java使用mybatis连接数据库，查找数据库信息

java项目使用mybatis连接数据库，前面创建工程，导入jar包，数据库的创建就不说了。看关键步骤：

1.在classpath下创建SqlMapConfig.xml文件，如下：

<?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>
	<!-- 和spring整合后 environments配置将废除-->
	<environments default="development">
		<environment id="development">
		<!-- 使用jdbc事务管理-->
			<transactionManager type="JDBC" />
		<!-- 数据库连接池-->
			<dataSource type="POOLED">
				<property name="driver" value="com.mysql.jdbc.Driver" />
				<property name="url" value="jdbc:mysql://localhost:3366/mybatis" />
				<property name="username" value="root" />
				<property name="password" value="root" />
			</dataSource>
		</environment>
	</environments>	
	
	<mappers>
		<mapper resource="sqlmap/User.xml"/>		
    </mappers>
   
</configuration>

SqlMapConfig.xml是mybatis核心配置文件，上边文件的配置内容为数据源、事务管理

2.创建User类：

package mybatis;

import java.util.Date;

public class User {
	private int id;
	private String username;// 用户姓名
	private String sex;// 性别
	private Date birthday;// 生日
	private String address;// 地址
	
	
	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 getSex() {
		return sex;
	}
	public void setSex(String sex) {
		this.sex = sex;
	}
	public Date getBirthday() {
		return birthday;
	}
	public void setBirthday(Date birthday) {
		this.birthday = birthday;
	}
	public String getAddress() {
		return address;
	}
	public void setAddress(String address) {
		this.address = address;
	}
	
	@Override
	public String toString() {
		return "User [id=" + id + ", username=" + username + ", sex=" + sex
				+ ", birthday=" + birthday + ", address=" + address + "]";
	}
}

3.在classpath下的sqlmap目录下创建sql映射文件Users.xml,namespace ：命名空间，用于隔离sql语句，后面会讲另一层非常重要的作用：

<?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="test">
</mapper>

4.mybatis框架需要加载映射文件，将Users.xml添加在SqlMapConfig.xml，如下：

<mappers>
		<mapper resource="sqlmap/User.xml"/>
</mappers>

5.在user.xml中添加映射：

<!-- 根据id获取用户信息 -->
	<select id="findUserById" parameterType="int" resultType="mybatis.User">
		select * from user where id = #{id}
	</select>

parameterType：定义输入到sql中的映射类型，#{id}表示使用preparedstatement设置占位符号并将输入变量id传到sql。resultType：定义结果映射类型。

6.测试程序：

package mybatis;

import java.io.IOException;
import java.io.InputStream;

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.Before;
import org.junit.Test;

public class TestMybatis {

	//会话工厂
	private SqlSessionFactory sqlSessionFactory;

	@Before
	public void createSqlSessionFactory() throws IOException {
		// 配置文件
		String resource = "SqlMapConfig.xml";
		InputStream inputStream = Resources.getResourceAsStream(resource);
		// 使用SqlSessionFactoryBuilder从xml配置文件中创建SqlSessionFactory
		sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
	}
	// 根据 id查询用户信息
	@Test
	public void testFindUserById() {
		// 数据库会话实例
		SqlSession sqlSession = null;
		try {
			// 创建数据库会话实例sqlSession
			sqlSession = sqlSessionFactory.openSession();
			// 查询单个记录，根据用户id查询用户信息
			User user = sqlSession.selectOne("test.findUserById", 88);
			// 输出用户信息
			System.out.println(user);
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			if (sqlSession != null) {
				sqlSession.close();
			}
		}
	}
}

 输出结果：

log4j:WARN No appenders could be found for logger (org.apache.ibatis.logging.LogFactory).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
User [id=88, username=张宇, sex=2, birthday=Fri Jul 30 00:00:00 CST 1993, address=苏州市]

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