Spring Boot基于数据库如何实现简单的分布式锁

 CREATE TABLE `lock_info` ( `id` bigint(20) NOT NULL, `expiration_time` datetime NOT NULL, `status` int(11) NOT NULL, `tag` varchar(255) NOT NULL, PRIMARY KEY (`id`), UNIQUE KEY `uk_tag` (`tag`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;

   4.0.0 org.springframework.bootspring-boot-starter-parent2.0.3.RELEASEcom.dalaoyangspringboot2_distributed_lock_mysql0.0.1-SNAPSHOTspringboot2_distributed_lock_mysqlspringboot2_distributed_lock_mysql 1.8  org.springframework.bootspring-boot-starter-web org.springframework.bootspring-boot-starter-data-jpa mysqlmysql-connector-javaruntime org.springframework.bootspring-boot-starter-testtest org.projectlomboklombok1.16.22provided   org.springframework.bootspring-boot-maven-plugin

 server.port=20001 ##数据库配置 ##数据库地址 spring.datasource.url=jdbc:mysql://localhost:3306/lock?characterEncoding=utf8&useSSL=false ##数据库用户名 spring.datasource.username=root ##数据库密码 spring.datasource.password=12345678 ##数据库驱动 spring.datasource.driver-class-name=com.mysql.jdbc.Driver ##validate 加载hibernate时，验证创建数据库表结构 ##create 每次加载hibernate，重新创建数据库表结构，这就是导致数据库表数据丢失的原因。 ##create-drop  加载hibernate时创建，退出是删除表结构 ##update     加载hibernate自动更新数据库结构 ##validate 启动时验证表的结构，不会创建表 ##none 启动时不做任何操作 spring.jpa.hibernate.ddl-auto=update ##控制台打印sql spring.jpa.show-sql=true ##设置innodb spring.jpa.database-platform=org.hibernate.dialect.MySQL5InnoDBDialect

 package com.dalaoyang.entity; import lombok.Data; import javax.persistence.*; import java.util.Date; @Data @Entity @Table(name = "LockInfo", uniqueConstraints={@UniqueConstraint(columnNames={"tag"},name = "uk_tag")}) public class Lock { public final static Integer LOCKED_STATUS = 1; public final static Integer UNLOCKED_STATUS = 0; /** * 主键id */ @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; /** * 锁的标示，以订单为例，可以锁订单id */ @Column(nullable = false) private String tag; /** * 过期时间 */ @Column(nullable = false) private Date expirationTime; /** * 锁状态，0，未锁，1，已经上锁 */ @Column(nullable = false) private Integer status; public Lock(String tag, Date expirationTime, Integer status) { this.tag = tag; this.expirationTime = expirationTime; this.status = status; } public Lock() { } }

 package com.dalaoyang.repository; import com.dalaoyang.entity.Lock; import org.springframework.data.jpa.repository.JpaRepository; public interface LockRepository extends JpaRepository { Lock findByTag(String tag); void deleteByTag(String tag); }

 package com.dalaoyang.service; public interface LockService { /** * 尝试获取锁 * @param tag 锁的键 * @param expiredSeconds 锁的过期时间（单位：秒），默认10s * @return */ boolean tryLock(String tag, Integer expiredSeconds); /** * 释放锁 * @param tag 锁的键 */ void unlock(String tag); }

 package com.dalaoyang.service.impl; import com.dalaoyang.entity.Lock; import com.dalaoyang.repository.LockRepository; import com.dalaoyang.service.LockService; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service; import org.springframework.transaction.annotation.Propagation; import org.springframework.transaction.annotation.Transactional; import org.springframework.util.StringUtils; import java.util.Calendar; import java.util.Date; import java.util.Objects; @Service public class LockServiceImpl implements LockService { private final Integer DEFAULT_EXPIRED_SECONDS = 10; @Autowired private LockRepository lockRepository; @Override @Transactional(rollbackFor = Throwable.class) public boolean tryLock(String tag, Integer expiredSeconds) { if (StringUtils.isEmpty(tag)) { throw new NullPointerException(); } Lock lock = lockRepository.findByTag(tag); if (Objects.isNull(lock)) { lockRepository.save(new Lock(tag, this.addSeconds(new Date(), expiredSeconds), Lock.LOCKED_STATUS)); return true; } else { Date expiredTime = lock.getExpirationTime(); Date now = new Date(); if (expiredTime.before(now)) { lock.setExpirationTime(this.addSeconds(now, expiredSeconds)); lockRepository.save(lock); return true; } } return false; } @Override @Transactional(rollbackFor = Throwable.class) public void unlock(String tag) { if (StringUtils.isEmpty(tag)) { throw new NullPointerException(); } lockRepository.deleteByTag(tag); } private Date addSeconds(Date date, Integer seconds) { if (Objects.isNull(seconds)){ seconds = DEFAULT_EXPIRED_SECONDS; } Calendar calendar = Calendar.getInstance(); calendar.setTime(date); calendar.add(Calendar.SECOND, seconds); return calendar.getTime(); } }

 package com.dalaoyang.controller; import com.dalaoyang.service.LockService; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.RestController; @RestController public class TestController { @Autowired private LockService lockService; @GetMapping("/tryLock") public Boolean tryLock(String tag, Integer expiredSeconds) { return lockService.tryLock(tag, expiredSeconds); } @GetMapping("/unlock") public Boolean unlock(String tag) { lockService.unlock(tag); return true; } @GetMapping("/test") public String test(String tag, Integer expiredSeconds) { if (lockService.tryLock(tag, expiredSeconds)) { try { //do something //这里使用睡眠两秒，方便观察获取不到锁的情况 Thread.sleep(2000); } catch (Exception e) { } finally { lockService.unlock(tag); } return "获取锁成功，tag是：" + tag; } return "当前tag：" + tag + "已经存在锁，请稍后重试！"; } }

 java -jar springboot2_distributed_lock_mysql-0.0.1-SNAPSHOT.jar --server.port=20001

 java -jar springboot2_distributed_lock_mysql-0.0.1-SNAPSHOT.jar --server.port=20000