mybatis基础-mybatis配置和使用

mybatis核心组件

• SqlSessionFactoryBuilder(构造器 根据配置信息或者代码来生SqlSessionFactory)
• SqlSessionFactory(依靠工厂来生成SqlSession(会话))
• SqlSession是一个既可以发送sql去执行并返回结果，也可以获取Mapper的接口

下面新建例子来看下如何利用上述组件进行操作
新建maven项目，pom.xml如下所示

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://maven.apache.org/POM/4.0.0"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.senye</groupId>
    <artifactId>mybatis</artifactId>
    <version>1.0</version>
    <!-- 数据库连接部分，以mysql为例-->
    <dependencies>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.3.0</version>
        </dependency>
        <!-- mysql数据库依赖 -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.35</version>
        </dependency>
        <!--打印日志用-->
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
        <!--测试用-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>3.8.1</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <build>
        <finalName>practice</finalName>
        <plugins>
            <!--mybatis自动生成插件-->
            <plugin>
                <groupId>org.mybatis.generator</groupId>
                <artifactId>mybatis-generator-maven-plugin</artifactId>
                <version>1.3.2</version>
                <configuration>
                    <configurationFile>src/main/resources/mybatis-generator/generatorConfig.xml</configurationFile>
                    <verbose>true</verbose>
                    <overwrite>true</overwrite>
                </configuration>
                <executions>
                    <execution>
                        <id>Generate MyBatis Artifacts</id>
                        <goals>
                            <goal>generate</goal>
                        </goals>
                    </execution>
                </executions>
                <dependencies>
                    <dependency>
                        <groupId>org.mybatis.generator</groupId>
                        <artifactId>mybatis-generator-core</artifactId>
                        <version>1.3.2</version>
                    </dependency>
                    <dependency>
                        <groupId>mysql</groupId>
                        <artifactId>mysql-connector-java</artifactId>
                        <version>5.1.38</version>
                        <scope>runtime</scope>
                    </dependency>
                </dependencies>
            </plugin>
        </plugins>
    </build>
</project>

新建数据库表blog作为测试

CREATE TABLE `blog` (
   `id` int(11) NOT NULL AUTO_INCREMENT,
   `content` varchar(45) DEFAULT NULL
   PRIMARY KEY (`id`)
 ) ENGINE=InnoDB AUTO_INCREMENT=21 DEFAULT CHARSET=utf8

为了使用mybatis-generator插件将数据表逆向生成为java代码此时可以在resources下新建文件 generatorConfig.xml如下

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE generatorConfiguration
        PUBLIC "-//mybatis.org//DTD MyBatis Generator Configuration 1.0//EN"
        "http://mybatis.org/dtd/mybatis-generator-config_1_0.dtd">
<generatorConfiguration>
    <context id="my" targetRuntime="MyBatis3">
        <commentGenerator>
            <property name="suppressDate" value="false"/>
            <property name="suppressAllComments" value="true"/>
        </commentGenerator>
        <jdbcConnection driverClass="com.mysql.jdbc.Driver"
                        connectionURL="jdbc:mysql://locaohost:3306/practice" userId="testuser"
                        password="testPassword123!@#"/>
        <javaModelGenerator targetPackage="com.senye.pojo.entity"
                            targetProject="src/main/java">
            <property name="enableSubPackages" value="true"/>
            <property name="trimStrings" value="true"/>
        </javaModelGenerator>
        <sqlMapGenerator targetPackage="mapper"
                         targetProject="src/main/resources">
            <property name="enableSubPackages" value="true"/>
        </sqlMapGenerator>
        <javaClientGenerator targetPackage="com.senye.pojo.xml"
                             targetProject="src/main/java" type="XMLMAPPER">
            <property name="enableSubPackages" value="true"/>
        </javaClientGenerator>
        <table tableName="blog" domainObjectName="Blog"
               enableCountByExample="false" enableUpdateByExample="false"
               enableDeleteByExample="false" enableSelectByExample="false"
               selectByExampleQueryId="false">
        </table>
    </context>
</generatorConfiguration>

然后cmd去到项目根目录执行 mvn mybatis-generator:generate 就可以自动生成相应的三个文件Blog.java、BlogMapper.xml、BlogMapper.java

