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Spring-Data-Redis--解决java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to xxx

作者：从前慢现在也慢 | 2024-03-24 22:44:56

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java.lang.classcastexception: java.util.linkedhashmap cannot be cast to com.

原文网址：Spring-Data-Redis--解决java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to xxx_IT利刃出鞘的博客-CSDN博客

简介

说明

本文介绍解决Spring-Data-Redis的“java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to xxx”报错的方法。

出现的场景

SpringBoot项目中使用Redis来进行缓存。把数据放到缓存中时没有问题，但从缓存中取出来反序列化为对象时报错：“java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to xxx”。（xxx为反序列化的目标对象对应的类。）

只有这个类里有其他对象字段才会报这个问题，如果这个类里都是初始的类型（比如：Integer，String）则不会报这个错误。

只要用到Redis序列化反序列化的地方都会遇到这个问题，比如：RedisTemplate，Redisson，@Cacheable注解等。

问题复现

业务代码

Controller

  1. package com.example.demo.controller;
  2.  
  3. import com.example.demo.entity.Result;
  4. import com.example.demo.service.UserService;
  5. import org.springframework.beans.factory.annotation.Autowired;
  6. import org.springframework.web.bind.annotation.GetMapping;
  7. import org.springframework.web.bind.annotation.RequestMapping;
  8. import org.springframework.web.bind.annotation.RestController;
  9.  
  10. @RestController
  11. @RequestMapping("user")
  12. public class UserController {
  13.     @Autowired
  14.     private UserService userService;
  15.  
  16.     @GetMapping("page")
  17.     public Result page(int pageNo, int pageSize) {
  18.         return userService.page(pageNo, pageSize);
  19.     }
  20. }

Service

接口

  1. package com.example.demo.service;
  2.  
  3. import com.example.demo.entity.Result;
  4.  
  5. public interface UserService {
  6.     Result page(int pageNo, int pageSize);
  7. }

实现

  1. package com.example.demo.service.impl;
  2.  
  3. import com.example.demo.constant.RedisConstant;
  4. import com.example.demo.entity.Result;
  5. import com.example.demo.entity.User;
  6. import com.example.demo.service.UserService;
  7. import org.springframework.cache.annotation.Cacheable;
  8. import org.springframework.stereotype.Service;
  9.  
  10. import java.util.ArrayList;
  11. import java.util.Arrays;
  12. import java.util.List;
  13.  
  14. @Service
  15. public class UserServiceImpl implements UserService {
  16.     private final List<User> allUsers = Arrays.asList(
  17.             new User(1L, "Tony1", 20),
  18.             new User(2L, "Tony2", 18),
  19.             new User(3L, "Tony3", 30),
  20.             new User(4L, "Tony4", 25),
  21.             new User(5L, "Tony5", 28)
  22.     );
  23.  
  24.     @Override
  25.     @Cacheable(cacheNames = "userPageCache")
  26.     public Result<List<User>> page(int pageNo, int pageSize) {
  27.         String format = String.format("pageNo: %s, pageSize: %s", pageNo, pageSize);
  28.         System.out.println("从数据库中读数据。" + format);
  29.  
  30.         int from = (pageNo - 1) * pageSize;
  31.         int to = Math.min(allUsers.size(), (pageNo) * pageSize);
  32.  
  33.         List<User> users = new ArrayList<>(allUsers.subList(from, to));
  34.         return new Result<List<User>>().data(users);
  35.     }
  36. }

Entity

User

  1. package com.example.demo.entity;
  2.  
  3. import lombok.AllArgsConstructor;
  4. import lombok.Data;
  5. import lombok.NoArgsConstructor;
  6.  
  7. @Data
  8. @AllArgsConstructor
  9. // 必须要有无参构造函数。因为Redis反序列化为对象时要用到
  10. @NoArgsConstructor
  11. public class User {
  12.     private Long id;
  13.  
  14.     private String userName;
  15.  
  16.     private Integer age;
  17. }

