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11 – OOP Design

11 – OOP Design. Session Aims & Objectives. Aims To cover a range of web-application design techniques Objectives, by end of this week’s sessions, you should be able to: create a servlet Create and use a Java Bean use a class to gather code common to different pages SQL insertion attacks.

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11 – OOP Design

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  1. 11 – OOP Design

  2. Session Aims & Objectives • Aims • To cover a range of web-application design techniques • Objectives,by end of this week’s sessions, you should be able to: • create a servlet • Create and use a Java Bean • use a class to gather code common to different pages • SQL insertion attacks

  3. most application programs – 3 major layers Top (Presentation) layer: human/machine interaction (the user interface) input from the keyboard / mouse output in the form of screen displays / sound Middle (Application or business logic) layer: core functionality – gives application program its character contains business rules -> drive an organisation e.g. order entry system vs. inventory control system Bottom layer general services needed by other layers e.g. file, print, communications, and database services Application Layers 3

  4. 2-Tier Architecture Presentation and Application layer located on client machine could be implemented using Applet interacting server Known as a ‘fat client’

  5. 3-Tier Architecture 3-tier architecture, only presentation layer on client application layer on server Database on server or third machine Known as a ‘thin-client’ very little (application) code / processing on client e.g. use of Java Servlets (JSP pages)

  6. Example: AddNum (JSP) AddNum.jsp <%@page contentType="text/html" pageEncoding="UTF-8"%> <% double N1; double N2; String Res = ""; if (request.getParameter("btnAdd") != null){ N1 = Double.parseDouble(request.getParameter("txtN1")); N2 = Double.parseDouble(request.getParameter("txtN2")); Res = Double.toString(N1 + N2); } %> <!DOCTYPE html> <html> <head><title>Add Numbers</title></head> <body> <form method="post"> <input name="txtN1" type="text" /><br /> <input name="txtN2" type="text" /><br /> <input name="btnAdd" type="submit" value="Add" /> <p><%=Res%></p> </form> </body> </html> Java - functionality HTML – user interface

  7. JSP pages & Servlets • all JSP pages converted to servlet • Servlet • Java program running in web server • Special type of Java class (.java file) • Can get servlet error – caused by error in JSP page (usually missing } ), but difficult to see the connection

  8. AddNum: Servlet (.html file) • Split • User interface (html) • Functionality (Java) <!DOCTYPE html> <html> <head><title>Add Numbers</title></head> <body> <form method="post" action="AddNum"> <input name="txtN1" type="text" /><br /> <input name="txtN2" type="text" /><br /> <input name="btnAdd" type="submit" value="Add" /> </form> </body> </html> Points to Servlet (.java)

  9. AddNum: Servlet (.java file) import java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class AddNum extends HttpServlet { protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { double N1; double N2; String Res = ""; response.setContentType("text/html;charset=UTF-8"); PrintWriter out = response.getWriter(); try { N1 = Double.parseDouble(request.getParameter("txtN1")); N2 = Double.parseDouble(request.getParameter("txtN2")); Res = Double.toString(N1 + N2); out.println("<html>"); out.println("<head>"); out.println("<title>Add Numbers</title>"); out.println("</head>"); out.println("<body>"); out.println(Res); out.println("</body>"); out.println("</html>"); } finally { out.close(); } } @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { processRequest(request, response); } @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { processRequest(request, response); } @Override public String getServletInfo() { return "Short description"; } } protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { double N1; double N2; String Res = ""; response.setContentType("text/html;charset=UTF-8"); PrintWriter out = response.getWriter(); try { N1 = Double.parseDouble(request.getParameter("txtN1")); N2 = Double.parseDouble(request.getParameter("txtN2")); Res = Double.toString(N1 + N2); out.println("<html>"); out.println("<head>"); out.println("<title>Add Numbers</title>"); out.println("</head>"); out.println("<body>"); out.println(Res); out.println("</body>"); out.println("</html>"); } finally { out.close(); } } Calculationcode Also, write html

