spring IOC——注入外部属性文件的属性值

我们在开发数据库项目时，会将数据库的连接放入属性文件中，这时我们需要使用spring中提供的PropertyPlacholderConfigurer类，将属性文件中的值取出来注入类的属性中

applicationContext中使用PropertyPlacholderConfigurer类将properties从classpath路径加载到内存中，然后通过${}的方式，指定属性文件中的key来将属性文件中的value注入到Test的属性中

<?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:p="http://www.springframework.org/schema/p"
	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd">
	
	<bean id="property" 
		class="org.springframework.beans.factory.config.PreferencesPlaceholderConfigurer">
			<property name="locations">
				<list>
					<value>dbconfig.properties</value>
				</list>
			</property>
	</bean>
	
	<bean id="properties" class="com.test.Test">
		<property name="username" value="${username}"/>
		<property name="password" value="${password}"/>
		<property name="url" value="${url}"/>
		<property name="driver" value="${driver}"/>
	</bean>

</beans>

Test

package com.test;

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

public class Test {

	String username;
	String password;
	String url;
	String driver;
	
	
	public static void main(String[] args) {
		//取得应用程序上下文接口
		ApplicationContext apl = new ClassPathXmlApplicationContext("applicationContext.xml");
		Test getprop = (Test) apl.getBean("properties");
		System.out.println("username:"+getprop.username);
		System.out.println("password:"+getprop.password);
		System.out.println("url:"+getprop.url);
		System.out.println("driver:"+getprop.driver);
	}
	
	
	
	public String getUsername() {
		return username;
	}
	public void setUsername(String username) {
		this.username = username;
	}
	public String getPassword() {
		return password;
	}
	public void setPassword(String password) {
		this.password = password;
	}
	public String getUrl() {
		return url;
	}
	public void setUrl(String url) {
		this.url = url;
	}
	public String getDriver() {
		return driver;
	}
	public void setDriver(String driver) {
		this.driver = driver;
	}
}

properties

username = root
password = 1234
url = jdbc:mysql://localhost:3306
driver =com.mysql.jdbc.Driver