如下错误：
log4j:WARN No appenders could be found for logger (dao.hsqlmanager).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
解决方式一（main函数添加）：
BasicConfigurator.configure();
解决方式二（添加log4j.properties）：
# Set root logger level to DEBUG and its only appender to A1. log4j.rootLogger=DEBUG, A1 # A1 is set to be a ConsoleAppender. log4j.appender.A1=org.apache.log4j.ConsoleAppender # A1 uses PatternLayout. log4j.appender.A1.layout=org.apache.log4j.PatternLayout log4j.appender.A1.layout.ConversionPattern=%-4r [%t] %-5p %c %x - %m%n
注意：需要添加log4j依赖：
<dependency> <groupId>log4j</groupId> <artifactId>log4j</artifactId> <version>1.2.17</version> </dependency>
