redis实现分布式锁

1、 概念

对于简单的单体项目，即运行时程序在同一个Java虚拟机中，使用Java的锁机制（synchronized或者ReentrantLock）可以解决多线程并发问题。。

package com.itheima.lock;


import org.springframework.data.redis.connection.RedisConnection;
import org.springframework.data.redis.connection.RedisConnectionFactory;
import org.springframework.data.redis.connection.RedisStringCommands;
import org.springframework.data.redis.connection.ReturnType;
import org.springframework.data.redis.core.RedisConnectionUtils;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.types.Expiration;
import org.springframework.stereotype.Repository;
import java.nio.charset.Charset;
import java.util.UUID;
import java.util.concurrent.TimeUnit;


/**
 * 基于redis实现分布式锁
 */
@Repository
public class RedisLock {


    /**
     * 解锁脚本，原子操作
     */
    private static final String unlockScript =
            "if redis.call(\"get\",KEYS[1]) == ARGV[1]\n"
                    + "then\n"
                    + "    return redis.call(\"del\",KEYS[1])\n"
                    + "else\n"
                    + "    return 0\n"
                    + "end";


    private RedisTemplate redisTemplate;


    public RedisLock(RedisTemplate redisTemplate) {
        this.redisTemplate = redisTemplate;
    }


    /**
     * 加锁，有阻塞
     *
     * @param name
     * @param expire
     * @param timeout
     * @return
     */
    public String lock(String name, long expire, long timeout) {
        long startTime = System.currentTimeMillis();
        String token;
        do {
            token = tryLock(name, expire);
            if (token == null) {
                if ((System.currentTimeMillis() - startTime) > (timeout - 50))
                    break;
                try {
                    Thread.sleep(50); //try 50 per sec
                } catch (InterruptedException e) {
                    e.printStackTrace();
                    return null;
                }
            }
        } while (token == null);


        return token;
    }


    /**
     * 加锁，无阻塞
     *
     * @param name
     * @param expire
     * @return
     */
    public String tryLock(String name, long expire) {
        name = name + "_lock";
        String token = UUID.randomUUID().toString();
        RedisConnectionFactory factory = redisTemplate.getConnectionFactory();
        RedisConnection conn = factory.getConnection();
        try {


            //参考redis命令：
            //set key value [EX seconds] [PX milliseconds] [NX|XX]
            Boolean result = conn.set(
                    name.getBytes(Charset.forName("UTF-8")),
                    token.getBytes(Charset.forName("UTF-8")),
                    Expiration.from(expire, TimeUnit.MILLISECONDS),
                    RedisStringCommands.SetOption.SET_IF_ABSENT //NX
            );
            if (result != null && result)
                return token;
        } finally {
            RedisConnectionUtils.releaseConnection(conn, factory,false);
        }
        return null;
    }


    /**
     * 解锁
     *
     * @param name
     * @param token
     * @return
     */
    public boolean unlock(String name, String token) {
        name = name + "_lock";
        byte[][] keysAndArgs = new byte[2][];
        keysAndArgs[0] = name.getBytes(Charset.forName("UTF-8"));
        keysAndArgs[1] = token.getBytes(Charset.forName("UTF-8"));
        RedisConnectionFactory factory = redisTemplate.getConnectionFactory();
        RedisConnection conn = factory.getConnection();
        try {
            Long result = (Long) conn.scriptingCommands().eval(unlockScript.getBytes(Charset.forName("UTF-8")), ReturnType.INTEGER, 1, keysAndArgs);
            if (result != null && result > 0)
                return true;
        } finally {
            RedisConnectionUtils.releaseConnection(conn, factory,false);
        }


        return false;
    }
}

复制