各类数据库的连接(java)

说出数据连接池的工作机制是什么?

J2EE服务器启动时会建立一定数量的池连接，并一直维持不少于此数目的池连接。客户端程序需要连接时，池驱动程序会返回一个未使用的池连接并将其表记为忙。如果当前没有空闲连接，池驱动程序就新建一定数量的连接，新建连接的数量由配置参数决定。当使用的池连接调用完成后，池驱动程序将此连接表记为空闲，其他调用就可以使用这个连接。

首先把使用数据库的驱动包准备好！

import java.sql.Connection;
import java.sql.DriverManager;

/**
 * 连接sqlserver2008r2
 */
public class Connect {
	public static void main(String[] args) {
		Connection conn = null;

		try {
			String url = "jdbc:jtds:sqlserver://localhost:1401;databaseName=edmms-jjjt;user=sa;password=sasa";
			Class.forName("net.sourceforge.jtds.jdbc.Driver");
			conn = DriverManager.getConnection(url);
			System.out.println("Database connection established");
		} catch (Exception e) {
			System.err.println("Cannot connect to database server");
		} finally {
			if (conn != null) {
				try {
					conn.close();
					System.out.println("Database connection terminated");
				} catch (Exception e) { /* ignore close errors */
				}
			}
		}
	}
}

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;

/**
 * java连接postgreSQL数据库。
 * */
public class TestDB {
	public TestDB() {
	}

	public static void main(String args[]) {
		try {
			Class.forName("org.postgresql.Driver").newInstance();
			String url = "jdbc:postgresql://localhost:5432/mydb";
			Connection con = DriverManager.getConnection(url, "postgres", "julong");
			Statement st = con.createStatement();
			//String sql = "select * from cities";
			String sql = "insert into organization(sn,title,remark) values(22,'123','测试序号')";
			ResultSet rs = st.executeQuery(sql);
			while (rs.next()) {
				System.out.println(rs.getString(1));
				System.out.println(rs.getString(2));
			}
			rs.close();
			st.close();
			con.close();

		} catch (Exception ee) {
			System.out.print(ee.getMessage());
		}
	}
}

import java.sql.Connection;
import java.sql.DriverManager;

public class MySqlConnect
   {
       public static void main (String[] args)
       {
           Connection conn = null;

           try
           {
               String userName = "root";
               String password = "root";
               String url = "jdbc:mysql://localhost/test";
               Class.forName ("com.mysql.jdbc.Driver").newInstance ();
               conn = DriverManager.getConnection (url, userName, password);
               System.out.println ("Database connection established");
           }
           catch (Exception e)
           {
               System.err.println ("Cannot connect to database server");
           }
           finally
           {
               if (conn != null)
               {
                   try
                   {
                       conn.close ();
                       System.out.println ("Database connection terminated");
                   }
                   catch (Exception e) { /* ignore close errors */ }
               }
           }
       }
   }

Java中数据库驱动程序加载及建立连接

//Oracle数据库:
Class.forName("oracle.jdbc.driver.OracleDriver");
Connection conn = DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:orcl" , "username" , "password");
//注:orcl为数据库的SID
//DB2数据库:
Class.forName("com.ibm.db2.jdbc.app.DB2Driver");
Connection conn = DriverManager.getConnection("jdbc:db2://localhost:5000/dbname" , "username" , "password");
// 注:dbname为数据库名
//SQL Server 2000数据库:
Class.forName("com.microsoft.jdbc.sqlserver.SQLServerDriver");
Connection conn = DriverManager.getConnection("jdbc:microsoft:sqlserver://localhost:1443;DatabaseName=dbaname" , "username" , "password");
//注:dbname为数据库名
//Sybase数据库:
Class.forName("com.sybase.jdbc.SybDriver");
Connection conn = DriverManager.getConnection("jdbc:sybase:Tds:localhost:5007/dbname" , "username" , "password");
注:dbname为数据库名
//Informix数据库:
Class.forName("com.informix.jdbc.IfxDriver");
//MySQL数据库:
Class.forName("org.gjt.mm.mysql.Driver"); 或者 Class.forName("com.mysql.jdbc.Driver");
Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/dbname" , "username" , "password");
//注:dbname为数据库名