使用ThreadLocal、Apache的dbutils的QueryRunner和dbcp2数据库连接池的BasicDataSource封装操作数据库工具

/**
 * 数据库操作助手类
 */
public class DatabaseHelper {
    private static final Logger LOGGER = LoggerFactory.getLogger(DatabaseHelper.class);

    private static final ThreadLocal<Connection> CONNECTION_HOLDER;
    private static final QueryRunner QUERY_RUNNER;
    private static final BasicDataSource DATA_SOURCE;

    static {
        CONNECTION_HOLDER = new ThreadLocal<Connection>();
        QUERY_RUNNER = new QueryRunner();
        DATA_SOURCE = new BasicDataSource();

        Properties conf = PropsUtil.loadProps("config.properties");
        String driver = conf.getProperty("jdbc.driver");
        String url = conf.getProperty("jdbc.url");
        String username = conf.getProperty("jdbc.username");
        String password = conf.getProperty("jdbc.password");
        DATA_SOURCE.setDriverClassName(driver);
        DATA_SOURCE.setUrl(url);
        DATA_SOURCE.setUsername(username);
        DATA_SOURCE.setPassword(password);

    }

    /**
     * 获取数据库连接
     */
    public static Connection getConnection() {
        Connection connection = CONNECTION_HOLDER.get();
        if (connection == null) {
            try {
                connection = DATA_SOURCE.getConnection();
            } catch (SQLException e) {
                LOGGER.error("get connection failure", e);
                throw new RuntimeException(e);
            } finally {
                CONNECTION_HOLDER.set(connection);
            }
        }
        return connection;
    }

    /**
     * 查询实体列表
     */
    public static <T> List<T> queryEntityList(Class<T> entityClass, String sql, Object... params) {
        List<T> entityList;
        try {
            Connection conn = getConnection();
            entityList = QUERY_RUNNER.query(conn, sql, new BeanListHandler<T>(entityClass), params);
        } catch (SQLException e) {
            LOGGER.error("query entity list failure", e);
            throw new RuntimeException(e);
        }
        return entityList;
    }

    /**
     * 查询实体
     */
    public static <T> T queryEntity(Class<T> entityClass, String sql, Object... params) {
        T entity;
        try {
            Connection connection = getConnection();
            entity = QUERY_RUNNER.query(connection, sql, new BeanHandler<T>(entityClass), params);
        } catch (SQLException e) {
            LOGGER.error("query entity failure", e);
            throw new RuntimeException(e);
        }
        return entity;
    }

    /**
     * 执行查询语句
     */
    public static List<Map<String, Object>> executeQuery(String sql, Object... params) {
        List<Map<String, Object>> result;
        try {
            Connection connection = getConnection();
            result = QUERY_RUNNER.query(connection, sql, new MapListHandler(), params);
        } catch (Exception e) {
            LOGGER.error("execute query failure", e);
            throw new RuntimeException(e);
        }
        return result;
    }

    /**
     * 执行更新语句（update、insert、delete）
     */
    public static int executeUpdate(String sql, Object... params) {
        int rows = 0;
        try {
            Connection connection = getConnection();
            rows = QUERY_RUNNER.update(connection, sql, params);
        } catch (SQLException e) {
            LOGGER.error("execute update failure", e);
            throw new RuntimeException(e);
        }
        return rows;
    }

    /**
     * 插入实体
     */
    public static <T> boolean insertEntity(Class<T> entityClass, Map<String, Object> fieldMap) {
        if (CollectionUtil.isEmpty(fieldMap)) {
            LOGGER.error("can not insert entity: fieldMap is empty");
            return false;
        }

        String sql = "insert into " + getTableName(entityClass);
        StringBuilder columns = new StringBuilder(" (");
        StringBuilder values = new StringBuilder(" (");
        for (String fieldName : fieldMap.keySet()) {
            columns.append(fieldName).append(", ");
            values.append("?, ");
        }
        columns.replace(columns.lastIndexOf(", "), columns.length(), ") ");
        values.replace(values.lastIndexOf(", "), values.length(), ") ");
        sql += columns + " values " + values;

        Object[] params = fieldMap.values().toArray();
        return executeUpdate(sql, params) == 1;
    }

    /**
     * 更新实体
     */
    public static <T> boolean updateEntity(Class<T> entityClass, long id, Map<String, Object> fieldMap) {
        if (CollectionUtil.isEmpty(fieldMap)) {
            LOGGER.error("can not update entity: fieldMap is empty");
            return false;
        }

        String sql = "update " + getTableName(entityClass) + " set ";
        StringBuilder columns = new StringBuilder();
        for (String fieldName : fieldMap.keySet()) {
            columns.append(fieldName).append("=?, ");
        }
        sql += columns.substring(0, columns.lastIndexOf(", ")) + " where id=?";

        List<Object> paramList = new ArrayList<Object>();
        paramList.addAll(fieldMap.values());
        paramList.add(id);
        Object[] params = paramList.toArray();
        return executeUpdate(sql, params) == 1;
    }

    /**
     * 删除实体
     */
    public static <T> boolean deleteEntity(Class<T> entityClass, long id) {
        String sql = "delete from " + getTableName(entityClass) + " where id=?";
        return executeUpdate(sql, id) == 1;
    }

    /**
     * 通过类名获取表名
     */
    private static String getTableName(Class<?> entityClass) {
        return entityClass.getSimpleName();
    }

    /**
     * 执行SQL文件
     */
    public static void executeSqlFile(String filePath) {
        InputStream is = Thread.currentThread().getContextClassLoader().getResourceAsStream(filePath);
        BufferedReader reader = new BufferedReader(new InputStreamReader(is));
        try {
            String sql;
            while ((sql = reader.readLine()) != null) {
                executeUpdate(sql);
            }
        } catch (IOException e) {
            LOGGER.error("execute sql file failure", e);
            throw new RuntimeException(e);
        }
    }
}

DatabaseHelper

相关代码下载

需要关注的地方

1、ThreadLocal<Connection>

泛型内指定存储数据类型

2、数据库连接对象创建后不再关闭，交由BasicDataSource管理

3、java中泛型T和？

　　T用于指定参数类型或返回类型，泛型方法要在方法名前标记<T>

　　?用于泛型类型指定，如Class<?>，任意类型的Class类；List<?> list，任意类型集合