阿里巴巴的开源数据库连接池工具Druid数据源，在实际使用的时候，通常会和Spring或SpringBoot整合一起使用。

但有些时候如果不用使用Spring或SpringBoot，而直接使用Druid的原生API来操作数据库的话，该如何正确使用呢？

下面是一个使用Druid连接池简单操作数据库的工具类，重点关注Druid数据源的创建和复用：

/**
 * 数据库操作工具类
 *
 * @author shiyanjun
 * @since 2020/01/05
 */
@Slf4j
public class DbUtil {
    private static final String DB_URL = "jdbc:mysql://localhost:3306/authapi"; // 数据库连接URL
    private static final String DB_USERNAME = "root"; // 数据库用户名
    private static final String DB_PASSWORD = "123456"; // 数据库密码

    // Druid数据源，全局唯一（只创建一次）
    private static DruidDataSource druidDataSource;

    /**
     * 执行SQL更新
     *
     * @param updateSql
     * @throws SQLException
     */
    public static void insert(String updateSql) throws SQLException {
        Connection connection = null;
        Statement statement = null;
        ResultSet resultSet = null;
        try {
            connection = getDruidConnection();
            statement = connection.createStatement();
            int count = statement.executeUpdate(updateSql);
            log.info(">>>>>>>>>>>>> 插入数据 {}", count);
        } finally {
            // 切记!!! 一定要释放资源
            closeResource(connection, statement, resultSet);
        }
    }

    /**
     * 执行SQL查询
     *
     * @param querySql
     * @return
     * @throws Exception
     */
    public static List<Map<String, Object>> executeQuery(String querySql) throws Exception {
        List<Map<String, Object>> resultList = new ArrayList<>();
        Connection connection = null;
        Statement statement = null;
        ResultSet resultSet = null;
        try {
            connection = getDruidConnection();
            statement = connection.createStatement();
            resultSet = statement.executeQuery(querySql);
            ResultSetMetaData metaData = resultSet.getMetaData();
            while (resultSet.next()) {
                int columnCount = metaData.getColumnCount();
                Map<String, Object> resultMap = new LinkedHashMap<>();
                for (int i = 1; i <= columnCount; i++) {
                    String columnName = metaData.getColumnName(i);// 字段名称
                    Object columnValue = resultSet.getObject(columnName);// 字段值
                    resultMap.put(columnName, columnValue);
                }
                resultList.add(resultMap);
            }
            log.info(">>>>>>>>>>>> 查询数据:{}", resultList);
        } finally {
            // 切记!!! 一定要释放资源
            closeResource(connection, statement, resultSet);
        }
        return resultList;
    }

    /**
     * 获取Druid数据源
     *
     * @return
     * @throws SQLException
     */
    private static DruidDataSource getDruidDataSource() throws SQLException {
        // 保证Druid数据源在多线程下只创建一次
        if (druidDataSource == null) {
            synchronized (DbUtil.class) {
                if (druidDataSource == null) {
                    druidDataSource = createDruidDataSource();
                    return druidDataSource;
                }
            }
        }
        log.info(">>>>>>>>>>> 复用Druid数据源:url={}, username={}, password={}",
                druidDataSource.getUrl(), druidDataSource.getUsername(), druidDataSource.getPassword());
        return druidDataSource;
    }

    /**
     * 创建Druid数据源
     *
     * @return
     * @throws SQLException
     */
    private static DruidDataSource createDruidDataSource() throws SQLException {
        DruidDataSource druidDataSource = new DruidDataSource();
        druidDataSource.setUrl(DB_URL);
        druidDataSource.setUsername(DB_USERNAME);
        druidDataSource.setPassword(DB_PASSWORD);

        /*----下面的具体配置参数自己根据项目情况进行调整----*/
        druidDataSource.setMaxActive(20);
        druidDataSource.setInitialSize(1);
        druidDataSource.setMinIdle(1);
        druidDataSource.setMaxWait(60000);

        druidDataSource.setValidationQuery("select 1 from dual");

        druidDataSource.setTimeBetweenEvictionRunsMillis(60000);
        druidDataSource.setMinEvictableIdleTimeMillis(300000);

        druidDataSource.setTestWhileIdle(true);
        druidDataSource.setTestOnBorrow(false);
        druidDataSource.setTestOnReturn(false);

        druidDataSource.setPoolPreparedStatements(true);
        druidDataSource.setMaxPoolPreparedStatementPerConnectionSize(20);

        druidDataSource.init();
        log.info(">>>>>>>>>>> 创建Druid数据源:url={}, username={}, password={}",
                druidDataSource.getUrl(), druidDataSource.getUsername(), druidDataSource.getPassword());
        return druidDataSource;
    }

    /**
     * 获取Druid连接
     *
     * @return
     * @throws SQLException
     */
    private static DruidPooledConnection getDruidConnection() throws SQLException {
        DruidDataSource druidDataSource = getDruidDataSource();
        DruidPooledConnection connection = druidDataSource.getConnection();
        return connection;
    }

    /**
     * 释放资源
     *
     * @param connection
     * @param statement
     * @param resultSet
     * @throws SQLException
     */
    private static void closeResource(Connection connection,
                                      Statement statement, ResultSet resultSet) throws SQLException {
        // 注意资源释放顺序
        if (resultSet != null) {
            resultSet.close();
        }
        if (statement != null) {
            statement.close();
        }
        if (connection != null) {
            connection.close();
        }
    }
}

一个简单的测试类，模拟多线程向数据库表中插入1w条数据：

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.UUID;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
 * CREATE TABLE `auth_code` (
 * `id` int(11) NOT NULL AUTO_INCREMENT COMMENT '自增主键',
 * `auth_code` varchar(255) CHARACTER SET utf8mb4 NOT NULL COMMENT '授权码',
 * `status` varchar(255) CHARACTER SET utf8mb4 NOT NULL DEFAULT '1' COMMENT '状态',
 * `remark` varchar(255) CHARACTER SET utf8mb4 DEFAULT NULL COMMENT '备注',
 * `create_date` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '创建日期',
 * `update_time` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '修改日期',
 * PRIMARY KEY (`id`)
 * ) ENGINE=InnoDB AUTO_INCREMENT=18 DEFAULT CHARSET=latin1;
 */
public class AppTest {
    private static SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    private static ExecutorService executorService = Executors.newCachedThreadPool();// 线程池

    public static void main(String[] args) throws Exception {
        String INSERT_SQL = "INSERT INTO `authapi`.`auth_code` " +
                "(`auth_code`, `status`, `remark`, `create_date`, `update_time`) VALUES ('%s',%s,'%s','%s','%s')";
        // 模拟多线程向数据库插入1万条数据
        for (int i = 0; i < 10000; i++) {
            Thread.sleep(5);
            String code = UUID.randomUUID().toString().replaceAll("-", "");
            String dateStr = dateFormat.format(new Date());
            String formatSql = String.format(INSERT_SQL, code, i, code, dateStr, dateStr);
            executorService.execute(() -> {
                try {
                    DbUtil.insert(formatSql);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            });
        }
    }
}