當我們使用log4j的時候，會出現以下錯誤：

log4j:WARN No appenders could be found for logger (org.springframework.context.support.ClassPathXmlApplicationContext).

log4j:WARN Please initialize the log4j system properly.

解決辦法：缺少一個檔案：log4j.properties（放在src下面）檔案內容如下：

### direct log messages to stdout ###
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %c:%L - %m%n


### direct messages to file hibernate.log ###
#log4j.appender.file=org.apache.log4j.FileAppender
#log4j.appender.file.File=hibernate.log
#log4j.appender.file.layout=org.apache.log4j.PatternLayout
#log4j.appender.file.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n


### set log levels - for more verbose logging change 'info' to 'debug' ###


log4j.rootLogger=warn, stdout


#log4j.logger.org.hibernate=info
#log4j.logger.org.hibernate=debug


### log HQL query parser activity
#log4j.logger.org.hibernate.hql.ast.AST=debug


### log just the SQL
#log4j.logger.org.hibernate.SQL=debug


### log JDBC bind parameters ###
#log4j.logger.org.hibernate.type=info
#log4j.logger.org.hibernate.type=debug


### log schema export/update ###
log4j.logger.org.hibernate.tool.hbm2ddl=debug


### log HQL parse trees
#log4j.logger.org.hibernate.hql=debug


### log cache activity ###
#log4j.logger.org.hibernate.cache=debug


### log transaction activity
#log4j.logger.org.hibernate.transaction=debug


### log JDBC resource acquisition
#log4j.logger.org.hibernate.jdbc=debug


### enable the following line if you want to track down connection ###
### leakages when using DriverManagerConnectionProvider ###
#log4j.logger.org.hibernate.connection.DriverManagerConnectionProvider=trace