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Web Applications Basic Web Servers and the HTTP Protocol Basic Dynamic Content Generation: Servlets, HTML Forms, JDBC Java Web Applications, JSP, JSTL, JSTL Expression Language … -- 1 -Web Servers and the HTTP Protocol 3 HTML could of course be used locally: To retrieve a document, just read it from the local file system To identify a document, use its filename: “/info/index.html” But it was developed to be used over the Internet! Retrieve: Communicate with a “web server” (HTTP protocol) To identify a document, we need to know: 1. Which server has the document 2. Which TCP port the server is running on 3. Some additional identifier (“filename”), such as “info/index.html” 4. And maybe which part of the document we want to start at Request HTTP Client (browser) HTTP Server Response File System or database… jonkv@ida Finding HTML Documents 4 We want a single string to provide all information! And we might also want to use such strings for FTP, local files, … URL: Universal/Uniform Resource Locator Orig. intention: specify how a resource can be found, generally on the net http://user:[email protected]:80/info/index.html#chapter2 ftp://user:[email protected]/pub/foo.zip file:///home/jonkv/book.pdf (unused fields can generally be omitted) Later we got URNs: Names Intention: Name a resource, without saying where it is urn:isbn:096139210x urn:newsml:reuters.com:20000206:… Eventually, one saw URLs and URNs as special cases of URIs: Identifiers Now, the distinction seems to be fading… jonkv@ida URIs and URLs 5 The web browser parses a URL http://www.ida.liu.se/info/index.html#chapter2 ▪ ▪ ▪ ▪ Protocol: Server name: Path: Anchor: HTTP default port is 80 www.ida.liu.se (DNS says IP number is 130.236.177.26) /info/index.html #chapter2 Uses standard TCP to contact 130.236.177.26, port 80 Uses text‐based HTTP request/response protocol on top of TCP… Client (connects to port 80) Requests “info/index.html" HTTP Request Server www.ida.liu.se (listens to port 80) HTTP Response jonkv@ida HTTP 1: Parsing a URL 6 The browser sends an HTTP request A set of request headers Request method: GET, HEAD, POST, PUT, ▪ GET /info/index.html HTTP/1.0 DELETE, CONNECT, TRACE, OPTIONS ▪ Host: www.ida.liu.se ▪ User‐Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en‐US; rv:1.1) Gecko/20020818 ▪ Accept: text/xml,application/xml, application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8, video/x‐mng,image/png,image/jpeg,image/gif;q=0.2,text/css,*/*;q=0.1 ▪ Accept‐Language: en‐us, en;q=0.50 ▪ Accept‐Encoding: gzip, deflate, compress;q=0.9 ▪ Accept‐Charset: ISO‐8859‐1, utf‐8;q=0.66, *;q=0.66 ▪ Keep‐Alive: 300 Request ▪ Connection: keep‐alive ▪ [empty line] Client Server jonkv@ida HTTP 2: Sending a Request 7 What resource (page, image, …) was requested? Early web servers (1989+) used a single directory of files ▪ Request “info/index.html” send file “<webroot>/info/index.html” Modern servers may serve many domains (especially web hotels) ▪ www.company.se and www.second.se both point to IP 12.34.56.78 ▪ ”Host: www.company.se” use ”host1” config / directories ▪ ”Host: www.second.se” use ”second” config / directories Some paths may be mapped to programs ▪ Is “/info/index.html” the name of a program? No. Other paths correspond to static files on disk ▪ /info/index.html send file “<IDA webroot>/info/index.html” jonkv@ida HTTP 3: Finding Requested Resources 8 The web server sends a reply Sequence of HTTP response headers => blank line => data ▪ HTTP/1.1 200 OK HTTP/version status explanation ▪ Date: Mon, 19 Aug 2123 16:05:14 GMT Code 200: ”OK, here’s what you ▪ Server: Apache/1.3.26 (Unix) PHP/4.2.2 mod_ssl/2.8.10 asked for”… OpenSSL/0.9.6e Mapped to English version: “You ▪ Content‐Location: index.en.shtml asked for index.html, you got ▪ Vary: negotiate,accept‐language index.en.shtml” ▪ TCN: choice ▪ Transfer‐Encoding: chunked Vary: “I may send another reply if ▪ Content‐Type: text/html you