关于java.lang.IllegalStateException异常

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本文介绍了一种在启动Tomcat时遇到的异常情况及其解决办法。异常源于webapps目录下的重复web应用根目录设置，通过删除冗余目录并配置webAppRootKey参数得以解决。

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今天上午在测试某功能时启动tomcat发现异常如下：

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: 'travel.root' = [D:\apache-tomcat-6.0.37\webapps\hljmobiletravel\] instead of [D:\apache-tomcat-6.0.37\webapps\hljmobiletravel myeclipse.bak\] - Choose unique values for the 'webAppRootKey' context-param in your web.xml files!
at org.springframework.web.util.WebUtils.setWebAppRootSystemProperty(WebUtils.java:144)
at org.springframework.web.util.Log4jWebConfigurer.initLogging(Log4jWebConfigurer.java:117)
at org.springframework.web.util.Log4jConfigListener.contextInitialized(Log4jConfigListener.java:45)
at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4206)
at org.apache.catalina.core.StandardContext.start(StandardContext.java:4705)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:799)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:779)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:601)
at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1079)
at org.apache.catalina.startup.HostConfig.deployDirectories(HostConfig.java:1002)
at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:506)
at org.apache.catalina.startup.HostConfig.start(HostConfig.java:1317)
at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:324)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:142)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1065)
at org.apache.catalina.core.StandardHost.start(StandardHost.java:840)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1057)
at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:463)
at org.apache.catalina.core.StandardService.start(StandardService.java:525)
at org.apache.catalina.core.StandardServer.start(StandardServer.java:754)
at org.apache.catalina.startup.Catalina.start(Catalina.java:595)
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:597)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:289)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:414)

通过上网查找资料发现导致这个异常的原因，原来在tomcat的webapps目录下还存在一个hljmobiletravel myeclipse.bak，这个可能是由于关闭项目之后再次加载到tomcat里面生成的一个目录。解决这个异常最简单的方法就是：将hljmobiletravel myeclipse.bak删除。

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

或者在web.XML中添加webAppRootKey指定好

查看IllegalStateException源代码

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。