Mybatis细节处理之mapper.xml的存放，properties配置文件，类型别名以及创建log4j配置文件

一.解决mapper.xml存放在resources以外路径中的读取问题

在pom.xml文件最后追加< build >标签，以便可以将xml文件复制到classes中，并在程序运行时正确读取。

<build>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>

二.properties配置文件

1.对于mybatis-config.xml的核心配置中，如果存在需要频繁改动的数据内容，可以提取到properties中。

#jdbc.properties
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/example?useUnicode=true&characterEncpding=utf8
username=root
password=123456

#jdbc.properties
#有多个.properties文件时可以加上jdbc，则对应的mybatis-config.xml中${jdbc.driver}...
jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/example?useUnicode=true&characterEncpding=utf8
jdbc.username=root
jdbc.password=123456

2.修改mybatis-config.xml。注意！properties至于顶部(点击)

<?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>
	<!--添加properties配置文件路径(外部配置、动态替换)-->
    <properties resource="jdbc.properties" />

    <environments default="MySqlDB">
        <environment id="MySqlDB">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <!--使用$ + 占位符-->
                <property name="driver" value="${driver}"/>
                 <!--<property name="driver" value="${jdbc.driver}"/>-->
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="UserDaoMapper.xml" />
    </mappers>
</configuration>

 

三.类型别名

为实体类定义别名，提高书写效率。

<?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>
    <properties ... />
    
    <!--定义别名二选一-->
    <typeAliases>
        <!--定义类的别名-->
        <typeAlias type="com.cos.entity.User" alias="user" />
        
        <!--自动扫描包，将原类名作为别名-->
        <package name="com.cos.entity" />
    </typeAliases>
  
  	...
</configuration>

四.创建log4j配置文件

1.pom.xml添加log4j依赖

<!-- log4j日志依赖 https://mvnrepository.com/artifact/log4j/log4j -->
<dependency>
		<groupId>log4j</groupId>
		<artifactId>log4j</artifactId>
		<version>1.2.17</version>
</dependency>

2.创建并配置log4j.properties

# Global logging configuration
log4j.rootLogger=DEBUG, stdout
# MyBatis logging configuration...
log4j.logger.org.mybatis.example.BlogMapper=TRACE
# Console output...
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%n