vary these fields” (for caching) ▪ Content‐Language: en ▪ [Empty line] <!DOCTYPE HTML PUBLIC "‐//W3C//DTD HTML 4.01 //EN" Contents of "http://www.w3.org/TR/html4/strict.dtd"> <HTML> Client Server index file <HEAD> Response … jonkv@ida HTTP 4: Receiving a Reply Sometimes a resource must be moved 301 Moved Permanently ▪ Header "Location: <new‐URL‐to‐resource>" ▪ Client may automatically send a new request for the new URL ▪ Client may automatically update links and bookmarks 302 Found / 307 Temporary Redirect ▪ Header "Location: <temporary‐URL‐to‐resource>" ▪ Client may automatically send a new request for the new URL ▪ Only temporary redirection; do not update links or bookmarks Configuration: Web‐server‐dependent 9 jonkv@ida HTTP 5: Redirection 10 Various errors on the client side 400 Bad Request ▪ Syntax error 403 Forbidden ▪ Server refuses to do this, regardless of authorization 404 Not Found ▪ May be permanently or temporarily unavailable; maybe never existed 410 Gone ▪ Used to exist, but is now intentionally, permanently unavailable … jonkv@ida HTTP 6: Client Errors 11 HTTP needs to specify the response data type Can't rely on simple file extensions – not robust Uses data types from MIME e‐mail standard Content‐type: type/subtype; param=value; param… Seven top level types ▪ text, image, audio, video, application ‐‐‐ discrete ▪ message, multipart ‐‐‐ composite Many subtypes ▪ text/plain, text/html, text/css, text/tab‐separated‐values, … ▪ image/jpeg, image/gif, image/png, image/t38, … ▪ application/postscript, application/octet‐stream, … ▪ Create your own, beginning with "x‐": application/x‐jonkv‐dbresult Can accept parameters ▪ text/html; charset=iso‐8859‐1 jonkv@ida HTTP 7: MIME Data Types -- 2 -Dynamic Content Generation CGI Scripts and Java Servlets HTML Forms and Servlet Request Parameters Java Database Connectivity 13 How to generate content dynamically? Example: Show a random quotation ("fortune") Early solution, 1993: CGI, Common Gateway Interface Simple standard for executing external programs, “CGI scripts” Place all external programs in a single directory, /cgi‐bin When server receives "GET /cgi‐bin/fortune"… ▪ Assume the file is a program, execute it, and send its output! Client (connects to port 80) Request Requests "cgi-bin/fortune" Response Server (listens to port 80) Execute /www/cgibin/fortune stdout Configured to serve "/www" jonkv@ida Dynamic Content Generation (1) 14 Your first CGI script Writes some simple HTML code to standard output Could use Perl or other languages. Here: plain shell script ▪ #!/bin/sh echo "Content-type: text/html“ # An empty line separates headers from body echo echo "<html>" echo "<head><title>Fortune</title></head>" echo "<body>" echo "<h1>This is today's fortune:</h1>" echo "<pre>" /bin/fortune # use standard Unix fortune command echo "</pre></body></html>" /www/cgibin/fortune jonkv@ida Your First CGI Script 15 CGI scripts have some limitations: Not completely well‐defined interface No support for common server‐side tasks Must start a new OS process for every request (inefficient!) Better alternatives were quickly developed Proprietary interfaces for commercial web servers Module interface for the common Apache server (open source) New languages intended to be used on the web, including PHP (first "full" version june 1998) jonkv@ida CGI Limitations 16 The Java approach: Servlets (”miniature servers”) Implemented as subclasses of HttpServlet Loaded dynamically into the server’s servlet container ▪ Created, init()ed, called for multiple requests, possibly destroy()ed ▪ doGet() for GET requests, doPost() for POST requests (some forms), doPut(), doDelete(), doOptions(), doTrace() ▪ public class FortuneServlet extends HttpServlet { public void doGet(HttpServletRequest req, HttpServletResponse res) throws … { res.setContentType("text/html"); PrintWriter out = res.getWriter(); out.println("<html><head><title>Fortune</title></head>"); out.println("<head><title>Hello