JDBC訪問embedded Derby數據庫

[b]Apache Derby:[/b] [url]http://db.apache.org/derby/index.html[/url]

最近在一個業餘項目中使用了derby數據庫來存儲task的創建及完成記錄。derby是apache的一個開源數據庫產品，有豐富的特性。它支持client/server模式外，也支持embedded模式，即只需一個包含embedded driver的jar包，就可以在代碼內啓動及關閉數據庫。在小項目中使用嵌入式的數據庫也是一個不錯的選擇。
這裏使用jdbc來連接derby進行操作並無特別之處。只需要將embedded driver包derby.jar包含進class_path,將創建driver實例，使用通常jdbc代碼即可訪問。

String driver = "org.apache.derby.jdbc.EmbeddedDriver";
Class.forName(driver).newInstance();

以下是用junit4框架寫的explore代碼：

package com.durian.derby;

import java.sql.Connection;
import java.sql.Driver;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Enumeration;
import java.util.Properties;

import org.junit.Test;

public class ExploreDerbyTest {

    @Test
    public void testCreateDB() 
        throws InstantiationException, IllegalAccessException, ClassNotFoundException, SQLException {
        String driver = "org.apache.derby.jdbc.EmbeddedDriver";
        String dbName = "derbyDB";
        String protocol = "jdbc:derby:";

        Properties props = new Properties();
        props.put("user", "user1");
        props.put("password", "password");

        Class.forName(driver).newInstance();

        System.out.println(DriverManager.getLoginTimeout());

        Enumeration<Driver> ds = DriverManager.getDrivers();
        while (ds.hasMoreElements()) {
            System.out.println(ds.nextElement());
        }
        Connection conn = DriverManager.getConnection(protocol+dbName+";create=true");
        //Properties p = conn.getClientInfo();
        //System.out.println(p);
        conn.setAutoCommit(false);

        Statement s = conn.createStatement();
        //s.execute("create table location2(num int, addr varchar(40))");
        //System.out.println(s.getFetchDirection() + " | " + 
        //        s.getFetchSize() + " | " +  s.getMaxFieldSize()  + " | " + 
        //        s.getMaxRows()  + " | " +  s.getQueryTimeout());
        conn.commit();
        conn.close();
    }

    @Test
    public void testCreateTables()
        throws ClassNotFoundException, InstantiationException, IllegalAccessException, SQLException {
        String driver = "org.apache.derby.jdbc.EmbeddedDriver";
        String protocol = "jdbc:derby:";
        String dbName="derbyDB";

        String[] sqls = {
                "create table mail_server(id int, name varchar(50), host varchar(50), port int, protocol varchar(10), is_deleted char(1), description varchar(100) )",
                "create table job_history(id int, mail_server_id int, user_id varchar(50), password varchar(50), folder_name varchar(50), befor_days int, status varchar(10), " +
                "created_time time, started_time time, stopped_time time)"
        };
        Class.forName(driver).newInstance();
        Connection conn = DriverManager.getConnection(protocol+dbName);
        conn.setAutoCommit(false);
        Statement stmt = conn.createStatement();
        for (int i = 0; i < sqls.length; i++) {
            stmt.addBatch(sqls[i]);
        }
        int[] r = stmt.executeBatch();
        System.out.println(r);
        conn.commit();
        conn.close();
    }
}

執行testCreateDB()後將在當前路徑下創建一個名爲derbyDB文件夾，包含derby數據庫的相庫文件。關於derby的配置問題，還有待研究。

由於對jdbc不是很熟悉，順便記一下jdbc訪問數據庫的過程，儘管以上代碼可以演示說明：
(1)所有相關類及接口都在包java.sql中。另外還有javax.sql,都是擴展內容
(2)由DriverManager獲得到要連接數據庫的Connection
(3)Connection創建Statement或PreparedStatement
(4)Statement或PreparedStatement執行sql語句，有可能返回ResultSet結果集。可以對ResultSet進行遍歷訪問
(5)若有insert/update/delete等數據操作，需調用Connection的commit().(如果設置爲不自動提交)
(6)conn.close()斷開與數據庫的連接。