基于用户的协同过滤推荐算法java实现报错

Question

使用springboot实现基于用户的协同过滤推荐算法时，在计算用户相似度的函数中采用余弦相似度计算公式，但是运行时报错，代码如下：

//采用余弦相似度计算公式计算两个用户的相似度
    public Double calculateSimilarity(List<Map<Integer, Double>> list1, List<Map<Integer, Double>> list2){//计算用户相似度
        double dotProduct = 0.0;
        double modList1 = 0.0;
        double modList2 = 0.0;

        for (int i = 0; i < list1.size(); i++) {
            Map<Integer, Double> map1 = list1.get(i);
            Map<Integer, Double> map2 = list2.get(i);
            for (Integer key: map1.keySet()) {
                if (map2.containsKey(key)) {
                    dotProduct += map1.get(key) * map2.get(key);
                }
                modList1 += Math.pow(map1.get(key), 2);
                modList2 += Math.pow(map2.get(key), 2);
            }
        }

        modList1 = Math.sqrt(modList1);
        modList2 = Math.sqrt(modList2);

        if (modList1 == 0 || modList2 == 0) {
            return 0.0;
        }

        return dotProduct / (modList1 * modList2);
    }

报错如下：

java.lang.ClassCastException: class java.lang.String cannot be cast to class java.lang.Integer (java.lang.String and java.lang.Integer are in module java.base of loader 'bootstrap')
    at com.example.utils.CollaborativeFiltering.calculateSimilarity(CollaborativeFiltering.java:21)
    at com.example.controller.RecommendController.getSimilarity(RecommendController.java:39)
    at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
    at java.base/java.lang.reflect.Method.invoke(Method.java:580)
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:261)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:189)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:118)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:917)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:829)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1089)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:979)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1014)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:903)
    at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:564)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:885)
    at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:658)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:205)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149)
    at org.springframework.web.filter.CorsFilter.doFilterInternal(CorsFilter.java:91)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149)
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149)
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149)
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:167)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:482)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:115)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:340)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:391)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:896)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1744)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52)
    at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)
    at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.base/java.lang.Thread.run(Thread.java:1583)

Answer 1

让阿豪来帮你解答，本回答参考chatgpt3.5编写提供，如果还有疑问可以评论或留言

问题描述：在使用Spring Boot实现基于用户的协同过滤推荐算法时，采用了余弦相似度计算公式，在计算用户相似度的函数中，代码如下：

public Double calculateSimilarity(List<Map<Integer, Double>> list1, List<Map<Integer, Double>> list2){
   double dotProduct = 0.0;
   double modList1 = 0.0;
   double modList2 = 0.0;
   for (int i = 0; i < list1.size(); i++) {
      Map<Integer, Double> map1 = list1.get(i);
      Map<Integer, Double> map2 = list2.get(i);
      for (Integer key: map1.keySet()) {
         if (map2.containsKey(key)) {
            dotProduct += map1.get(key) * map2.get(key);
         }
         modList1 += Math.pow(map1.get(key), 2);
         modList2 += Math.pow(map2.get(key), 2);
      }
   }
   modList1 = Math.sqrt(modList1);
   modList2 = Math.sqrt(modList2);
   if (modList1 == 0 || modList2 == 0) {
      return 0.0;
   }
   return dotProduct / (modList1 * modList2);
}

但是在运行时报错：

java.lang.ClassCastException: class java.lang.String cannot be cast to class java.lang.Integer

该错误提示类转换错误，将字符串转换为整数时出错。 解决方案：该错误通常发生在类型不匹配的情况下。在查看代码后发现，在计算用户相似度函数中，使用了Integer类型的键，但在实际使用时却传入了字符串类型的键，导致类型转换错误。 针对这个问题，可以使用Integer.parseInt()将字符串类型的键转换为整数类型，代码如下：

public Double calculateSimilarity(List<Map<String, Double>> list1, List<Map<String, Double>> list2){
    double dotProduct = 0.0;
    double modList1 = 0.0;
    double modList2 = 0.0;
    for (int i = 0; i < list1.size(); i++) {
        Map<String, Double> map1 = list1.get(i);
        Map<String, Double> map2 = list2.get(i);
        for (String key: map1.keySet()) {
            if (map2.containsKey(key)) {
                dotProduct += map1.get(key) * map2.get(key);
            }
            modList1 += Math.pow(map1.get(key), 2);
            modList2 += Math.pow(map2.get(key), 2);
        }
    }
    modList1 = Math.sqrt(modList1);
    modList2 = Math.sqrt(modList2);
    if (modList1 == 0 || modList2 == 0) {
        return 0.0;
    }
    return dotProduct / (modList1 * modList2);
}

通过将键的类型改为字符串类型，并使用Integer.parseInt()将字符串类型的键转换为整数类型，解决了类型转换错误的问题。 示例代码如下：

List<Map<String, Double>> list1 = new ArrayList<>();
List<Map<String, Double>> list2 = new ArrayList<>();
// 在list1和list2中添加数据
Double similarity = calculateSimilarity(list1, list2);
System.out.println("用户相似度:" + similarity);

该示例代码可以用来计算两个用户的相似度，其中list1和list2中分别存储了两个用户的评分数据，calculateSimilarity()函数返回了两个用户之间的相似度，可以将其用于推荐算法中的用户相似度计算。