MyBatis首次使用并查询数据库中表的数据
MyBatis首次使用并查询数据库中表的数据
1、传统Jdbc代码问题分析
public class JdbcTest {
public static void main(String[] args) {
try {
//1.加载数据库驱动
Class.forName("com.mysql.jdbc.Driver");
//2.创建连接对象
String url = "jdbc:mysql://192.168.10.137:3306/ssm";
Connection connection = DriverManager.getConnection(url,
"root",
"1111");
String sql = "select * from account";
//3.准备PreparedStatement对象
PreparedStatement pst = connection.prepareStatement(sql);
//4.执行sql语句
ResultSet rs = pst.executeQuery();
//5.遍历结果集
while(rs.next()){
Integer id = rs.getInt("id");
String name = rs.getString("name");
Double money = rs.getDouble("money");
System.out.println(id + " " + name + " " + money);
}
//6.关闭资源
rs.close();
pst.close();
connection.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
传统JDBC存在的问题
手动创建和释放链接
sql语句在代码中硬编码
对结果的解析
2、MyBatis框架概述
MyBatis是一个优秀的持久层框架，它对jdbc的操作数据库的过程进行封装，使开发者只需要关注 SQL 本身，而不需要花费精力去处理例如注册驱动、创建connection、创建statement、手动设置参数、获取结果集等jdbc繁杂的过程代码。
MyBatis 本是apache的一个开源项目iBatis, 2010年这个项目由apache software foundation 迁移到了google code，并且改名为MyBatis。iBatis一词来源于“internet”和“abatis”的组合，是一个基于Java的持久层框架。
3、MyBatis入门案例
3.1、使用idea创建一个maven项目后，修改pom.xml文件中内容为：
<properties>
<project.build.sourceEncoding>UTF-8project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8project.reporting.outputEncoding>
<maven.compiler.source>8maven.compiler.source>
<maven.compiler.target>8maven.compiler.target>
properties>
<dependencies>
<dependency>
<groupId>org.mybatisgroupId>
<artifactId>mybatisartifactId>
<version>3.4.5version>
dependency>
<dependency>
<groupId>mysqlgroupId>
<artifactId>mysql-connector-javaartifactId>
<version>5.1.47version>
dependency>
<dependency>
<groupId>log4jgroupId>
<artifactId>log4jartifactId>
<version>1.2.17version>
dependency>
<dependency>
<groupId>junitgroupId>
<artifactId>junitartifactId>
<version>4.12version>
dependency>
dependencies>
<build>
<resources>
<resource>
<directory>src/main/javadirectory>
<includes>
<include>**/*.xmlinclude>
includes>
resource>
<resource>
<directory>src/main/resourcesdirectory>
resource>
resources>
build>
3.2、在src-main-resources下创建log4j.properties和mybatis-config.xml两个配置文件
log4j.properties内容如下：
# Global logging configuration
log4j.rootLogger=DEBUG, stdout
# Console output...
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%n
mybatis-config.xml内容如下(一定要按自己的路径填写)：
DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<environments default="dev">
<environment id="dev">
<transactionManager type="JDBC">transactionManager>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/mybatis?characterEncoding=UTF-8"/>
<property name="username" value="root"/>
<property name="password" value=""/>
dataSource>
environment>
environments>
<mappers>
<mapper resource="cn/fpl1116/dao/UserDao.xml"/>
mappers>
configuration>
3.3、创建Java代码，在自定义包下创建dao包和pojo包，dao包下创建UserDao.java和UserDao.xml，pojo包下创建User.java
UserDao.java内容如下：
package cn.fpl1116.dao;
import cn.fpl1116.pojo.User;
import java.util.List;
public interface UserDao {
List<User> findAll();
}
UserDao.xml内容如下(一定要按自己的路径填写)：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--namespace：唯一，接口全类名-->
<mapper namespace="cn.fpl1116.dao.UserDao">
<!--
id：和接口方法名保持一致
resultType：和接口返回类型保持一致
-->
<select id="findAll" resultType="cn.fpl1116.pojo.User">
select * from user
</select>
</mapper>
User.java内容如下:
package cn.fpl1116.pojo;
import java.io.Serializable;
import java.util.Date;
public class User implements Serializable {
private Integer id;
private String username;
private Date birthday;
private String sex;
private String address;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public Date getBirthday() {
return birthday;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", username='" + username + '\'' +
", birthday=" + birthday +
", sex='" + sex + '\'' +
", address='" + address + '\'' +
'}';
}
}
3.4、在test下创建测试类MyBatisTest.java
