单机下：
只适用于单机环境下（单个JVM），多个客户端访问同一个服务器
1.synchronized
package com.cloud.SR.controller;import org.springframework.beans.factory.annotation.Value;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;import javax.annotation.Resource;@RestController
public class TestConrtoller1 {@Value("${server.port}")private String serverPort;@Resourceprivate StringRedisTemplate stringRedisTemplate;@GetMapping("/buy1")public String shopping(){synchronized (this){String result = stringRedisTemplate.opsForValue().get("goods:001");int total = result == null? 0 :Integer.parseInt(s);if(total > 0){int realTotal = total - 1;stringRedisTemplate.opsForValue().set("goods:001",String.valueOf(realCount ));System.out.println("剩余商品为："+realCount +",提供服务的端口号："+serverPort);return "剩余商品为："+realTotal +",提供服务的端口号："+serverPort;}else{System.out.println("购买商品失败！");}return "购买商品失败！";}}
}2.ReentrantLock
@RestController
public class TestConrtoller2 {@Value("${server.port}")private String serverPort;// 使用ReentrantLock锁解决单体应用的并发问题Lock lock = new ReentrantLock();@AutowiredStringRedisTemplate stringRedisTemplate;@RequestMapping("/buy2")public String index() {lock.lock();try {String result = stringRedisTemplate.opsForValue().get("goods:001");int total = result == null ? 0 : Integer.parseInt(result);if (total > 0) {int realTotal = total - 1;stringRedisTemplate.opsForValue().set("goods:001", String.valueOf(realTotal));System.out.println("购买商品成功，库存还剩：" + realTotal + "，服务端口为:"+serverPort);return "购买商品成功，库存还剩：" + realTotal + "，服务端口为："+serverPort;} else {System.out.println("购买商品失败！");}} catch (Exception e) {lock.unlock();} finally {lock.unlock();}return "购买商品失败！";}
}
分布式下：
而在服务器分布式集群下，，单个服务器的synchronized和ReentrantLock
1.SETNX
SET key value [EX seconds] [PX milliseconds] [NX|XX]EXseconds – 设置键key的过期时间，单位时秒PXmilliseconds – 设置键key的过期时间，单位时毫秒NX– 只有键key不存在的时候才会设置key的值XX– 只有键key存在的时候才会设置key的值
例子：
1.set lock01 01 NX ：意思就是说只要谁把key为lock01的值设置为01且key不存在的时候就能拿到锁
2. set lock01 01 NX EX 30 ：在例1的基础上把锁设置的时间设置为30秒后过期。避免有服务挂了而没有释放锁的情况、或者业务处理完但一直拿着锁不释放导致死锁。
项目中使用SETNX：
template.opsForValue().setIfAbsent()
测试的话就得本机模拟集群，当然有虚拟机的也可以用两台虚拟机，但此处用两台JVM即可完成简易集群
本机实现集群的可以看这篇文章：http://t.csdn.cn/jvZFx
先让集群跑起来，然后启动Nginx，再通过Jmeter实现高并发的秒杀环节
用template.opsForValue().setIfAbsent()命令进行加锁。加上了过期时间后就解决了key无法删除的问题，但如果key设置的时间太短，当业务处理的时间长于key设置的时间，key过期后其他请求就可以设置这个key而当这个线程再回来处理这个程序的时候就会把人家设置的key给删除了，因此我们规定谁设置的锁只能由谁删除。
finally {// 谁加的锁，谁才能删除if(template.opsForValue().get(REDIS_LOCK).equals(value)){template.delete(REDIS_LOCK);}
而新的问题就是finally块的判断和del删除操作不是原子操作，并发的时候也会出问题。因此采用lua（原子性）来进行删除
finally {// 谁加的锁，谁才能删除，使用Lua脚本，进行锁的删除Jedis jedis = null;try{jedis = RedisUtils.getJedis();String script = "if redis.call('get',KEYS[1]) == ARGV[1] " +"then " +"return redis.call('del',KEYS[1]) " +"else " +" return 0 " +"end";Object eval = jedis.eval(script, Collections.singletonList(REDIS_LOCK), Collections.singletonList(value));if("1".equals(eval.toString())){System.out.println("-----del redis lock ok....");}else{System.out.println("-----del redis lock error ....");}}catch (Exception e){}finally {if(null != jedis){jedis.close();}}
总的代码：
@RestController
