java使用基于达梦数据库8.0版本的分布式锁来实现，展示一下具体代码

首先，需要引入达梦数据库的Java驱动包，可以在Maven中添加以下依赖：

<dependency>
    <groupId>dm</groupId>
    <artifactId>dmjdbc</artifactId>
    <version>8.0.0-jar-with-dependencies</version>
</dependency>

接下来，我们可以使用Java的ReentrantLock类来实现分布式锁，然后通过达梦数据库的事务来确保锁的正确性。以下是一个示例代码：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class DmLock implements Lock {

    private static final String LOCK_TABLE = "t_dm_lock";
    private static final String LOCK_NAME = "my_lock";

    private static final String URL = "jdbc:dm://localhost:5236";
    private static final String USERNAME = "username";
    private static final String PASSWORD = "password";

    private Connection connection;
    private Lock innerLock = new ReentrantLock();

    public DmLock() throws SQLException {
        connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
        createLockTable();
    }

    private void createLockTable() throws SQLException {
        String sql = "CREATE TABLE IF NOT EXISTS " + LOCK_TABLE +
                " (name VARCHAR(255) PRIMARY KEY, locked BOOLEAN)";
        try (PreparedStatement statement = connection.prepareStatement(sql)) {
            statement.executeUpdate();
        }
    }

    @Override
    public void lock() {
        innerLock.lock();
        try {
            while (!tryLock()) {
                Thread.sleep(100);
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void lockInterruptibly() throws InterruptedException {
        innerLock.lockInterruptibly();
        try {
            while (!tryLock()) {
                Thread.sleep(100);
            }
        } catch (InterruptedException e) {
            innerLock.unlock();
            throw e;
        }
    }

    @Override
    public boolean tryLock() {
        try {
            connection.setAutoCommit(false);

            String sql = "SELECT locked FROM " + LOCK_TABLE + " WHERE name = ? FOR UPDATE";
            try (PreparedStatement statement = connection.prepareStatement(sql)) {
                statement.setString(1, LOCK_NAME);
                if (!statement.execute()) {
                    return false;
                }
                if (statement.getResultSet().next()) {
                    boolean locked = statement.getResultSet().getBoolean(1);
                    if (locked) {
                        return false;
                    }
                }

                sql = "INSERT INTO " + LOCK_TABLE + " (name, locked) VALUES (?, ?)";
                try (PreparedStatement insertStatement = connection.prepareStatement(sql)) {
                    insertStatement.setString(1, LOCK_NAME);
                    insertStatement.setBoolean(2, true);
                    insertStatement.executeUpdate();
                }
                connection.commit();
                return true;
            }
        } catch (SQLException e) {
            try {
                connection.rollback();
            } catch (SQLException ex) {
                ex.printStackTrace();
            }
            return false;
        }
    }

    @Override
    public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
        long timeout = unit.toMillis(time);
        long start = System.currentTimeMillis();
        innerLock.lockInterruptibly();
        try {
            while (!tryLock()) {
                if (System.currentTimeMillis() - start >= timeout) {
                    return false;
                }
                Thread.sleep(100);
            }
        } catch (InterruptedException e) {
            innerLock.unlock();
            throw e;
        }
        return true;
    }

    @Override
    public void unlock() {
        try {
            connection.setAutoCommit(false);

            String sql = "UPDATE " + LOCK_TABLE + " SET locked = ? WHERE name = ?";
            try (PreparedStatement statement = connection.prepareStatement(sql)) {
                statement.setBoolean(1, false);
                statement.setString(2, LOCK_NAME);
                statement.executeUpdate();
            }
            connection.commit();
        } catch (SQLException e) {
            try {
                connection.rollback();
            } catch (SQLException ex) {
                ex.printStackTrace();
            }
        } finally {
            innerLock.unlock();
        }
    }

    @Override
    public Condition newCondition() {
        throw new UnsupportedOperationException();
    }
}

以上是一个基于达梦数据库8.0版本的分布式锁实现的示例代码。需要注意的是，该实现仅供参考，实际使用中需要根据具体的场景和需求进行调整和优化。