1.jdbc的概述
是sun公司统一提供的一套接口规范,各个数据库生产商提供实现
注册驱动,获得连接,获得执行的SQL语句对象,释放资源
package com.learn.jdbc;import java.sql.Connection; import java.sql.DriverManager; import java.sql.SQLException;import org.junit.Test;public class Demo1 {Connection conn = null;@Testpublic void test() {try {//注册驱动Class.forName("com.mysql.jdbc.Driver");//获得连接String url = "jdbc:mysql///mydatebase";String user = "root";String password = "root";conn = DriverManager.getConnection(url, user, password);} catch (Exception e) {e.printStackTrace();//释放资源if( conn != null) {try {conn.close();} catch (SQLException e1) {e1.printStackTrace();}//垃圾回收尽快回收对象conn = null;}}} }
2.JDBC的API
connection
statement
3.JDBC的元数据MataDate(提高通用性较高的代码)
- DatabaseMetaData：获得数据库连接的信息,获得数据库的表的信息.
* 获得数据库元数据:Connection中getMetaData();
- ParameterMetaData：获得SQL中的参数的个数及类型.
* 获得参数元数据：PreparedStatement中getParameterMetaData()
- ResultSetMetaData：获得结果集中的列名及列的类型.
* 获得结果集元数据：ResultSet中getMeta()
4.元数据的使用
public void demo2(){Connection conn = null;conn = JDBCUtils2.getConnection();// 获得数据库元数据:try {DatabaseMetaData metaData = conn.getMetaData();System.out.println("获得驱动名称:"+metaData.getDriverName());System.out.println("获得驱动URL:"+metaData.getURL());System.out.println("获得用户名:"+metaData.getUserName());// 获得表中的主键：ResultSet rs = metaData.getPrimaryKeys(null, null, "category");if(rs.next()){String name = rs.getString("COLUMN_NAME");System.out.println(name);}} catch (SQLException e) {e.printStackTrace();}}
参数元数据
public void demo3(){Connection conn = null;PreparedStatement stmt = null;try{conn = JDBCUtils2.getConnection();String sql = "update category set cname = ? where cid = ?";stmt = conn.prepareStatement(sql);ParameterMetaData metaData = stmt.getParameterMetaData();int count = metaData.getParameterCount();System.out.println(count);}catch(Exception e){}}
结果集元数据
public void demo4(){Connection conn = null;PreparedStatement stmt = null;ResultSet rs = null;try{conn = JDBCUtils2.getConnection();String sql = "select * from category";stmt = conn.prepareStatement(sql);rs = stmt.executeQuery();ResultSetMetaData metaData = rs.getMetaData();int count = metaData.getColumnCount();for(int i = 1;i<=count ;i++){String name = metaData.getColumnName(i);String type = metaData.getColumnTypeName(i);System.out.println(name+type);}}catch(Exception e){}}
)
