struts2,去掉煩人的warn

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<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
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  <layout class="org.apache.log4j.PatternLayout">
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 <category name="com.opensymphony.xwork2.ognl.OgnlValueStack">     
  <priority value="error"/>  
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 <root>
  <priority value="error"/>
  <appender-ref ref="STDOUT"/>
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</log4j:configuration>