinkedHashMap */ @SuppressWarnings("rawtypes") public CustomMapEditor(Class<? extends Map> mapType, boolean nullAsEmptyMap) { Assert.notNull(mapType, "Map type is required"); if (!Map.class.isAssignableFrom(mapType)) { throw new IllegalArgumentException( "Map type [" + mapType.getName() + "] does not implement [java.util.Map]"); } this.mapType = mapType; this.nullAsEmptyMap = nullAsEmptyMap; } /** * Convert the given text value to a Map with a single element. */ @Override public void setAsText(String text) throws IllegalArgumentException { setValue(text); } /** * Convert the given value to a Map of the target type. */ @Override public void setValue(@Nullable Object value) { if (value == null && this.nullAsEmptyMap) { super.setValue(createMap(this.mapType, 0)); } else if (value == null || (this.mapType.isInstance(value) && !alwaysCreateNewMap())) { // Use the source value as-is, as it matches the target type. super.setValue(value); } else if (value instanceof Map) { // Convert Map elements. Map<?, ?> source = (Map<?, ?>) value; Map<Object, Object> target = createMap(this.mapType, source.size()); source.forEach((key, val) -> target.put(convertKey(key), convertValue(val))); super.setValue(target); } else { throw new IllegalArgumentException("Value cannot be converted to Map: " + value); } } /** * Create a Map of the given type, with the given * initial capacity (if supported by the Map type). * @param mapType a sub-interface of Map * @param initialCapacity the initial capacity * @return the new Map instance */ @SuppressWarnings({ "rawtypes", "unchecked" }) protected Map<Object, Object> createMap(Class<? extends Map> mapType, int initialCapacity) { if (!mapType.isInterface()) { try { return ReflectionUtils.accessibleConstructor(mapType).newInstance(); } catch (Throwable ex) { throw new IllegalArgumentException("Could not instantiate map class: " + mapType.getName(), ex); } } else if (SortedMap.class == mapType) { return new TreeMap<>(); } else { return new LinkedHashMap<>(initialCapacity); } } /** * Return whether to always create a new Map, * even if the type of the passed-in Map already matches. * <p>Default is "false"; can be overridden to enforce creation of a * new Map, for example to convert elements in any case. * @see #convertKey * @see #convertValue */ protected boolean alwaysCreateNewMap() { return false; } /** * Hook to convert each encountered Map key. * The default implementation simply returns the passed-in key as-is. * <p>Can be overridden to perform conversion of certain keys, * for example from String to Integer. * <p>Only called if actually creating a new Map! * This is by default not the case if the type of the passed-in Map * already matches. Override {@link #alwaysCreateNewMap()} to * enforce creating a new Map in every case. * @param key the source key * @return the key to be used in the target Map * @see #alwaysCreateNewMap */ protected Object convertKey(Object key) { return key; } /** * Hook to convert each encountered Map value. * The default implementation simply returns the passed-in value as-is. * <p>Can be overridden to perform conversion of certain values, * for example from String to Integer. * <p>Only called if actually creating a new Map! * This is by default not the case if the type of the passed-in Map * already matches. Override {@link #alwaysCreateNewMap()} to * enforce creating a new Map in every case. * @param value the source value * @return the value to be used in the target Map * @see #alwaysCreateNewMap */ protected Object convertValue(Object value) { return value; } /** * This implementation returns {@code null} to indicate that * there is no appropriate text representation. */ @Override @Nullable public String getAsText() { return null; } }