拆分字符串、对其进行平面映射并使用Java流创建对象？

我有两门课是这样的：

public class Seat extends Moviefiable {

        private int number;
        private Hall hall;

        public Seat(int id, boolean active, int number, Hall hall) {
            super(id, active);
            this.number = number;
            this.hall = hall;
        }

        public Seat() {this(-1, false, -1, null);}

        public static Seat getById(int idSeat) throws SQLException {
            Seat seat = SeatDAO.getById(idSeat);
            return seat;
        }
}

public class Ticket extends Moviefiable {

private Projection projection;
private Seat seat;
private LocalDateTime purchasingDate;
private User user;

public Ticket(int id, boolean active, Projection projection, Seat seat, LocalDateTime purchasingDate, User user) {
    super(id, active);
    this.projection = projection;
    this.seat = seat;
    this.purchasingDate = purchasingDate;
    this.user = user;
}

public Ticket() {this(-1, false, null, null, null, null);}

String uri = request.getQueryString(); //uri looks like this: seats=2&seats=3

s -> s * 10

现在，我需要创建两个或多个

票证

，具体取决于用户选择的票证数量。从我的

JSP

页面，我将得到如下内容：

public class Seat extends Moviefiable {

        private int number;
        private Hall hall;

        public Seat(int id, boolean active, int number, Hall hall) {
            super(id, active);
            this.number = number;
            this.hall = hall;
        }

        public Seat() {this(-1, false, -1, null);}

        public static Seat getById(int idSeat) throws SQLException {
            Seat seat = SeatDAO.getById(idSeat);
            return seat;
        }
}

public class Ticket extends Moviefiable {

private Projection projection;
private Seat seat;
private LocalDateTime purchasingDate;
private User user;

public Ticket(int id, boolean active, Projection projection, Seat seat, LocalDateTime purchasingDate, User user) {
    super(id, active);
    this.projection = projection;
    this.seat = seat;
    this.purchasingDate = purchasingDate;
    this.user = user;
}

public Ticket() {this(-1, false, null, null, null, null);}

String uri = request.getQueryString(); //uri looks like this: seats=2&seats=3

s -> s * 10

我想为两个

Seat

对象创建两个

Ticket

对象。在

uri

字符串中，字符2和3是seats的主键

其思想是使用Java流来执行拆分和创建对象。这是我到目前为止所做的

ArrayList<Ticket> newTicketsForSeats = Stream.of(uri.split("&"))
                   .map(s -> s.split("seats=")[1])
                   //.flatMap(Arrays::stream)
                   .mapToInt(Integer::valueOf)
                   .mapToObj(s -> {
                    try {
                        return new Ticket(-1, true, projection, SeatDAO.getById(s), 
                                 LocalDateTime.now(), loggedInUser);
                    } catch (SQLException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                        return null;
                    }
                })
                   .collect(Collectors.toCollection(ArrayList::new));

没关系。但当我运行上面的代码时，我得到：

java.lang.ArrayIndexOutOfBoundsException: 1
at servlets.ConfirmPurchaseServlet.lambda$0(ConfirmPurchaseServlet.java:62)
at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
at java.util.Spliterators$ArraySpliterator.forEachRemaining(Spliterators.java:948)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482)
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472)
at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)

projection

也是我获得的对象，这只是参考，它在servlet的其他地方<代码>日志用户我从会话中获得。我是Java流方面的新手，任何额外的解释都会非常好

我知道

map（）

需要

IntUnaryOperator

lambda表达式，类似这样：

public class Seat extends Moviefiable {

        private int number;
        private Hall hall;

        public Seat(int id, boolean active, int number, Hall hall) {
            super(id, active);
            this.number = number;
            this.hall = hall;
        }

        public Seat() {this(-1, false, -1, null);}

        public static Seat getById(int idSeat) throws SQLException {
            Seat seat = SeatDAO.getById(idSeat);
            return seat;
        }
}

public class Ticket extends Moviefiable {

private Projection projection;
private Seat seat;
private LocalDateTime purchasingDate;
private User user;

public Ticket(int id, boolean active, Projection projection, Seat seat, LocalDateTime purchasingDate, User user) {
    super(id, active);
    this.projection = projection;
    this.seat = seat;
    this.purchasingDate = purchasingDate;
    this.user = user;
}

public Ticket() {this(-1, false, null, null, null, null);}

String uri = request.getQueryString(); //uri looks like this: seats=2&seats=3

s -> s * 10

我不知道如何将int（座椅主键）映射到

Seat

object

---

干杯。

您的主要问题是试图将流输出分配给

数组列表
Collectors.toList（）
返回一个不能作为特定实现的
列表

因此，要么这样做：

List<SomeClass> list = ...collect(Collectors.toList());

List List=…collect（collector.toList（））；

还是这个

ArrayList<SomeClass> list = ... collect(Collectors.toCollection(ArrayList::new));

ArrayList=。。。collect（Collectors.toCollection（ArrayList:：new））；

以下内容应该可以工作，但可能需要根据其他类进行一些调整

ArrayList<Ticket> newTicketsForSeats = Stream.of(uri.split("&"))
               .map(s -> s.split("seats="))
               .flatMap(Arrays::stream)
               .mapToInt(Integer::valueOf)
               .mapToObj(s -> new Ticket(-1, true, projection, SeatDAO.getById(s), 
                     LocalDateTime.now(), loggedInUser))
               .collect(Collectors.toCollection(ArrayList::new));

ArrayList newticketsforsets=Stream.of（uri.split（“&”））
.map（s->s.split（“seats=））
.flatMap（数组：：流）
.mapToInt（整数：：valueOf）
.mapToObj->新票证（-1，true，projection，SeatDAO.getById），
LocalDateTime.now（），loggedInUser））
.collect（收集器.toCollection（ArrayList:：new））；
这两种方法中的任何一种都可能有效：

List<Ticket> newTicketsForSeats = Stream.of(uri.split("&"))
        .map(s -> s.replace("seats=", ""))
        .mapToInt(Integer::valueOf)
        .mapToObj(s -> new Ticket(-1, true, projection, SeatDAO.getById(s), LocalDateTime.now(), loggedInUser))
        .collect(Collectors.toList());

我想您需要
mapToObj
而不是
map
…我将
map
更改为
mapToObj
，第二个
mapToObj
报告错误：方法mapToObj（（s）->{}）对于类型stream是未定义的，也发布在这里：非常感谢您的重播。我编辑了我的原始问题。getById（int-idSeat）可能会抛出一个异常，所以Eclipse本身建议使用这个try-catch块，但是，不知怎么的，我得到了一些未检查的异常…谢谢Ron，在这里和Ranch论坛上的回复。互联网有时，看起来很奇怪，可能是一个小地方：）我编辑了我的答案。关于Ticket构造函数，我的类是这样的：Ticket（int-id，boolean-active，Projection-Projection，Seat-Seat，LocalDateTime-date-date，User-User）希望您能帮助我。顺便说一句，您肯定想要
.mapToInt（Integer:：parseInt）
而不是
。mapToInt（Integer:：valueOf）
，否则，您正在装箱到一个
Integer
对象中，只需立即取消装箱到
int
。如果您不关心装箱开销，请使用
.map（Integer:：valueOf）
…