Mybatis入门第二节--->优化

入门的时候感觉写了很多的代码，其实这些并不多

接下来对之前写的代码进行优化

首先Mybatis-config.xml

<?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.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/testdb?serverTimezone=UTC&amp;useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="com/xian/dao/UserMapper.xml"/>
    </mappers>
</configuration>

对上面的这些代码进行优化

官方给出的样式是

<?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="${driver}"/>
        <property name="url" value="${url}"/>
        <property name="username" value="${username}"/>
        <property name="password" value="${password}"/>
      </dataSource>
    </environment>
  </environments>
  <mappers>
    <mapper resource="org/mybatis/example/BlogMapper.xml"/>
  </mappers>
</configuration>

我们看到冗长的url和driver，name，pwd应该都是固定的，运用properties,引用数据简化代码

1.创建db.properties

driver=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://localhost:3306/testdb?serverTimezone=UTC&useUnicode=ture&characterEncoding=UTF-8
nm=root
pwd=123456

注意：这里的url代码就不需要&转译了

2.在mybatis-config.xml 中指定文件

<?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>-->
<!--        <property name="useranme" value="root"/>-->
<!--        <property name="pwd" value="123456"/>-->
<!--    </properties>-->
    <properties resource="db.properties">
    </properties>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${nm}"/>
                <property name="password" value="${pwd}"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/xian/dao/UserMapper.xml"/>
    </mappers>
</configuration>

注意：properties的位置一定要靠前，并且程序优先读取文件里的配置，其次才是代码块里的，注意不要写错

属性优化就到这