protected FastIDSet getAllOtherItems(long[] theNeighborhood, long theUserID, boolean includeKnownItems) throws Exception { DataModel dataModel = getDataModel(); FastIDSet possibleItemIDs = new FastIDSet(); for (long userID : theNeighborhood) { possibleItemIDs.addAll(dataModel.getItemIDsFromUser(userID)); } if (!includeKnownItems) { possibleItemIDs.removeAll(dataModel.getItemIDsFromUser(theUserID)); } return possibleItemIDs; } 解释代码

这段代码实现了一个获取邻居用户（theNeighborhood参数）所评价过的所有物品集合（possibleItemIDs）的方法。如果includeKnownItems为false，则排除当前用户（theUserID参数）已评价过的物品。

具体实现思路为，在循环遍历邻居用户ID时，使用DataModel对象获取该用户评价过的所有物品ID，并将这些物品ID添加到可能的物品集合中。如果includeKnownItems为false，则使用DataModel对象再获取当前用户已评价过的所有物品ID，并在可能的物品集合中去除这些物品ID。最终返回可能的物品集合。

相关问题

@Slf4j public class LoopCallInterceptor implements HandlerInterceptor { @Override public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { //调用接口 // 头部获取当前请求所经过且没结束请求的path列表 // 判定path列表中是否包含当前path //无则正常访问 并记录到列表中 //有则告警循环调用，并终止调用，返回异常 return true; //return HandlerInterceptor.super.preHandle(request, response, handler); } @Override public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception { //HandlerInterceptor.super.postHandle(request, response, handler, modelAndView); //正常结束接口 //获取头部path列表 //从path列表中删除当前path } }

This is a Java class named `LoopCallInterceptor` that implements the `HandlerInterceptor` interface. The `HandlerInterceptor` interface is part of the Spring MVC framework and provides a way to intercept and handle requests and responses for Spring MVC applications.

The purpose of the `LoopCallInterceptor` class is to prevent circular or recursive calls to a Spring MVC controller method, which can cause infinite loops and consume excessive resources.

The `preHandle` method is called before a request is handled by a controller method. It takes in the `HttpServletRequest` and `HttpServletResponse` objects, as well as the `Object` representing the handler method that will handle the request.

The `preHandle` method first checks if the current request path is already present in the request header path list. If it is not present, it adds the current request path to the path list and returns `true` to indicate that the request can proceed normally. If it is already present, it logs a warning message for the circular or recursive call and returns `false` to indicate that the request should be stopped.

The `postHandle` method is called after a request has been handled by a controller method. It takes in the `HttpServletRequest`, `HttpServletResponse`, `Object` representing the handler method, and the `ModelAndView` object that contains the view and model data returned by the handler method.

The `postHandle` method removes the current request path from the request header path list.

Note that the `HandlerInterceptor` interface has three methods, but the `LoopCallInterceptor` class only implements the `preHandle` and `postHandle` methods. The `afterCompletion` method is called after the response has been rendered, but before the response has been committed.

基于SpringCloud Alibaba微服务架构的酒店预定系统设计与实现中实体类为pojo、采用Controller、Service、Mapper三层结构，订单数据表为order、酒店数据表为hotel，怎么使用Apache Mahou 的推荐算法基于用户已预定的订单对用户进行酒店推荐的具体代码实现

首先，需要引入Apache Mahout的依赖。这里以Maven为例，在pom.xml文件中添加以下依赖：

<dependency>
    <groupId>org.apache.mahout</groupId>
    <artifactId>mahout-core</artifactId>
    <version>0.13.0</version>
</dependency>

接下来，我们需要将订单数据和酒店数据转换成Mahout中的数据模型。Mahout中的数据模型主要有两种：User-Item数据模型和Item-Item数据模型。在这里，我们选择使用User-Item数据模型，即将用户和酒店看作是两个不同的实体，然后通过用户已预定的订单数据来推荐酒店。

我们可以先定义一个名为Order的类，用来表示订单数据：

public class Order {
    private int userId;
    private int hotelId;
    private double rating;
    
    // getters and setters
}

其中，rating表示用户对酒店的评分，可以根据实际情况进行设置。

接下来，我们定义一个名为Hotel的类，用来表示酒店数据：

public class Hotel {
    private int hotelId;
    private String name;
    private String location;
    
    // getters and setters
}

然后，我们需要将订单数据和酒店数据转换成Mahout中的数据模型。Mahout中的User-Item数据模型需要使用一个名为DataModel的类来表示，我们可以自定义一个实现该接口的类，例如：

public class OrderDataModel implements DataModel {
    private List<Order> orders;
    private Map<Integer, List<Preference>> userData;
    private Map<Integer, List<Preference>> itemData;
    
    public OrderDataModel(List<Order> orders) {
        this.orders = orders;
        this.userData = new HashMap<>();
        this.itemData = new HashMap<>();
        
        for (Order order : orders) {
            Preference preference = new GenericPreference(order.getUserId(), order.getHotelId(), order.getRating());
            
            if (!userData.containsKey(order.getUserId())) {
                userData.put(order.getUserId(), new ArrayList<>());
            }
            userData.get(order.getUserId()).add(preference);
            
            if (!itemData.containsKey(order.getHotelId())) {
                itemData.put(order.getHotelId(), new ArrayList<>());
            }
            itemData.get(order.getHotelId()).add(preference);
        }
    }
    
    @Override
    public LongPrimitiveIterator getUserIDs() {
        return new LongPrimitiveIterator() {
            private final Iterator<Integer> iterator = userData.keySet().iterator();
            
