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

package com.example.demo.controller;import com.example.demo.entity.Result;
import com.example.demo.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;@RestController
@RequestMapping("user")
public class UserController {@Autowiredprivate UserService userService;@GetMapping("page")public Result page(int pageNo, int pageSize) {return userService.page(pageNo, pageSize);}
}

Service

接口

package com.example.demo.service;import com.example.demo.entity.Result;public interface UserService {Result page(int pageNo, int pageSize);
}

实现

package com.example.demo.service.impl;import com.example.demo.constant.RedisConstant;
import com.example.demo.entity.Result;
import com.example.demo.entity.User;
import com.example.demo.service.UserService;
import org.springframework.cache.annotation.Cacheable;
import org.springframework.stereotype.Service;import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;@Service
public class UserServiceImpl implements UserService {private final List<User> allUsers = Arrays.asList(new User(1L, "Tony1", 20),new User(2L, "Tony2", 18),new User(3L, "Tony3", 30),new User(4L, "Tony4", 25),new User(5L, "Tony5", 28));@Override@Cacheable(cacheNames = "userPageCache")public Result<List<User>> page(int pageNo, int pageSize) {String format = String.format("pageNo: %s, pageSize: %s", pageNo, pageSize);System.out.println("从数据库中读数据。" + format);int from = (pageNo - 1) * pageSize;int to = Math.min(allUsers.size(), (pageNo) * pageSize);List<User> users = new ArrayList<>(allUsers.subList(from, to));return new Result<List<User>>().data(users);}
}

Entity

User

package com.example.demo.entity;import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;@Data
@AllArgsConstructor
// 必须要有无参构造函数。因为Redis反序列化为对象时要用到
@NoArgsConstructor
public class User {private Long id;private String userName;private Integer age;
}

Result

package com.example.demo.entity;import lombok.Data;@Data
public class Result<T> {private boolean success = true;private int code = 1000;private String message;private T data;public Result() {}public Result(boolean success) {this.success = success;}public Result<T> success(boolean success) {Result<T> result = new Result<>(success);if (success) {result.code = 1000;} else {result.code = 1001;}return result;}public Result<T> success() {return success(true);}public Result<T> failure() {return success(false);}/*** @param code {@link ResultCode#getCode()}*/public Result<T> code(int code) {this.code = code;return this;}public Result<T> message(String message) {this.message = message;return this;}public Result<T> data(T data) {this.data = data;return this;}
}