  10. Example: PeopleList.jsp v2 <%@page import="java.sql.*"%> <%@page contentType="text/html"%> <% Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); Connection cn = DriverManager.getConnection("jdbc:odbc:PeopleDB", "", ""); Statement st = cn.createStatement(); ResultSet r = st.executeQuery("SELECT * FROM Person;"); String html = ""; String id; while(r.next()){ id = Integer.toString(r.getInt("PersonID")); html += "<a href='Person2.jsp?id=" + id + "'>"; html += r.getString("Surname") + "</a><br />"; } cn.close(); %> <!DOCTYPE html> <html> <head><title></title></head> <body> <%=html%> </body> </html> Connect to db

  11. Example: Person.jsp v2 <%@page import="java.sql.*"%> <%@page contentType="text/html" pageEncoding="UTF-8"%> <% String id = request.getParameter("id"); Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); Connection cn = DriverManager.getConnection("jdbc:odbc:PeopleDB", "", ""); Statement st = cn.createStatement(); ResultSet r = st.executeQuery("SELECT * FROM Person WHERE PersonID = " + id + ";"); String surname = ""; if(r.next()){ surname = r.getString("Surname"); } cn.close(); %> <!DOCTYPE html> <html> <head><title>Person</title></head> <body> Surname: <input name="txtSurname" type="text" value="<%=surname%>" /> </body> </html> Connect to DB

  12. Person & PeoplList v2 <%@page import="java.sql.*"%> <%@page contentType="text/html" pageEncoding="UTF-8"%> <% String id = request.getParameter("id"); Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); Connection cn = DriverManager.getConnection("jdbc:odbc:PeopleDB", "", ""); Statement st = cn.createStatement(); ResultSet r = st.executeQuery("SELECT * FROM Person WHERE PersonID = " + id + ";"); String surname = ""; if(r.next()){ surname = r.getString("Surname"); } cn.close(); %> <!DOCTYPE html> <html> <head><title>Person</title></head> <body> Surname: <input name="txtSurname" type="text" value="<%=surname%>" /> </body> </html> • both JSP page duplicate common code <%@page import="java.sql.*"%> <%@page contentType="text/html"%> <% Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); Connection cn = DriverManager.getConnection("jdbc:odbc:PeopleDB", "", ""); Statement st = cn.createStatement(); ResultSet r = st.executeQuery("SELECT * FROM Person;"); String html = ""; String id; while(r.next()){ id = Integer.toString(r.getInt("PersonID")); html += "<a href='Person2.jsp?id=" + id + "'>"; html += r.getString("Surname") + "</a><br />"; } cn.close(); %> <!DOCTYPE html> <html> <head><title></title></head> <body> <%=html%> </body> </html>

  13. Class People • Contains common code for both pages People cn st r Open Select Close

  14. JavaBean: People.java 1 • Common code package Main; import java.sql.*; public class People{ private Connection cn; private Statement st; private ResultSet r; public void Open(){ try{ Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); cn = DriverManager.getConnection("jdbc:odbc:PeopleDB", "", ""); } catch (Exception e){ //e.printStackTrace(); } } public void Select(String sql){ try{ st = cn.createStatement(); r = st.executeQuery(sql); } catch (Exception e){ //e.printStackTrace(); } } package Main; import java.sql.*; public class People{ private Connection cn; private Statement st; private ResultSet r; public void Open(){ try{ Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); cn = DriverManager.getConnection("jdbc:odbc:PeopleDB", "", ""); } catch (Exception e){ //e.printStackTrace(); } } public void Select(String sql){ try{ st = cn.createStatement(); r = st.executeQuery(sql); } catch (Exception e){ //e.printStackTrace(); } } public boolean Next(){ boolean found = false; try{ found = r.next(); } catch (Exception e){ //e.printStackTrace(); } return found; } public String get(String id){ String s = ""; try{ s = r.getString(id); } catch (Exception e){ //e.printStackTrace(); } return s; } public void Close(){ try{ cn.close(); } catch (Exception e){ //e.printStackTrace(); } } }