public class TestConrtoller3 {@Value("${server.port}")private String serverPort;public static final String REDIS_LOCK = "good_lock";@AutowiredStringRedisTemplate stringtemplate;@RequestMapping("/buy3")public String shopping(){// 每个人进来先要进行加锁，key值为"good_lock",且用UUID保证每个人的锁不同String value = UUID.randomUUID().toString().replace("-","");try{// 为key加一个过期时间Boolean flag = stringtemplate.opsForValue().setIfAbsent(REDIS_LOCK, value,10L,TimeUnit.SECONDS);// 加锁失败if(!flag){return "抢锁失败！";}System.out.println( value+ " 抢锁成功");String result = stringtemplate.opsForValue().get("goods:001");int total = result == null ? 0 : Integer.parseInt(result);if (total > 0) {// 如果在此处需要调用其他微服务，处理时间较长。。。int realTotal = total - 1;stringtemplate.opsForValue().set("goods:001", String.valueOf(realTotal));System.out.println("购买商品成功，库存还剩：" + realTotal + "，服务端口为"+serverPort);return "购买商品成功，库存还剩：" + realTotal + "服务端口为"+serverPort;} else {System.out.println("购买商品失败");}return "购买商品失败！";}finally {// 谁加的锁，谁才能删除，使用Lua脚本，进行锁的删除Jedis jedis = null;try{jedis = RedisUtils.getJedis();String script = "if redis.call('get',KEYS[1]) == ARGV[1] " +"then " +"return redis.call('del',KEYS[1]) " +"else " +" return 0 " +"end";Object eval = jedis.eval(script, Collections.singletonList(REDIS_LOCK), Collections.singletonList(value));if("1".equals(eval.toString())){System.out.println("-----del redis lock ok....");}else{System.out.println("-----del redis lock error ....");}}catch (Exception e){}finally {if(null != jedis){jedis.close();}}}}
}
2.Redisson(推荐)
考虑缓存续命，以及Redis集群部署下，异步复制造成的锁丢失：主节点没来得及把刚刚set进来这条数据给从节点，就挂了。所以直接上RedLock的Redisson落地实现
@RestController
public class TestConrtoller4 {@Value("${server.port}")private String serverPort;public static final String REDIS_LOCK = "good_lock";@AutowiredStringRedisTemplate stringtemplate;@AutowiredRedisson redisson;@RequestMapping("/buy4")public String shopping(){RLock lock = redisson.getLock(REDIS_LOCK);lock.lock();// 每个人进来先要进行加锁，key值为"good_lock"String value = UUID.randomUUID().toString().replace("-","");try{String result = stringtemplate.opsForValue().get("goods:001");int total = result == null ? 0 : Integer.parseInt(result);if (total > 0) {// 如果在此处需要调用其他微服务，处理时间较长int realTotal = total - 1;stringtemplate.opsForValue().set("goods:001", String.valueOf(realTotal));System.out.println("购买商品成功，库存还剩：" + realTotal + "件， 服务端口为"+serverPort);return "购买商品成功，库存还剩：" + realTotal + "件， 服务端口为"+serverPort;} else {System.out.println("购买商品失败");}return "购买商品失败";}finally {if(lock.isLocked() && lock.isHeldByCurrentThread()){lock.unlock();}}}
}
Redis工具类
import com.myfutech.common.util.constant.RedisPrefix;
import lombok.extern.slf4j.Slf4j;
import org.springframework.data.redis.connection.RedisStringCommands;
import org.springframework.data.redis.connection.ReturnType;
import org.springframework.data.redis.core.RedisCallback;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.types.Expiration;import java.nio.charset.StandardCharsets;
import java.util.UUID;/*** 基于redis分布式锁*/
@Slf4j
public class RedisLockUtils {/*** 默认轮休获取锁间隔时间， 单位：毫秒*/private static final int DEFAULT_ACQUIRE_RESOLUTION_MILLIS = 100;private static final String UNLOCK_LUA;static {StringBuilder sb = new StringBuilder();sb.append("if redis.call(\"get\",KEYS[1]) == ARGV[1] ");sb.append("then ");sb.append(" return redis.call(\"del\",KEYS[1]) ");sb.append("else ");sb.append(" return 0 ");sb.append("end ");UNLOCK_LUA = sb.toString();}/*** 获取锁，没有获取到则一直等待，异常情况则返回null** @param redisTemplate redis连接* @param key redis key* @param expire 锁过期时间, 单位 秒* @return 当前锁唯一id，如果没有获取到，返回 null*/public static String lock(RedisTemplate redisTemplate, final String key, long