1.264 Lecture 15. Web development environments: JavaScript Java applets, servlets Java (J2EE) Active Server Pages

Transcription

1 1.264 Lecture 15 Web development environments: JavaScript Java applets, servlets Java (J2EE) Active Server Pages

2 Development environments XML, WSDL are documents SOAP is HTTP extension UDDI is a directory/registry of services, sites Allow servers, services to be found Browsers and client apps can handle these new protocols Less need for dynamic content to be downloaded Servers must generate and receive XML, SOAP, Straightforward extensions to HTTP, MIME types Java (J2EE) and Active Server Pages (ASP.NET) are the server environments that manage this Java (J2EE) and C#, C++ and Visual Basic (ASP) are programming languages used on servers Scripts and applets are used on the client side, but are relatively less important JavaScript, VBScript, Java applets are used on clients

3 Java, JavaScript, Java Beans < Run on server > -----Run on client-----> Developed independently by Sun (Java, Java Beans) and Netscape (JavaScript) Java and JavaScript, by chance, released in Netscape Navigator 2.0 JavaScript, JavaScriptBeans (JS components): Scripting language for HTML pages, using several new tags Can run on either browser (client) or Web server Java: Full programming language: Web and general programming Java applets: Limited Java programs running on browser (client) Java servlets: Full featured Java programs running on Web server Java Beans: Java programming language components Component model with standard interfaces (on server) PME (properties, methods, events) paradigm Enterprise Java Beans: database-oriented Java component Database transaction components: load balancing, rollbacks, Session components: maintaining state Java Server Pages: Simpler way of writing Java servlets on the Web server

4 Script basics (Java Script, VB Script) Script is program run on client or server in response to browser request Early scripts (Common Gateway Interface, or CGI) run on server only Modern script languages (VBScript, JavaScript) run on client or server JavaScript, VBScript are at least three times faster than CGI on server Active Server Pages specifies scripts to run on client and/or server Web scripts can be written in many languages Perl, C are typical choices in the past (and present) for server only VBScript and JavaScript are major options now for client Server side includes are a very simple script capability Include server variables, files, command outputs in html page sent to browser. SSI runs on server only. First part of this lecture focuses on scripts, primarily running on the browser These client scripts are loosely termed Dynamic HTML or DHTML Microsoft and Netscape DHTMLs are different and incompatible, though both support JavaScript (MS Jscript essentially identical) Server side scripts are used in the same way as server side programs, but only for simple operations

5 Motivation for scripts If sophisticated programs (Java, etc.) execute on server only, there are some problems: Send and receive html from browser, which is treated as dumb terminal Not very good interactively: long round-trip delay in displaying and getting forms with any internal logic or operations Economic issue (still unsolved): idle clients and expensive, loaded servers Solution is to put small programs on client machine to execute locally (though it hasn t been a great solution) Forms with built-in checking, animations, popup window prompts, (XML, XForms are better) Java, JavaScript, VBScript are distinct and confusingly named languages that address these issues JavaScript is now considered unsuitable: Security issues with loading unknown scripts on browser JavaScript capabilities limited; can be superseded by server

6 Browser-server interaction Step 1: Browser requests page without any parameters Step 2: Server fetches page, and returns empty input form Step 3: User fills out input form and presses submit button Step 4: Browser packages form into query string and sends to server Step 5: Program synthesizes a response document and returns it Browser Side GET /MyApp/MyPage xxxxxx xxxxxx GET /MyApp/MyProg?name=Pat Server Side Web svr Web svr MyProg MyProg Every dynamic validation, fill-in requires server intervention. - If later choices depend on earlier choices, etc. - JavaScript was felt to be solution, now XML, XSLT are - Pages can be XML or HTML

7 JavaScript (or VBScript) on browser Can read and write parts of their own documents and other documents the browser has open Limited access to browser resources (e.g., history list, back and forward buttons) Can read and set contents of fill-out forms, open new windows, create new documents (access to local folders!) Library of math and text manipulation functions Limited network communications, graphics and window creation Must use Java, not JavaScript, if you need to go beyond the bounds of an html document or a simple feature, such as: Animation, simulation, network communications, modules JavaScript has no modules and gets unwieldy after lines Use server side includes to fake a JavaScript library JavaScript code can t be kept private; Java can be compiled

8 Common JavaScript applications Create forward and backward buttons using history list Hard to know how user got to a static html page without JavaScript Create menus that select among URLs Conserve space by having list boxes instead of text lists Create scrolling or active headers or marquees Use function to shift strings one character at a time using settimeout() Create navigation bars in frames Allow menu in one frame to control display in another frame Extension of menus that select among URLs Again, these are simple enough that XML and XSLT can provide these features without downloading active content to the browser from a server

9 JavaScript applications, cont Validating fill-out form before submitting it Routine runs to check for required fields and valid formats If not correct, display alert box and refuse to submit form Creating pick lists for text fields using popup menus Creating shopping cart (not the best way to do it, though) Ecommerce application to add selected items to an order Frames can be used for short catalogs; windows for long catalogs Cookies must be used to maintain current status of cart Browsers reload JavaScript every time user resizes windows or frames Use local disk storage with cookie

10 JavaScript shopping cart example

11 Java applets (on browser) Java-enabled browsers can download and execute Java applets (small Java programs) Java applets are much more powerful than JavaScript Open own windows Create buttons Create animations on the fly, 3D model views, calculators, etc. Open network connections to home server, etc. Libraries for networks, graphics, multimedia, controls (widgets) Platform-independent: UNIX, Windows, Mac, Security features (much better than scripts or ActiveX) However, applets are still very limited because they run on the browser: No direct database access, little access to client hardware, less access to browser internal objects than JavaScript (due to security concerns)

12 Java applets Applets are embedded in HTML documents (like images) <APPLET> Browser examines tag to find location of Java code Browser downloads code, makes room on page, and runs it Usually from same server as HTML but not always Applet does the rest: Draws text, graphics into its space Interacts with user with its own buttons Most applets run in same windows, but some open new one Applet runs until user closes browser window or moves to different page

13 <APPLET> tag <APPLET CODE= name of applet compiled file (.class file) WIDTH= width of applet (pixels) HEIGHT= height of applet (pixels) CODEBASE= URL of applet ALT= alternate text to display NAME= applet name ALIGN= alignment VSPACE= extra whitespace above and below applet HSPACE= extra whitespace to left and right of applet > <PARAM NAME= first parameter VALUE= first value > <PARAM NAME= second parameter VALUE= second value > HTML text (ignored by applet; displayed by non-javaenabled browsers) </APPLET>

14 Java applet (runs on client, not server)

15 Java applet HTML <html> <head><title>charting Applet</title></head> <body><h1>charting Applet</h1> <APPLET CODEBASE="./applets" CODE="ChartUI" WIDTH=400 HEIGHT=300> <PARAM NAME="LocationType" VALUE=URL> <PARAM NAME="Location" VALUE="applets/goatdata.txt"> <PARAM NAME="Style" VALUE="3D Pie"> </APPLET>

16 Typical current Java applet examples Page decorations Marquees, banners, etc. Animation (set of.gif files that are looped through) Multimedia buttons Image maps (client side) Graphics (charts, graphs) Slide shows Real applications implemented as applets are rare... JavaScript can now pass parameters to applets Signed applets have more permissions than anonymous applets CORBA ORBs allow Java applets still more permissions (next lecture) Similar to JavaScript (or VB Script), this has not been very useful yet

17 Java on servers Java servlets. Implement the following steps: Read data sent by browser Usually entered by user, but could be from applet or JavaScript Look up other information from the HTTP request Browser capabilities, cookies, host, etc. from HTTP headers Generate results Access database, execute program (possibly via CORBA/COM), etc. Format the results as an HTML, XML or other Servlets can generate GIF, gzip, many MIME types Set HTTP response parameters in headers Send document back to browser Java Virtual Machine (JVM) runs the servlets on the server These evolved from applets (useless) into servlets (extremely useful, secure, standard)

18 import java.io.*; import javax.servlet.*; import javax.servlet.http.*; Servlet example public class Hello1264 extends HttpServlet { public void doget(httpservletrequest request, HttpServletResponse response) throws ServletException, IOException { response.setcontenttype("text/html"); PrintWriter out = response.getwriter(); String doctype = "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.0 " + "Transitional//EN\">\n"; out.println(doctype + "<HTML>\n" + "<HEAD><TITLE>Hello 1.264</TITLE></HEAD>\n" + "<BODY>\n" + "<H1>Hello 1.264</H1>\n" + "</BODY></HTML>");}}

19 Java Server Pages (JSP) Allows us to mix static HTML with dynamically generated content from servlets Many Web pages are primarily static Changeable parts are in only a few locations on the page A servlet requires us to generate the entire page dynamically each time JSP allows the Web designer to write static HTML and leave stubs for dynamic content Java programmers can then write the stubs Active Server Pages is very similar (homework 6) You won t need to write any code!

20 JSP example <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML> <HEAD> <TITLE>JSP Example</TITLE> <LINK REL=STYLESHEET HREF="JSP-Styles.css" TYPE="text/css"> </HEAD> <BODY> <H2>JSP Expressions</H2> <UL> <LI>Current time: <%= new java.util.date() %> <LI>Your hostname: <%= request.getremotehost() %> <LI>Your session ID: <%= session.getid() %> <LI>The <CODE>testParam</CODE> form parameter: <%= request.getparameter("testparam") %> </UL> </BODY> </HTML>

21 JSP Example 2 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML> <HEAD> <TITLE>Color Testing</TITLE> </HEAD> <% String bgcolor = request.getparameter("bgcolor"); boolean hasexplicitcolor; if (bgcolor!= null) { hasexplicitcolor = true; } else { hasexplicitcolor = false; bgcolor = "WHITE";} %>

22 JSP Example 2, cont. <BODY BGCOLOR="<%= bgcolor %>"> <H2 ALIGN="CENTER">Color Testing</H2> <% if (hasexplicitcolor) { out.println("you supplied an explicit background color of " + bgcolor + "."); } else { out.println("using default background color of WHITE. " + "Supply the bgcolor request attribute to try " + "a standard color, an RRGGBB value, or to see " + "if your browser supports X11 color names."); } %> </BODY> </HTML>

23 Example Active Server Page or ServerSide JavaScript page <HTML> <HEAD> Normal HTML page sections </HEAD> <BODY> <% %> Script that runs on server as pg created <SCRIPT LANGUAGE= JavaScript > Script that runs in browser as pg interpreted </SCRIPT> <SERVER> Script executed on server, as pg created </SERVER> <!--#include --!> Server-side include, e.g., script or HTML stored in files <TABLE> Normal HTML code... </TABLE> </BODY> </HTML>

24 Coordinating scripts on server and client Browsers support VBScript, JavaScript and Java (JVM) Server may execute some scripts or programs on its own machine, and return others to the browser for execution on the client Java applets, client side JavaScript and ActiveX controls are always executed on client: Applets are sent between <APPLET> and </APPLET> tags ActiveX controls are sent between <OBJECT> and </OBJECT> tags JavaScript is sent between <SCRIPT> and </SCRIPT> tags Scripts to be executed on server: <% %> or <SERVER> encloses scripts to be run on server This code executes as page is being generated/interpreted on server

25 JavaBeans Component model for Java servlets and Java Server Pages Support reusable application components Components are pre-developed pieces of application code that can be assembled and integrated into working applications Beans are encapsulated classes whose code cannot be changed All data (properties) have SetXxx and GetXxx methods This allows a visual Properties box to display and set all data (Beans also need a 0-argument constructor and have no public data) Beans are usually used in Java Server Pages, which offer the best component environment

26 Enterprise Java Beans (EJBs) HTTP server Servlet, JSP Session object Entity object Web client Web server/ container EJB server/ container Database

27 EJBs, cont Session beans Represents client (browser), always a single client Keeps state : the status and current representation of the session (or can be stateless) Creates session bean just in time when needed, for efficiency and load balancing Entity beans Representations of back end data: a database, almost always Persistent, represent one object (often a table) Manages transactions, including rollbacks if failures Two phase commit, just as databases use Both EJBs are highly reusable and portable Sharply reduce programming effort Can be attached, configured in many ways by nonprogrammers

28 Summary: Java (J2EE) environment Application server Application server HTML, XML Java virtual machine Web server Java virtual machine Java RMI, XML EJBs XML databases Other Windows Linux

29 Active Server Pages Architecture Internet Internet Information Server (IIS) CGI Perl, Awk Active Server Pages (DLLs) Server-side includes VB Script J Script ASP ADO ODBC components Active Server Pages (.ASP files) Data