opcolumns.java

本套光盘提供了本书各章实例的所需的部分源程序文件以及数据库文件。读者 需要使用JDK 1.4(必需）版

import java.sql.*;
import java.net.URL;

class opcolumns{
public static void main (String args[]) {
String url="jdbc:microsoft:sqlserver://localhost:1433;User=JavaDB;Password=javadb;DatabaseName=northwind";
	
	String query0 = "ALTER TABLE SecondTable ADD temp Int";
 	String query1 = "ALTER TABLE SecondTable ALTER COLUMN temp smallint";
	String query = " SELECT * FROM SecondTable";
	
try {
		//加载驱动程序
		Class.forName ("com.microsoft.jdbc.sqlserver.SQLServerDriver");
		Connection con = DriverManager.getConnection (url);
		DatabaseMetaData dbmd = con.getMetaData();

		//建立一个Statement对象,用这个对象向驱动程序发送SQL语句

		Statement stmt = con.createStatement ();

		//执行SQL操作
		stmt.executeUpdate(query0);
		stmt.executeUpdate(query1);

		//显示数据表内容
		ResultSet rs = stmt.executeQuery(query);
		ResultSetMetaData rsmd = rs.getMetaData();
		displayMetadata(rsmd);

		// 关闭结果集
		rs.close();

		// 关闭statement对象
		stmt.close();

		// 关闭连接
		con.close();
	}
	catch (SQLException ex) {

		System.out.println ("\n*** SQLException caught ***\n");
		while (ex != null) {
			System.out.println ("SQLState: " + ex.getSQLState ());
			System.out.println ("Message:  " + ex.getMessage ());
			System.out.println ("Vendor:   " +	ex.getErrorCode ());
			ex = ex.getNextException ();
			System.out.println ("");
		}
	}
	catch (java.lang.Exception ex) {
			//捕获其他类型的例外
			ex.printStackTrace ();
	}
}
//显示数据表元数据
private static void displayMetadata(ResultSetMetaData rsmd)
{
try{
	int cols = rsmd.getColumnCount();
	for (int i = 1; i <= cols; i++) 
	{
        System.out.println("Column " + i);
        System.out.println("Name: " + rsmd.getColumnName(i));
        System.out.println("Class: " + rsmd.getColumnClassName(i));
        System.out.println("Type: " + rsmd.getColumnType(i));
        System.out.println("Type name: " + rsmd.getColumnTypeName(i));
	}
   }
catch(Exception e)
	{System.out.println(e.getMessage());}
}
}