mybatis详解-(2)helloworld

本系列都是通过maven构建项目，如果不清楚maven的请先看我的maven系列
本次选用mybatis-3.2.1版本作为演示版本，log4j作为日志的实现，mysql作为数据库。

1.pom.xml配置mybatis包

<dependency>        <groupId>mysql</groupId>        <artifactId>mysql-connector-java</artifactId>        <version>5.1.35</version>    </dependency>    <dependency>        <groupId>org.mybatis</groupId>        <artifactId>mybatis</artifactId>        <version>3.2.1</version>    </dependency>    <dependency>        <groupId>org.slf4j</groupId>        <artifactId>slf4j-api</artifactId>        <version>1.7.12</version>    </dependency>    <dependency>        <groupId>org.slf4j</groupId>        <artifactId>slf4j-log4j12</artifactId>        <version>1.7.6</version>    </dependency>    <dependency>        <groupId>log4j</groupId>        <artifactId>log4j</artifactId>        <version>1.2.17</version>    </dependency>

2.引入log4j

maven工程resources文件夹创建log4j.xml文件，配置如下内容（该内容从log4j官方网站下载，未做任何修改）

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE log4j:configuration PUBLIC "-//APACHE//DTD LOG4J 1.2//EN" "log4j.dtd"><log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">  <appender name="A1" class="org.apache.log4j.FileAppender">    <param name="File"   value="A1.log" />    <param name="Append" value="false" />    <layout class="org.apache.log4j.xml.XMLLayout" />  </appender>  <appender name="STDOUT" class="org.apache.log4j.ConsoleAppender">    <layout class="org.apache.log4j.SimpleLayout" />  </appender>  <category name="org.apache.log4j.xml">    <priority value="debug" />    <appender-ref ref="A1" />  </category>  <root>    <priority value ="debug" />    <appender-ref ref="STDOUT" />  </root></log4j:configuration>

3.添加mapper配置文件

新建helloworldmapper.xml，添加如下信息（这里的数据库表mybatis_employee创建就不在演示）

<?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:命名空间-可随便写    id:唯一标识    resultType:返回值类型，想要封装成什么对象    #{id}:从传递的参数取得的值 --><mapper namespace="org.mybatis.helloworld.EmployeeMapper">    <select id="selectEmployee" resultType="org.mybatis.helloworld.Employee">        select id,last_name lastName,email,gender from mybatis_employee where id = #{id}    </select></mapper>

4.添加主配置文件

新建mybatis-config.xml文件，添加如下信息

<?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>    <!-- mybatis官方说明，可以不使用该配置文件完成操作，但是通过该配置文件可以简化很多操作 -->    <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/td_xkd" />                <property name="username" value="root" />                <property name="password" value="1234" />            </dataSource>        </environment>    </environments>    <mappers>        <mapper resource="helloworldmapper.xml" /><!-- 添加的配置文件 -->    </mappers></configuration>

5.创建实体类

新建employee.java

package org.mybatis.helloworld;public class Employee {    private Integer id;    private String lastName;    private String email;    private String gender;    public Integer getId() {        return id;    }    public void setId(Integer id) {        this.id = id;    }    public String getLastName() {        return lastName;    }    public void setLastName(String lastName) {        this.lastName = lastName;    }    public String getEmail() {        return email;    }    public void setEmail(String email) {        this.email = email;    }    public String getGender() {        return gender;    }    public void setGender(String gender) {        this.gender = gender;    }    @Override    public String toString() {        return "Employee [id=" + id + ", lastName=" + lastName + ", email=" + email                + ", gender=" + gender + "]";    }}

创建测试类

package org.mybatis.helloworld;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.Test;public class MybatisTest {    @Test    public void test1(){        //全局配置文件        String resource = "mybatis-config.xml";        InputStream inputStream = null;        SqlSessionFactory sqlSessionFactory = null;        SqlSession sqlSession = null;        try {            inputStream = Resources.getResourceAsStream(resource);            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);            sqlSession = sqlSessionFactory.openSession();//第一個参数org.mybatis.helloworld.EmployeeMapper为映射文件helloworldmapper.xml中的namespace，selectEmployee为映射文件helloworldmapper.xml中的select标签中的id。在这里拼接为一个字符串，第二個参数为传递的参数对应数据库中的id            Employee employee = sqlSession.selectOne("org.mybatis.helloworld.EmployeeMapper.selectEmployee", 1);            System.out.println(employee);        } catch (IOException e) {            e.printStackTrace();        } finally {            sqlSession.close();        }    }}

DEBUG - Logging initialized using ‘class org.apache.ibatis.logging.slf4j.Slf4jImpl’ 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 - Openning JDBC Connection
DEBUG - Created connection 503195940.
DEBUG - ooo Using Connection [com.mysql.jdbc.JDBC4Connection@1dfe2924]
**DEBUG - ==> Preparing: select id,last_name lastName,email,gender from mybatis_employee where id = ?
DEBUG - ==> Parameters: 1(Integer)
Employee [id=1, lastName=zhangsan, email=[e-mail], gender=1]**
DEBUG - Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@1dfe2924]
DEBUG - Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@1dfe2924]
DEBUG - Returned connection 503195940 to pool.

这里lastName使用的是别名：select id,last_name lastName,email,gender from mybatis_employee where id = ?
如果没有别名lastName，那么获取到的数据是null，因为mybatis暂时还没法那么智能的判别数据库使用的到底是什么名。这个会在以后的文章中指出驼峰命名来解决问题。