Mybatis
环境:
JDK1.8
Mysql 5.7
maven 3.6.1
IDEA
回顾:
JDBC
Mysql
Java基础
Maven
Junit
SSM框架:配置文件的。 最好的方式:看官网文档;
如何获得Mybatis?
maven仓库:
<!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.2</version>
</dependency>
Github : https://github.com/mybatis/mybatis-3/releases
中文文档:https://mybatis.org/mybatis-3/zh/
数据持久化
为什么需要需要持久化?
有一些对象,不能让他丢掉。
内存太贵了
Dao层,Service层,Controller层….
帮助程序猿将数据存入到数据库中。
传统的JDBC代码太复杂了。简化。框架。自动化。
不用Mybatis也可以。更容易上手。 技术没有高低之分
优点:
缺点:
思路:搭建环境(建数据库,导入Mybatis的依赖,配置MyBatis核心配置文件,实体类pojo,工具类拿到sqlSession)–>编写接口,接口对应的mapper.xml–>测试类!
搭建数据库
CREATE DATABASE `mybatis`;
USE `mybatis`;
CREATE TABLE `user`(
`id` INT(20) NOT NULL PRIMARY KEY,
`name` VARCHAR(30) DEFAULT NULL,
`pwd` VARCHAR(30) DEFAULT NULL
)ENGINE=INNODB DEFAULT CHARSET=utf8;
INSERT INTO `user`(`id`,`name`,`pwd`) VALUES
(1,'狂神','123456'),
(2,'张三','123456'),
(3,'李四','123890')
新建项目
新建一个普通的maven项目
删除src目录
(这样一个好处是通过Maven构建的项目作为总项目将项目依赖导入pom.xml,方便管理其子模块,子模块的pom.xml不用每次都需要去导入公共依赖项)
导入maven依赖
<!--导入依赖-->
<dependencies>
<!--mysql驱动-->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.47</version>
</dependency>
<!--mybatis-->
<!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.2</version>
</dependency>
<!--junit-->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
</dependency>
</dependencies>
<!--在build中配置resources,来防止我们资源导出失败的问题-->
<build>
<resources>
<resource>
<directory>src/main/resources</directory>
<includes>
<include>**/*.properties</include>
<include>**/*.xml</include>
</includes>
</resource>
<resource>
<directory>src/main/java</directory>
<includes>
<include>**/*.properties</include>
<include>**/*.xml</include>
</includes>
<filtering>true</filtering>
</resource>
</resources>
</build>
<?xml version="1.0" encoding="UTF8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<!--configuration核心配置文件-->
<configuration>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&useUnicode=true&characterEncoding=UTF-8"/>
<property name="username" value="root"/>
<property name="password" value="root"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="com/wu/Dao/UserMapper.xml"/>
</mappers>
</configuration>
//sqlSessionFactory --> sqlSession
public class MybatisUtils {
private static SqlSessionFactory sqlSessionFactory;
static{
try {
//使用Mybatis第一步:获取sqlSessionFactory对象
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
} catch (IOException e) {
e.printStackTrace();
}
}
//既然有了 SqlSessionFactory,顾名思义,我们就可以从中获得 SqlSession 的实例了。
// SqlSession 完全包含了面向数据库执行 SQL 命令所需的所有方法。
public static SqlSession getSqlSession(){
return sqlSessionFactory.openSession();
}
}
package com.wu.pojo;
//实体类
public class User {
private int id;
private String name;
private String pwd;
public User() {
}
public User(int id, String name, String pwd) {
this.id = id;
this.name = name;
this.pwd = pwd;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPwd() {
return pwd;
}
public void setPwd(String pwd) {
this.pwd = pwd;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", name='" + name + '\'' +
", pwd='" + pwd + '\'' +
'}';
}
}
package com.wu.Dao;
import com.wu.pojo.User;
import java.util.List;
import java.util.Map;
//接口中的属性的默认是public static final
//方法是public abstract
public interface UserDao {
List<User> getUserList();//查询全部
User getUserById(int id);//通过id查询
List<User> getUserLike(String value);//模糊查询
int addUser(User user);//增
int addUser2(Map<String,Object>map);//map传值
int updateUser(User user);//改
int deleteUser(int id);//删
}
<?xml version="1.0" encoding="UTF8"?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.wu.Dao.UserDao">
<!--select查询语句-->
<select id="getUserList" resultType="com.wu.pojo.User">
select * from mybatis.user
</select>
<select id="getUserById" resultType="com.wu.pojo.User" parameterType="int">
select * from mybatis.user where id=#{id};
</select>
<select id="getUserLike" resultType="com.wu.pojo.User" parameterType="String">
select * from mybatis.user where name like "%"#{values}"%";
</select>
<insert id="addUser" parameterType="com.wu.pojo.User">
insert into mybatis.user(id,name,pwd) values(#{id},#{name},#{pwd})
</insert>
<insert id="addUser2" parameterType="Map">
insert into mybatis.user (id,name,pwd) values (#{userId},#{userName},#{userPwd});
</insert>
<update id="updateUser" parameterType="com.wu.pojo.User">
update mybatis.user set name = #{name} ,pwd = #{pwd} where id=#{id};
</update>
<delete id="deleteUser" parameterType="int">
delete from mybatis.user where id = #{id};
</delete>
</mapper>
注意:
org.apache.ibatis.binding.BindingException: Type interface com.kuang.dao.UserDao is not known to the MapperRegistry.
