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在Java中，分布式鎖是一種在多個(gè)JVM或多臺(tái)服務(wù)器上實(shí)現(xiàn)同步訪問(wèn)共享資源的機(jī)制，為了解決這個(gè)問(wèn)題，我們可以使用以下三種方式來(lái)實(shí)現(xiàn)分布式鎖：

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1、基于數(shù)據(jù)庫(kù)的分布式鎖

2、基于Redis的分布式鎖

3、基于Zookeeper的分布式鎖

接下來(lái)，我們將詳細(xì)介紹這三種實(shí)現(xiàn)方式的操作方法。

基于數(shù)據(jù)庫(kù)的分布式鎖

1、創(chuàng)建一個(gè)表，用于存儲(chǔ)鎖信息。

CREATE TABLE distributed_lock (
  id bigint(20) NOT NULL AUTO_INCREMENT,
  resource_id varchar(255) NOT NULL,
  lock_value varchar(255) NOT NULL,
  expire_time datetime NOT NULL,
  PRIMARY KEY (id),
  UNIQUE KEY uk_resource_id (resource_id,lock_value)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

2、在Java代碼中使用數(shù)據(jù)庫(kù)操作進(jìn)行加鎖和解鎖：

public class DistributedLock {
    private static final String LOCK_TABLE = "distributed_lock";
    private static final String LOCK_COLUMN = "lock_value";
    private static final String RESOURCE_ID = "resource_id";
    private static final String EXPIRE_TIME = "expire_time";
    public boolean lock() {
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        try {
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "password");
            String lockValue = generateLockValue(); // 生成鎖值，例如UUID
            String updateSql = "INSERT INTO " + LOCK_TABLE + "(" + RESOURCE_ID + ", " + LOCK_COLUMN + ", " + EXPIRE_TIME + ") VALUES (?, ?, NOW() + INTERVAL 30 SECOND) ON DUPLICATE KEY UPDATE " + LOCK_COLUMN + " = ?, " + EXPIRE_TIME + " = NOW() + INTERVAL 30 SECOND";
            preparedStatement = connection.prepareStatement(updateSql);
            preparedStatement.setString(1, "resource_id"); // 設(shè)置資源ID
            preparedStatement.setString(2, lockValue); // 設(shè)置鎖值
            preparedStatement.setString(3, lockValue); // 更新鎖值和過(guò)期時(shí)間
            int result = preparedStatement.executeUpdate();
            return result > 0; // 如果插入成功，則表示獲取鎖成功
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            if (preparedStatement != null) {
                try {
                    preparedStatement.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if (connection != null) {
                try {
                    connection.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        }
        return false; // 如果獲取鎖失敗，則返回false
    }
    public void unlock() {
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        try {
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "password");
            String deleteSql = "DELETE FROM " + LOCK_TABLE + " WHERE " + RESOURCE_ID + " = 'resource_id' AND " + LOCK_COLUMN + " = 'lock_value'"; // 根據(jù)資源ID和鎖值刪除記錄
            preparedStatement = connection.prepareStatement(deleteSql);
            int result = preparedStatement.executeUpdate();
            if (result > 0) { // 如果刪除成功，則表示釋放鎖成功
                System.out.println("釋放鎖成功");
            } else { // 如果刪除失敗，則表示沒(méi)有獲取到鎖，無(wú)需釋放鎖
                System.out.println("沒(méi)有獲取到鎖，無(wú)需釋放鎖");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            if (preparedStatement != null) {
                try {
                    preparedStatement.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if (connection != null) {
                try {
                    connection.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

基于Redis的分布式鎖

1、使用Redis的SETNX命令實(shí)現(xiàn)加鎖和解鎖：

import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.ValueOperations;
import java.util.concurrent.TimeUnit;
import java.util.UUID;
import javax.annotation.Resource;
import org.springframework.stereotype.Component;
import org.springframework.util.StringUtils;
@Component("distributedLock") // Spring容器中的bean名稱(chēng)為distributedLock，以便在其他類(lèi)中注入使用@Resource(name = "distributedLock") private DistributedLock distributedLock; public void doSomething() { if (distributedLock.lock()) { try { // 執(zhí)行業(yè)務(wù)邏輯 } finally { distributedLock.unlock(); } } } @Override public boolean lock() { ValueOperations valueOperations = this.redisTemplate.opsForValue(); String key = this.resourceId + this.lockValuePrefix; String lockValue = generateLockValue(); if (valueOperations.setIfAbsent(key, lockValue, this.lockExpireTime, TimeUnit.SECONDS)) { return true; } else { return false; } } @Override public void unlock() { String key = this.resourceId + this.lockValuePrefix; String lockValue = generateLockValue(); if (!StringUtils.isEmpty(lockValue)) { this.redisTemplate.delete(key); } } private String generateLockValue() { return UUID.randomUUID().toString(); } private String resourceId; private String lockValuePrefix = "lock:"; private int lockExpireTime = 30; // 默認(rèn)鎖定時(shí)間為30秒}```

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