Result

  1. package com.example.demo.entity;
  2.  
  3. import lombok.Data;
  4.  
  5. @Data
  6. public class Result<T> {
  7.     private boolean success = true;
  8.  
  9.     private int code = 1000;
  10.  
  11.     private String message;
  12.  
  13.     private T data;
  14.  
  15.     public Result() {
  16.     }
  17.  
  18.     public Result(boolean success) {
  19.         this.success = success;
  20.     }
  21.  
  22.     public Result<T> success(boolean success) {
  23.         Result<T> result = new Result<>(success);
  24.         if (success) {
  25.             result.code = 1000;
  26.         } else {
  27.             result.code = 1001;
  28.         }
  29.         return result;
  30.     }
  31.  
  32.     public Result<T> success() {
  33.         return success(true);
  34.     }
  35.  
  36.     public Result<T> failure() {
  37.         return success(false);
  38.     }
  39.  
  40.     /**
  41.      * @param code {@link ResultCode#getCode()}
  42.      */
  43.     public Result<T> code(int code) {
  44.         this.code = code;
  45.         return this;
  46.     }
  47.  
  48.     public Result<T> message(String message) {
  49.         this.message = message;
  50.         return this;
  51.     }
  52.  
  53.     public Result<T> data(T data) {
  54.         this.data = data;
  55.         return this;
  56.     }
  57. }

Redis配置代码

  1. package com.example.demo.config;
  2.  
  3. import com.example.demo.constant.RedisConstant;
  4. import com.fasterxml.jackson.annotation.JsonAutoDetect;
  5. import com.fasterxml.jackson.annotation.JsonTypeInfo;
  6. import com.fasterxml.jackson.annotation.PropertyAccessor;
  7. import com.fasterxml.jackson.databind.ObjectMapper;
  8. import org.springframework.cache.CacheManager;
  9. import org.springframework.cache.annotation.CachingConfigurerSupport;
  10. import org.springframework.cache.annotation.EnableCaching;
  11. import org.springframework.cache.interceptor.KeyGenerator;
  12. import org.springframework.context.annotation.Bean;
  13. import org.springframework.context.annotation.Configuration;
  14. import org.springframework.data.redis.cache.RedisCacheConfiguration;
  15. import org.springframework.data.redis.cache.RedisCacheManager;
  16. import org.springframework.data.redis.connection.RedisConnectionFactory;
  17. import org.springframework.data.redis.core.RedisTemplate;
  18. import org.springframework.data.redis.serializer.*;
  19. import org.springframework.util.StringUtils;
  20.  
  21. import java.time.Duration;
  22. import java.util.HashMap;
  23. import java.util.Map;
  24.  
  25. @Configuration
  26. @EnableCaching
  27. public class RedisConfig extends CachingConfigurerSupport {
  28.  
  29.     /**
  30.      * 重写缓存Key生成策略。
  31.      * 包名+方法名+参数列表。防止缓存Key冲突
  32.      */
  33.     @Bean
  34.     @Override
  35.     public KeyGenerator keyGenerator() {
  36.         return (target, method, params) -> {
  37.             // 存放最终结果
  38.             StringBuilder resultStringBuilder = new StringBuilder("cache:key:");
  39.             // 执行方法所在的类
  40.             resultStringBuilder.append(target.getClass().getName()).append(".");
  41.             // 执行的方法名称
  42.             resultStringBuilder.append(method.getName()).append("(");
  43.  
  44.             // 存放参数
  45.             StringBuilder paramStringBuilder = new StringBuilder();
  46.             for (Object param : params) {
  47.                 if (param == null) {
  48.                     paramStringBuilder.append("java.lang.Object[null],");
  49.                 } else {
  50.                     paramStringBuilder
  51.                             .append(param.getClass().getName())
  52.                             .append("[")
  53.                             .append(String.valueOf(param))
  54.                             .append("],");
  55.                 }
  56.             }
  57.             if (StringUtils.hasText(paramStringBuilder.toString())) {
  58.                 // 去掉最后的逗号
  59.                 String trimLastComma = paramStringBuilder.substring(0, paramStringBuilder.length() - 1);
  60.                 resultStringBuilder.append(trimLastComma);
  61.             }
  62.  
  63.             return resultStringBuilder.append(")").toString();
  64.         };
  65.     }
  66.  
  67.     @Bean
  68.     public CacheManager cacheManager(RedisConnectionFactory factory) {
  69.         Map<String, RedisCacheConfiguration> configurationMap = new HashMap<>();
  70.  
  71.         RedisCacheConfiguration config = RedisCacheConfiguration.defaultCacheConfig()
  72.                 .entryTtl(Duration.ofMinutes(5))
  73.                 .serializeKeysWith(RedisSerializationContext.SerializationPair.fromSerializer(keySerializer()))
  74.                 .serializeValuesWith(RedisSerializationContext.SerializationPair.fromSerializer(valueSerializer()))
  75.                 .disableCachingNullValues();
  76.  
  77.         return RedisCacheManager.builder(factory)
  78.                 .initialCacheNames(configurationMap.keySet())
  79.                 .withInitialCacheConfigurations(configurationMap)
  80.                 .cacheDefaults(config)
  81.                 .build();
  82.     }
  83.  
  84.     @Bean
  85.     public RedisTemplate<?, ?> redisTemplate(RedisConnectionFactory factory) {
  86.         RedisTemplate<Object, Object> template = new RedisTemplate<>();
  87.         template.setConnectionFactory(factory);
  88.  
  89.         template.setKeySerializer(keySerializer());
  90.         template.setValueSerializer(valueSerializer());
  91.  
  92.         template.setHashKeySerializer(keySerializer());
  93.         template.setHashValueSerializer(valueSerializer());
  94.  
  95.         template.afterPropertiesSet();
  96.         return template;
  97.     }
  98.  
  99.     private RedisSerializer<String> keySerializer() {
  100.         return new StringRedisSerializer();
  101.     }
  102.  
  103.     private RedisSerializer<Object> valueSerializer() {
  104.         Jackson2JsonRedisSerializer<Object> jackson2JsonRedisSerializer =
  105.                 new Jackson2JsonRedisSerializer<>(Object.class);
  106.         ObjectMapper objectMapper = new ObjectMapper();
  107.         objectMapper.setVisibility(PropertyAccessor.ALL, JsonAutoDetect.Visibility.ANY);
  108.  
  109.         jackson2JsonRedisSerializer.setObjectMapper(objectMapper);
  110.  
  111.         return jackson2JsonRedisSerializer;
  112.     }
  113. }

