如何避免在tomcat的server.xml中以明文形式存储密码？DataSource的资源定义？

而对于定制工厂:

package mypackage;

....

public class MyCustomBasicDataSourceFactory extends org.apache.tomcat.dbcp.dbcp.BasicDataSourceFactory {

@Override
public Object getObjectInstance(Object obj, Name name, Context nameCtx, Hashtable environment) throws Exception {
    Object o = super.getObjectInstance(obj, name, nameCtx, environment);
    if (o != null) {
        BasicDataSource ds = (BasicDataSource) o;
        if (ds.getPassword() != null && ds.getPassword().length() > 0) {
            String pwd = MyPasswordUtilClass.unscramblePassword(ds.getPassword());
            ds.setPassword(pwd);
        }
        return ds;
    } else {
        return null;
    }
}