World</title></head><body>"); out.println("<h1>This is today's “ + • From early 1997, before PHP “fortune:</h1><pre>"); • Extensive API support out.println(Fortune.getFortune()); • Servlet container always loaded – no need to create new processes out.println("</pre></body></html>"); } jonkv@ida Servlets: The Java Approach 18 Users must be able to send information to the server Online store example: ▪ User registration form – enter name, address, … and store in database ▪ Click‐to‐buy: Which item did you click? Store in shopping cart ▪ … Solution: Add forms to HTML, send form input to the servlet ▪ Each GUI control has a name and a value ▪ Submitting sends name=value pairs to the servlet General format: ▪ <form action="http://somehost/address‐of‐servlet‐or‐script"> …HTML code… …"input" tags generating GUI controls… </form> jonkv@ida Scripts Need Input! Text input tags: Name: <input Password: <input type="text" name="firstName" value="initial" maxlength="30"> type="password" name="pass" maxlength="30"> 19 jonkv@ida HTML Forms 1: Text Input 20 Yes/no input tags: Checkboxes ▪ <p>Which operating systems do you use?</p> <input type="checkbox" name="os" value="Linux">Linux<br> <input type="checkbox" name="os" value="Solaris">Solaris<br> <input type="checkbox" name="os" value="Win">Windows<br> <input type="checkbox" name="os" value="MacOS">MacOS<br> <input type="checkbox" name="os" value="C64 Basic V2">C64 Basic V2 ▪ Multiple choices result in for example "os=Linux,Solaris" ▪ Can of course use multiple groups (each group has a different name) jonkv@ida HTML Forms 2: Checkboxes Yes/no input tags: Radio buttons ▪ <p>Your gender:<br> <INPUT type="radio" name="gnd" value="Male">Male<br> <INPUT type="radio" name="gnd" value="Female">Female<br> ▪ Only one selected radio button within each named group 21 jonkv@ida HTML Forms 3: Radio Buttons Button input tags: <input type="submit" name="ok" value="Do this"> <input type="submit" name="ok" value="Do that"> ▪ Value is also used as label ▪ Pressing one results in "ok" being set to "Do this" or "Do that", and in submitting the form to the specified URL <input type="reset" name="reset" value="Reset this form"> Additional tags (see spec): Image buttons Hidden controls (predefined data to be submitted) File selector control (upload files to CGI scripts) 22 jonkv@ida HTML Forms 4: Buttons + misc 23 Complete form example: <FORM action="http://somesite.com/cgi-bin/adduser” method=“(next page)”> <table class="mytable"> <tbody> <tr><td>First name:<td><INPUT type="text" name="first"> <tr><td>Last name: <td><INPUT type="text" name="last"> <tr><td>E-mail: <td><INPUT type="text" name="email"> <tr><td><INPUT type="radio" name="gender" value="Male"> Male <tr><td><INPUT type="radio" name="gender" value="Female"> Female <tr><td><INPUT type="submit" value="Send"> <INPUT type="reset"> </tbody> </table> </FORM> jonkv@ida HTML Forms 5: Complete Example 25 Sending form data, method 1: GET Same HTTP method as when retrieving a static page ▪ <FORM action="http://somesite.com/cgi-bin/adduser" method="get"> Form input ends up in the URL query string ▪ Adds a “?” after the action URL ▪ Adds each name=value pair separated by “&” ▪ Uses a special 7‐bit query string format ▪ a‐z, A‐Z, 0‐9 remain the same ▪ Space is converted into '+' ▪ Other characters are converted into ‘%xy’: Hexadecimal representation of the lower 8 bits of the char ▪ Request: GET /cgi-bin/adduser?first=Jonas&last=Kvarnstr%F6m&… HTTP/1.0 The server automatically splits the URL at the question mark ▪ Resource: ▪ Query string: /cgi-bin/adduser first=Jonas&last=Kvarnstr%F6m&… jonkv@ida Form Requests 1: Using GET Consequences of using GET: Parameters end up in the URL field in the browser ▪ Positive: Can add a bookmark pointing to the query ▪ Negative: Many fields and lots of text very long URLs! ▪ Definitely not useful if you upload files! Browsers assume it is safe to request the same URL again ▪ They don’t ask for permission to reload