Redis配置代码

package com.example.demo.config;import com.example.demo.constant.RedisConstant;
import com.fasterxml.jackson.annotation.JsonAutoDetect;
import com.fasterxml.jackson.annotation.JsonTypeInfo;
import com.fasterxml.jackson.annotation.PropertyAccessor;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.cache.CacheManager;
import org.springframework.cache.annotation.CachingConfigurerSupport;
import org.springframework.cache.annotation.EnableCaching;
import org.springframework.cache.interceptor.KeyGenerator;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.data.redis.cache.RedisCacheConfiguration;
import org.springframework.data.redis.cache.RedisCacheManager;
import org.springframework.data.redis.connection.RedisConnectionFactory;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.serializer.*;
import org.springframework.util.StringUtils;import java.time.Duration;
import java.util.HashMap;
import java.util.Map;@Configuration
@EnableCaching
public class RedisConfig extends CachingConfigurerSupport {/*** 重写缓存Key生成策略。* 包名+方法名+参数列表。防止缓存Key冲突*/@Bean@Overridepublic KeyGenerator keyGenerator() {return (target, method, params) -> {// 存放最终结果StringBuilder resultStringBuilder = new StringBuilder("cache:key:");// 执行方法所在的类resultStringBuilder.append(target.getClass().getName()).append(".");// 执行的方法名称resultStringBuilder.append(method.getName()).append("(");// 存放参数StringBuilder paramStringBuilder = new StringBuilder();for (Object param : params) {if (param == null) {paramStringBuilder.append("java.lang.Object[null],");} else {paramStringBuilder.append(param.getClass().getName()).append("[").append(String.valueOf(param)).append("],");}}if (StringUtils.hasText(paramStringBuilder.toString())) {// 去掉最后的逗号String trimLastComma = paramStringBuilder.substring(0, paramStringBuilder.length() - 1);resultStringBuilder.append(trimLastComma);}return resultStringBuilder.append(")").toString();};}@Beanpublic CacheManager cacheManager(RedisConnectionFactory factory) {Map<String, RedisCacheConfiguration> configurationMap = new HashMap<>();RedisCacheConfiguration config = RedisCacheConfiguration.defaultCacheConfig().entryTtl(Duration.ofMinutes(5)).serializeKeysWith(RedisSerializationContext.SerializationPair.fromSerializer(keySerializer())).serializeValuesWith(RedisSerializationContext.SerializationPair.fromSerializer(valueSerializer())).disableCachingNullValues();return RedisCacheManager.builder(factory).initialCacheNames(configurationMap.keySet()).withInitialCacheConfigurations(configurationMap).cacheDefaults(config).build();}@Beanpublic RedisTemplate<?, ?> redisTemplate(RedisConnectionFactory factory) {RedisTemplate<Object, Object> template = new RedisTemplate<>();template.setConnectionFactory(factory);template.setKeySerializer(keySerializer());template.setValueSerializer(valueSerializer());template.setHashKeySerializer(keySerializer());template.setHashValueSerializer(valueSerializer());template.afterPropertiesSet();return template;}private RedisSerializer<String> keySerializer() {return new StringRedisSerializer();}private RedisSerializer<Object> valueSerializer() {Jackson2JsonRedisSerializer<Object> jackson2JsonRedisSerializer =new Jackson2JsonRedisSerializer<>(Object.class);ObjectMapper objectMapper = new ObjectMapper();objectMapper.setVisibility(PropertyAccessor.ALL, JsonAutoDetect.Visibility.ANY);jackson2JsonRedisSerializer.setObjectMapper(objectMapper);return jackson2JsonRedisSerializer;}
}

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：

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 causejava.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to com.example.demo.entity.Resultat com.sun.proxy.$Proxy56.page(Unknown Source) ~[na:na]at com.example.demo.controller.UserController.page(UserController.java:18) ~[classes/:na]at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_201]at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_201]at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_201]at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_201]at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190) ~[spring-web-5.2.15.RELEASE.jar:5.2.15.RELEASE]at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.2.15.RELEASE.jar:5.2.15.RELEASE]......at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1707) [tomcat-embed-core-9.0.46.jar:9.0.46]at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.46.jar:9.0.46]at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_201]at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_201]at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.46.jar:9.0.46]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

修改RedisTemplate这个bean的valueSerializer，设置默认类型。

关键代码：

private RedisSerializer<Object> valueSerializer() {Jackson2JsonRedisSerializer<Object> jackson2JsonRedisSerializer =new Jackson2JsonRedisSerializer<>(Object.class);ObjectMapper objectMapper = new ObjectMapper();objectMapper.setVisibility(PropertyAccessor.ALL, JsonAutoDetect.Visibility.ANY);// 此项必须配置，否则如果序列化的对象里边还有对象，会报如下错误：//     java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to XXXobjectMapper.activateDefaultTyping(objectMapper.getPolymorphicTypeValidator(),ObjectMapper.DefaultTyping.NON_FINAL,JsonTypeInfo.As.PROPERTY);旧版写法：// objectMapper.enableDefaultTyping(ObjectMapper.DefaultTyping.NON_FINAL, JsonTypeInfo.As.PROPERTY);jackson2JsonRedisSerializer.setObjectMapper(objectMapper);return jackson2JsonRedisSerializer;
}

