使用javaslang 2.1.0-alpha 将a Stream<Tuple2<T,U>>转换为a 的最惯用的方法是什么Map<T,List<U>>？
// initial stream
Stream.of(
Tuple.of("foo", "x"),
Tuple.of("foo", "y"),
Tuple.of("bar", "x"),
Tuple.of("bar", "y"),
Tuple.of("bar", "z")
)
应成为:
// end result
HashMap.ofEntries(
Tuple.of("foo", List.of("x","y")),
Tuple.of("bar", List.of("x","y","z"))
);
这是我的代码片段：
public static void main(String[] args) {
Try.of(Main::getLines)
.onFailure(cause -> log.error("An error has occurred while parsing the file", cause));
}
private static List<Fiche> getLines() {
return Files.lines(Paths.get("insurance_sample.csv"))
.skip(1)
.map(Main::toPojo)
.filter(fiche -> fiche.getPointLongitude().equals(-81.711777))
.peek(fiche -> log.info("Fiche added with success {}", fiche))
.collect(Collectors.toList());
}
我正在使用 try-with-resources 或在“finally”子句中关闭此“Stream”。在这条线上Files.lines(Paths.get("insurance_sample.csv"))
任何人都可以帮助我使用 Vavr 使用 try-with-resources 吗？
我有一个对象列表.该对象如下所示:
public class Slots {
String slotType;
Visits visit;
}
public class Visits {
private long visitCode;
private String agendaCode;
private String scheduledTime;
private String resourceType;
private String resourceDescription;
private String visitTypeCode;
...
}
我需要找到具有相同元素的元素agendaCode,visitTypeCode并且scheduledTime在我的生活中我无法完成它.
我试过这个:
Set<String> agendas = slotsResponse.getContent().stream()
.map(Slots::getVisit)
.map(Visits::getAgendaCode)
.collect(Collectors.toUnmodifiableSet());
Set<String> visitTypeCode = slotsResponse.getContent().stream()
.map(Slots::getVisit)
.map(Visits::getVisitTypeCode)
.collect(Collectors.toUnmodifiableSet());
Set<String> scheduledTime = slotsResponse.getContent().stream()
.map(Slots::getVisit)
.map(Visits::getScheduledTime)
.collect(Collectors.toUnmodifiableSet());
List<Slots> collect = slotsResponse.getContent().stream()
.filter(c -> agendas.contains(c.getVisit().getAgendaCode()))
.filter(c -> visitTypeCode.contains(c.getVisit().getVisitTypeCode()))
.filter(c -> scheduledTime.contains(c.getVisit().getScheduledTime()))
.collect(Collectors.toList());
但它没有做我想的那样.理想情况下,我会有一个列表列表,其中每个子列表是共享相同的Slots对象的列表agendaCode, …
The expectation is derive 3 lists itemIsBoth, aItems, bItems from the input list items.
How to convert code like below to functional style? (I understand this code is clear enough in an imperative style, but I want to know does declarative style really fail to deal with such a simple example). Thanks.
for (Item item: items) {
if (item.isA() && item.isB()) {
itemIsBoth.add(item);
} else if (item.isA()) {
aItems.add(item);
} else if (item.isB()){
bItems.add(item)
}
}
java functional-programming declarative-programming java-8 vavr
我有一个函数，当某些条件不满足时，它应该不返回任何内容（ void ）或字符串。
我尝试这条线 Either.left(Void)
private Either<Void,String> processOrReturnErrorMessage(){
//Do something and in some case return a message of failed conditions
return Either.left(Void);
}
我想避免：
Either<Error, Employee> processEmployee(Employee e)
并使用：
Result<Employee> processEmployee(Employee e)
其中 left 是固定的：
Result<T> extends Either<Error, T>
有这样的例子吗？
当我尝试这个时，没有任何东西可以为我编译，我被迫实现一个Result<T>我想避免的具体类。
我想这样做的原因是为了简化方法签名和使用这些方法的流代码。
是否有一种简洁,惯用的方式来创建来自Javaslang/Vavr的订单保留地图List？List.toMap()返回一个普通的HashMap,所以不这样做.我现在拥有的是这样的 -
listOfKeys.foldLeft(
LinkedHashMap.<Key, Value>.empty(),
(m, k) -> m.put(k, valueFor(k))
);
- 但这似乎比必要的更冗长,也可能效率更低.
