Servlet tutorial notes

web folder html file:

1 <form action="login" method="post">
2 User: <input type="text" name="name"><br>
3 Password: <input type="password" name="password"><br>
4 <input type="submit" value="login">
5 </form>

action for the login, the corresponding mapped login -> LoginServlet

After clicking submit, automatically jump to / login

WEB-INF web.xml file in the file is configured to:

1     <servlet>
2         <servlet-name>LoginServlet</servlet-name>
3         <servlet-class>LoginServlet</servlet-class>
4     </servlet>
5  
6     <servlet-mapping>
7         <servlet-name>LoginServlet</servlet-name>
8         <url-pattern>/login</url-pattern>
9     </servlet-mapping>

When comparing two values, the previous constants, avoid NullPointerException

Examples of the servlet tomcat, and call its doGet or doPost method, the incoming request and response; the method of operation of unwinding ordered through the following response, tomcat get response, based on the content of the response generated html string to the browser, html browser to obtain the string according to the http protocol, and rendered on screen.

HttpServleti in the service without having to rewrite the source code

607       protected void service(HttpServletRequest req, HttpServletResponse resp)
  608           throws ServletException, IOException {
  609   
  610           String method = req.getMethod();
  611   
  612           if (method.equals(METHOD_GET)) {
  613               long lastModified = getLastModified(req);
  614               if (lastModified == -1) {
  615                   // servlet doesn't support if-modified-since, no reason
  616                   // to go through further expensive logic
  617                   doGet(req, resp);
  618               } else {
  619                   long ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);
  620                   if (ifModifiedSince < (lastModified / 1000 * 1000)) {
  621                       // If the servlet mod time is later, call doGet()
  622                       // Round down to the nearest second for a proper compare
  623                       // A ifModifiedSince of -1 will always be less
  624                       maybeSetLastModified(resp, lastModified);
  625                       doGet(req, resp);
  626                   } else {
  627                       resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
  628                   }
  629               }
  630   
  631           } else if (method.equals(METHOD_HEAD)) {
  632               long lastModified = getLastModified(req);
  633               maybeSetLastModified(resp, lastModified);
  634               doHead(req, resp);
  635   
  636           } else if (method.equals(METHOD_POST)) {
  637               doPost(req, resp);
  638               
  639           } else if (method.equals(METHOD_PUT)) {
  640               doPut(req, resp);        
  641               
  642           } else if (method.equals(METHOD_DELETE)) {
  643               doDelete(req, resp);
  644               
  645           } else if (method.equals(METHOD_OPTIONS)) {
  646               doOptions(req,resp);
  647               
  648           } else if (method.equals(METHOD_TRACE)) {
  649               doTrace(req,resp);
  650               
  651           } else {
  652               //
  653               // Note that this means NO servlet supports whatever
  654               // method was requested, anywhere on this server.
  655               //
  656   
  657               String errMsg = lStrings.getString("http.method_not_implemented");
  658               Object[] errArgs = new Object[1];
  659               errArgs[0] = method;
  660               errMsg = MessageFormat.format(errMsg, errArgs);
  661               
  662               resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg);
  663           }
  664       }

service doGet, doPost, service parameter passing are the same

Servlet is a single instance, constructors and initialization methods only once

destroy:

1. Servlet web application that resides restart

2. tomcat Close

reloadable: If this property is set to true, tomcat server running in the state will monitor the changes in class files in the WEB-INF / classes and WEB-INF / lib directory, if there is to monitor the class file is updated, the server will automatically re Web application load.
During the development phase will reloadable property to true, useful for debugging and other servlet class files, but that the server is running with heavier loads, it is recommended fat deposit stage of the reloadable Web application is set to false.

Jump server

request.getRequestDispatcher("success.html").forward(request, response);

Jump Client

response.sendRedirect("fail.html");

servlet life cycle is to start in the browser to access the specified directory before, but in some cases they need to start using servlet's service, so it is necessary from the start, since the start in the init () can do some work in the business code

<load-on-startup> 10 </ load-on-startup> where 10 represents the priority, the lower the number, the priority

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