mybatis详解-(2)helloworld

Love The Way You Lie 2022-06-06 00:48 142阅读 0赞

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。  
![这里写图片描述][SouthEast]

# 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">
    
    
    <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>
        
        <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" />
        </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 \[id=1, lastName=zhangsan, email=bestjinyi@163.com, gender=1\]\*\*  
> 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。

[SouthEast]: /images/20220606/1a818b9cb907423ba035c6d04f794d5e.png