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启动Tomcat是报错：

Web app root system property already set to different value: 'webapp.root' = [E:\AIT\poscoGroup\web\] instead of [E:\AIT\TOMCAT-6.0\webapps\posco\] - Choose unique values for the 'webAppRootKey'

解决方案：

以下是转帖：

由于懒惰想copy一份工程来做测试用因此当AVerPortal 和AverPortalTest 都在tomcat的编译项目的时候会出现错误

2010-5-14 9:45:40 org.apache.catalina.core.StandardContext listenerStart
严重: Exception sending context initialized event to listener instance of class org.springframework.web.util.Log4jConfigListener
java.lang.IllegalStateException: Web app root system property already set to different value: 'webapp.root' = [F:/JDKandTOMCAT/TOMCAT/Tomcat 6.0/webapps/AVerPortal/] instead of [F:/JDKandTOMCAT/TOMCAT/Tomcat 6.0/webapps/AVerPortalTest/] - Choose unique values for the 'webAppRootKey' context-param in your web.xml files!

原因是当在web.xml中没指定

   <context-param>
     <param-name>webAppRootKey</param-name>
     <param-value>AVerPortalTest</param-value>
 </context-param>

的时候按照默认的

做法1

      在tomcatserver启动项目目录删除AVerPortal 和AverPortalTest 其中一个

做法2

      在web.XML中添加webAppRootKey指定好

 近日，因为懒惰，直接从原有项目切出一个分块成了一个项目，然后同时发布启动，出现以下异常

Exception sending context initialized event to listener instance of class org.springframework.web.util.Log4jConfigListener
java.lang.IllegalStateException: Web app root system property already set to different value: 'webapp.root' = [D:/tomcat-5.0.19/webapps/tzbms/] instead of [D:/tomcat-5.0.19/webapps/its/] - Choose unique values for the 'webAppRootKey' context-param in your web.xml files!

at org.springframework.web.util.WebUtils.setWebAppRootSystemProperty(WebUtils.java:99)
    at org.springframework.web.util.Log4jWebConfigurer.initLogging(Log4jWebConfigurer.java:116)
    at org.springframework.web.util.Log4jConfigListener.contextInitialized(Log4jConfigListener.java:51)
    at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:3773)
    at org.apache.catalina.core.StandardContext.start(StandardContext.java:4270)
    at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:866)
    at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:850)
    at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:638)
    at org.apache.catalina.core.StandardHostDeployer.install(StandardHostDeployer.java:320)
    at org.apache.catalina.core.StandardHost.install(StandardHost.java:875)
    at org.apache.catalina.startup.HostConfig.deployWARs(HostConfig.java:657)
    at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:476)
    at org.apache.catalina.startup.HostConfig.start(HostConfig.java:1008)
    at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:394)
    at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:166)
    at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1134)
    at org.apache.catalina.core.StandardHost.start(StandardHost.java:832)
    at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1126)
    at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:521)
    at org.apache.catalina.core.StandardService.start(StandardService.java:519)
    at org.apache.catalina.core.StandardServer.start(StandardServer.java:2345)
    at org.apache.catalina.startup.Catalina.start(Catalina.java:594)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:324)
    at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:297)
    at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:398)

看看异常，还是挺简单的，应该是两个项目的设置重复了，导致出错，但我发现web.xml里并没有配置webAppRootKey项，然后查阅网上资料，参考

hwctl的专栏//blog.csdn.net/hwctl/archive/2007/07/31/1719597.aspx
，原来是因为如果没有web.xm 内没有设置webAppRootKey项，是为默认设置

public  static  void  setWebAppRootSystemProperty(ServletContext servletContext) throws IllegalStateException  {
        String  param = servletContext.getInitParameter(WEB_APP_ROOT_KEY_PARAM);
        String  key = (param != null  ? param : DEFAULT_WEB_APP_ROOT_KEY);
        String  oldValue = System .getProperty(key);
        if  (oldValue != null ) {
            throw  new  IllegalStateException ("WARNING: Web app root system property already set: "  + key + " = "  +
                                                                

            oldValue + " - Choose unique webAppRootKey values in your web.xml files!" );
        }
        String  root = servletContext.getRealPath("/" );
        if  (root == null ) {
            throw  new  IllegalStateException ("Cannot set web app root system property when WAR file is not 

expanded");
        }
        System .setProperty(key, root);
        servletContext.log("Set web app root system property: "  + key + " = "  + root);
    }

从代码看出，该方法其实就是把该web application的根目录的绝对文件路径作为属性保存在 System的属性列表中。该属性的名字，由web.xml文件中的名为"webAppRootKey"的参数值指出。如果不在web.xml中定义 webAppRootKey参数，那么属性名就是缺省的"webapp.root".在我们的petclinic项目中已经定义了 webAppRootKey参数，其值为"petclinic.root",因此，属性的名字就是"petclinic.root".

最后将webAppRootKey项配置好，错误解决。

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