Redis缓存相关的几个问题 - ToB企服应用市场:ToB评测及商务社交产业平台

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.6.7</version>
<relativePath/>
</parent>
<groupId>com.example</groupId>
<artifactId>demo426</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>demo426</name>
<properties>
<java.version>1.8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-redis</artifactId>
</dependency>
<dependency>
<groupId>org.redisson</groupId>
<artifactId>redisson</artifactId>
<version>3.17.1</version>
</dependency>
<dependency>
<groupId>com.github.ben-manes.caffeine</groupId>
<artifactId>caffeine</artifactId>
<version>2.9.2</version>
</dependency>
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>fastjson</artifactId>
<version>2.0.1</version>
</dependency>
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-lang3</artifactId>
<version>3.12.0</version>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<optional>true</optional>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<configuration>
<excludes>
<exclude>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
</exclude>
</excludes>
</configuration>
</plugin>
</plugins>
</build>
</project>

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package com.example.demo426.domain;
import lombok.Data;
import java.io.Serializable;
import java.time.LocalDateTime;
/**
* @Author ChengJianSheng
* @Date 2022/4/26
*/
@Data
public class Product implements Serializable {
private Long productId;
private String productName;
private Integer stock;
private LocalDateTime createTime;
private LocalDateTime updateTime;
private Integer isDeleted;
private Integer version;
}

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package com.example.demo426.controller;
import com.alibaba.fastjson.JSON;
import com.example.demo426.domain.Product;
import com.example.demo426.service.ProductService;
import com.github.benmanes.caffeine.cache.Cache;
import com.github.benmanes.caffeine.cache.Caffeine;
import org.apache.commons.lang3.StringUtils;
import org.redisson.api.RLock;
import org.redisson.api.RReadWriteLock;
import org.redisson.api.RedissonClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.web.bind.annotation.*;
import javax.annotation.Resource;
import java.time.Duration;
import java.util.Random;
import java.util.concurrent.TimeUnit;
/**
* @Author ChengJianSheng
* @Date 2022/4/26
*/
@RestController
@RequestMapping("/product")
public class ProductController {
@Autowired
private RedissonClient redissonClient;
@Resource
private StringRedisTemplate stringRedisTemplate;
@Autowired
private ProductService productService;
private final Cache<long, product=""> PRODUCT_LOCAL_CACHE = Caffeine.newBuilder()
.maximumSize(100)
.expireAfterWrite(Duration.ofMinutes(60))
.build();
private final String PRODUCT_CACHE_PREFIX = "cache:product:";
private final String PRODUCT_LOCK_PREFIX = "lock:product:";
private final String PRODUCT_RW_LOCK_PREFIX = "lock:rw:product:";
/**
* 更新
* 写缓存的方式有这么几种：
* 1. 更新完数据库后，直接删除缓存
* 2. 更新完数据库后，主动更新缓存
* 3. 更新完数据库后，发MQ消息，由消费者去刷新缓存
* 4. 利用canal等工具，监听MySQL数据库binlog，然后去刷新缓存
*/
@PostMapping("/update")
public void update(@RequestBody Product productDTO) {
RReadWriteLock readWriteLock = redissonClient.getReadWriteLock(PRODUCT_RW_LOCK_PREFIX + productDTO.getProductId());
RLock wLock = readWriteLock.writeLock();
wLock.lock();
try {
// 写数据库
// update product set name=xxx,...,version=version+1 where id=xx and version=xxx
Product product = productService.update(productDTO);
// 放入缓存
PRODUCT_LOCAL_CACHE.put(product.getProductId(), product);
stringRedisTemplate.opsForValue().set(PRODUCT_CACHE_PREFIX + product.getProductId(), JSON.toJSONString(product), getProductTimeout(60), TimeUnit.MINUTES);
} finally {
wLock.unlock();
}
}
/**
* 查询
*/
@GetMapping("/query")
public Product query(@RequestParam("productId") Long productId) {
// 1. 尝试从缓存读取
Product product = getProductFromCache(productId);
if (null != product) {
return product;
}
// 2. 准备从数据库中加载
// 互斥锁
RLock lock = redissonClient.getLock(PRODUCT_LOCK_PREFIX + productId);
lock.lock();
try {
// 再次先查缓存
product = getProductFromCache(productId);
if (null != product) {
return product;
}
// 为了避免缓存与数据库双写不一致
// 读写锁
RReadWriteLock readWriteLock = redissonClient.getReadWriteLock(PRODUCT_RW_LOCK_PREFIX + productId);
RLock rLock = readWriteLock.readLock();
rLock.lock();
try {
// 查数据库
product = productService.getById(productId);
if (null == product) {
// 如果数据库中没有，则放置一个空对象，这样做是为了避免”缓存穿透“问题
product = new Product();
} else {
PRODUCT_LOCAL_CACHE.put(productId, product);
}
// 放入缓存
stringRedisTemplate.opsForValue().set(PRODUCT_CACHE_PREFIX + productId, JSON.toJSONString(product), getProductTimeout(60), TimeUnit.MINUTES);
} finally {
rLock.unlock();
}
} finally {
lock.unlock();
}
return null;
}
/**
* 查缓存
*/
private Product getProductFromCache(Long productId) {
// 1. 尝试从本地缓存读取
Product product = PRODUCT_LOCAL_CACHE.getIfPresent(productId);
if (null != product) {
return product;
}
// 2. 尝试从Redis中读取
String key = PRODUCT_CACHE_PREFIX + productId;
String value = stringRedisTemplate.opsForValue().get(key);
if (StringUtils.isNotBlank(value)) {
product = JSON.parseObject(value, Product.class);
return product;
}
return null;
}
/**
* 为了避免缓存集体失效，故而加了随机时间
*/
private int getProductTimeout(int initVal) {
Random random = new Random(10);
return initVal + random.nextInt();
}
}</long,>

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