内容如下：
package cn.fpl1116.test;
import cn.fpl1116.dao.UserDao;
import cn.fpl1116.pojo.User;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
public class MyBatisTest {
private InputStream inputStream;
private SqlSession sqlSession;
@Before
public void createSqlSession() throws IOException {
// 加载配置文件
String resource = "mybatis-config.xml";
inputStream = Resources.getResourceAsStream(resource);
// 创建SqlSessionFactory
SqlSessionFactory sqlSessionFactory =
new SqlSessionFactoryBuilder().build(inputStream);
//获得数据库会话实例
sqlSession = sqlSessionFactory.openSession();
}
@Test
public void testFindAll(){
UserDao userDao = sqlSession.getMapper(UserDao.class);
List<User> userList = userDao.findAll();
for(User user : userList) {
System.out.println(user);
}
}
@After
public void closeSqlSession() throws IOException {
sqlSession.close();
inputStream.close();
}
}
3.5、创建好的项目结构如下
4、创建对应的数据库mybatis
/*
Navicat MySQL Data Transfer
Source Server : localhost_3306
Source Server Version : 50732
Source Host : localhost:3306
Source Database : mybatis
Target Server Type : MYSQL
Target Server Version : 50732
File Encoding : 65001
Date: 2021-12-24 11:51:18
*/
SET FOREIGN_KEY_CHECKS=0;
-- ----------------------------
-- Table structure for account
-- ----------------------------
DROP TABLE IF EXISTS `account`;
CREATE TABLE `account` (
`id` int(11) NOT NULL COMMENT '编号',
`uid` int(11) DEFAULT NULL COMMENT '用户编号',
`money` double DEFAULT NULL COMMENT '金额',
PRIMARY KEY (`id`),
KEY `FK_Reference_8` (`uid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of account
-- ----------------------------
INSERT INTO `account` VALUES ('1', '41', '1000');
INSERT INTO `account` VALUES ('2', '45', '1000');
INSERT INTO `account` VALUES ('3', '41', '2000');
-- ----------------------------
-- Table structure for role
-- ----------------------------
DROP TABLE IF EXISTS `role`;
CREATE TABLE `role` (
`ID` int(11) NOT NULL COMMENT '编号',
`ROLE_NAME` varchar(30) DEFAULT NULL COMMENT '角色名称',
`ROLE_DESC` varchar(60) DEFAULT NULL COMMENT '角色描述',
PRIMARY KEY (`ID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of role
-- ----------------------------
INSERT INTO `role` VALUES ('1', '院长', '管理整个学院');
INSERT INTO `role` VALUES ('2', '总裁', '管理整个公司');
INSERT INTO `role` VALUES ('3', '校长', '管理整个学校');
-- ----------------------------
-- Table structure for user
-- ----------------------------
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`username` varchar(32) NOT NULL COMMENT '用户名称',
`password` varchar(20) DEFAULT NULL,
`birthday` datetime DEFAULT NULL COMMENT '生日',
`sex` char(1) DEFAULT NULL COMMENT '性别',
`address` varchar(256) DEFAULT NULL COMMENT '地址',
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=49 DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of user
-- ----------------------------
INSERT INTO `user` VALUES ('41', '张三丰', '111', '2018-02-27 17:47:08', '男', '上海徐汇');
INSERT INTO `user` VALUES ('42', '宋远桥', '111', '2018-03-02 15:09:37', '女', '北京昌平');
INSERT INTO `user` VALUES ('43', '俞莲舟', '111', '2018-03-04 11:34:34', '女', '陕西西安');
INSERT INTO `user` VALUES ('45', '张翠山', '111', '2018-03-04 12:04:06', '男', '山东济南');
INSERT INTO `user` VALUES ('46', '殷梨亭', '111', '2018-03-07 17:37:26', '男', '河北张家口');
INSERT INTO `user` VALUES ('48', '莫声谷', '111', '2018-03-08 11:44:00', '女', '山西太原');
-- ----------------------------
-- Table structure for user_role
-- ----------------------------
DROP TABLE IF EXISTS `user_role`;
CREATE TABLE `user_role` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`uid` int(11) DEFAULT NULL,
`rid` int(11) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of user_role
-- ----------------------------
INSERT INTO `user_role` VALUES ('1', '45', '1');
INSERT INTO `user_role` VALUES ('2', '41', '1');
INSERT INTO `user_role` VALUES ('3', '45', '2');
5、修改好自己数据库的账号和密码后，运行测试类结果如下:
