06 使用外部属性文件

在配置文件中配置Bean时,有时需要在Bean的配置中混入系统部署的细节信息(例如文件路径,数据源配置信息等).而这些部署细节实际上需要和Bean配置相分离

Spring提供了一个PropertyPlaceholderConfigurer的BeanFactory后置处理器,这个处理器允许用户将Bean配置的部分内容外移到属性文件中.可以在Bean配置文件中使用形式为${var}的变量,PropertyPlaceholderConfigurer从属性文件中嘉爱属性,并使用这些属性来替换变量

Spring还允许在属性文件中使用${propName},以实现属性之间的相互引用

正常获取数据库连接的配置如下:

pom.xml引入c3p0和MySQL驱动:

<dependency>
    <groupId>com.mchange</groupId>
    <artifactId>c3p0</artifactId>
	<version>0.9.5.2</version>
</dependency>

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
	<version>8.0.16</version>
</dependency>

applicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd   http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
    <bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
        <property name="user" value="root"/>
        <property name="password" value="@SWZDL231100"/>
        <property name="driverClass" value="com.mysql.cj.jdbc.Driver"/>
        <property name="jdbcUrl"
                  value="jdbc:mysql://localhost:3306/wechat?useUnicode=true&amp;characterEncoding=UTF-8&amp;useJDBCCompliantTimezoneShift=true&amp;useLegacyDatetimeCode=false&amp;serverTimezone=UTC"/>
    </bean>
    
</beans>

Main.java

package relation;/*
 * @Author Sheng WenZeng
 * @Date 2019/8/10 23:31
 * @Version 1.0
 */

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import javax.sql.DataSource;
import java.sql.SQLException;

/**
 * @author Sheng Wenzeng
 * @ClassName Main
 * @Description TODO
 * @Date 2019/8/10 23:31
 * @Version 1.0
 */
public class Main {
    public static void main(String[] args) throws SQLException {
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
        DataSource dataSource = (DataSource) applicationContext.getBean("dataSource");
        System.out.println(dataSource.getConnection());
    }
}

运行结果为

com.mchange.v2.c3p0.impl.NewProxyConnection@27c6e487 [wrapping: com.mysql.cj.jdbc.ConnectionImpl@49070868]

表示连接成功

但是此时数据库密码等都在applicationContext.xml中,不方便修改,可以将这些配置放在外部的配置文件中

新建配置文件名为DataSource.properties

user=root
password=@SWZDL231100
driverClass=com.mysql.cj.jdbc.Driver
jdbcUrl=jdbc:mysql://localhost:3306/wechat?useUnicode=true&characterEncoding=UTF-8&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC

修改applicationContext.xml为:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd   http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">

    <context:property-placeholder location="relation/DataSource.properties"/>

    <bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
        <property name="user" value="${user}"/>
        <property name="password" value="${password}"/>
        <property name="driverClass" value="${driverClass}"/>
        <property name="jdbcUrl"
                  value="${jdbcUrl}"/>
    </bean>

</beans>

运行结果相同