Framework: A semi-finished product, a set of components, of an application that is mature, continuously upgraded software.
(1) Application: The reusable design of the whole or part of the system, expressed as a set of abstract components and the method of interaction between component instances;
(2) Purpose: Application skeleton customized by application developers
Different frameworks solve different problems. The framework encapsulates many details, enabling developers to implement functions in a minimalist way and greatly improve development efficiency.
Three-tier architecture:
Presentation layer: display data
Business layer: handles business requirements
Persistence layer: interacting with the database
JDBC技术:Connection,prepareStatement,ResultSet,JDBCTemplate
JDBC is not a framework, it is a specification, and JDBCTemplate is a tool class.
JDBC problems:
The real concern is the sql statement, and jdbc has to prepare a lot of content, which is repetitive and can be simplified.
mybatis overview:
(1) An excellent java-based persistence layer framework, which encapsulates jdbc internally , so that developers only need to pay attention to the sql statement itself, and do not need to spend energy on loading drivers, creating connections, creating statements and other complicated processes.
(2) Configure the various statements to be executed through xml or annotations, and map the java object and the sql dynamic parameters in the statement to generate the final executed sql statement. Finally, the mybatis framework executes the sql and maps the result to java object and return
(3) The ORM idea is used to solve the problem of entity and database mapping, encapsulates jdbc, and shields the underlying access details of jdbc api
ORM: object relational Mapping Object relational mapping, which maps database tables to entity classes and attributes of entity classes, so that we can operate the database by operating entity classes
Data persistence:
*Persistence is the process of converting program data in persistent state and transient state
*Memory: lost when power off
Persistence layer: the code block that completes the persistence work
The first Mybatis program:
Build the environment--->Import MyBatis--->Write code--->Test
Build the database:
New Project:
1. Create a new maven project
2. Delete src
3. Import dependencies
pom.xml:
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.kuang</groupId>
<artifactId>Mybatis-study</artifactId>
<packaging>pom</packaging>
<version>1.0-SNAPSHOT</version>
<modules>
<module>mybatis-01</module>
</modules>
<properties>
<maven.compiler.source>17</maven.compiler.source>
<maven.compiler.target>17</maven.compiler.target>
</properties>
<dependencies>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.47</version>
</dependency>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.2</version>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
</dependency>
</dependencies>
<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>
</project>
4. Create sub-projects
5. Write the mybatis core configuration file
<?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">
<!--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?userSSL=true&
userUnicode=true&characterEncoding=UTF-8"/>
<property name="username" value="root"/>
<property name="password" value="lfd011003"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="com/kuang/dao/UserMapper.xml"/>
</mappers>
</configuration>Write the tool class:
package com.kuang.utils;
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 java.io.IOException;
import java.io.InputStream;
//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，我们可以从中获得 SqlSession 的实例。SqlSession 提供了在数据库执行 SQL 命令所需的所有方法。
// 你可以通过 SqlSession 实例来直接执行已映射的 SQL 语句
public static SqlSession getSqlSession(){
return sqlSessionFactory.openSession();
}
}entity class
package com.kuang.pojo;
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 + '\'' +
'}';
}
}
Dao interface
package com.kuang.dao;
import com.kuang.pojo.User;
import java.util.List;
public interface UserDao {
List<User> getUserList();
}
interface implementation class
<?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.kuang.dao.UserDao">
<select id="getUserList" resultType="com.kuang.pojo.User">
select * from mybatis.user
</select>
</mapper>Test class:
package com.kuang.dao;
import com.kuang.pojo.User;
import com.kuang.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.util.List;
public class UserDaoTest {
@Test
public void test(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
UserDao mapper = sqlSession.getMapper(UserDao.class);
List<User> userList = mapper.getUserList();
for (User user : userList) {
System.out.println(user);
}
}
}