7 Servlet Introduction
Development of the 7.1 Servlet
@WebServlet (name = "HelloServlet", Urlpatterns = {"/helloservlet")}) Public classHelloServletextendsHttpServlet {@Overrideprotected voidService (HttpServletRequest req, HttpServletResponse resp)throwsservletexception, IOException {req.setcharacterencoding ("UTF-8"); Resp.setcharacterencoding ("UTF-8"); String username= Req.getparameter ("username"); PrintStream out=NewPrintStream (Resp.getoutputstream ()); OUT.PRINTLN (username); }}
After you start Tomcat, use the link http://localhost/helloServlet?username=admin.
Configuration of the 7.2 Servlet
Starting with Servlet 3.0, there are two ways to configure a servlet: @WebServlet annotations or Web. XML configuration.
The life cycle of the 7.3 Servlet
7.4 Load-on-startup Servlet
There are two opportunities to create a Servlet: When the app starts or when the user requests it. The Load-on-startup parameter configures the Servlet instantiation priority, and the smaller the value, the higher the priority.
7.5 Configuration parameters for access Servlet
There are two ways to configure parameters for a Servlet: The InitParams property of the @WebServlet or the <init-param> child element of the <servlet> element in Web. Xml.
@WebServlet (name = "HelloServlet", Urlpatterns = {"/helloservlet")}, InitParams={@WebInitParam (name= "Password", value = "admin123") }) Public classHelloServletextendsHttpServlet {@Overrideprotected voidService (HttpServletRequest req, HttpServletResponse resp)throwsservletexception, IOException {req.setcharacterencoding ("UTF-8"); Resp.setcharacterencoding ("UTF-8"); PrintStream out=NewPrintStream (Resp.getoutputstream ()); ServletConfig Config=Getservletconfig (); Out.println (Config.getinitparameter ("Password")); }}
7.6 Using a Servlet as a controller
In the standard MVC pattern, JSP is responsible for collecting the user request parameters and presenting the data only as the presentation layer technology, the Servlet is used only as the controller, all requests are sent to the Servlet,servlet call Model processing request, and the JSP renders the processing result.
<%@ Page ContentType="Text/html;charset=utf-8"language="Java" %><HTML><Head> <title>User Login</title></Head><Body><span> <% Stringmessage= (String) Request.getattribute ("message"); if(Message! )= NULL) {out.println (message); } %></span>Please enter your user name and password:<BR><formID= "Login"Method= "POST"Action= "/loginservlet">User name:<inputtype= "text"name= "username"><BR>Password:<inputtype= "Password"name= "Password"><BR> <inputtype= "Submit"value= "Login"></form></Body></HTML>login.jsp
@WebServlet (name = "Loginservlet", Urlpatterns = {"/loginservlet")}) Public classLoginservletextendsHttpServlet {@Overrideprotected voidService (HttpServletRequest req, HttpServletResponse resp)throwsservletexception, IOException {req.setcharacterencoding ("UTF-8"); String username= Req.getparameter ("username"); String Password= Req.getparameter ("Password"); String message= ""; Dbutil Dbutil=NewDbutil (); Try{ResultSet ResultSet= Dbutil.query ("Select password from t_user where username =?", username); if(Resultset.next ()) {if(Resultset.getstring ("Password"). Equals (password)) {//Save username to sessionHttpSession session =req.getsession (); Session.setattribute ("Username", username); //forward to welcome pageReq.getrequestdispatcher ("/welcome.jsp"). Forward (req, resp); } Else{message= "Bad password"; } } Else{message= "User name does not exist"; } } Catch(Exception e) {e.printstacktrace (); } if(!message.equals ("") {Req.setattribute ("Message", message); Req.getrequestdispatcher ("/login.jsp"). Forward (req, resp); } }}Loginservlet.java
8 Automatic labeling of JSP 2
< lightweight Java EE Enterprise Application Combat >1:jsp/servlet and related technical details (II.)
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