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背景

经常有这种情况，就是获取到一个对象列表之后，需要根据对象里某个字段的值去获取另一个字段的值。如下所示，有个Item对象列表，Item对象里有个id字段和Value字段，现需要根据id的值去查询value的值。

        // 测试数据List<Item> items = Arrays.asList(new Item("1", "Item1"),new Item("2", "Item2"),new Item("3", "Item3"));

    @Datastatic class Item {private final String id;private final String name;private String value;public Item(String id, String name) {this.id = id;this.name = name;}}@Datastatic class Value {private String id;private String value;public Value(String id, String value) {this.id = id;this.value = value;}}

实现

常规写法

如下：

        // 先将id取出来List<String> ids = items.stream().map(Item::getId).collect(Collectors.toList());// 根据id获取valueMap<String, Value> valueMap = getValueMap(ids);// 遍历items，设置valueitems.stream().forEach(item -> {String id = item.getId();Value value = valueMap.get(id);if (Objects.nonNull(value)) {item.setValue(value.getValue());}});

使用工具类

写法如下：

        Collection<Item> res = keyValueMapping(items,Item::getId,keys -> getValueList(keys),Value::getId,(item, values) -> item.setValue(values.get(0).getValue()),false);// 模拟工具id获取valuepublic static List<Value> getValueList(List<String> ids) {List<Value> values = Lists.newArrayList();for (String id : ids) {values.add(new Value(id, "Value" + id));}values.remove(2);return values;}

工具类代码

public class FieldMappingUtil {private FieldMappingUtil() {}public static <T, K, V> void keyValueMapping(Collection<T> list, Function<T, K> getKey,Function<List<K>, List<V>> key2Values,Function<V, K> valueGroup,BiConsumer<T, List<V>> setGroupedValues) {keyValueMapping(list, getKey, key2Values, valueGroup, setGroupedValues, false);}public static <T, K, V> void keyValueMapping(Collection<T> list, Function<T, K> getKey,Function<List<K>, List<V>> key2Values,Function<V, K> valueGroup,BiConsumer<T, List<V>> setGroupedValues,Consumer<Collection<T>> unmappedData) {boolean returnUnmappedData = Objects.nonNull(unmappedData);Collection<T> unmapped = keyValueMapping(list, getKey, key2Values,valueGroup, setGroupedValues, returnUnmappedData);if (returnUnmappedData && CollUtil.isNotEmpty(unmapped)) {unmappedData.accept(unmapped);}}public static <T, K, V, R> R keyValueMappingReturn(Collection<T> list,Function<T, K> getKey,Function<List<K>, List<V>> key2Values,Function<V, K> valueGroup,BiConsumer<T, List<V>> setGroupedValues,Function<Collection<T>, R> unmappedData) {boolean returnUnmappedData = Objects.nonNull(unmappedData);Collection<T> unmapped = keyValueMapping(list, getKey, key2Values,valueGroup, setGroupedValues, returnUnmappedData);if (returnUnmappedData && CollUtil.isNotEmpty(unmapped)) {return unmappedData.apply(unmapped);}return null;}private static <T, K, V> Collection<T> keyValueMapping(Collection<T> list,Function<T, K> getKey,Function<List<K>, List<V>> key2Values,Function<V, K> valueGroup,BiConsumer<T, List<V>> setGroupedValues,boolean returnUnmappedData) {if (CollUtil.isNotEmpty(list)) {// 源数据中非空的keyList<K> nonNullKeys = list.stream().map(getKey).filter(Objects::nonNull).collect(Collectors.toList());if (CollUtil.isNotEmpty(nonNullKeys)) {// 根据源数据获取目标数据List<V> allValues = key2Values.apply(nonNullKeys);if (CollUtil.isNotEmpty(allValues)) {// 目标数据按照key分组Map<K, List<V>> map = allValues.stream().collect(Collectors.groupingBy(valueGroup));// 遍历源数据，设置分组后的目标值return list.stream().filter(t -> {// 获取当前对象keyK key = getKey.apply(t);// 根据key获取目标数据List<V> values = map.get(key);if (CollUtil.isNotEmpty(values)) {// 设置目标值到当前对象setGroupedValues.accept(t, values);return true;} else {return returnUnmappedData;}}).collect(Collectors.toList());}}}return returnUnmappedData ? list : null;}
}