  15. JavaBean: People.java 2 • Common code public boolean Next(){ boolean found = false; try{ found = r.next(); } catch (Exception e){ //e.printStackTrace(); } return found; } public String get(String id){ String s = ""; try{ s = r.getString(id); } catch (Exception e){ //e.printStackTrace(); } return s; } public void Close(){ try{ cn.close(); } catch (Exception e){ //e.printStackTrace(); } } } package Main; import java.sql.*; public class People{ private Connection cn; private Statement st; private ResultSet r; public void Open(){ try{ Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); cn = DriverManager.getConnection("jdbc:odbc:PeopleDB", "", ""); } catch (Exception e){ //e.printStackTrace(); } } public void Select(String sql){ try{ st = cn.createStatement(); r = st.executeQuery(sql); } catch (Exception e){ //e.printStackTrace(); } } public boolean Next(){ boolean found = false; try{ found = r.next(); } catch (Exception e){ //e.printStackTrace(); } return found; } public String get(String id){ String s = ""; try{ s = r.getString(id); } catch (Exception e){ //e.printStackTrace(); } return s; } public void Close(){ try{ cn.close(); } catch (Exception e){ //e.printStackTrace(); } } }

  16. PersonList.jsp • Class complex • Pages simpler Create Bean <jsp:useBean id="p" scope="session" class="Main.People" /> <%@page contentType="text/html" pageEncoding="UTF-8"%> <% String html = ""; p.Open(); p.Select("SELECT * FROM Person;"); while(p.Next()){ html += p.get("Surname") + "<br />"; } p.Close(); %> <!DOCTYPE html> <html> <head><title>People</title></head> <body> <%=html%> </body> </html> Use methods

  17. Apache – http server (html pages) Tomcat – runs JSP + Servlets servlet container (interpreter/compiler) Can run: Standalone Handles simple page requests Handles servlet requests Apache plugin Apache handles HTML pages, CGI, PHP etc Tomcat handles servlets Apache TOMCAT

  18. Tomcat: LocalHost

  19. TOMCAT DIRECTORY STRUCTURE

  20. Tomcat Folder Structure Context root Starting html page Netbeans Will create this Structure … Web application deployment descriptor (web.xml) Package name of the HelloServlet class The HelloServlet class

  21. fgfg Tomcat Folder Structure But each need WEB-INF and web.xml Default location is in webapps Can have any number of webapplications in webapps

  22. Apache Tomcat - NetBeans • JRE_HOME = C:\Program Files\Java\jre6 • Control Panel • System • Advanced • Environment Variables • C:\Program Files\Apache Software Foundation\Apache Tomcat 7.0.14\bin • startup.bat (run from command line) • http://localhost:8080/

  23. JSP programming style strongly encourages the use of JavaBeans. There are special tags built-in to support JavaBean properties. JSP + Bean combination separates the html look of the page from the ‘logic’ i.e. the presentation from the code A JavaBean, or sometimes just called a bean, is basically an instance of a Java class. JSP AND JAVABEAN 23

  24. A Java class meeting specific requirements: Must have a zero-argument constructor: e.g. public MyBean() {… } Must have no public attributes All attributes should be private All data should be accessed via access methods WHAT IS A JAVABEAN 24

  25. BANKACCOUNT BEAN Get and set methods MUST conform to getXxxx() and setXxxx() Beans MUST be in packages No Parameter constructor Important Exception is for boolean attributes isXxxx() Can have other methods but method names cannot look like property get / set 25

  26. An attribute is a variable which belongs to an class/object For objects also known as instance variables For classes also known as class variables Remember final static int COLOUR_ONE Math.PI is a class variable A property is an attribute which has getter and setter methods And that’s it ! REFINING THE TERMINOLOGY 26

  27. Read-only properties: String getAccountID() returns the accountID property Read/write properties: void setBalance(double bal) double getBalance() Boolean properties: boolean isActive() void setActive(boolean act) JAVABEAN PROPERTIES 27

  28. It is important to distinguish between a JavaBean as used in a: GUI development tool This is a visual component i.e. will subclass Panel, Button etc. Note there is a visual Bean design tool at: http://java.sun.com/products/javabeans/beanbuilder/index.jsp Server-Side application We are only dealing with the latter MORE THAN ONE BEAN 28

  29. <jsp: useBean ……… > <jsp: setProperty ……… > <jsp: getProperty ……… > BEAN RELATED TAGS 29

  30. BEANS WITH JSP A JSP file which makes use of the Class Bank Note: file called Bank.jsp 30

  31. CREATING AN OBJECT Creates a bean instance called ‘myAccount’ of type ‘BankAccount’ The id attribute is the name of the variable Similar to the following JSP code: <% BankAccountmyAccount = new BankAccount(); %> Or Java: BankAccountmyAccount = new BankAccount(); Note: use of package name Important This / is important 31

