JDBC

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什么是JDBC？为什么使用JDBC

所以sum公司就给出了方法然后让各个开发数据库公司实现这些方法，这样子程序员就是使用一套规则操作所有数据库，这个就是所谓的JDBC，也就是javadatebaseconnectitify

关闭流的顺序
    a)依次按resul->statement->connection顺序关闭
    b)在能完成业务的情况下，尽早关闭、

    result，statement：轻量级，创建和销毁rs所需要的时间和资源较小。

    connection：重量级，上面要关闭的两个都是通过这个来的，如果实在不行，其他可以不管，这个一定要关闭。

JDBC的六个固定步骤
   1，注册数据库驱动[利用反射]
   2，取得数据库连接对象Connection
   3，创建SQL对象
   4，执行SQL命令，并返回结果集
   5，处理结果集
   6，依次关闭结果集

基于JDBC的CURD操作

属性配置文件

driver = com.mysql.jdbc.Driver
url = jdbc:mysql://127.0.0.1:3306/mydb2
user = root
password =root

package cn.itcast.web.jdbc;

import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.Properties;

//JDBC工具类：关闭流和取得连接
public final class JdbcUtil {
	
	private static String driver;
	private static String url;
	private static String user;
	private static String password;
	
	//静态块：加载文件
	static{
		Properties props = new Properties();
		InputStream is = Crud.class.getClassLoader().getResourceAsStream("cn/itcast/web/jdbc/db.properties");
		//其实也可以不用demo3，而用this，但是因为这里是static，所以就没有this
		try {
			props.load(is);
		} catch (Exception e) {
			e.printStackTrace();
		}
		driver = props.getProperty("driver");
		url = props.getProperty("url");
		user = props.getProperty("user");
		password = props.getProperty("password");
	}
	
	//静态块：注册驱动
	static{
		try {
			Class.forName(driver);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	//取得连接
	public static Connection getMySqlConnection(){
		Connection conn = null;
		try {
			conn = DriverManager.getConnection(url,user,password);
		} catch (Exception e) {
			e.printStackTrace();
		}
		return conn;
	}
	//关闭连接	
	public static void close(ResultSet rs){
		if(rs!=null){
			try {
				rs.close();
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
	}
	public static void close(Statement stmt){
		if(stmt!=null){
			try {
				stmt.close();
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
	}
	public static void close(Connection conn){
		if(conn!=null){
			try {
				conn.close();
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
	}
}

package cn.itcast.web.jdbc;

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

import org.junit.Test;

//基于JDBC的CURD操作
public class Crud {
	@Test
	public void create(){
		Connection conn = null;
		Statement stmt = null;
		ResultSet rs = null;
		String sql = "insert into user(name,gender,salary) values(‘丝丝‘,‘女‘,3000)";
		try {
			conn = JdbcUtil.getMySqlConnection();
			stmt = conn.createStatement();
			int i = stmt.executeUpdate(sql);    //返回的是印象的行数
			System.out.println(i>0?"成功":"失败");
		} catch (Exception e) {
			e.printStackTrace();
		}finally{
			JdbcUtil.close(rs);
			JdbcUtil.close(stmt);
			JdbcUtil.close(conn);
		}
	}
	@Test
	public void read(){
		Connection conn = null;
		Statement stmt = null;
		ResultSet rs = null;
		String sql = "select * from user where gender=‘male‘";
		try {
			conn = JdbcUtil.getMySqlConnection();
			stmt = conn.createStatement();
			rs = stmt.executeQuery(sql);
			while(rs.next()){
				String name = rs.getString("name");
				String gender = rs.getString("gender");
				System.out.println(name+":"+gender);
			}
		} catch (Exception e) {
			e.printStackTrace();
		}finally{
			JdbcUtil.close(rs);
			JdbcUtil.close(stmt);
			JdbcUtil.close(conn);
		}
	}
	@Test
	public void update(){
		Connection conn = null;
		Statement stmt = null;
		ResultSet rs = null;
		String sql = "update user set gender=‘female‘ where id = 8";
		try {
			conn = JdbcUtil.getMySqlConnection();
			stmt = conn.createStatement();
			int i = stmt.executeUpdate(sql);       //返回的是影响到的行数，也就是有多少记录
			System.out.println(i>0?"成功":"失败");
		} catch (Exception e) {
			e.printStackTrace();
		}finally{
			JdbcUtil.close(rs);
			JdbcUtil.close(stmt);
			JdbcUtil.close(conn);
		}
	}
	@Test
	public void delete(){
		Connection conn = null;
		Statement stmt = null;
		ResultSet rs = null;
		String sql = "delete from user where salary IS NULL";
		try {
			conn = JdbcUtil.getMySqlConnection();
			stmt = conn.createStatement();
			int i = stmt.executeUpdate(sql);
			System.out.println(i>0?"成功":"失败");
		} catch (Exception e) {
			e.printStackTrace();
		}finally{
			JdbcUtil.close(rs);
			JdbcUtil.close(stmt);
			JdbcUtil.close(conn);
		}
	}
	@Test
	public void read(String name){
		Connection conn = null;
		Statement stmt = null;
		ResultSet rs = null;
		String sql = "select * from user where name=‘"+name+"‘";
		System.out.println("sql="+sql);
		try {
			conn = JdbcUtil.getMySqlConnection();
			stmt = conn.createStatement();
			rs = stmt.executeQuery(sql);
			while(rs.next()){
				//while(rs!=null)
				name = rs.getString("name");
				String gender = rs.getString("gender");
				System.out.println(name+":"+gender);
			}
		} catch (Exception e) {
			e.printStackTrace();
		}finally{
			JdbcUtil.close(rs);
			JdbcUtil.close(stmt);
			JdbcUtil.close(conn);
		}
	}
	public void createTable(String tableName){
	}
	public void dropTable(String tableName){
	}
	public static void main(String[] args) {
		Crud crud = new Crud();
		//crud.read(" ‘or true or‘ ");
		crud.createTable("system");
		crud.dropTable("system");
	}
}

内容补充

JDBC

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原文地址：http://my.oschina.net/u/2356176/blog/467076