这还是相当丑陋的,我认为通过稍微改变建模方式可以改进它,但到目前为止我只想出了以下内容:
public static void main(String[] args) {
Person[] people = {new Person("00001"), new Person("00002"), new Person("00005")};
Region[] regions = {
new Region("Region 1", Arrays.asList("00001", "00002", "00003")),
new Region("Region 2", Arrays.asList("00002", "00003", "00004")),
new Region("Region 3", Arrays.asList("00001", "00002", "00005"))
};
Map<Person, List<Region>> result = Stream.of(regions)
.flatMap(region -> region.getZipCodes().stream()
.map(zip -> new SimpleEntry<>(zip, region)))
.flatMap(entry -> Stream.of(people)
.filter(person -> person.getZip().equals(entry.getKey()))
.map(person -> new SimpleEntry<>(person, entry.getValue())))
.collect(Collectors.groupingBy(Entry::getKey, Collectors.mapping(Entry::getValue, Collectors.toList())));
result.entrySet().forEach(entry -> System.out.printf("[%s]: {%s}\n", entry.getKey(), entry.getValue()));
}
拥有一个包含映射并且可以进行键控的
ZipCode
类会使事情更加清晰:
public static void main(String[] args) {
Region r1 = new Region("Region 1");
Region r2 = new Region("Region 2");
Region r3 = new Region("Region 3");
ZipCode zipCode1 = new ZipCode("00001", Arrays.asList(r1, r3));
ZipCode zipCode2 = new ZipCode("00002", Arrays.asList(r1, r2, r3));
ZipCode zipCode3 = new ZipCode("00003", Arrays.asList());
ZipCode zipCode4 = new ZipCode("00004", Arrays.asList());
ZipCode zipCode5 = new ZipCode("00005", Arrays.asList(r3));
Person[] people = {
new Person(zipCode1),
new Person(zipCode2),
new Person(zipCode5)
};
Map<Person, List<Region>> result = Stream.of(people)
.collect(Collectors.toMap(person -> person,
person -> person.getZip().getRegions()));
result.entrySet().forEach(entry -> System.out.printf("[%s]: {%s}\n", entry.getKey(), entry.getValue()));
}