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.

java把map转为对象

### 将 Java 中的 `Map` 转换为自定义对象

为了将 `Map<Object, Object>` 转换为自定义的对象实例，通常的做法是遍历 map 并根据键名设置对应的字段值。下面是一个最佳实践的例子，展示了如何实现这一功能。

#### 定义目标类
首先定义一个简单的 `User` 类作为转换的目标：

public class User {
    private String username;
    private Integer age;

    // Getters and Setters
}

#### 创建工具方法用于转换
创建一个通用的方法来处理从 `Map` 到对象的映射过程。此方法应能够接收任意类型的 `Map` 和相应的类类型参数，并通过反射机制完成属性填充操作。

import java.lang.reflect.Field;
import java.util.Map;

public final class MapToObjectConverter {

    /**
     * Converts a given map to an instance of the specified targetClass.
     */
    public static <T> T convert(Map<String, ?> source, Class<T> targetClass) throws IllegalAccessException, InstantiationException {
        T result = targetClass.newInstance();
        
        for (Field field : targetClass.getDeclaredFields()) {
            field.setAccessible(true);
            
            if (source.containsKey(field.getName())) {
                try {
                    field.set(result, parseValue(source.get(field.getName()), field.getType()));
                } catch (IllegalArgumentException e) {
                    System.out.println("Failed to set value for " + field.getName());
                }
            }

            field.setAccessible(false);    
        }

        return result;
    }

    @SuppressWarnings("unchecked")
    private static <V> V parseValue(Object obj, Class<V> type) {
        if (type.isInstance(obj)) {
            return (V) obj;
        } else if (obj instanceof Number && type == Long.class || type == long.class) {
            return (V) ((Number)obj).longValue();
        } else if (obj instanceof Number && type == Integer.class || type == int.class) {
            return (V) ((Number)obj).intValue();
        } else if (obj instanceof Boolean && type == boolean.class) {
            return (V) Boolean.valueOf((Boolean)obj);
        } else if (obj instanceof String && type == String.class){
            return (V) obj.toString();
        }
        throw new IllegalArgumentException("Cannot cast object [" + obj.getClass().getName() + "] to [" + type.getName() + "]");
    }
}

这段代码实现了基本的功能，即利用反射访问并修改私有成员变量[^3]。注意这里简化了一些边界情况处理逻辑，在实际应用中可能还需要考虑更多细节如日期格式化等问题。

#### 测试用例
最后编写一段测试程序验证上述函数的工作效果:

import org.junit.jupiter.api.Test;

import java.util.HashMap;
import java.util.Map;

class TestConvert {

    @Test
    void testConversion() throws Exception{
        HashMap<String,Object> data=new HashMap<>();
        data.put("username","JohnDoe");
        data.put("age",28);

        User user=MapToObjectConverter.convert(data,User.class);
        System.out.println(user.getUsername());  // 输出 JohnDoe
        System.out.println(user.getAge());       // 输出 28
    }
}

以上就是一种较为常见且有效的做法，适用于大多数场景下的需求。当然也可以借助第三方库比如 Jackson 或者 ModelMapper 来简化这个流程[^5]。