?????? jdbc.properties配置文件中的信息（用户名、用户密码、url）是经过加密的，然后放在系统的WEB-INF文件夹下供系统使用。由于这些信息是加密的，系统将数据库连接交给了spring管理，所以在spring初始化datasource-bean装配这些属性对应的值时，必须先解密。

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<!--修改前spirng的配置文件：-->
<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
	<property name="locations">
	<list>
	<value>classpath:jdbc.properties</value>
	</list>
	</property>
</bean>
<bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
	<property name="driverClass" value="${driverClass}"></property>
	<property name="jdbcUrl" value="${jdbcUrl}"></property>
	<property name="user" value="${username}"></property>
	<property name="password" value="${password}"></property>
	<property name="initialPoolSize" value="${initialPoolSize}"></property>
	<property name="maxPoolSize" value="${maxPoolSize}"></property>
	<property name="minPoolSize" value="${minPoolSize}"></property>
	<property name="acquireIncrement" value="${acquireIncrement}"></property>
	<property name="checkoutTimeout" value="${checkoutTimeout}"></property>
	<property name="acquireRetryAttempts" value="${acquireRetryAttempts}"></property>
</bean>

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//org.springframework.beans.factory.config.PropertyPlaceholderConfi//gurer这个类是用来从指定的配置文件中取值，替换bean中的${}。我们现在要
//做的是，在从指定的配置文件中取出值返回时，对该值进行解密，再返回。对该
//类进行扩展，代码如下：

import java.util.Properties;

import org.springframework.beans.factory.config.PropertyPlaceholderConfigurer;

public class MyPropertyPlaceholderConfigurer extends
		PropertyPlaceholderConfigurer {
	
	
	@Override
	protected String resolvePlaceholder(String placeholder, Properties props) {
		String val = props.getProperty(placeholder);
		if(placeholder.equals("jdbcUrl") || placeholder.equals("username") || placeholder.equals("password")) {
			String result = DESDecrypt.execDecrypt(val);
		    return result;
		} else {
			return val;
		}
		 
	}
}

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<!-- 修改后的spirng配置文件 -->
<bean class="cn.com.jit.pki.util.MyPropertyPlaceholderConfigurer">
	<property name="locations">
	<list>
	<value>classpath:jdbc.properties</value>
	</list>
	</property>
</bean>
<bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
	<property name="driverClass" value="${driverClass}"></property>
	<property name="jdbcUrl" value="${jdbcUrl}"></property>
	<property name="user" value="${username}"></property>
	<property name="password" value="${password}"></property>
	<property name="initialPoolSize" value="${initialPoolSize}"></property>
	<property name="maxPoolSize" value="${maxPoolSize}"></property>
	<property name="minPoolSize" value="${minPoolSize}"></property>
	<property name="acquireIncrement" value="${acquireIncrement}"></property>
	<property name="checkoutTimeout" value="${checkoutTimeout}"></property>
	<property name="acquireRetryAttempts" value="${acquireRetryAttempts}"></property>
</bean>

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