the page ▪ Can be OK for information requests ▪ But don’t use GET for actions having side effects ▪ Add new user ▪ Send email ▪ … 26 jonkv@ida Form Requests 2: Using GET 27 Sending form data, method 2: POST Designed for sending form data ▪ <FORM action="http://somesite.com/cgi-bin/adduser" method="post"> Request data ends up in the HTTP request data section ▪ POST /cgi-bin/adduser HTTP/1.0 [other headers] (blank line) first=Jonas&last=Kvarnstr%F6m&… Positive: Much better if you send large quantities of data Negative: No parameters in the URL, so not possible to bookmark Must be used when you don’t want to re‐submit by accident (you don’t want to purchase the same item twice!) ▪ Browsers generally ask whether to really re‐post data if you try to reload the page jonkv@ida Form Requests 3: Using POST Information about the request: HttpServletRequest This is where you get your form parameters (already parsed) ▪ req.getParameter(“first") == “Jonas” ▪ req.getParameter(“last") == “Kvarnström” (no %xy codes!) Sending a response: HttpServletResponse First, set the content type ▪ void setContentType(String mimetype) Then, send a response (tunneled through the web server) ▪ PrintWriter getWriter() ▪ ServletOutputStream getOutputStream() 28 jonkv@ida ServletRequest / Response HTML: 29 jonkv@ida Servlet Example: Queries <form action="http://foo.com/employees/list" method="get"> Name pattern: <input type="text" name="pat">… </form> ----------------------------------------------------------------------------------------------------------------public class ListEmployeeServlet extends HttpServlet { public void doGet(HttpServletRequest req, HttpServletResponse res) throws … { res.setContentType("text/html"); Error handling and PrintWriter out = res.getWriter(); many details omitted! String pattern = req.getParameter("pat"); DBs covered later. Connection con = …; String query = "SELECT * FROM employees WHERE id like ‘?‘ "; PreparedStatement stmt = con.prepareStatement(query); stmt.setString(1, pat); ResultSet emp = stmt.executeQuery(query); out.println("<HTML><BODY><p>Employees matching pattern:</p>"); while (emp.next()) { /* get and print employee information */ } out.println("</BODY></HTML>"); } Webapp: Servlet: HTML: 30 jonkv@ida Servlet Example: Adding Employees Employee database (context path: /employees) NewEmployeeServlet (configured within the webapp as "new") <form action="http://foo.com/employees/new" method="post"> Name: <input type="text" name="name">… </form> ----------------------------------------------------------------------------------------------------------------public class NewEmployeeServlet extends HttpServlet { public void doPost(HttpServletRequest req, HttpServletResponse res) throws … { res.setContentType("text/html"); String name = req.getParameter("name"); String address = req.getParameter("address"); // … String query = "INSERT INTO employees VALUES(?,?,?,…)"; PreparedStatement stmt = con.prepareStatement(query); stmt.setString(1, name); /* … */ int modified = stmt.executeUpdate(query); // … out.println("<HTML><BODY><p>Added new user: " + name + “</p></BODY></ } JDBC: Java Database Connectivity Interface to relational databases / SQL 2010-01-21 Jonas Kvarnström 31 32 Java keeps track of a set of DataSources Using JNDI: Java Naming and Directory Interface Application servers take care of much of the setup In the labs: configure/name a database in Tomcat’s config (XML) ▪ Example: <Resource name="jdbc/MyDB” auth="Container” type="javax.sql.DataSource” username=”…” password=”…" driverClassName=”…” url=”…” maxActive="8" /> ▪ This creates a DataSource named ”jdbc/MyDB” ▪ Automatically creates a connection pool: When you close a connection, it is actually stored and can be reused jonkv@ida JDBC 1: DataSource Use the DataSource to connect to a database Use getConnection() to get a connection ▪ InitialContext ic = new InitialContext(); DataSource ds = (DataSource) ic.lookup("java:comp/env/jdbc/MyDB"); Connection