  32. SETTING BEAN PROPERTIES 1 Sets the value of the myAccountpropertybalance to 500 Basically the same operation as: <%= myAccount.setBalance(500) %> Or in Java as: BankAccountmyAccount = newBankAccount(); mybalance = myAccount.setBalance(500); 32

  33. SETTING BEAN PROPERTIES 2 Also can have a dynamic property which uses an expression tag This example is just setting the balance to some random value between 0 and 100 33

  34. SETTING BEAN PROPERTIES 3 Although this value is text It is converted automatically in the right type In this case a double 34

  35. READING BEAN PROPERTIES Inserts the value of myAccountpropertybalance into the web page Basically the same as: <%= myAccount.getBalance() %> Or in Java as: BankAccountmyAccount = newBankAccount(); double mybalance; mybalance = myAccount.getBalance(); 35

  36. BEANS WITH JSP - REVIEW Note how the value is displayed on the html page This line creates an object called myAccount of class BankAccount This line sets the balance property to 500 This line gets the balance 36

  37. SETTING BEAN PROPERTIES FROM TEXT BOXES This the same as: String bal = request.getParamter(“openingbalance”); double tempBal = Double.parseDouble(bal); myaccount.setBalance(tempBal); .htmlPage Sets the property ‘balance’ to what ever was typed in the textbox. .jsp Page 37

  38. USING TEXTBOXES If the textbox name is the same name as the property Then we do not need a ‘param’ 38

  39. SETTING BEAN PROPERTIES … ‘WILDCARDS’ Using wildcards to set properties: • Sets the value of all ‘somebean’ properties to JSP parameters with the same name • If the parameters do not exist, the value of the bean properties do not change 39

  40. ‘WILDCARDS’ EXAMPLE OpenAccount.html NewAccount.jsp 40

  41. ‘WILDCARDS’ EXAMPLE 41

  42. scope= “page” scope= “request” These beans will not last after the request is completed The difference between these 2 scopes is very small Beans such as this do not allow you to share data between servlets and JSPs scope= “application” scope= “session” These beans will last between requests, thus allowing sharing of data between requests Again, the differences between these two requests are mostly cosmetic JAVABEAN SCOPE 1 The default scope 42

  43. SESSION BEANS As Bank.jsp and Rent.jsp are scoped at session level, the object myAccount is not created in Rent.jsp File: Rent.jsp 43

  44. SESSION BEANS File: Bank.jsp File: Rent.jsp The file Bank.jsp Creates the object myAccount, which is then used by Rent.jsp Essentially passing information between JSP pages 44

  45. CONDITIONAL BEANS So far we have used the <jsp: useBean id =“somebean…. > tag jsp:useBean results in new bean being created only if no bean with same id and scope can be found. If a bean with same id and scope is found, then that bean is used. This means that any property we initially set will be again be set each time we visit the page This is ok when we visit the a page for the 1st time as we want to set the properties of the bean which will be used across several pages. But what if we wanted to set initial bean properties for a bean which is shared by multiple pages. Since we don’t know which page will be accessed first, we don’t know which page should contain the initialization code. 45

  46. EXAMPLE: Lets assume we have a ‘back’ link on the PayRent.jsp ??? Balance should be 350.00  46

  47. Problem is that when we return to the Bank.jsp page the setProperty sets the balance to 500 again 47

  48. SOLUTION USE A CONDITIONAL BEAN The <jsp:useBean ... /> replaced by <jsp:useBean ...> statements </jsp:useBean> The statements (i.e. jsp:setProperty elements) are executed only if a new bean is created, not if an existing bean is found. This is subtle but the effects are profound Modified file: Bank.jsp 48

  49. EXAMPLE: Now we have Balance is correct at 350.00  49

  50. Hall, M. Servlets and Java Server Pages 2nd Edition Chapter 14: Using Beans with JSP Best coverage Armstrong, E. (2003) The J2EE 1.4 Tutorial chapter 12: Pages 515 - 525 http://java.sun.com/j2ee/1.4/docs/tutorial/doc/index.html REFERENCES - READ AT LEAST ONE OF … 50

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