JavaWeb学习心得之JDBC对数据库CRUD

一、statement对象简介

       Jdbc中statement对象用于向数据库发送SQL语句，statement对象executeUpdate方法，用于向数据库发送增、删、改的sql语句，执行完后返回整数；executeQuery方法用于向数据库发送查询语句，返回代表查询结果的ResultSet对象。

CRUD操作

1.create

			Statement st = conn.createStatement();
			String sql = "insert into users(id,name,password,email,birthday) values (4,'天山童老','123456','[email protected]','2012-12-12')";
			int result = st.executeUpdate(sql);
			if(result>0){
				System.out.println("插入成功!!!!");
			}

2.update

			Statement st = conn.createStatement();
			String sql = "update users set name='caocao1' where name='caocao'";
			int result = st.executeUpdate(sql);
			if(result>0){
				System.out.println("跟新成功!!!!");
			}

3.delete

			Statement st = conn.createStatement();
			String sql = "delete from users where id = 4";
			int result = st.executeUpdate(sql);
			if(result>0){
				System.out.println("删除成功!!!!");
			}

4.read

			Statement st = conn.createStatement();
			String sql = "select * from users";
			ResultSet result = st.executeQuery(sql);
			while(result.next()){
				//根据获取列的数据类型，分别调用rs的相应方法映射到java对象中
			}

二、使用JDBC对数据库操作

1.环境搭建：创建表users和插入数据

CREATE DATABASE jdbcdemo CHARACTER SET utf8 COLLATE utf8_general_ci

CREATE TABLE users(
		id int PRIMARY KEY,
		name VARCHAR(40),
		password VARCHAR(40),
		email VARCHAR(60),
		birthday date 
);

INSERT INTO users(id,name,password,email,birthday) VALUES(1,'zhangfei','123456','[email protected]','1987-2-18');
INSERT INTO users(id,name,password,email,birthday) VALUES(2,'caocao','123456','[email protected]','1989-8-16');
INSERT INTO users(id,name,password,email,birthday) VALUES(3,'libai','123456','[email protected]','1995-3-22');

2.创建JavaWeb工程，并导入MySql数据库驱动

3.创建db.properties文件

4.编写JdbcUtils工具类

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

public class JdbcUtils {
	private static String url = null;
	private static String driver = null;
	private static String username = null;
	private static String password = null;
	static{
		InputStream in = JdbcUtils.class.getClassLoader().getResourceAsStream("db.properties");
		Properties properties = new Properties();
		try {
			properties.load(in);
			url = properties.getProperty("url");
			driver = properties.getProperty("driver");
			username = properties.getProperty("username");
			password = properties.getProperty("password");
			Class.forName(driver);
		} catch (Exception e) {
			e.printStackTrace();
		}finally {
			try {
				in.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}
	/*
	 * 获取数据库连接对象
	 */
	public static Connection getConnection() throws SQLException{
		return DriverManager.getConnection(url,username,password);
	}
	/*
	 *  要释放的资源包括Connection数据库连接对象，负责执行SQL命令的Statement对象，存储查询结果的ResultSet对象
	 */
	public static void release(Connection conn,Statement st,ResultSet rs){
		if(rs != null){
			try {
				rs.close();
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}
		
		if(st!=null){
			try {
				st.close();
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}
		if(conn!=null){
			try {
				conn.close();
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}
	}
}

5.CURD操作

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

public class JdbcDemo02 {
	public void insert(){
		Connection conn = null;
		Statement st = null;
		try{
			conn = JdbcUtils.getConnection();
			st = conn.createStatement();
			String sql = "insert into users(id,name,username,password,email,birthday) values(5,'唐明皇','123456','[email protected]','2001-12-12')";
			int result = st.executeUpdate(sql);
			if(result>0){
				System.out.println("插入成功");
			}
		}catch(Exception e){
			e.printStackTrace();
		}finally {
			JdbcUtils.release(conn, st, null);
		}
	}
	
