Spring PropertyPlaceholderConfigurer类重写对properties属性文件加密解密启动tomcat为什么报错？

Spring对外部属性文件db.properties进行des加密后解密。重写了spring的PropertyPlaceholderConfigurer类，spring如下配置。

<bean id="propertyConfigurer"
        class="com.gamutsoft.itsm.util.DecryptPropertyPlaceholderConfigurer">
        <property name="locations">
            <list>      
                <value>classpath:db.properties</value>
            </list>
        </property>
        <property name="fileEncoding" value="utf-8"/>
    </bean>

tomcat启动正常，可以正确连接数据库，启动成功后报错

Exception invoking periodic operation:
java.lang.IllegalMonitorStateException
    at java.util.concurrent.locks.ReentrantReadWriteLock$Sync.tryReleaseShared(ReentrantReadWriteLock.java:363)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer.releaseShared(AbstractQueuedSynchronizer.java:1253)
    at java.util.concurrent.locks.ReentrantReadWriteLock$ReadLock.unlock(ReentrantReadWriteLock.java:745)
    at org.apache.catalina.core.ContainerBase.getRealmInternal(ContainerBase.java:752)
    at org.apache.catalina.core.ContainerBase.backgroundProcess(ContainerBase.java:1357)
    at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1530)
    at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.run(ContainerBase.java:1519)
    at java.lang.Thread.run(Thread.java:619)