我正在使用vavr和jOOQ,最近出现了两个出色的库,允许我们在常规Java服务器应用程序中使用功能方言.
我试图使用jOOQ,相当于SQL的选择计数(*).
查询以这种方式形成:
ResultQuery query = dsl.selectCount()
.from(Tables.SH_PLAYER_REPORT)
.join(Tables.SH_PLAYERS)
.on(Tables.SH_PLAYERS.PLAYER_ID.eq(Tables.SH_PLAYER_REPORT.PLAYER_ID))
.join(Tables.SH_LOCATION)
.on(Tables.SH_LOCATION.LOCATION_ID.eq(Tables.SH_PLAYERS.LOCATION))
.and(Tables.SH_PLAYER_REPORT.START_ON.ge(Timestamp.from(fromWhenInUTCInstant)))
.and(Tables.SH_PLAYER_REPORT.START_ON.le(Timestamp.from(toWhenInUTCInstant)))
.and(Tables.SH_LOCATION.LOCATION_ID.eq(criteriaAllFieldsTeam.getLocation_id()));
jOOQ的生成器工作得很好,这里没有任何类型不匹配.所以,我想,查询是正确形成的.
然后,我使用vavr的尝试,因此:
Optional<Integer> mayBeCount = Optional.empty();
try (final Connection cn = this.ds.getConnection()) {
DSLContext dsl = DSL.using(cn, this.dialect);
Try<Integer> countFromDBAttempted =
Try
.of(() -> prepareCountOfGamesPlayedQuery(dsl,criteriaAllFieldsTeam))
.map(e -> e.fetchOne(0, Integer.class)) // Here's the problem!
.onFailure(e -> logger.warning(String.format("Count Of Games Played, status=Failed, reason={%s}",e.getMessage())));
mayBeCount = (countFromDBAttempted.isFailure() ? Optional.empty() : Optional.of(countFromDBAttempted.getOrElse(0)));
} catch (SQLException ex) {
logger.warning(
String.format("DB(jOOQ): Failed, counting games played, using criteria {%s},reason={%s}",criteriaAllFieldsTeam.toString(),ex.getMessage()));
} …并感谢您查看我的问题!
我在使用Streams并且按特定顺序应用多个谓词时遇到了一些麻烦.
例如,请考虑以下IntPredicates:
IntPredicate divisibleByThree = i -> i % 3 == 0;
IntPredicate divisibleByFour = i -> i % 4 == 0;
IntPredicate divisibleByFive = i -> i % 5 == 0;
IntPredicate divisibleByThreeAndFour = divisibleByThree.and(divisibleByFour);
IntPredicate divisibleByThreeAndFive = divisibleByThree.and(divisibleByFive);
IntPredicate divisibleByThreeAndFiveAndFour = divisibleByThreeAndFour.and(divisibleByFive);
//....arbitrary Number of predicates.
我已将我遇到的问题转换为"FizzBuzz"-esque版本,试图通过将谓词应用于特定顺序的流来找到正确的答案.像这样:
IntStream.range(1, 100).forEach(i -> {
//Order matters here!
if(divisibleByThreeAndFiveAndFour.test(i)){
System.out.println("Three and four and five");
} else if(divisibleByThreeAndFour.test(i)){
System.out.println("Three and four");
} else if(divisibleByThreeAndFive.test(i)){
System.out.println("Three and four");
} else if(divisibleByFive.test(i)){
System.out.println("Five"); …VAVR集合是"不可变的".
所以,如果我有静态变量,例如,持有所有WebSocket会话,我将如何使用VAVR以使该集合是线程安全的？
例如:
@ServerEndpoint("/actions")
public class DeviceWebSocketServer {
private static Set<Session> sessions = //???; // how should I initialize this?
@OnOpen
public void open(Session session) {
sessions = sessions.add(session); // is this OK???
}
@OnClose
public void close(Session session) {
sessions = sessions.remove(session); // is this OK??
}
}