TypeConverter.java 文件源码

/**
 * Null-safely convert between two maps by applying a function to each key and value. A predicate is also specified to filter
 * the results, in case the mapping function were to generate duplicate keys, etc.
 */
public static <T1, T2, U1, U2> Map<U1, U2> convert(Map<T1, T2> toConvert,
                                                   Function<? super T1, ? extends U1> keyConverter,
                                                   Function<? super T2, ? extends U2> valueConverter,
                                                   BiPredicate<U1, U2> resultFilter) {
    if (toConvert == null) {
        return null;
    }

    Map<U1, U2> result = toConvert.entrySet().stream()
                                  .map(e -> new SimpleImmutableEntry<>(keyConverter.apply(e.getKey()),
                                                                       valueConverter.apply(e.getValue())))
                                  .filter(p -> resultFilter.test(p.getKey(), p.getValue()))
                                  .collect(Collectors.toMap(Entry::getKey, Entry::getValue));
    return Collections.unmodifiableMap(result);
}