解决高并发下的缓存穿透问题

　　目前我们针对高并发场景，这种问题很常见，一般有如下两种解决方式：

　　一：在方法上加上同步锁 synchronized（用的比较少）

　　

//加同步锁,解决高并发下缓存穿透

@Test
public synchronized void getMyUser(){
//字符串的序列化器 redis
RedisSerializer redisSerializer = new StringRedisSerializer();
redisTemplate.setKeySerializer(redisSerializer);
//查询缓存
MyUser myUser = (MyUser) redisTemplate.opsForValue().get("myUser");
if(null == myUser){
System.out.println("当缓存没有myUser时显示.");
//缓存为空,查询数据库
myUser = myUserMapper.selectByPrimaryKey(1l);
//把数据库查询出来的数据放入redis
redisTemplate.opsForValue().set("myUser",myUser);
}
System.out.println(myUser);
}

　　二：使用双重检测锁（常用）

　　

 public void getMyUser(){
//字符串的序列化器 redis
RedisSerializer redisSerializer = new StringRedisSerializer();
redisTemplate.setKeySerializer(redisSerializer);
//查询缓存
MyUser myUser = (MyUser) redisTemplate.opsForValue().get("myUser");
//双层检测锁
if(null == myUser){
synchronized(this){
myUser = (MyUser) redisTemplate.opsForValue().get("myUser");
if(null == myUser){
System.out.println("当缓存没有myUser时显示.");
//缓存为空,查询数据库
myUser = myUserMapper.selectByPrimaryKey(1l);
//把数据库查询出来的数据放入redis
redisTemplate.opsForValue().set("myUser",myUser);
}
}
}
System.out.println(myUser);
}

　　三：进行高并发测试

　　

import com.ykmimi.job.bean.MyUser;
import com.ykmimi.job.mapper.MyUserMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.serializer.RedisSerializer;
import org.springframework.data.redis.serializer.StringRedisSerializer;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import javax.annotation.Resource;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
@RestController
public class MyUserController {
@Autowired
private RedisTemplate<Object,Object> redisTemplate;
@Resource
private MyUserMapper myUserMapper;
public Integer insertNew(){
return 0;
}
@RequestMapping("/getMyUserTest")
public void getMyUserTest(){
//线程,该线程调用底层查询MyUser的方法
Runnable runnable = new Runnable() {
@Override
public void run() {
getMyUser();
}
};
//多线程测试一下缓存穿透的问题
ExecutorService executorService = Executors.newFixedThreadPool(25);
for(int i=0;i<10000;i++){
executorService.submit(runnable);
}
}
public void getMyUser(){
//字符串的序列化器 redis
RedisSerializer redisSerializer = new StringRedisSerializer();
redisTemplate.setKeySerializer(redisSerializer);
//查询缓存
MyUser myUser = (MyUser) redisTemplate.opsForValue().get("myUser");
//双层检测锁
if(null == myUser){
System.out.println("当缓存没有myUser时显示.没有进入同步锁");
synchronized(this){
myUser = (MyUser) redisTemplate.opsForValue().get("myUser");
if(null == myUser){
System.out.println("当缓存没有myUser时显示.已经进入同步锁");
//缓存为空,查询数据库
myUser = myUserMapper.selectByPrimaryKey(1l);
//把数据库查询出来的数据放入redis
redisTemplate.opsForValue().set("myUser",myUser);
}
}
}
System.out.println(myUser);
}
}

　　住：线程池中不要特别大的线程