0053、redis锁的定义以及使用

 

1、  pom.xml中引入相关依赖

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.data</groupId>
        <artifactId>spring-data-redis</artifactId>
        <version>2.2.1.RELEASE</version>
    </dependency>
    <dependency>
        <groupId>org.apache.commons</groupId>
        <artifactId>commons-lang3</artifactId>
        <version>3.8.1</version>
    </dependency>
    <dependency>
        <groupId>com.google.guava</groupId>
        <artifactId>guava</artifactId>
        <version>20.0</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-web</artifactId>
        <version>5.1.2.RELEASE</version>
    </dependency>
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <optional>true</optional>
    </dependency>
</dependencies>

 

 

2、  定义获取redis锁和释放redis锁方法的工具类

package com.example.java8test;



import com.google.common.base.Throwables;

import lombok.extern.slf4j.Slf4j;

import org.apache.commons.lang3.StringUtils;

import org.springframework.data.redis.core.RedisTemplate;

import org.springframework.stereotype.Component;



import javax.annotation.Resource;



@Component

@Slf4j

public class RedisUtils {

    @Resource

    private RedisTemplate<String,Object> redisTemplate;



    /**

     * 获取redis锁

     * @param key 键

     * @param value 当前时间 +　超时时间

     * @return　是否成功获得锁

     */

    public boolean lock(String key,String value){

        Boolean success = redisTemplate.opsForValue().setIfAbsent(key,value);

        if(null != success && success){

            return true;

        }

        String currentValue = (String) redisTemplate.opsForValue().get(key);

        //如果当前值不为空，且值小于系统时间，说明锁已过期（过期的锁由于某种原因未被删除）

        if(!StringUtils.isEmpty(currentValue) && Long.parseLong(currentValue) < System.currentTimeMillis()){

            //当两个线程都满足上边的条件，进入该if语句，需要只有一个线程能够获得锁成功返回true，另一个返回false,

            //所以需要用再次获取到的值与最开始的原值进行比较，相同才说明获得锁成功

            String oldValue = (String) redisTemplate.opsForValue().getAndSet(key,value);

            return StringUtils.isNotEmpty(oldValue) && oldValue.equals(currentValue);

        }

        return false;

    }





    public void unlock(String key,String value){

        try {

            String currentValue = (String)redisTemplate.opsForValue().get(key);

            if(!StringUtils.isEmpty(currentValue) && currentValue.equals(value)){

                redisTemplate.opsForValue().getOperations().delete(key);

            }

        } catch (Exception e) {

            log.error("redis unlock exception: {}", Throwables.getStackTraceAsString(e));

        }

    }



}

 

 

3、  在程序中使用redis锁

package com.example.java8test;



import lombok.extern.slf4j.Slf4j;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.web.bind.annotation.PostMapping;

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RestController;



@RequestMapping("/example")

@RestController

@Slf4j

public class ExampleController {

    private static final  String key = "example:redis:test:";

    @Autowired

    private RedisUtils redisUtils;



    @PostMapping("/saveRecord")

    public String saveRecord(String recordId){

        //仅是为了演示如何使用redis锁

        long time = System.currentTimeMillis();

        boolean lock = redisUtils.lock(key + recordId,String.valueOf(time + 10 * 1000));

        if(!lock){

            return "fail";

        }

        try {

            log.info("进行保存记录的相关操作");

            return "success";

        } catch (Exception e) {

            log.error("saveRecord failed: {}",e);

            return "fail";

        } finally {

            redisUtils.unlock(key + recordId,String.valueOf(time + 10 * 1000));

        }



    }



}