con = null; try { con = ds.getConnection(url, "ID", "passwd"); // Use the connection } finally { try { if (con != null) con.close(); } catch (SQLException e) { /* handle it, log it, … */ } } Remember to close it! ▪ If you forget, you may run out of connections… ▪ The pattern above (with try/finally) ensures it is closed even if there is an exception inside “try” ▪ Note that there can be an exception when you close it! 33 jonkv@ida JDBC 2: Getting a Connection A connection can handle many concurrent queries Each query is handled by a separate Statement Each Statement keeps track of its own settings (timeouts, …) ds.getConnection() Connection to MyDB createStatement() Statement (settings for one query) createStatement() Statement (settings for one query) 34 jonkv@ida JDBC 3: Making a Statement Use executeQuery() to execute a SELECT query ▪ String query="SELECT * FROM employees WHERE salary<12000"; Statement myStatement = null; ResultSet rs = null; try { myStatement = connection.createStatement(); rs = myStatement.executeQuery(query); // use rs } finally { try { if (rs != null) rs.close(); } catch (SQLException e) { /* handle it */ } try { if (myStatement != null) myStatement.close(); } catch (SQLException e) { /* handle it */ } } 35 jonkv@ida JDBC 4: Executing a SELECT query Use PreparedStatements for non‐constant queries! If you put user‐generated information into query strings: ▪ String pattern = req.getParameter("pat"); String query = "SELECT * FROM employees WHERE id like ‘“ + pattern + “’”; ▪ suppose the user enters x’; DELETE * FROM employees; ▪ Quoting is possible, but you have to get everything right Let PreparedStatement take care of everything instead! ▪ Use ”?” as a placeholder ▪ String pattern = req.getParameter("pat"); String query = "SELECT * FROM employees WHERE id like ‘?‘ "; PreparedStatement stmt = con.prepareStatement(query); stmt.setString(1, pat); boolean success = ps.executeQuery(); ▪ Easier and safer 36 jonkv@ida JDBC 5: PreparedStatement 37 executeQuery() returns a ResultSet – a set of rows Similar to an Iterator ▪ "Cursor" points to the "current" row of data, ▪ next() advances the cursor – returns false if there were no more rows Retrieve data from the current row ▪ Use column numbers or names: getFloat(name), getInt(name), getString(name), … ▪ while (rs.next()) { final String name = rs.getString("name"); final String address = rs.getString("address"); prettyPrint(name, address); } Find out more about the result set using ResultSetMetaData ▪ ResultSetMetadata rsmd = rs.getMetaData(); jonkv@ida JDBC 6: Using a ResultSet 38 Use executeUpdate() for update queries Can also use prepared statements more than once ▪ String q = "UPDATE employees SET salary = ? WHERE name = ?"; PreparedStatement stmt = con.prepareStatement(q); stmt.setInt(1, 15000); stmt.setString(2, "John Doe"); int changedRows = stmt.executeUpdate(); stmt.setInt(1, 17000); stmt.setString(2, "Jane Doe"); changedRows += stmt.executeUpdate(); jonkv@ida JDBC 7: Updates 39 Connections are normally in auto‐commit mode Turn this off if you want to handle transactions ▪ con.setAutoCommit(false); String q = "UPDATE employees SET salary = ? WHERE name = ?"; PreparedStatement stmt = con.prepareStatement(q); stmt.setInt(1, 15000); stmt.setString(2, "John Doe"); stmt.executeUpdate(); stmt.setInt(1, 17000); stmt.setString(2, "Jane Doe"); stmt.executeUpdate(); con.commit(); // or con.rollback(); con.setAutoCommit(true); jonkv@ida JDBC 8: Transactions -- 3 -Java Web Applications 41 “External Interface" presented to web browsers A webapp is a single coherent application Message Forum ▪ Shopping system, message forum, … Web applications ▪ Consists of HTML files, servlets, images, … Appears as a hierarchical URL structure ▪ Rooted in the context path, specified in the global web server config Ex: Message forum at www.myserver.com ▪ Configure with context path "/forum" => http://www.myserver.com/forum /login /index.html … ▪ Configure with