spring设置webAppRootKey

今天一个同事来问webAppRootKey 在哪设置的

<context-param>
        <param-name>webAppRootKey</param-name>
        <param-value>xxxxx.root</param-value>
    </context-param>

spring干的，代码在org.springframework.web.util.WebUtils类的setWebAppRootSystemProperty方法

代码如下，简单

public static void setWebAppRootSystemProperty(ServletContext servletContext) throws IllegalStateException {
        Assert.notNull(servletContext, "ServletContext must not be null");
        String root = servletContext.getRealPath("/");
        if (root == null) {
            throw new IllegalStateException(
                "Cannot set web app root system property when WAR file is not expanded");
        }
        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 && !StringUtils.pathEquals(oldValue, root)) {
            throw new IllegalStateException(
                "Web app root system property already set to different value: '" +
                key + "' = [" + oldValue + "] instead of [" + root + "] - " +
                "Choose unique values for the 'webAppRootKey' context-param in your web.xml files!");
        }
        System.setProperty(key, root);
        servletContext.log("Set web app root system property: '" + key + "' = [" + root + "]");
    }

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