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

 1 <?xml version="1.0" encoding="UTF-8" ?>
 2 <!DOCTYPE configuration
 3         PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
 4         "http://mybatis.org/dtd/mybatis-3-config.dtd">
 5 <configuration>
 6     <environments default="development">
 7         <environment id="development">
 8             <transactionManager type="JDBC"/>
 9             <dataSource type="POOLED">
10                 <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
11                 <property name="url" value="jdbc:mysql://localhost:3306/testdb?serverTimezone=UTC&amp;useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
12                 <property name="username" value="root"/>
13                 <property name="password" value="123456"/>
14             </dataSource>
15         </environment>
16     </environments>
17 
18     <mappers>
19         <mapper resource="com/xian/dao/UserMapper.xml"/>
20     </mappers>
21 </configuration>

对上面的这些代码进行优化

官方给出的样式是

 1 <?xml version="1.0" encoding="UTF-8" ?>
 2 <!DOCTYPE configuration
 3   PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
 4   "http://mybatis.org/dtd/mybatis-3-config.dtd">
 5 <configuration>
 6   <environments default="development">
 7     <environment id="development">
 8       <transactionManager type="JDBC"/>
 9       <dataSource type="POOLED">
10         <property name="driver" value="${driver}"/>
11         <property name="url" value="${url}"/>
12         <property name="username" value="${username}"/>
13         <property name="password" value="${password}"/>
14       </dataSource>
15     </environment>
16   </environments>
17   <mappers>
18     <mapper resource="org/mybatis/example/BlogMapper.xml"/>
19   </mappers>
20 </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

1 driver=com.mysql.cj.jdbc.Driver
2 url=jdbc:mysql://localhost:3306/testdb?serverTimezone=UTC&useUnicode=ture&characterEncoding=UTF-8
3 nm=root
4 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

 1 <?xml version="1.0" encoding="UTF-8" ?>
 2 <!DOCTYPE configuration
 3         PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
 4         "http://mybatis.org/dtd/mybatis-3-config.dtd">
 5 <configuration>
 6 <!--    <properties>-->
 7 <!--        <property name="useranme" value="root"/>-->
 8 <!--        <property name="pwd" value="123456"/>-->
 9 <!--    </properties>-->
10     <properties resource="db.properties">
11     </properties>
12     <environments default="development">
13         <environment id="development">
14             <transactionManager type="JDBC"/>
15             <dataSource type="POOLED">
16                 <property name="driver" value="${driver}"/>
17                 <property name="url" value="${url}"/>
18                 <property name="username" value="${nm}"/>
19                 <property name="password" value="${pwd}"/>
20             </dataSource>
21         </environment>
22     </environments>
23     <mappers>
24         <mapper resource="com/xian/dao/UserMapper.xml"/>
25     </mappers>
26 </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