Java乐观锁防止数据冲突的详细过程

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Version;

@Entity
public class Account {
    @Id
    private Long id;
    private Double balance;
    @Version
    private Integer version;

    // Getters and Setters
}

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;
import java.util.Date;

@Entity
public class Account {
    @Id
    private Long id;
    private Double balance;
    @Temporal(TemporalType.TIMESTAMP)
    private Date lastModified;

    // Getters and Setters
}

public class User {
    private Long id;
    private String username;
    private Integer version; // 版本号字段
}
 
// 更新用户信息时检查版本号
String sql = "UPDATE user SET username=?, version=version+1 WHERE id=? AND version=?";
int affectedRows = jdbcTemplate.update(sql, newUsername, userId, currentVersion);
if (affectedRows == 0) {
    throw new OptimisticLockException("数据已被修改，请重新加载最新版本。");
}

import java.util.concurrent.atomic.AtomicInteger;
 
public class OptimisticCounter {
    private AtomicInteger count = new AtomicInteger(0);
 
    public int increment() {
        int current;
        int next;
        do {
            current = count.get();
            next = current + 1;
        } while (!count.compareAndSet(current, next));
        return next;
    }
}

import java.util.concurrent.locks.StampedLock;
 
public class StampedLockExample {
    private final StampedLock lock = new StampedLock();
    private long version; // 版本号
    private int data;
 
    public int read() {
        long stamp = lock.tryOptimisticRead();
        int value = data;
        if (!lock.validate(stamp)) {
            // 乐观读失败，尝试加悲观锁
            stamp = lock.readLock();
            try {
                value = data;
            } finally {
                lock.unlock(stamp);
            }
        }
        return value;
    }
}