context path "/msg" => http://www.myserver.com/msg /login /index.html … /login [servlet] /listmsg [servlet] /newmsg [servlet] /newuser [servlet] /index.html /welcome.html /img/logo.png jonkv@ida Webapps 1: Introduction 42 jonkv@ida Webapps 2: Directory Structure Physical directory structure matches URL hierarchy Except WEB‐INF directory: Contains config files, servlets, … Message Forum /login [servlet] Virtual mapping through <servlet-config> and <servlet-mapping> in web.xml /listmsg [servlet] /newmsg [servlet] /newuser [servlet] /index.html /welcome.html /img/logo.png File System [approot]/index.html [approot]/welcome.html [approot]/img/logo.png [approot]/WEB-INF/web.xml [approot]/WEB-INF/classes/… Can be packaged as a single WAR file (Web Archive) for easy distribution. Unpacked version is called exploded directory. 43 The WEB‐INF directory: Contains configuration files, servlets, and resources ▪ [approot]/WEB-INF/web.xml: [approot]/WEB-INF/lib/*.jar: [approot]/WEB-INF/classes/*: [approot]/WEB-INF/res.foo: A deployment descriptor (webapp config) Libraries used from servlets and JSP Compiled servlet classes Resources to use in servlets (see below) Example: ▪ …/WEB-INF/lib/jdbcdriver.jar …/WEB-INF/classes/com/mycorp/LoginServlet.class …/WEB-INF/classes/com/mycorp/ListMsgServlet.class Files in WEB‐INF cannot be retrieved directly via HTTP ▪ Classes accessed through servlet mappings (discussed later) ▪ Files can be accessed from servlet code: ServletContext ctxt = getServletConfig().getServletContext(); // Use ctxt.getResourceAsStream(…) or ctxt.getResource(…); jonkv@ida Webapps 3: WEB-INF Deployment descriptor (web.xml) XML header, then <web‐app> tag – example: ▪ <?xml version="1.0" encoding="ISO-8859-1"?> <web-app xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd" version="2.4"> … miscellaneous configuration items … … miscellaneous configuration items … … miscellaneous configuration items … … miscellaneous configuration items … </web-app> 44 jonkv@ida Webapps 4: Deployment Descriptor 45 Configuring webapps should not require recompilation Easiest to change configuration if you store it in a database Also built‐in support for parameters in web.xml ▪ At the top level in web.xml: <context-param> <param-name>Webmaster</param-name> <param-value>[email protected]</param-value> </context-param> Parameters accessed through ServletContext ▪ ServletContext ctxt = getServletConfig().getServletContext(); String webmaster = ctxt.getInitParameter("Webmaster"); jonkv@ida Webapps 5: Configuration Each servlet must be specified in web.xml Configuration + possibly user‐specified init params ▪ <servlet> <servlet-name>mylogin</servlet-name> <servlet-class>com.mycorp.LoginServlet</servlet-class> <display-name>Login Servlet</display-name> <description>Log in using name / password</description> <init-param> <description>Maximum number of login attempts</description> <param-name>maxattempts</param-name> <param-value>3</param-value> </init-param> <init-param>…</init-param> </servlet> ▪ String maxattempts = getServletConfig().getInitParameter(“maxattempts"); Internal ID: mylogin Class name: com.mycorp.LoginServlet 46 jonkv@ida Webapps 6: Configuring a Servlet Mapping URLs to webapps: 47 Context path /forum Web server assigns a context path ▪ The webapp itself does not control this! ▪ Setup: Server‐specific Example: ▪ Web server at http://www.myserver.com ▪ Suppose admin downloads forum software, places it at context path "/forum" ▪ any requests to http://www.myserver.com/forum/… go to the forum webapp! ▪ The remainder of the URL, after “http://www.myserver.com/forum/”, is an address within the webapp ▪ How do we find the intended resource? Web Application: Message Forum LoginServlet ListMsgServlet NewMsgServlet NewUserServlet index.html welcome.html smiley.png jonkv@ida Mapping 1: Context paths 48 Suppose someone asks for http://www.myserver.com/forum/index.html ▪ Server part is http://www.myserver.com ▪ Context path /forum