创建项目：
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创建测试表
在数据库中：创建测试表user
create table user
(
id bigint not null AUTO_INCREMENT comment '主键' primary key,
age int null comment '年龄',
password varchar(32) null comment '密码',
sex int null comment '性别',
username varchar(32) null comment '用户名'
);
mybats 集成
配置数据库 db.properties
在资源文件夹下创建db子目录，然后创建db.properties文件
driver=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://localhost:3306/helloworld?useUnicode=true&characterEncoding=utf8&serverTimezone=UTC
username=root
password=root
配置mybatis: mybatis-config.xml
在资源文件夹下创建mybatis/config子目录，然后创建mybatis-config.xml 文件。注意如下几个地方:
1.引用了db.properties文件，注意路径是否配置正确
2.在 <mappers> 中配置了映射文件（后续将创建该文件）
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<properties resource="db/db.properties"/>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="${driver}"/>
<property name="url" value="${url}"/>
<property name="username" value="${username}"/>
<property name="password" value="${password}"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="mybatis/mapper/UserMapper.xml"/>
</mappers>
</configuration>
创建数据访问接口UserMapper.java
package com.example.mybatis.mapper;
import com.example.mybatis.entity.User;
public interface UserMapper {
// 从User表中查询所有记录
List<Map> selectAll_map();
// 从User表中查询指定ID的记录
Map selectByID_map(int id);
}
创建映射xml文件 UserMapper.xml
创建UserMapper.xml文件，该文件路径，应与 mybatis-conifg.xml中配置的路径匹配。
注意:
- namespase 需要与 UserMapper接口一致（接口绑定）
- id的值（selectAll_map）需要与 UserMapper接口中的方法名一致（SQL绑定：将接口中的方法，绑定到XML中定义的SQL）
- resultType指定查询结果映射类型，这里使用hashmap ，即将每条记录映射为hashmap.
<?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">
<mapper namespace="com.example.mybatis.mapper.UserMapper">
<select id="selectByID_map" resultType="hashmap">
select * from user where id = #{id}
</select>
<select id="selectAll_map" resultType="hashmap">
select * from user
</select>
</mapper>
访问数据库
@Test
public void testMybatis() throws IOException {
//创建SqlSessionFactory
String resource = "mybatis/config/mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
try (SqlSession session = sqlSessionFactory.openSession()) {
UserMapper mapper = session.getMapper(UserMapper.class);
List<Map> list = mapper.selectAll_map();
System.out.println(list);
Map map = mapper.selectByID_map(1);
System.out.println(map);
}
}
映射到实体对象 ------------
创建实体类 User.java
package com.example.mybatis.entity;
public class User {
private int id;
private String username;
private String password;
private int age;
private int sex;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public int getSex() {
return sex;
}
public void setSex(int sex) {
this.sex = sex;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", username='" + username + '\'' +
", age=" + age +
", sex=" + sex +
'}';
}
}
接口定义
User selectAll();
SQL及对象映射
<select id="selectAll" resultType="com.example.mybatis.entity.User">
select * from user
</select>
查询（返回对象）
List<User> list = mapper.selectAll();
System.out.println(list);
DELETE
<delete id="deleteUserByID">
delete from user where id = #{id}
</delete>
//接口定义
int deleteUserByID(int id);
int deleteUserByID(User user);
//测试DELETE
int n = mapper.deleteUserByID(2);
session.commit();
System.out.println(n);
//测试DELETE
User user = new User();
user.setId(2);
int n = mapper.deleteUserByID(user);
session.commit();
System.out.println(n);
INSERT
<insert id="insertUser">
insert into user (id,username,password,age,sex)
values (#{id},#{username},#{password},#{age},#{sex})
</insert>
int insertUser(User user);
int insertUser(int id,String username, String password, int sex, int age);
User user = new User();
user.setUsername("Jack");
user.setPassword("PW123456");
user.setAge(18);
int n = mapper.insertUser(user);
session.commit();
System.out.println(n);
mapper.insertUser(0, "Jack02", "PW12345678", 1, 28);
session.commit();
UPDATE
略
执行SQL
public interface SqlMapper {
//select
List<Map> selectBySql(String sql);
//insert update delete
int executeBySql(String sql);
}
<mapper namespace="com.example.mybatis.mapper.SqlMapper">
<select id="selectBySql" parameterType="String" resultType="hashmap">
${value}
</select>
<insert id="executeBySql" parameterType="String">
${value}
</insert>
</mapper>
SqlMapper mapper = session.getMapper(SqlMapper.class);
int i = mapper.executeBySql("insert into user(username,age,sex) values('bbbb',9,8)");
System.out.println(i);
session.commit();
List<Map> list = mapper.selectBySql("select * from user");
System.out.println(list);
执行SQL(批处理模式-ExecutorType.BATCH)
非批处理模式下，每执行一个SQL会访问一次数据库。
在批处理模式下，多个SQL语句只会访问一次数据库。
//使用批处理模式
try (SqlSession session = sqlSessionFactory.openSession(ExecutorType.BATCH)) {
SqlMapper mapper = session.getMapper(SqlMapper.class);
mapper.executeBySql("insert into user(username,age,sex) values('bbbb',9,8)");
mapper.executeBySql("insert into user(username,age,sex) values('bccc',9,8)");
session.commit(); //提交事务时批量操作才会写入数据库
}
-end-
