Spring Boot RestController重复创建对象致重复购票检测失效问题

我在Spring Boot项目里碰到个问题：RestController的每次Post请求都会导致座位对象被重新创建，根本没法基于初始的座位状态做重复购票检测。核心需求是调用Post接口时，如果用户重复请求同一个已售出的座位，就抛出异常，但现在每次请求都会重置所有座位状态，完全触发不了这个异常逻辑。

相关代码 #

Controller代码 #

@RestController
public class ControllerRoom {

    private final Room cinema;

    public ControllerRoom() {
        this.cinema = new Room(9,9);
    }
}

Post购票接口代码 #

@PostMapping("/purchase")
public ResponseEntity<Seats> sellSeat(@RequestBody Seats seat){
    System.out.println("Requested body =" + seat.getRow() +" "+ seat.getColumn() + " " + seat.getPrice() );
    for (Seats s : cinema.getSeats()){
        if (s.getColumn() == seat.getColumn() && s.getRow() == seat.getRow()){
            if (!s.isTaken()) {
                System.out.println(s.setTaken(true));
                return new ResponseEntity<>(s, HttpStatus.OK);
            } if (s.isTaken()){
                throw new SeatRequestException("The ticket has been already purchased!");
            }
        }
    }
    throw new SeatRequestException("The number of a row or a column is out of bounds!");
}

问题根源 #

排查后发现问题出在Room类的getSeats()方法里——这个方法每次被调用时，都会重新往available_seats列表里添加全新的Seats对象，相当于每次请求都重置了所有座位的状态：

@JsonGetter(value = "available_seats")
public ArrayList<Seats> getSeats() {
    for (int i=1; i<=total_columns; i++){
        for (int j=1; j<=total_rows; j++){
            if (i<=4) {
                available_seats.add(new Seats(i, j, false, 10));
            } else {
                available_seats.add(new Seats(i,j, false,8));
            }
        }
    }
    System.out.println(available_seats.size());
    return available_seats;
}

解决方案 #

1. 将座位初始化逻辑移到Room类的构造方法 #

把创建所有座位的代码从getSeats()移到Room的构造方法中，确保只在Room对象实例化时生成一次座位列表，后续调用getSeats()直接返回已初始化好的列表：

public class Room {
    private ArrayList<Seats> available_seats;
    private int total_rows;
    private int total_columns;

    public Room(int total_rows, int total_columns) {
        this.total_rows = total_rows;
        this.total_columns = total_columns;
        this.available_seats = new ArrayList<>();
        // 仅在构造时初始化座位
        for (int i=1; i<=total_columns; i++){
            for (int j=1; j<=total_rows; j++){
                if (i<=4) {
                    available_seats.add(new Seats(i, j, false, 10));
                } else {
                    available_seats.add(new Seats(i,j, false,8));
                }
            }
        }
    }

    @JsonGetter(value = "available_seats")
    public ArrayList<Seats> getSeats() {
        // 直接返回已有的座位列表，不再重复创建
        return available_seats;
    }

    // 其他必要方法...
}

2. 确认Controller的单例特性（默认已满足） #

Spring Boot中@RestController注解的类默认是单例Bean，所以Controller里的Room对象只会被创建一次，不会每次请求都实例化新的Controller和Room实例，这一步不需要额外代码，只需确保没有手动修改Controller的作用域。

3. 可选：优化座位查找逻辑（提升性能） #

如果座位数量较多，遍历列表查找座位的效率较低，可以改用Map存储座位，以行_列作为key直接定位：

public class Room {
    private ArrayList<Seats> available_seats;
    private Map<String, Seats> seatMap;
    private int total_rows;
    private int total_columns;

    public Room(int total_rows, int total_columns) {
        this.total_rows = total_rows;
        this.total_columns = total_columns;
        this.available_seats = new ArrayList<>();
        this.seatMap = new HashMap<>();
        
        // 初始化座位列表和Map
        for (int i=1; i<=total_columns; i++){
            for (int j=1; j<=total_rows; j++){
                Seats seat;
                if (i<=4) {
                    seat = new Seats(i, j, false, 10);
                } else {
                    seat = new Seats(i,j, false,8);
                }
                available_seats.add(seat);
                seatMap.put(i + "_" + j, seat);
            }
        }
    }

    @JsonGetter(value = "available_seats")
    public ArrayList<Seats> getSeats() {
        return available_seats;
    }

    // 根据行和列快速获取座位
    public Seats getSeat(int row, int column) {
        return seatMap.get(row + "_" + column);
    }
}

修改后的Controller购票接口：

@PostMapping("/purchase")
public ResponseEntity<Seats> sellSeat(@RequestBody Seats seat){
    System.out.println("Requested body =" + seat.getRow() +" "+ seat.getColumn() + " " + seat.getPrice() );
    
    Seats targetSeat = cinema.getSeat(seat.getRow(), seat.getColumn());
    if (targetSeat == null) {
        throw new SeatRequestException("The number of a row or a column is out of bounds!");
    }
    
    if (!targetSeat.isTaken()) {
        targetSeat.setTaken(true);
        return new ResponseEntity<>(targetSeat, HttpStatus.OK);
    } else {
        throw new SeatRequestException("The ticket has been already purchased!");
    }
}

内容的提问来源于stack exchange，提问作者huga721