maps to this webapp ▪ Remainder is /index.html There is no special configuration for /index.html in web.xml ▪ Search for a file at the root of the webapp ▪ If found, serve this file File System ▪ If not, send error 404 [approot]/index.html But what about servlets? ▪ People aren’t supposed to know about internal class names, package structures… ▪ We want to define “external” names! [approot]/welcome.html [approot]/img/logo.png [approot]/WEB-INF/web.xml [approot]/WEB-INF/classes/… jonkv@ida Mapping 2: General Files 49 Simple servlet mapping http://www.myserver.com/forum/login ‐> LoginServlet ▪ Server part is http://www.myserver.com ▪ Context path /forum maps to this webapp ▪ Remainder is /login ▪ <servlet-mapping> <url-pattern>/login</url-pattern> <servlet-name>mylogin</servlet-name> </servlet-mapping> public void doGet(HttpServletRequest req, HttpServletResponse res) throws … { String contextPath = req.getContextPath(); // "/forum" String servletPath = req.getServletPath(); // "/login" String pathInfo = req.getPathInfo(); // null } URL: Internal ID: Class name: http://<server>/<ctxt>/login mylogin com.mycorp.LoginServlet (http://www.myserver.com/forum/login) jonkv@ida Mapping 3: Servlets Wildcard matching http://www.myserver.com/forum/view/102 –> show msg 102 ▪ <servlet-mapping> <url-pattern>/view/*</servlet-name> <servlet-name>ViewMessage</servlet-name> </servlet-mapping> ▪ The complete request path is sent to the servlet, which can extract the message number public void doGet(HttpServletRequest req, HttpServletResponse res) throws … { String contextPath = req.getContextPath(); // "/forum" String servletPath = req.getServletPath(); // "/view" String pathInfo = req.getPathInfo(); // "/102" // … Parse pathInfo as a query parameter } 50 jonkv@ida Mapping 4: Path Wildcards How to map: Extension matching Can be used to define automatic pre‐processing for *.foo files ▪ Suppose we want any *.foo to be handled by FooServlet, regardless of where in the webapp the *.foo file is located ▪ <servlet-mapping> <servlet-name>foo</servlet-name> <url-pattern>*.foo</servlet-name> </servlet-mapping> public void doGet(HttpServletRequest req, HttpServletResponse res) throws … { String contextPath = req.getContextPath(); // "/forum" String servletPath = req.getServletPath(); // "/sub/test.foo" String pathInfo = req.getPathInfo(); // null } 51 jonkv@ida Mapping 5: File Extensions The server returns a MIME type for every file Servlets set this using response.setContentType() Files are given MIME types using extension mapping ▪ <mime‐mapping> <extension>pdf</extension> <mime‐type>application/pdf</mime‐type> </mime‐mapping> Can use the ServletContext to find the MIME type of a file ▪ ServletContext ctxt = getServletConfig().getServletContext(); String mimetype = ctxt.getMimeType("misc/test.zip"); 52 jonkv@ida Mapping 6: MIME Types 53 The webapp does not know where it will end up! May be placed at "/forum", at "/users/jonkv/msgs", even at "/"! Should not contain hardcoded links to a single path! To link to another part of the application: Use a relative link ▪ <a href="../topiclist?start=100">Next page</a> ▪ Must know "where you are" – address is relative to your own location! Servlets: Can use the context path ▪ public void doGet(HttpServletRequest req, HttpServletResponse res) … { String contextPath = req.getContextPath(); // "/forum", or "/board", or … String linkURL = contextPath + "/topiclist?start=100"; … } JSP: <jsp:getProperty name="request" property="contextPath"/> JSTL: The <c:url> tag can locate resources relative to this webapp jonkv@ida Mapping 7: Where is the application? Summary of servlet configuration: 1) Give each servlet class an ID ▪ <servlet> <servlet-name>mylogin</servlet-name> <servlet-class>com.mycorp.LoginServlet</servlet-class> </servlet> 2) Associate various paths with servlet IDs ▪ <servlet-mapping> <url-pattern>/login</url-pattern> <servlet-name>mylogin</servlet-name> </servlet-mapping> 54 jonkv@ida Summary