idea编辑器可直接在右上角maven处点击插件直接生成

配置数据库

resource文件下新建mybatis-config.xml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>
    <!--属性-->
   <!-- <properties resource="jdbc.properties">
        <property name="test" value="test"></property>
    </properties>-->
    <!--设置-->
    <!--<settings>-->
        <!--<setting name="abc" value="abc"/>-->
    <!--</settings>-->
    <!--类名转换-->
   <!-- <typeAliases>
        &lt;!&ndash;测试类&ndash;&gt;
        <typeAlias type="com.senye.pojo.entity.Blog" alias="abc"></typeAlias>
    </typeAliases>-->
    <!--类型处理器-->
  <!--  <typeHandlers>
        <typeHandler jdbcType="VARCHAR" javaType="String" handler="com.senye.common.util.MyStringTypeHandler"></typeHandler>
    </typeHandlers>-->
    <!--对象工厂-->
    <!--<objectFactory type=""></objectFactory>-->
    <!--对象-->
    <!--<plugins>-->
    <!--<plugin interceptor=""></plugin>-->
    <!--</plugins>-->
    <!-- 数据库配置 -->
    <environments default="development">
        <environment id="development">
            <transactionManager type="${jdbc.transactionManager}"/>
            <dataSource type="${jdbc.dataSource}">
                <property name="driver" value="${jdbc.driver}"/>
                <property name="url" value="${jdbc.url}"/>
                <property name="username" value="${jdbc.username}"/>
                <property name="password" value="${jdbc.password}"/>
            </dataSource>
        </environment>
    </environments>
    <!-- mybatis的SQL语句和映射配置文件 -->
    <mappers>
        <mapper resource="mapper/BlogMapper.xml"/>
    </mappers>
</configuration>

文件放了所有mybatis-config.xml初始化的配置，上面有些注释的属性暂时不会用到的可以不管，核心是environments下的jdbc配置
resource文件夹下新建数据库配置jdbc.properties

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/practice?useUnicode=true&characterEncoding=utf8
jdbc.username=testuser
jdbc.password=testPassword123!@#
jdbc.transactionManager=JDBC
jdbc.dataSource=POOLED

到了这一步配置基本完成，可以写代码进行试验

新建一个工具类获取SqlSessionFactory

package com.senye.common.util;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

/**
 * mybatis工具类
 */
public class MyBatisUtil {
    private static SqlSessionFactory sqlSessionFactory;

    public static SqlSessionFactory getSqlSessionFactory() {
        if (sqlSessionFactory == null) {
            try {
                String resource = "mybatis-config.xml";
                sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream(resource));
            } catch (Exception e) {
                System.err.println(e.getMessage());
                e.printStackTrace();
            }
        }
        return sqlSessionFactory;
    }
}

通过SqlSessionFactory获取SqlSession来操作获取对应的Blog对象

package demo1;
import com.senye.common.util.MyBatisUtil;
import com.senye.pojo.xml.BlogMapper;
import org.apache.ibatis.session.SqlSession;
/**
 * 例子
 */
public class MyBatisExample {
    public static void main(String[] args) {
        SqlSession sqlSession = null;
        try {
            sqlSession = MyBatisUtil.getSqlSessionFactory().openSession();
            BlogMapper blogMapper = sqlSession.getMapper(BlogMapper.class);
            System.out.println(blogMapper.seletBlog(18));
			
			/*新增时记得调用sqlSession.commit()才回提交生效
            Blog test = new Blog();
            test.setContent("a2");
            blogMapper.insert(test);
            sqlSession.commit();*/
        } catch (Exception e) {
            sqlSession.rollback();
            if (sqlSession != null) {
                sqlSession.close();
            }
            e.printStackTrace();
        }
    }
}

为了看到执行过程的sql，可以在resource目录下新建文件log4j.properties如下

# Global logging configuration 输出debug级别以上
log4j.rootLogger=DEBUG, stdout
# Console output... log输出到控制台，ConsoleAppender表示log输出到控制台
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
# log布局
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
# 输入格式
log4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%n
log4j.logger.org.mybatis=DEBUG

整个项目的结构如下:

其它相关知识点:
mybatis初始化读取配置文件的顺序

1. 首先读取的是properties元素体内的参数
2. 然后读取的是resource配置下，例如jdbc.poroperties文件的参数，如有同名参数则覆盖
3. 读取作为方法参数传递的熟悉，如有同名参数则覆盖 此时文件如下

package com.senye.common.util;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.InputStreamReader;
import java.io.Reader;
import java.util.Properties;
/**
 * mybatis工具类
 */
public class MyBatisUtil {
    private static SqlSessionFactory sqlSessionFactory;
    public static SqlSessionFactory getSqlSessionFactory() {
        Reader cfgReader = null;
        Properties properties = null;
        if (sqlSessionFactory == null) {
            try {
                //读入默认初始化文件
                String resource = "mybatis-config.xml";
                cfgReader = new InputStreamReader(Resources.getResourceAsStream(resource));
                //读入属性文件
                Reader proReader = new InputStreamReader(Resources.getResourceAsStream("jdbc.properties"))
                properties = new Properties();
                properties.load(proReader);
                //此处可以覆盖已有参数
                properties.setProperty("username", "覆盖jdbc.properties已有的参数");
            } catch (Exception e) {

            }
            synchronized (MyBatisUtil.class) {
                if (sqlSessionFactory == null) {
                    sqlSessionFactory = new SqlSessionFactoryBuilder().build(cfgReader, properties);
                }
            }
        }
        return sqlSessionFactory;
    }
}

建议使用单一的配置文件下读取的方式，避免多种方式造成管理不方便

总结
SqlSessionFactory的责任是创建SqlSession(相当于jdbc的Connection),采用的是单例模式，对应一个数据库连接池。如果采用多例，对数据库连接的消耗较大，所以一个数据库只对应一个SqlSessionFactory，避免过多的Connection被消耗。此处的单例在多线程环境下初始化，需要加线程锁以避免类对象被多次初始化