tomcat源码之处理web.xml中<load-on-startup>标签

/**
* 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)
*/
/**
* StandardContext类，代表webapps目录下的一个web应用
* 方法会被startInternal调用()，也就是应用在启动的时候
* @param children
* @return
*/
public boolean loadOnStartup(Container children[]) {

// Collect "load on startup" servlets that need to be initialized
//用TreeMap来排序 默认为natural order，也就是按ascii码
TreeMap<Integer, ArrayList<Wrapper>> map =
new TreeMap<Integer, ArrayList<Wrapper>>();
for (int i = 0; i < children.length; i++) {
Wrapper wrapper = (Wrapper) children[i];
//每个Wrapper对应一个Servlet，负责创建、初始化、销毁servlet，并为其提供ServletConfig
int loadOnStartup = wrapper.getLoadOnStartup();
if (loadOnStartup < 0) //如果loadOnStartup的配置参数小于0，则不添加到TreeMap中
continue;
Integer key = Integer.valueOf(loadOnStartup);
ArrayList<Wrapper> list = map.get(key);
if (list == null) {
list = new ArrayList<Wrapper>();
map.put(key, list);
}
list.add(wrapper);
}

// Load the collected "load on startup" servlets
//按loadOnStartup 的natural order即升序，依次对servlet进行初始化
for (ArrayList<Wrapper> list : map.values()) {
for (Wrapper wrapper : list) {
try {
//此方法包含对servlet的实例化和init方法的调用
wrapper.load();
} catch (ServletException e) {
getLogger().error(sm.getString("standardContext.loadOnStartup.loadException",
getName(), wrapper.getName()), StandardWrapper.getRootCause(e));
// NOTE: load errors (including a servlet that throws
// UnavailableException from the init() method) are NOT
// fatal to application startup
// unless failCtxIfServletStartFails="true" is specified
if (getComputedFailCtxIfServletStartFails()) {
return false;
}
}
}
}
return true;

}

<load-on-startup>

正数的值越小，启动该servlet的优先级越高