MyBatis系列：（2）快速入门

学习一个新的组件，一要看需要哪些JAR包，二要看需要哪些配置，三要看API如何使用。

0、准备Emp数据表
MySQL语法

create table emp(
id  int(5) primary key,
name varchar(10),
sal double(8,2)
);

Oracle语法

create table emp(
id  number(5) primary key,
name varchar2(10),
sal number(8,2)
);

1、新建web工程，添加jar

需要的jar包包括三部分：mybatis的jar包、mybatis依赖的jar包、数据库驱动包

我使用的mybatis版本是mybatis-3.2.7

mybatis	mybatis-3.2.7.jar
mybatis的依赖包	位于lib目录下 asm-3.3.1.jar cglib-2.2.2.jar commons-logging-1.1.1.jar log4j-1.2.17.jar
数据库驱动	MySQL mysql-connector-java-5.1.38-bin.jar 或 Oracle ojdbc5.jar

log4j的配置文件，放到src目录下
log4j.properties

log4j.rootLogger=debug,stdout,logfile
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.SimpleLayout
log4j.appender.logfile=org.apache.log4j.FileAppender
log4j.appender.logfile.layout=org.apache.log4j.PatternLayout
log4j.appender.logfile.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %F %p %m%n
log4j.logger.com.ibatis=DEBUG
log4j.logger.com.ibatis.common.jdbc.SimpleDataSource=DEBUG
log4j.logger.com.ibatis.common.jdbc.ScriptRunner=DEBUG
log4j.logger.com.ibatis.sqlmap.engine.impl.SqlMapClientDelegate=DEBUG
log4j.logger.java.sql.Connection=DEBUG
log4j.logger.java.sql.Statement=DEBUG
log4j.logger.java.sql.PreparedStatement=DEBUG

2、创建Emp.java
Emp.java

package com.rk.entity;

public class Emp {
private Integer id;
private String name;
private Double sal;
public Emp(){}

public Emp(Integer id, String name, Double sal) {
this.id = id;
this.name = name;
this.sal = sal;
}

public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Double getSal() {
return sal;
}
public void setSal(Double sal) {
this.sal = sal;
}

}

3、在entity包下添加EmpMapper.xml文件
EmpMapper.xml

<?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属性是名称空间，必须唯一 -->
<mapper namespace="mynamespace">
<!--
insert标签：要书写insert这么一个sql语句
id属性：为insert这么一个sql语句取一个任意唯一的名字
parameterType:要执行的dao中的方法的参数，如果是类的话，必须使用全路径类
-->
<insert id="add1">
insert into emp(id,name,sal) values(1,'Tomcat',800)
</insert>
<!-- 这里用的是类的全路径：com.rk.entity.Emp -->
<insert id="add2" parameterType="com.rk.entity.Emp">
insert into emp(id,name,sal) values(#{id},#{name},#{sal});
</insert>

</mapper>

4、在src目录下创建mybatis.xml文件
mybatis.xml

<?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>
<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://127.0.0.1:3306/testdb"/>
<property name="username" value="root"/>
<property name="password" value="root"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="com/rk/entity/EmpMapper.xml"/>
</mappers>
</configuration>

5、在utils包下添加MyBatisUtils.java，并进行测试是否能够连接数据库
MyBatisUtils.java

package com.rk.utils;

import java.io.IOException;
import java.io.Reader;
import java.sql.Connection;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

public class MyBatisUtils {
private static ThreadLocal<SqlSession> threadLocal = new ThreadLocal<SqlSession>();
private static SqlSessionFactory sqlSessionFactory;
static{
try {
Reader reader = Resources.getResourceAsReader("mybatis.xml");
sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
} catch (IOException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
}
private MyBatisUtils() {}
public static SqlSession getSqlSession(){
SqlSession sqlSession = threadLocal.get();
if(sqlSession == null){
sqlSession = sqlSessionFactory.openSession();
threadLocal.set(sqlSession);
}
return sqlSession;
}

public static void closeSqlSession(){
SqlSession sqlSession = threadLocal.get();
if(sqlSession != null){
sqlSession.close();
threadLocal.remove();
}
}

public static void main(String[] args) {
Connection conn = MyBatisUtils.getSqlSession().getConnection();
System.out.println(conn!=null ? "连接成功" : "连接失败");
}
}