测试

第1次访问（成功）

http://localhost:8080/user/page?pageNo=1&pageSize=2

结果：成功访问，结果或存入Redis

第2次访问（失败）

http://localhost:8080/user/page?pageNo=1&pageSize=2

结果：报错

后端输出：

  1. 2022-01-11 14:59:23.805 ERROR 68468 --- [nio-8080-exec-5] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to com.example.demo.entity.Result] with root cause
  2.  
  3. java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to com.example.demo.entity.Result
  4. 	at com.sun.proxy.$Proxy56.page(Unknown Source) ~[na:na]
  5. 	at com.example.demo.controller.UserController.page(UserController.java:18) ~[classes/:na]
  6. 	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_201]
  7. 	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_201]
  8. 	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_201]
  9. 	at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_201]
  10. 	at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190) ~[spring-web-5.2.15.RELEASE.jar:5.2.15.RELEASE]
  11. 	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.2.15.RELEASE.jar:5.2.15.RELEASE]
  12. 	......
  13. 	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1707) [tomcat-embed-core-9.0.46.jar:9.0.46]
  14. 	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.46.jar:9.0.46]
  15. 	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_201]
  16. 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_201]
  17. 	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.46.jar:9.0.46]
  18. 	at java.lang.Thread.run(Thread.java:748) [na:1.8.0_201]

原因分析

SpringBoot 的缓存使用 jackson 来做数据的序列化与反序列化，如果默认使用 Object 作为序列化与反序列化的类型，则其只能识别 java 基本类型，遇到复杂类型时，jackson 就会先序列化成 LinkedHashMap ，然后再尝试强转为所需类别，这样大部分情况下会强转失败。

解决方案

上边是文章的部分内容，为便于维护，全文已转移到此网址：Spring-Data-Redis-解决java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to xxx - 自学精灵

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