            @Override
            public long nextLong() {
                return iterator.next();
            }
            
            @Override
            public long peek() {
                return iterator.hasNext() ? iterator.next() : 0L;
            }
            
            @Override
            public boolean hasNext() {
                return iterator.hasNext();
            }
            
            @Override
            public void remove() {
                throw new UnsupportedOperationException();
            }
        };
    }
    
    @Override
    public PreferenceArray getPreferencesFromUser(long userId) {
        List<Preference> preferences = userData.get((int) userId);
        if (preferences == null || preferences.isEmpty()) {
            return new GenericUserPreferenceArray(0);
        }
        return new GenericUserPreferenceArray(preferences.toArray(new Preference[0]));
    }
    
    @Override
    public FastIDSet getItemIDsFromUser(long userId) {
        List<Preference> preferences = userData.get((int) userId);
        if (preferences == null || preferences.isEmpty()) {
            return new FastIDSet();
        }
        FastIDSet itemIDs = new FastIDSet(preferences.size());
        for (Preference preference : preferences) {
            itemIDs.add(preference.getItemID());
        }
        return itemIDs;
    }
    
    @Override
    public LongPrimitiveIterator getItemIDs() {
        return new LongPrimitiveIterator() {
            private final Iterator<Integer> iterator = itemData.keySet().iterator();
            
            @Override
            public long nextLong() {
                return iterator.next();
            }
            
            @Override
            public long peek() {
                return iterator.hasNext() ? iterator.next() : 0L;
            }
            
            @Override
            public boolean hasNext() {
                return iterator.hasNext();
            }
            
            @Override
            public void remove() {
                throw new UnsupportedOperationException();
            }
        };
    }
    
    @Override
    public PreferenceArray getPreferencesForItem(long itemId) {
        List<Preference> preferences = itemData.get((int) itemId);
        if (preferences == null || preferences.isEmpty()) {
            return new GenericItemPreferenceArray(0);
        }
        return new GenericItemPreferenceArray(preferences.toArray(new Preference[0]));
    }
    
    @Override
    public Float getPreferenceValue(long userId, long itemId) {
        List<Preference> preferences = userData.get((int) userId);
        if (preferences == null || preferences.isEmpty()) {
            return null;
        }
        for (Preference preference : preferences) {
            if (preference.getItemID() == itemId) {
                return preference.getValue();
            }
        }
        return null;
    }
    
    @Override
    public Long getPreferenceTime(long userId, long itemId) {
        return null;
    }
    
    @Override
    public int getNumUsers() {
        return userData.size();
    }
    
    @Override
    public int getNumItems() {
        return itemData.size();
    }
    
    @Override
    public int getNumUsersWithPreferenceFor(long itemId) {
        List<Preference> preferences = itemData.get((int) itemId);
        if (preferences == null || preferences.isEmpty()) {
            return 0;
        }
        Set<Integer> userIds = new HashSet<>();
        for (Preference preference : preferences) {
            userIds.add(preference.getUserID());
        }
        return userIds.size();
    }
    
    @Override
    public int getNumUsersWithPreference() {
        return userData.size();
    }
    
    @Override
    public void setPreference(long userId, long itemId, float value) {
        throw new UnsupportedOperationException();
    }
    
    @Override
    public void removePreference(long userId, long itemId) {
        throw new UnsupportedOperationException();
    }
    
    @Override
    public boolean hasPreferenceValues() {
        return true;
    }
    
    @Override
    public float getMaxPreference() {
        return 5.0f;
    }
    
    @Override
    public float getMinPreference() {
        return 1.0f;
    }
    
    @Override
    public void refresh(Collection<Refreshable> alreadyRefreshed) {
        // do nothing
    }
}

在上面的代码中，我们将订单数据转换成Mahout中的数据模型，并实现了DataModel接口中的各个方法。这样，我们就可以将OrderDataModel对象传入Mahout中的推荐算法中来进行推荐了。

最后，我们需要编写一个Controller来接收用户id，然后根据该用户已预定的订单数据来进行酒店推荐。代码示例如下：

@RestController
public class HotelRecommendationController {
    @Autowired
    private OrderMapper orderMapper;
    @Autowired
    private HotelMapper hotelMapper;
    
    @GetMapping("/hotel/recommendation")
    public List<Hotel> recommend(@RequestParam("userId") int userId) throws TasteException {
        List<Order> orders = orderMapper.getOrdersByUserId(userId);
        OrderDataModel dataModel = new OrderDataModel(orders);
        UserSimilarity similarity = new LogLikelihoodSimilarity(dataModel);
        UserNeighborhood neighborhood = new NearestNUserNeighborhood(10, similarity, dataModel);
        Recommender recommender = new GenericUserBasedRecommender(dataModel, neighborhood, similarity);
        List<RecommendedItem> recommendedItemList = recommender.recommend(userId, 5);
        List<Hotel> recommendedHotels = new ArrayList<>();
        for (RecommendedItem recommendedItem : recommendedItemList) {
            Hotel hotel = hotelMapper.getHotelById((int) recommendedItem.getItemID());
            recommendedHotels.add(hotel);
        }
        return recommendedHotels;
    }
}

在上面的代码中，我们使用了Mahout中的User-Based Collaborative Filtering算法来进行推荐，并返回推荐的酒店列表。其中，NearestNUserNeighborhood表示选择与当前用户最相似的10个用户，LogLikelihoodSimilarity表示使用对数似然相似度计算用户之间的相似度。最后，我们根据推荐的酒店id从数据库中获取酒店信息，然后返回推荐的酒店列表。