Презентация Java 4 WEB онлайн

Содержание слайда: Java 4 WEB Lesson 12 – Servlet API

Содержание слайда: Lesson goals Client-Server Static vs dynamic content Java Servlet Tomcat

Содержание слайда: Client-Server architecture A person enters a URL string into the browser. The browser generates HTTP-request. The server receives a request, processes, and sends an HTTP response. The browser receives a response and displays it.

Содержание слайда: Client-Server architecture • Web-server for static content (popular): Apache, nginx, GWS, IIS, ... • Software for dynamic content: CGI programs & modules, PHP AS, MS IIS AS, Java EE, ...

Содержание слайда: CGI - Common Gateway Interface Standard used to communicate of the web server with an external program for generating dynamic web content. CGI-script - a program that works on the CGI-interface. Web-server is configured to redirect certain URL requests for CGI scripts.

Содержание слайда: CGI - Common Gateway Interface Shortcomings of CGI technology: ● Start an OS process for each request ● A lot of low-level coding ● No sharing resources across requests ● No session state

Содержание слайда: Http Servlet service(HttpServletRequest, HttpServletResponse) doGet(HttpServletRequest, HttpServletResponse) doPost(HttpServletRequest, HttpServletResponse)

Содержание слайда: Java Servlet @WebServlet(name = "helloServlet", urlPatterns = {"/hello"}) public class HelloServlet extends HttpServlet { public void doGet( HttpServletRequest request, HttpServletResponse response ) throws IOException { response.setContentType("text/html"); PrintWriter out = response.getWriter(); out.println("<h1>Hello World</h1>"); } }

Содержание слайда: Java Servlet 4.0 HTTP /2 Request/Response multiplexing Stream Prioritization Server Push Upgrade from HTTP 1.1 

Содержание слайда: Servlet Lifecycle Loads the servlet class Creates an instance of the servlet class Initializes the servlet instance by calling the init() method Does all work When the container needs to remove the servlet, it calls the servlet’s destroy() method

Содержание слайда: HttpServletRequest Container creates HttpServletRequest object and passes it as argument to Servlet's service methods (doGet, doPost, etc.) HttpServletRequest provides client request info to Servlet. Passed to the service(...) method, doGet (...), doPost (...), do ... ().

Содержание слайда: HttpServletRequest Methods:   - getHeader (String)   - getParameter (String)   - getInputStream ()   - getSession ()   - getServletContext () - etc

Содержание слайда: HttpServletResponse Container creates HttpServletResponse object and passes it to Servlet's service methods (doGet, doPost, etc.) HttpServletResponse assists a servlet in sending a response to the client. As well as HttpServletRequest is passed in service(...) and do...(...)

Содержание слайда: HttpServletResponse Methods:   - addHeader (String, String)   - setStatus (int)   - sendError (int)   - sendRedirect (String)   - setHeader (String, String)   - getWriter ()   - etc

Содержание слайда: HttpSession HttpSession session = request.getSession(); Main methods:   - invalidate ()   - getAttributeNames ()   - getAttribute (String)   - removeAttribute (String)   - setAttribute (String, Object) - etc

Содержание слайда: ServletContext Servlet uses ServletContext to communicate with its servlet container, access the servlet container. ServletContext sc = request.getServletContext(); Main methods:   - getAttributeNames ()   - getAttribute (String)   - removeAttribute (String)   - setAttribute (String, Object) - etc

Содержание слайда: Filter @WebFilter(urlPatterns = {"/*"}) public class HelloFilter implements Filter { public void init(FilterConfig cfg) { } public void doFilter( ServletRequest req, ServletResponse resp, FilterChain chain ) throws ServletException, IOException { chain.doFilter(req, resp); } public void destroy() { } }

Содержание слайда: Error Handling @WebServlet("/error") public class ErrorHandler extends HttpServlet { private static final long serialVersionUID = 1L; @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException { resp.setContentType("text/html; charset=utf-8"); try (PrintWriter writer = resp.getWriter()) { writer.write("<html><head><title>Error description</title></head><body>"); writer.write("<h2>Error description</h2>"); writer.write("<ul>"); Arrays.asList( ERROR_STATUS_CODE, ERROR_EXCEPTION_TYPE, ERROR_MESSAGE) .forEach(e -> writer.write("<li>" + e + ":" + req.getAttribute(e) + " </li>") ); writer.write("</ul>"); writer.write("</html></body>"); } } }

Содержание слайда: Error Handling <?xml version="1.0" encoding="UTF-8"?> <web-app version="4.0" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"> <display-name>Web Project</display-name> <error-page> <exception-type>java.lang.RuntimeException</exception-type> <location>/error</location> </error-page> </web-app>

Содержание слайда: Web (servlet) container A Web server - component that interacts with Java Servlets. Primary responsibilities are:   - Management of servlets and their life cycle - Mapping the URL to a specific servlet. - Check access rights

Содержание слайда: Java EE & Servlet (Web) Container Most popular Servlet (Web) Containers • Apache Tomcat • Jetty • JBoss Application Server (WildFly) • …

Содержание слайда: Apache Tomcat

Содержание слайда: WAR Web application ARchive - is a JAR file used to distribute a collection of JavaServer Pages, Java Servlets, Java classes, XML files, libraries, static web pages (HTML, JS, CSS, etc) and other resources…

Содержание слайда: WAR

Содержание слайда: Literature Building Java Web Applications Servlets (by Baeldung) Servlets (by Tutorialspoint) How to Install Apache Tomcat What is servlet container Servlets (by Jetbrains)

Содержание слайда: Homework Task 1 Implement a servlet with interface: `/session?action=[add/update/remove/invalidate]&name=...&value=...` 1. The servlet generates a form with input fields "action", "name", "value" and button "Submit". Below print is a list of all attributes of the user session. action - depending on the value, the servlet adds, updates, or removes an attribute in/from a session; name - the name of the attribute; value - is the value of the attribute. 2. If any error happens – log and redirect user to custom error page 3. Add request blocking filter, when user browser is ‘Microsoft Edge’ – block request and show error page. Use 4. Add separate request logging filter. Log endpoints path and total execution time. Should measure all actions (even when request blocked) 5. Add separate request blocking filter. When today is weekend – deny all operations. Microsoft Edge users should never come here and be stopped by user-agent filter. 6. Attributes lists should not be shared between two browsers

Содержание слайда: Homework Task 1