	public void delete(){
		Connection conn = null;
		Statement st = null;
		try{
			conn = JdbcUtils.getConnection();
			st = conn.createStatement();
			String sql = "delete ftom users where id = 5";
			int result = st.executeUpdate(sql);
			if(result>0){
				System.out.println("删除成功");
			}
		}catch(Exception e){
			e.printStackTrace();
		}finally {
			JdbcUtils.release(conn, st, null);
		}
	}
	public void update(){
		Connection conn = null;
		Statement st = null;
		try{
			conn = JdbcUtils.getConnection();
			st = conn.createStatement();
			String sql = "update users set name = '杨贵妃' where id = 5";
			int result = st.executeUpdate(sql);
			if(result>0){
				System.out.println("跟新成功");
			}
		}catch(Exception e){
			e.printStackTrace();
		}finally {
			JdbcUtils.release(conn, st, null);
		}
	}
	
	public void find(){
		Connection conn = null;
		Statement st = null;
		ResultSet rs = null;
		try{
			conn = JdbcUtils.getConnection();
			st = conn.createStatement();
			String sql = "select * from users where id = 5";
		    rs = st.executeQuery(sql);
			if(rs.next()){
				System.out.println(rs.getString("name"));
			}
		}catch(Exception e){
			e.printStackTrace();
		}finally {
			JdbcUtils.release(conn, st, rs);
		}
	}
}

三、PreparedStatement对象简介

       　　PreperedStatement是Statement的子类，它的实例对象可以通过调用Connection.preparedStatement()方法获得，相对于Statement对象而言：PreperedStatement可以避免SQL注入的问题。
　　Statement会使数据库频繁编译SQL，可能造成数据库缓冲区溢出。PreparedStatement可对SQL进行预编译，从而提高数据库的执行效率。并且PreperedStatement对于sql中的参数，允许使用占位符的形式进行替换，简化sql语句的编写。

CURD操作

package com.hanxin;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.Date;


public class JdbcDemo3 {
	
	public void insert(){
		Connection conn = null;
		PreparedStatement st = null;
		try{
			conn = JdbcUtils.getConnection();
			String sql = "insert into users (id,name,password,email,birthday) values(?,?,?,?,?)";
			st = conn.prepareStatement(sql);
			st.setInt(1, 6);
			st.setString(2, "鲁迅");
			st.setString(3, "123456");
			st.setString(4, "[email protected]");
			st.setDate(5, new java.sql.Date(new Date().getTime()));
			int result = st.executeUpdate();
			if(result>0){
				System.out.println("插入成功");
			}
		}catch(Exception e){
			e.printStackTrace();
		}finally {
			JdbcUtils.release(conn, st, null);
		}
	}
	
	public void update(){
		Connection conn = null;
		PreparedStatement st = null;
		try{
			conn = JdbcUtils.getConnection();
			String sql = "update users set name=? where id = ?";
			st = conn.prepareStatement(sql);
			st.setString(1,"李大钊");
			st.setInt(2, 6);
			int result = st.executeUpdate();
			if(result>0){
				System.out.println("跟新成功");
			}
		}catch(Exception e){
			e.printStackTrace();
		}finally {
			JdbcUtils.release(conn, st, null);
		}
	}
	
	public void delete(){
		Connection conn = null;
		PreparedStatement st = null;
		try{
			conn = JdbcUtils.getConnection();
			String sql = "delete from users where id = ?";
			st = conn.prepareStatement(sql);
			st.setInt(1, 6);
			int result = st.executeUpdate();
			if(result>0){
				System.out.println("删除成功");
			}
		}catch(Exception e){
			e.printStackTrace();
		}finally {
			JdbcUtils.release(conn, st, null);
		}
	}
	
	public void find(){
		Connection conn = null;
		PreparedStatement st = null;
		ResultSet rs = null;
		try{
			conn = JdbcUtils.getConnection();
			String sql = "select * from users";
			st = conn.prepareStatement(sql);
			rs = st.executeQuery();
			while(rs.next()){
				System.out.println(rs.getString("name"));
			}
		}catch(Exception e){
			e.printStackTrace();
		}finally {
			JdbcUtils.release(conn, st, rs);
		}
	}
}