servlet and jsp programming: an introduction spiros papadimitriou [email protected]
TRANSCRIPT
Overview
Introduction Static vs. Dynamic Servlets Java Server Pages (JSP)
Introduction
What you know:– Java– JDBC
What we’ll tell you:– How to use Java inside a webserver!
Why you might care:– Building non-trivial web interfaces and applications– In particular: database-backed web applications
Plain Old Static Pages
Static webpages– Plain files stored in the filesystem– Webserver accepts pathnames– Returns contents of corresponding file
Boring!– Can’t generate customized content—always serve
the same static pages…
Static Pages
GET /path/index.html
Web Server
Filesystem
read /path/index.html<file contents>
STATUS …<file contents>
Dynamic Content
CGI: Easy “fix”– Common Gateway Interface– Oldest standard– But at least a standard!– Inefficient– No persistent state
Forward requests to external programs– Spawn one process for each new request (ouch!)– Communicate via
• Standard input/output• Environment variables
– Process terminates after request is handled
CGI
GET /cgi-bin/query?KEY=foo
STATUS …<response text foo>
CGI ProgramKEY=foo
<response text foo>
Web Server
Filesystem Database, etc
stdin
stdout
CGI
GET /cgi-bin/query?KEY=bar
STATUS …<response text bar>
CGI ProgramKEY=bar
<responsetext bar>
Web Server
Filesystem Database, etc
stdin
stdout
Servlets to the rescue…
Little Java programs…– Contain application-specific code– Web server does generic part of request handling– Servlets run “in” the web server and do some of the
handling
Highlights– Standard!– Efficiency (much better than CGI)– Security (Java!)– Persistence (handle multiple requests)
Servlets
GET /srv/pkg.Servlet?KEY=foo
STATUS …<response foo>
Web Server
Filesystem Database, etc
JVM
Servlet
doGet(req, res)res <respose foo>
Servlets
GET /srv/pkg.Servlet?KEY=foo
STATUS …<response bar>
Web Server
Filesystem Database, etc
JVM
Servlet
doGet(req, res
)
res <response ba
r>
Servlet Examplepackage pkg;
import java.io.*;import javax.servlet.*;import javax.servlet.http.*;
public class Servlet extends HttpServlet { public void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException, ServletException { res.setContentType("text/html"); PrintWriter out = res.getWriter(); out.println("<html><head><title>Sample Servlet"); out.println("</title></head><body>"); out.println("<h1>Hello World at " + req.getRequestURI() + " !</h1>"); out.println(”<p>Key is " + req.getParameter("KEY")); out.println(”</p></body></html>"); } }
More Servlets A catalog of servlet methods:
– init(config)– service(req, res)
• doGet(req, res)• doPut(req, res)• doDelete(req, res)• etc…
A catalog of request methods:– getParameter(name)– getParameterNames(), getParameterValues(name)– getCookies()
A catalog of response methods:– sendRedirect(url), sendError(errCode, errStr)– setContentType(mimeType)– addCookie(cookieObj)
JSP… Sugar
Printing to output not really a special case when writing heaps of HTML!
Well… why not make that the common case in the syntax and program statements the “special case?”
And while we’re at it, why not hide the compilation steps (let the server do it)?
Now things look more like “plain old HTML” (only they aren’t… they can produce dynamic content and really are Java programs)
First JSP Example (1/3)<%@ page import=“java.io.*” %><html><head><title>Sample JSP</title></head><% String s = “JSP”; %><body><h1>Hello <%= s %> World!</h1><p><% out.print(“Scriptlet Statement Hello!”); %></p><p>Key is <%= request.getParameter(“KEY”) %></p></body></html>
Core syntactic elements:– Directives <%@ page … %>– Declarations <%! … %> (outside service method)– Scriptlets <% … %>– Expressions <%= … %>
First JSP Example (2/3)package jsp._jsp;
// line:/jsp/hello.jsp:1import java.io.*;
import javax.servlet.*;import javax.servlet.http.*;import javax.servlet.jsp.*;
public class _hello_2ejsp extends org.gjt.jsp.HttpJspPageImpl implements org.gjt.jsp.GnuJspPage { […] public void _jspService (HttpServletRequest request, HttpServletResponse response) throws ServletException, java.io.IOException { response.setContentType ("text/html"); […] HttpSession session = pageContext.getSession (); JspWriter out = pageContext.getOut (); […]
First JSP Example (3/3) try { // line:/jsp/hello.jsp:2 out.print("<html>\n[…]"); // line:/jsp/hello.jsp:4 String s = "GNUJSP"; // line:/jsp/hello.jsp:5 out.print("\n<body>[…]"); // line:/jsp/hello.jsp:6 out.print(s); […] // line:/jsp/hello.jsp:7 out.print(“Scriptlet Statement Hello!”); […] // line:/jsp/hello.jsp:8 out.print(request.getParameter(“KEY”)); // line:/jsp/hello.jsp:8 out.print(“</p>\n</body>[…]”); } catch (Throwable e) { […] } }}
Second JSP Example (1/2)<%@ page import=“java.io.*” %><%@ page import=“java.util.*” %><%@ page import=“java.sql.*” %><%! Static final String dbHost = “…”; %> Static final String oracleDriver = “…”;%><% String courseId = request.getParameter(“courseid”); Class.forName(oracleDriver); Connection conn = DriverManager.getConnection(…); Statement stmt = con.createStatement(); String qry = “SELECT STUDENT.SID, SNAME, COURSE.CID ” + “FROM STUDENT, COURSE, TAKE ” + “WHERE TAKE.CID = ‘” + courseId + “’ AND ” + “STUDENT.SID = TAKE.SID AND ” + “COURSE.CID = TAKE.CID;” ResultSet res = conn.executeQuery(qry);%>
Second JSP Example (2/2)<html><head><title>Student Information</title></head>
<body><h1>Student Information for <%= courseId %></h1>
<p><table border=“1”><tr><th>CourseID</th><th>Student</th><th>StudentID</th></tr><% while (rs.next()) { %> <tr> <td><%= rs.getString(“cid”) %></td> <td><%= rs.getString(“sname”) %></td> <td><%= rs.getString(“sid”) %></td> </tr><% } // end while %></table></p>
</body></html>
Alternatives
Dynamically loadable server modules– Web server offers standard API for request handlers– Request handlers are dynamic libraries– Loaded into server address space (security?!)– Very efficient!– Better suited for generic server extensions than
application-specific logic
CGI flavors– Persistent CGI (PCGI) / FastCGI– Too little, too late
Modern web publishing systems– Essentially databases that “speak HTTP”
More Information
Servlets and JSPs:– http://java.sun.com/products/servlet/– http://java.sun.com/products/jsp/
JDBC:– http://java.sun.com/products/jdbc/