elasticsearch-sql 增加 jdbc支持

增加该功能，纯粹是在关issue的时候看到了第一个issue,参看Is there any plan for JDBC drivers?。

大家讨论的时候，提供了两个选择，一个是apache calcite, 另外一个是利用 alibaba 的jdbc 连接池 druid。最后我选择了使用druid 来完成。为啥不用第一个的原因如下：

I have tried calcite to add this feature to es-sql. It's proved to be unsuitable. calcite kind like spark datasource API which provide scanTable,filterTabe,translateTable which means you cannot access original sql(Raw SQL) but some expressions . Also, this means join ,group by action are all done in calcite which really impact performance .

PS: 该功能还只是Demo阶段，很多功能还不完备。等稳定后会合并到原项目中。目前经过几轮PR,

• https://github.com/NLPchina/elasticsearch-sql/pull/269
• https://github.com/NLPchina/elasticsearch-sql/pull/273
• https://github.com/NLPchina/elasticsearch-sql/pull/271

elasticsearch-sql 已经支持比较复杂的SQL语法了。

安装步骤

• 下载项目  https://github.com/allwefantasy/elasticsearch-sql/tree/jdbc-support
• build jar 包
• 添加jar包到你的项目即可。

代码示例

public class JDBCTests {
    @Test
    public void testJDBC() throws Exception {
        Properties properties = new Properties();
        properties.put("url", "jdbc:elasticsearch://127.0.0.1:9300/twitter2");
        DruidDataSource dds = (DruidDataSource) ElasticSearchDruidDataSourceFactory.createDataSource(properties);
        dds.setInitialSize(1);
        Connection connection = dds.getConnection();
        PreparedStatement ps = connection.prepareStatement("SELECT split(trim(concat_ws('dd',newtype,num_d)),'dd')[0] as nt from  twitter2");
        ResultSet resultSet = ps.executeQuery();
        while (resultSet.next()) {
            System.out.println(resultSet.getString("nt"));
        }

        ps.close();
        connection.close();
        dds.close();
    }

}