web容器调用Filter和Servlet顺序学习

web容器调用Filter和Servlet顺序学习

 

 一直对Filter和Servlet在哪里被web容器调用迷惑，后查看tomcat源码，揭开了其面纱。
1. 下面是一个简单的时序图：

2. 对上面时序图中用到的主要类进行分析

1)         ApplicationFilterChain类,有两个主要函数，下面是省略过会的代码

public voiddoFilter(request, response) {//暴露在外面的调用接口

if( Globals.IS_SECURITY_ENABLED ) {

finalServletRequest req = request;

finalServletResponse res = response;

internalDoFilter(req,res);

return null;

} else {

internalDoFilter(request,response);

}

}

private voidinternalDoFilter(request, response) {

if (pos < n) {//判断是否还有filter需要执行

ApplicationFilterConfig filterConfig = filters[pos++];

Filter filter = null;

filter = filterConfig.getFilter();

filter.doFilter(request, response, this);

return ;

}

{//filter执行完后，执行servlet

if ((request instanceofHttpServletRequest) &&

(response instanceof HttpServletResponse)) {

servlet.service((HttpServletRequest) request,

(HttpServletResponse) response);

}

}

void addFilter(ApplicationFilterConfig filterConfig) {

if (n == filters.length) {

ApplicationFilterConfig[] newFilters =

new ApplicationFilterConfig[n + INCREMENT];

System.arraycopy(filters, 0, newFilters, 0, n);

filters = newFilters;

}

filters[n++] = filterConfig;

}

2)         Servlet类的主要方法，以HttpServlet类为例，其主要方法是service(Request,Response)

public voidservice(ServletRequest req, ServletResponse res)

throws ServletException, IOException {

HttpServletRequest  request;

HttpServletResponse response;

try {

request = (HttpServletRequest) req;

response = (HttpServletResponse) res;

} catch (ClassCastException e) {

throw new ServletException("non-HTTP request or response");

}

service(request, response);//内部的方法

}

protected voidservice(HttpServletRequest , HttpServletResponse)

throws ServletException, IOException {

String method = req.getMethod();

if (method.equals(METHOD_GET)) {

long lastModified = getLastModified(req);

if (lastModified == -1) {

doGet(req, resp); //常用的方法

} else {

long ifModifiedSince;

try {

ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);

} catch (IllegalArgumentException iae) {

ifModifiedSince = -1;

}

if (ifModifiedSince < (lastModified / 1000 * 1000)) {

maybeSetLastModified(resp, lastModified);

doGet(req, resp);

} else {

resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);

}

}

} else if (method.equals(METHOD_HEAD)) {

long lastModified = getLastModified(req);

maybeSetLastModified(resp, lastModified);

doHead(req, resp);

} else if (method.equals(METHOD_POST)) {

doPost(req, resp);//常用的方法

} else if (method.equals(METHOD_PUT)) {

doPut(req, resp);

} else if (method.equals(METHOD_DELETE)) {

doDelete(req, resp);

} else if (method.equals(METHOD_OPTIONS)) {

doOptions(req,resp);

} else if (method.equals(METHOD_TRACE)) {

doTrace(req,resp);

} else {

String errMsg =lStrings.getString("http.method_not_implemented");

Object[] errArgs = new Object[1];

errArgs[0] = method;

errMsg = MessageFormat.format(errMsg, errArgs);

resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg);