WHAT is JAVA

1. WHAT is JAVA

2. What is Java? • Object-oriented programming (OOP) language developed bySUN Microsystems • Similar to C and C++, except without some of the confusing,poorly understood features of C++ • Extensive networking facilities • Extensive set of APIs for GUIs, distributed computing, 2D/3Dgraphics, mail, and others • Portable: Write Once, Run Anywhere • Multithreading support built into the language

3. Java Features • Automatic garbage collection • No manual memory allocation and deallocation • Never have to worry about memory leaks • No pointers or pointer arithmetic • No off-by-one bugs • Arrays are first-class objects • Array bounds are always checked • Multiple inheritance replaced by interfaces • Eliminates complexities of multiple inheritance

4. Features removed from C++ • No typedefs, defines or preprocessor • No header files • No structures or unions • No enums • No functions - only methods in classes • No multiple inheritance • No goto • No operator overloading (except “+” for string concatenation) • No automatic type conversions (except for primitive types) • No pointers

5. Java Virtual Machine • Java is compiled into bytecodes • Bytecodes are high-level, machine-independent instructions for ahypothetical machine, the Java Virtual Machine (JVM) • The Java run-time system provides the JVM • The JVM interprets the bytecodes during program execution • Since the bytecodes are interpreted, the performance of Javaprograms slower than comparable C/C++ programs • But the JVM is continually being improved and new techniquesare achieving speeds comparable to native C++ code

6. Types of Java Programs • Application • Standalone Java program that can run independent of any Web browser • Applet • Java program that runs within a Java-enabled Web browser • Servlet • Java software that is loaded into a Web server to provide additional serverfunctionality ala CGI programs

7. The Hello World Program • Create source file: Hello.java • public class Hello { • public static void main (String args[]) { • System.out.println("Hello World!"); • } • } • Note that the name of the file is the name of the public class witha .java extension added • Compile: javac Hello.java • Produces the class file Hello.class • Run: java Hello • Starts up the JVM • Note that the .class extension is not specified

8. Some Java OO Technology • Class - collection of data (attributes) and methods that operate onthat data • Member - either an attribute or a method of a class • Public Member - member which is accessible by any method inany class • Private Member - member which is accessible only by methodsdefined within the class • Public Class - class that is visible everywhere and can be used byany method in any class • Object - instance of a class • Object Instantiation - the creation of a new object

9. Some Java OO Technology • Constructor - method which performs object initialization (notcreation!) • Object Reference - variable that holds a reference to (really thememory address of) an object • Instance Variable - attribute for which each object (instance) hasits own copy • Class Variable - attribute for which there is only one copy for theclass. • Each object (instance) shares this copy. Also called astatic variable

10. Some Java OO Technology • Instance Method - method which operates on the attributes of anobject (instance) • Class Method - method which does not operate on a particularobject, but performs some utility function or operates on staticvariables. Also called a static method. • Method Signature - the number, type and order of arguments of amethod • Method Overloading - defining a method with the same name butdifferent signature as another method in the same class

11. Download & Install the JavaSDK (or JDK) • Recommended Java version– JDK 1.6 • Obtain at http://java.com/en/download/index.jsp • Minimum supported Java version • – Servlets 2.3 and JSP 1.2 (standalone servers). • Java 1.2 or later. • – J2EE 1.3 (which includes servlets 2.3 and JSP 1.2). • Java 1.3 or later. • – Servlets 2.4 and JSP 2.0 (standalone servers). • Java 1.3 or later. • – J2EE 1.4 (which includes servlets 2.4 and JSP 2.0). • Java 1.4 or later.

12. Server Setup and Configuration • Download and install the Java SoftwareDevelopment Kit (SDK) • Download a server. • Configure the server • Set up your development environment • Test your setup • Establish a simplified deployment method • Create custom Web applications

13. Download a Free Serverfor Your Desktop • Apache Tomcat • – http://jakarta.apache.org/tomcat/ • – For installation and setup details, see http://www.coreservlets.com/Apache-Tomcat-Tutorial/ • Macromedia JRun • – http://www.macromedia.com/software/jrun/ • Caucho Resin • – http://caucho.com/products/resin/ • New Atlanta ServletExec • – http://www.newatlanta.com/products/servletexec/ • Jetty • – http://jetty.mortbay.org/jetty/

14. Apache Tomcat • Apache Tomcat is developed in an open and participatory environment and released under the Apache License version 2. • Apache Tomcat is intended to be a collaboration of the best-of-breed developers from around the world. • Apache Tomcat powers numerous large-scale, mission-critical web applications across a diverse range of industries and organizations. • Some of these users and their stories are listed on the PoweredBy wiki page.

15. Apache Tomcat • Setup Tomcat 5.0.27 on your computer.  • Download from http://www.coreservlets.com/Apache-Tomcat-Tutorial/index.html. • Unzip into the top level of the C drive. • Set JAVA_HOME • Set this environment variable to point at the top-level of your Java installation directory (e.g.,C:\Program Files\Java\jdk1.7.0_03). • Use the Control Panel or start this 

16. Apache Tomcat • Test the server. • Make sure you can start/stop the server. Test some sample HTML files, JSP pages, and servlets. • For Tomcat, click oninstall_dir/bin/startup.bat. Next, enter the URL http://localhost/ in your browser and make sure you get the Tomcat welcome page, • not an error message saying that the page could not be displayed or that the server could not be found.

17. Configure the Server • Identify the SDK installation directory. • – For Tomcat: set JAVA_HOME • Specify the port. • – Change the port from default (usually 8080) to 80 • Make server-specific customizations. • – For Tomcat: • Enable servlet reloading • Enable the ROOT context • Turn on the invoker servlet • See book or refer to http://www.coreservlets.com/ApacheTomcat-Tutorial/

18. Set Up Your DevelopmentEnvironment • Create a development directory • – Choose a location in which to develop your servlets, JSP documents, and supporting classes (e.g., C:\Servlets+JSP) • Set your CLASSPATH • – Tell the compiler about the servlet and JSP JAR file and the location of your development directory. • – Setting this variable incorrectly is the single mostcommon cause of problems for beginners. • Make shortcuts to start and stop the server • – Make sure it is convenient to start and stop the server. • Bookmark or install the servlet and JSP APIdocumentation • – You’ll refer to this documentation frequently, so keep ithandy.

19. Test Your Setup • Verify your Java installation • – Be sure that you get meaningful results for both of these: • java -version • javac -help • Check your basic server configuration • – Start server and access the server home page (http://localhost/) • – Access a simple user-defined HTML page • Download Hello.html from book's source code archive • Put in install_dir/webapps/ROOT • Access with http://localhost/Hello.html • – Access a simple user-defined JSP page • Download Hello.jsp and put in install_dir/webapps/ROOT • Access with http://localhost/Hello.jsp

20. Test Your Setup • Compile and deploy a packagelessservlet – Download HelloServlet.java from source code archive – Place in development directory (e.g., C:\Servlets+JSP) – Compile (if errors, check CLASSPATH) – Move HelloServlet.class to install_dir/webapps/ROOT/WEB-INF/classes – Access with http://localhost/servlet/HelloServlet

21. Test Your Setup • Compile and deploy a packaged servlet • – Download HelloServlet2.java from source code archive • – Place in coreservlets subdirectory of development directory (e.g., C:\Servlets+JSP\coreservlets) – Compile (if errors, check CLASSPATH) – Move HelloServlet2.class toinstall_dir/webapps/ROOT/WEBINF/classes/coreservlets – Access with http://localhost/servlet/coreservlets.HelloServlet2

22. Test Your Setup • Compile and deploy a packaged servlet that uses a helper class • – Download HelloServlet3.java and ServletUtilities.java • – Place in coreservlets subdirectory of development dir • – Compile (if errors, check CLASSPATH) • – Move both class files to install_dir/webapps/ROOT/WEBINF/classes/coreservlets • – Access with http://localhost/servlet/coreservlets.HelloServlet3

23. A Servlet’s Job • Read explicit data sent by client (form data) • Read implicit data sent by client (request headers) • Generate the results • Send the explicit data back to client (HTML) • Send the implicit data to client (status codes and response headers)

24. The Advantages of ServletsOver “Traditional” CGI • Efficient – Threads instead of OS processes, one servlet copy • • Convenient • – Lots of high-level utilities • • Powerful • – Sharing data, pooling, persistence • • Portable • – Run on virtually all operating systems and servers • • Inexpensive • – There are plenty of free and low-cost servers • • Secure • – No shell escapes, no buffer overflows

25. Mainstream • Popular: • – The single most common use of Java technology • – The leading technology for medium/large Web applications • • Supported by: • – Apache, Oracle, IBM, Sybase, BEA, Macromedia, Caucho, • Sun/iPlanet, New Atlanta, ATG, Fujitsu, Lutris, Silverstream, the • World Wide Web Consortium (W3C), and many others • – Plugins for IIS and Zeus • • Runs on: • – Windows, Unix/Linux, MacOS,VMS, and IBM mainframe OSs • • Used for: • – Airline companies, hotels,e-commerce sites, search engines, banks, financial sites, etc., etc., etc.

26. Extending the Power of Servlets:JavaServer Pages (JSP) • Uses of JSP ConstructsUses of JSP Constructs • Scripting elements calling servletcode directly • Scripting elements calling servletcode indirectly (by means of utilityclasses) • Beans • Servlet/JSP combo (MVC) • MVC with JSP expression language • Custom tags

27. Extending the Power of Servlets:JavaServer Pages (JSP) • Idea: • – Use regular HTML for most of page • – Mark dynamic content with special tags • <HTML> • <HEAD><TITLE>Welcome to Our Store</TITLE></HEAD> • <BODY> • <H1>Welcome to Our Store</H1> • <SMALL>Welcome, • <!-- User name is "New User" for first-time visitors --> • <%= coreservlets.Utils.getUserNameFromCookie(request) %> • To access your account settings, click • <A HREF="Account-Settings.html">here.</A></SMALL> • <P> • Regular HTML for rest of on-line store’s Web page • </BODY></HTML>

28. Basic Syntax • HTML Text • – <H1>Blah</H1> • – Passed through to client. Really turned into servlet code • that looks like • out.print("<H1>Blah</H1>"); • HTML Comments • – <!-- Comment --> • – Same as other HTML: passed through to client • JSP Comments • – <%-- Comment --%> • – Not sent to client • To get <% in output, use <\%

29. Types of Scripting Elements Expressions • – Format: <%= expression %> • – Evaluated and inserted into the servlet’s output. I.e., results in something like out.print(expression) • Scriptlets • – Format: <% code %> • – Inserted verbatim into the servlet’s _jspService method(called by service) • Declarations • – Format: <%! code %> • – Inserted verbatim into the body of the servlet class,outside of any existing methods

30. JSP Expressions • Format • – <%= Java Expression %> • Result • – Expression evaluated, converted to String, and placed into HTML page at the place it occurred in JSP page • – That is, expression placed in _jspService inside out.print • Examples • – Current time: <%= new java.util.Date() %> • – Your hostname: <%= request.getRemoteHost() %> • XML-compatible syntax • – <jsp:expression>Java Expression</jsp:expression> • – You cannot mix versions within a single page. You must use XML for entire page if you use jsp:expression.

31. JSP/Servlet Correspondence • Original JSP • <H1>A Random Number</H1> • <%= Math.random() %> • Representative resulting servlet code • public void _jspService(HttpServletRequest request, • HttpServletResponse response) • throws ServletException, IOException { • response.setContentType("text/html"); • HttpSession session = request.getSession(true); • JspWriter out = response.getWriter(); • out.println("<H1>A Random Number</H1>"); • out.println(Math.random()); • ... • }

32. Hello Web App • As a first web application, we'll use the Hello World example : • Create a directory called hello within webapps, then within that create a file called Hello.jsp.  • Copy the following text into it: • <html> • <head> <title> Hello JSP </title> </head> • <body> • <p> Hello World: <%= new java.util.Date() %> </p> • </body> • </html>

33. Hello Web App Now click on this URL: http://localhost/hello/Hello.jsp, and you should see a page like this one:

34. JSP Expressions: Example • <HTML> <BODY> • <H2>JSP Expressions</H2> • <UL> • <LI>Current time: <%= new java.util.Date() %> • <LI>Server: <%= application.getServerInfo() %> • <LI>Session ID: <%= session.getId() %> • <LI>The <CODE>testParam</CODE> form parameter: • <%= request.getParameter("testParam") %> • </UL> • </BODY></HTML>

35. Predefined Variables • request • – The HttpServletRequest (1st argument to service/doGet) • response • – The HttpServletResponse (2nd arg to service/doGet) • out • – The Writer (a buffered version of type JspWriter) used to send output to the client • session • – The HttpSession associated with the request (unless • disabled with the session attribute of the page directive) • application • – The ServletContext (for sharing data) as obtained via • getServletContext().

36. JSP Declarations: Example • <!DOCTYPE …> • <HTML> • <HEAD> • <TITLE>JSP Declarations</TITLE> • <LINK REL=STYLESHEET HREF="JSP-Styles.css“ TYPE="text/css"> • </HEAD> • <BODY> • <H1>JSP Declarations</H1> • <%! private int accessCount = 0; %> • <H2>Accesses to page since server reboot: • <%= ++accessCount %></H2> • </BODY></HTML>

37. Making Custom Web Apps • Make a directory whose structure mirrorsthe structure of the default Webapplication. • HTML (and, eventually, JSP) documents go in the toplevel directory (e.g. sample) • apache-tomcat-1.6.028/webapp/sample • The web.xml file goes in the WEB-INF subdirectory • Servlets and other classes go either in WEB-INF/classes or a subdirectory of WEB-INF/lib that matches thepackage name. • On Tomcat, entire directory goes in install_dir/webapps • Update your CLASSPATH. • Add webAppDir/WEB-INF/classes to it.

38. Making Custom Web Apps • Use the directory name in the URL • • All URLs should be of the formhttp://host/webAppDir/… • • Use web.xml to assign custom URLs • • Use the servlet and servlet-mapping elements • <servlet> • <servlet-name>Servlet2</servlet-name> • <servlet-class> • coreservlets.HelloServlet2 • </servlet-class> • </servlet> • <servlet-mapping> • <servlet-name>Servlet2</servlet-name> • <url-pattern>/servlet2</url-pattern> • </servlet-mapping>

39. The Servlet Life Cycle • init • – Executed once when the servlet is first loaded. • Not called for each request. • service • – Called in a new thread by server for each request. • Dispatches to doGet, doPost, etc. • Do not override this method! • doGet, doPost, doXxx • – Handles GET, POST, etc. requests. • – Override these to provide desired behavior. • destroy • – Called when server deletes servlet instance. • Not called after each request.

40. The Role of Form Data • Example URL at online travel agent • http://host/path?user=Marty+Hall&origin=bwi&dest=lax • Names come from HTML author; values from end user • Parsing form (query) data in traditional CGI • – Read the data one way (QUERY_STRING) for GET requests, another way (standard input) for POST requests • – Chop pairs at ampersands, then separate parameter names (left of the =) from parameter values (right of the =) • – URL decode values (e.g., "%7E" becomes "~") • Greatly simplified in servlets • – Use request.getParameter in all cases. • – Gives URL-decoded result

41. Creating Form Data:HTML Forms • <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0Transitional//EN"> • <HTML> • <HEAD><TITLE>A Sample Form Using GET</TITLE></HEAD> • <BODY BGCOLOR="#FDF5E6"> • <H2 ALIGN="CENTER">A Sample Form Using GET</H2> • <FORM ACTION="http://localhost:8088/SomeProgram"> • <CENTER> • First name: • <INPUT TYPE="TEXT" NAME="firstName" VALUE="Joe"><BR> • Last name: • <INPUT TYPE="TEXT" NAME="lastName" VALUE="Hacker"><P> • <INPUT TYPE="SUBMIT"> <!-- Press this to submit form --> • </CENTER></FORM> • </BODY></HTML>

