在Spring中如何使用加密外部属性文件

package com.baobaotao;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.security.Key;
import java.util.Properties;
import org.springframework.beans.factory.config.PropertyPlaceholderConfigurer;
import org.springframework.core.io.Resource;
import org.springframework.util.DefaultPropertiesPersister;
import org.springframework.util.PropertiesPersister;
public class DecryptPropertyPlaceholderConfigurer
        extends PropertyPlaceholderConfigurer ...{
    private Resource[] locations;   ① 重新定义父类中的这个同名属性
    private Resource keyLocation; ② 用于指定密钥文件
    public void setKeyLocation(Resource keyLocation) ...{
        this.keyLocation = keyLocation;
    }
    public void setLocations(Resource[] locations) ...{
        this.locations = locations;
    }
    public void loadProperties(Properties props) throws IOException ...{
        if (this.locations != null) ...{
            PropertiesPersister propertiesPersister = new DefaultPropertiesPersister();
            for (int i = 0; i < this.locations.length; i++) ...{
                Resource location = this.locations[i];
                if (logger.isInfoEnabled()) ...{
                    logger.info("Loading properties file from " + location);
                }
                InputStream is = null;
                try ...{
                    is = location.getInputStream();
                        ③ 加载密钥
                    Key key = DESEncryptUtil.getKey(keyLocation.getInputStream());
                    ④ 对属性文件进行解密
is = DESEncryptUtil.doDecrypt(key, is);
⑤ 将解密后的属性流装载到props中
                    if(fileEncoding != null)...{
                        propertiesPersister.load(props,
        new InputStreamReader(is,fileEncoding));
                    }else...{
                        propertiesPersister.load(props ,is);
                    }
                } finally ...{
                    if (is != null)
                        is.close();
                }
            }
        }
    }
    }
}