MyBatisUtils工具类的作用
1）在静态初始化块中加载mybatis配置文件和EmpMapper.xml文件
2）使用ThreadLocal对象让当前线程与SqlSession对象绑定在一起
3）获取当前线程中的SqlSession对象，如果没有的话，从SqlSessionFactory对象中获取SqlSession对象
4）关闭SqlSession，首先获取当前线程中的SqlSession对象，再将其关闭，释放其占用的资源

6、在dao包下添加EmpDao.java，并进行测试
EmpDao.java

package com.rk.dao;

import org.apache.ibatis.session.SqlSession;

import com.rk.entity.Emp;
import com.rk.utils.MyBatisUtils;

public class EmpDao {
/**
* 添加员工（无参数）
*/
public void add1() throws Exception {
SqlSession sqlSession = null;
try{
sqlSession = MyBatisUtils.getSqlSession();
//事务开始（默认）
//读取EmpMapper.xml映射文件中的SQL语句
int i = sqlSession.insert("mynamespace.add1");
System.out.println("本次操作影响"+i+"行数据");
//事务提交
sqlSession.commit();
}
catch(Exception e){
e.printStackTrace();
if(sqlSession != null){
//事务回滚
sqlSession.rollback();
}
}
finally{
MyBatisUtils.closeSqlSession();
}
}

/**
* 添加员工（带参数）
*/
public void add2(Emp emp) throws Exception{
SqlSession sqlSession = null;
try{
sqlSession = MyBatisUtils.getSqlSession();
//事务开始（默认）
//读取EmpMapper.xml映射文件中的SQL语句
int i = sqlSession.insert("mynamespace.add2",emp);
System.out.println("本次操作影响"+i+"行数据");
//事务提交
sqlSession.commit();
}
catch(Exception e){
e.printStackTrace();
if(sqlSession != null){
//事务回滚
sqlSession.rollback();
}
}
finally{
MyBatisUtils.closeSqlSession();
}
}

public static void main(String[] args) throws Exception {
EmpDao dao = new EmpDao();
dao.add1();
dao.add2(new Emp(2,"小明",500D));
}
}

输出：

DEBUG - Logging initialized using 'class org.apache.ibatis.logging.commons.JakartaCommonsLoggingImpl' adapter.
DEBUG - PooledDataSource forcefully closed/removed all connections.
DEBUG - PooledDataSource forcefully closed/removed all connections.
DEBUG - PooledDataSource forcefully closed/removed all connections.
DEBUG - PooledDataSource forcefully closed/removed all connections.
DEBUG - Opening JDBC Connection
DEBUG - Created connection 236749989.
DEBUG - Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@e1c84a5]
DEBUG - ==>  Preparing: insert into emp(id,name,sal) values(1,'Tomcat',800)
DEBUG - ==> Parameters:
DEBUG - <==    Updates: 1
本次操作影响1行数据
DEBUG - Committing JDBC Connection [com.mysql.jdbc.JDBC4Connection@e1c84a5]
DEBUG - Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@e1c84a5]
DEBUG - Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@e1c84a5]
DEBUG - Returned connection 236749989 to pool.
DEBUG - Opening JDBC Connection
DEBUG - Checked out connection 236749989 from pool.
DEBUG - Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@e1c84a5]
DEBUG - ==>  Preparing: insert into emp(id,name,sal) values(?,?,?);
DEBUG - ==> Parameters: 2(Integer), 小明(String), 500.0(Double)
DEBUG - <==    Updates: 1
本次操作影响1行数据
DEBUG - Committing JDBC Connection [com.mysql.jdbc.JDBC4Connection@e1c84a5]
DEBUG - Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@e1c84a5]
DEBUG - Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@e1c84a5]
DEBUG - Returned connection 236749989 to pool.

7、MyBatis工作流程

1）通过Reader对象读取src目录下的mybatis.xml配置文件(该文件的位置和名字可以任意)
2）通过SqlSessionFactoryBuilder对象创建SqlSessionFactory对象
3）从当前线程中获取SqlSession对象
4）事务开始，在mybatis中默认
5）通过SqlSession对象读取EmpMapper.xml映射文件中的操作编号，从而读取sql语句
6）事务提交（必写）
7）关闭SqlSession对象，并且分开当前线程与SqlSession对象，让GC尽早回收