expire){return lock(redisTemplate, key, expire, -1);}/*** 获取锁，acquireTimeout时间内没有获取到，则返回null，异常情况返回null** @param redisTemplate redis连接* @param key redis key* @param expire 锁过期时间, 单位 秒* @param acquireTimeout 获取锁超时时间, -1代表永不超时, 单位 秒* @return 当前锁唯一id，如果没有获取到，返回 null*/public static String lock(RedisTemplate redisTemplate, final String key, long expire, long acquireTimeout){try {return acquireLock(redisTemplate, key, expire, acquireTimeout);} catch (Exception e) {log.error("acquire lock exception", e);}return null;}/*** 获取锁，没有获取到则一直等待，没有获取到则抛出异常** @param redisTemplate redis连接* @param key redis key* @param expire 锁过期时间, 单位 秒* @return 当前锁唯一id，如果没有获取到，返回 null*/public static String lockFailThrowException(RedisTemplate redisTemplate, final String key, long expire){return lockFailThrowException(redisTemplate, key, expire, -1);}/*** 获取锁，到达超时时间时没有获取到，则抛出异常** @param redisTemplate redis连接* @param key redis key* @param expire 锁过期时间, 单位 秒* @param acquireTimeout 获取锁超时时间, -1代表永不超时, 单位 秒* @return 当前锁唯一id，如果没有获取到，返回 null*/public static String lockFailThrowException(RedisTemplate redisTemplate, final String key, long expire, long acquireTimeout){try {String lockId = acquireLock(redisTemplate, key, expire, acquireTimeout);if (lockId != null) {return lockId;}throw new RuntimeException("acquire lock fail");} catch (Exception e) {throw new RuntimeException("acquire lock exception", e);}}private static String acquireLock(RedisTemplate redisTemplate, String key, long expire, long acquireTimeout) throws InterruptedException {long acquireTime = -1;if (acquireTimeout != -1) {acquireTime = acquireTimeout * 1000 + System.currentTimeMillis();}synchronized (key) {String lockId = UUID.randomUUID().toString();while (true) {if (acquireTime != -1 && acquireTime < System.currentTimeMillis()) {break;}//调用tryLockboolean hasLock = tryLock(redisTemplate, key, expire, lockId);//获取锁成功if (hasLock) {return lockId;}Thread.sleep(DEFAULT_ACQUIRE_RESOLUTION_MILLIS);}}return null;}/*** 释放锁** @param redisTemplate redis连接* @param key redis key* @param lockId 当前锁唯一id*/public static void unlock(RedisTemplate redisTemplate, String key, String lockId) {try {RedisCallback<Boolean> callback = (connection) ->connection.eval(UNLOCK_LUA.getBytes(StandardCharsets.UTF_8),ReturnType.BOOLEAN, 1,(RedisPrefix.LOCK_REDIS_PREFIX + key).getBytes(StandardCharsets.UTF_8), lockId.getBytes(StandardCharsets.UTF_8));redisTemplate.execute(callback);} catch (Exception e) {log.error("release lock exception", e);}}/*** 获取当前锁的id** @param key redis key* @return 当前锁唯一id*/public static String get(RedisTemplate redisTemplate, String key) {try {RedisCallback<String> callback = (connection) -> {byte[] bytes = connection.get((RedisPrefix.LOCK_REDIS_PREFIX + key).getBytes(StandardCharsets.UTF_8));if (bytes != null){return new String(bytes, StandardCharsets.UTF_8);}return null;};return (String)redisTemplate.execute(callback);} catch (Exception e) {log.error("get lock id exception", e);}return null;}private static boolean tryLock(RedisTemplate redisTemplate, String key, long expire, String lockId) {RedisCallback<Boolean> callback = (connection) ->connection.set((RedisPrefix.LOCK_REDIS_PREFIX + key).getBytes(StandardCharsets.UTF_8),lockId.getBytes(StandardCharsets.UTF_8), Expiration.seconds(expire), RedisStringCommands.SetOption.SET_IF_ABSENT);return (Boolean)redisTemplate.execute(callback);}
}