MapperRegistry是什么?
核心配置文件中注册 mappers
package com.wu;
import com.wu.Dao.UserDao;
import com.wu.pojo.User;
import com.wu.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class UserDaoTest {
@Test
public void test() {
//第一步:获得SqlSession对象
SqlSession sqlSession = MybatisUtils.getSqlSession();
//方式一:getMapper
UserDao userDao = sqlSession.getMapper(UserDao.class);
List<User> userLists = userDao.getUserList();
for (User userList : userLists) {
System.out.println(userList);
}
//关闭SqlSession
sqlSession.close();
}
@Test
public void getUserById() {
SqlSession sqlSession = MybatisUtils.getSqlSession();
UserDao userDao = sqlSession.getMapper(UserDao.class);
User user = userDao.getUserById(1);
System.out.println(user);
sqlSession.close();
}
@Test
public void getUserLike(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
UserDao userDao = sqlSession.getMapper(UserDao.class);
List<User> users = userDao.getUserLike("李");
for(User user:users){
System.out.println(user);
}
sqlSession.close();
}
@Test
public void addUser() {
SqlSession sqlSession = MybatisUtils.getSqlSession();
UserDao userDao = sqlSession.getMapper(UserDao.class);
userDao.addUser(new User(5, "呵呵", "root"));
sqlSession.commit();
sqlSession.close();
}
@Test
public void addUser2(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
UserDao userDao = sqlSession.getMapper(UserDao.class);
Map<String,Object>map = new HashMap<String, Object>();
map.put("userId",5);
map.put("userName","李五");
map.put("userPwd","roots");
userDao.addUser2(map);
sqlSession.commit();
sqlSession.close();
}
@Test
public void updateUser() {
SqlSession sqlSession = MybatisUtils.getSqlSession();
UserDao userMapper = sqlSession.getMapper(UserDao.class);
userMapper.updateUser(new User(4, "WXY", "666"));
sqlSession.commit();
sqlSession.close();
}
@Test
public void deleteUser(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
UserDao userDao = sqlSession.getMapper( UserDao.class);
userDao.deleteUser(5);
sqlSession.commit();
sqlSession.close();
}
}
你们可以能会遇到的问题:
<mappers>
<mapper resource="com/wu/Dao/UserMapper.xml"/>
</mappers>
出现异常
org.apache.ibatis.binding.BindingException: Type interface com.kuang.dao.UserDao is not known to the MapperRegistry.
没有在mybatis-config.xml中配置
<mappers>
<mapper resource="com/wu/Dao/UserDao.xml"/>
</mappers>
java.lang.ExceptionInInitializerError
**措施:**在maven的配置文件pom.xml配置build标签
<!--在build中配置resources,来防止我们资源导出失败的问题-->
<build>
<resources>
<resource>
<directory>src/main/resources</directory>
<includes>
<include>**/*.properties</include>
<include>**/*.xml</include>
</includes>
</resource>
<resource>
<directory>src/main/java</directory>
<includes>
<include>**/*.properties</include>
<include>**/*.xml</include>
</includes>
<filtering>true</filtering>
</resource>
</resources>
</build>
措施:将UserDao.xml和mybatis-config.xml中的"UTF-8"改为"UTF8"
Caused by: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: org.apache.ibatis.builder.BuilderException: Error creating document instance. Cause: com.sun.org.apache.xerces.internal.impl.io.MalformedByteSequenceException: **1 字节的 UTF-8 序列的字节 1 无效。**
类似映射找不到的字样可能是用于实现接口的配置文件UserDao.xml中绑定失误,比如namespace和id等属性。
UserDao //接口
List<User> getUserLike(String value);//模糊查询
UserMapper.xml
<select id="getUserLike" resultType="com.wu.pojo.User" parameterType="String">
select * from mybatis.user where name like "%"#{values}"%";
</select>
UserMapperTest.java
public void getUserLike(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
UserDao userDao = sqlSession.getMapper(UserDao.class);
List<User> users = userDao.getUserLike("李");
for(User user:users){
System.out.println(user);
}
sqlSession.close();
}
注意:
Type interface com.wu.Dao.UserMapper is not known to the MapperRegistry.(在UserMapper从哪里产生,干了什么,最终去哪里思考)
是资源导出失败问题,在pom.xml配置build标签。
<!--在build中配置resources,来防止我们资源导出失败的问题-->
<build>
<resources>
<resource>
<directory>src/main/resources</directory>
<includes>
<include>**/*.properties</include>
<include>**/*.xml</include>
</includes>
</resource>
<resource>
<directory>src/main/java</directory>
<includes>
<include>**/*.properties</include>
<include>**/*.xml</include>
</includes>
<filtering>true</filtering>
</resource>
</resources>
</build>
另外还有一种情况是,namespace那里出错,导致无法映射UserMapper。
本文地址:https://blog.csdn.net/weixin_43215223/article/details/107142676
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