解决后的测试

代码

只修改Redis配置类

package com.example.demo.config;import com.example.demo.constant.RedisConstant;
import com.fasterxml.jackson.annotation.JsonAutoDetect;
import com.fasterxml.jackson.annotation.JsonTypeInfo;
import com.fasterxml.jackson.annotation.PropertyAccessor;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.cache.CacheManager;
import org.springframework.cache.annotation.CachingConfigurerSupport;
import org.springframework.cache.annotation.EnableCaching;
import org.springframework.cache.interceptor.KeyGenerator;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.data.redis.cache.RedisCacheConfiguration;
import org.springframework.data.redis.cache.RedisCacheManager;
import org.springframework.data.redis.connection.RedisConnectionFactory;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.serializer.*;
import org.springframework.util.StringUtils;import java.time.Duration;
import java.util.HashMap;
import java.util.Map;@Configuration
@EnableCaching
public class RedisConfig extends CachingConfigurerSupport {/*** 重写缓存Key生成策略。* 包名+方法名+参数列表。防止缓存Key冲突*/@Bean@Overridepublic KeyGenerator keyGenerator() {return (target, method, params) -> {// 存放最终结果StringBuilder resultStringBuilder = new StringBuilder("cache:key:");// 执行方法所在的类resultStringBuilder.append(target.getClass().getName()).append(".");// 执行的方法名称resultStringBuilder.append(method.getName()).append("(");// 存放参数StringBuilder paramStringBuilder = new StringBuilder();for (Object param : params) {if (param == null) {paramStringBuilder.append("java.lang.Object[null],");} else {paramStringBuilder.append(param.getClass().getName()).append("[").append(String.valueOf(param)).append("],");}}if (StringUtils.hasText(paramStringBuilder.toString())) {// 去掉最后的逗号String trimLastComma = paramStringBuilder.substring(0, paramStringBuilder.length() - 1);resultStringBuilder.append(trimLastComma);}return resultStringBuilder.append(")").toString();};}@Beanpublic CacheManager cacheManager(RedisConnectionFactory factory) {Map<String, RedisCacheConfiguration> configurationMap = new HashMap<>();RedisCacheConfiguration config = RedisCacheConfiguration.defaultCacheConfig().entryTtl(Duration.ofMinutes(5)).serializeKeysWith(RedisSerializationContext.SerializationPair.fromSerializer(keySerializer())).serializeValuesWith(RedisSerializationContext.SerializationPair.fromSerializer(valueSerializer())).disableCachingNullValues();return RedisCacheManager.builder(factory).initialCacheNames(configurationMap.keySet()).withInitialCacheConfigurations(configurationMap).cacheDefaults(config).build();}@Beanpublic RedisTemplate<?, ?> redisTemplate(RedisConnectionFactory factory) {RedisTemplate<Object, Object> template = new RedisTemplate<>();template.setConnectionFactory(factory);template.setKeySerializer(keySerializer());template.setValueSerializer(valueSerializer());template.setHashKeySerializer(keySerializer());template.setHashValueSerializer(valueSerializer());template.afterPropertiesSet();return template;}private RedisSerializer<String> keySerializer() {return new StringRedisSerializer();}private RedisSerializer<Object> valueSerializer() {Jackson2JsonRedisSerializer<Object> jackson2JsonRedisSerializer =new Jackson2JsonRedisSerializer<>(Object.class);ObjectMapper objectMapper = new ObjectMapper();objectMapper.setVisibility(PropertyAccessor.ALL, JsonAutoDetect.Visibility.ANY);// 此项必须配置，否则如果序列化的对象里边还有对象，会报如下错误：//     java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to XXXobjectMapper.activateDefaultTyping(objectMapper.getPolymorphicTypeValidator(),ObjectMapper.DefaultTyping.NON_FINAL,JsonTypeInfo.As.PROPERTY);// 旧版写法：// objectMapper.enableDefaultTyping(ObjectMapper.DefaultTyping.NON_FINAL, JsonTypeInfo.As.PROPERTY);jackson2JsonRedisSerializer.setObjectMapper(objectMapper);return jackson2JsonRedisSerializer;}
}

测试

第1次访问（成功）

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

可以看到，在写入Redis时，会带上类全名。这样在反序列化时就能成功了。

第2次访问（成功）

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

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

简介

问题复现

业务代码

Redis配置代码

测试

原因分析

解决方案

解决后的测试

代码

测试

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

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