42. Installing HTML Files • HTML files do not go in WEB-INF/classes • – They go in directory that contains WEB-INF • Tomcat • – install_dir\webapps\ROOT\Form.html or • – install_dir\webapps\ROOT\SomeDir\Form.html • URL • – http://localhost/Form.html or • – http://localhost/SomeDir/Form.html • Custom Web applications • – Use a different dir with the same structure as the default • Web app • – Use directory name in URL (http://host/dirName/…)

43. Sending POST Data • <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0Transitional//EN"> • <HTML> • <HEAD><TITLE>A Sample Form Using POST</TITLE></HEAD> • <BODY BGCOLOR="#FDF5E6"> • <H2 ALIGN="CENTER">A Sample Form Using POST</H2> • <FORM ACTION="http://localhost:8088/SomeProgram" • METHOD="POST"> • <CENTER> • First name: • <INPUT TYPE="TEXT" NAME="firstName" VALUE="Joe"><BR> • Last name: • <INPUT TYPE="TEXT" NAME="lastName" VALUE="Hacker"><P> • <INPUT TYPE="SUBMIT"> • </CENTER> • </FORM> • </BODY></HTML>

44. Reading Form Data In Servlets • request.getParameter("name") • – Returns URL-decoded value of first occurrence of name in query string • – Works identically for GET and POST requests • – Returns null if no such parameter is in query data • request.getParameterValues("name") • – Returns an array of the URL-decoded values of all • occurrences of name in query string • – Returns a one-element array if param not repeated • – Returns null if no such parameter is in query • request.getParameterNames() orrequest.getParameterMap() • – Returns Enumeration or Map of request params • – Usually reserved for debugging

45. Handling Input in MultipleLanguages • Use server's default character set • String firstName = request.getParameter("firstName"); • Convert from English (Latin-1) to Japanese • String firstNameWrongEncoding = • request.getParameter("firstName"); • String firstName = • new String(firstNameWrongEncoding.getBytes(),"Shift_JIS"); • Accept either English or Japanese • request.setCharacterEncoding("JISAutoDetect"); • String firstName = • request.getParameter("firstName");

46. Reading Raw Form Data andParsing Uploaded Files • Raw data • – request.getReader • – request.getInputStream • • Data no longer available via getParameter after this • Parsing uploaded files • – HTML has a way of submitting entire files • <INPUT TYPE="FILE"…> • – Servlet/JSP APIs have no builtin way to parse files • – Popular third-party library available from theApache/Jakarta “Commons” library • http://jakarta.apache.org/commons/fileupload/

47. An HTML Form With ThreeParameters • <FORM ACTION="/servlet/coreservlets.ThreeParams"> • First Parameter: <INPUT TYPE="TEXT" NAME="param1"><BR> • Second Parameter: <INPUT TYPE="TEXT" NAME="param2"><BR> • Third Parameter: <INPUT TYPE="TEXT" NAME="param3"><BR> • <CENTER><INPUT TYPE="SUBMIT"></CENTER> • </FORM>

48. Reading the Three Parameters • public class ThreeParams extends HttpServlet { • public void doGet(HttpServletRequest request, • HttpServletResponse response) • throws ServletException, IOException { • … • out.println(docType + "<HTML>\n" + • "<HEAD><TITLE>"+title + "</TITLE></HEAD>\n" + • "<BODY BGCOLOR=\"#FDF5E6\">\n" + • "<H1 ALIGN=\"CENTER\">" + title + "</H1>\n" + • "<UL>\n" +" <LI><B>param1</B>: " • + request.getParameter("param1") + "\n" + " <LI><B>param2</B>: " • + request.getParameter("param2") + "\n" + " <LI><B>param3</B>: " • + request.getParameter("param3") + "\n" + "</UL>\n" + • "</BODY></HTML>"); }}