servlet初始化

 　　今天复习下servlet的初始化过程，如果xml配置文件没有设置<load-on-startup>大于1的数字</load-on-startup>，

tomcat启动的时候默认是不会初始化servlet的。下面是tomcat开启时，context容器standardContext执行

/**
     * Load and initialize all servlets marked "load on startup" in the
     * web application deployment descriptor.
     *
     * @param children Array of wrappers for all currently defined
     *  servlets (including those not declared load on startup)
     */
    public void loadOnStartup(Container children[]) {

        // Collect "load on startup" servlets that need to be initialized
        TreeMap map = new TreeMap();
        for (int i = 0; i < children.length; i++) {
            Wrapper wrapper = (Wrapper) children[i];
            int loadOnStartup = wrapper.getLoadOnStartup();
            if (loadOnStartup < 0)
                continue;
            Integer key = Integer.valueOf(loadOnStartup);
            ArrayList list = (ArrayList) map.get(key);
            if (list == null) {
                list = new ArrayList();
                map.put(key, list);
            }
            list.add(wrapper);
        }

        // Load the collected "load on startup" servlets
        Iterator keys = map.keySet().iterator();
        while (keys.hasNext()) {
            Integer key = (Integer) keys.next();
            ArrayList list = (ArrayList) map.get(key);
            Iterator wrappers = list.iterator();
            while (wrappers.hasNext()) {
                Wrapper wrapper = (Wrapper) wrappers.next();
                try {
                    wrapper.load();
                } catch (ServletException e) {
                    getLogger().error(sm.getString("standardWrapper.loadException",
                                      getName()), StandardWrapper.getRootCause(e));
                    // NOTE: load errors (including a servlet that throws
                    // UnavailableException from tht init() method) are NOT
                    // fatal to application startup
                }
            }
        }

    }

 如果loadOnStartup 小于0就不初始化wrapper（也就是一个servlet）。

 TreeMap默认是按key升序排列，所以loadOnStartup设置的值越大就越先初始化。