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);