6- JSP pages. Juan M. Gimeno, Josep M. Ribó. January, 2008

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1 6- JSP pages Juan M. Gimeno, Josep M. Ribó January, 2008

2 Contents Introduction to web applications with Java technology 1. Introduction. 2. HTTP protocol 3. Servlets 4. Servlet container: Tomcat 5. Web application deployment 6. JSP 1

3 6- JSP. Contents From servlets to JSP pages Components of a JSP page Directives Expressions Scriptlets Declarations Implicit objects Examples 2

4 2. Web applications. 2.6 JSP pages 2.6 JSP pages. Difficulties with servlets A servlet manages the creation of a web page through its output stream in a way which is non-intuitive and difficult to generate and to maintain: Both the static and the dynamic elements of the web page are managed by the same code Static elements: Those elements that do not change in the resulting page through different requests (e.g., page headers and footers, table structure...) Dynamic elements: Those elements that depends on the parameters of the request and may change in different requests (e.g., table contents) Page contents are generated by means of calls to usual output methods (e.g., println...), which are combined with other programming instructions. The structure of the resulting page is obscure. Each servlet is a complete class with several methods and a complex lifecycle. 3

5 2. Web applications. 2.6 JSP pages JSP pages. A solution Idea: Do not program servlets directly, but a JSP web page What is a JSP web page It is a usual web page written in html that incorporates some dynamic elements (e.g., java expressions, java code, tag actions and java beans). A JSP page is translated automatically into a servlet. When the JSP page is requested, the servlet associated to it is executed. The result of the execution of that servlet is an html page that contains: The static (html) code of the JSP page The result of the execution of the java expressions and code of its dynamic part JSP pages are executed within a JSP container. TOMCAT is a servlet and JSP container 4

6 2. Web applications. 2.6 JSP pages JSP pages. How do they work hello.jsp NO is there a servlet for hello.jsp? YES Translate into a servlet hello.jsp >hello_jsp.java NO is the servlet more recent than hello.jsp? Compile hello_jsp.java > hello_jsp.class YES Create an object obj of the class hello_jsp.class NO is there already an object obj of hello_jsp.class? send the request to obj YES 5

7 2. Web applications. 2.6 JSP pages The first JSP page page import="java.io.*,java.text.*,java.util.*"%> <HTML> <head> <title> First JSP page </title> </head> <body> <h3> First JSP page </h3> <p>hola... <p>1+2= <% int p; p=1+2; %> <%=p%> </body> </html> 6

8 Introduction to web applications with Java. 2.6 JSP pages. Components of a JSP page Components of a JSP page A JSP page is an html page which incorporates some dynamic items which are executed at run time by the server. A JSP page is translated automatically into a specific servlet. As a result of the execution of this servlet, the client receives a new page which consists of The html elements of the original JSP page returned verbatim and The result of the execution of the dynamic ones by the servlet. We call resulting page to the page resulting from the execution of the servlet associated to the JSP page. 7

9 Introduction to web applications with Java. 2.6 JSP pages. Components of a JSP page Components of a JSP page (2) The dynamic items in a JSP page: Directives Expressions Scriptlets Declarations Tag actions Java beans 8

10 Introduction to web applications with Java. 2.6 JSP pages. Directives Directives Definition Directive elements specify attributes of the page itself (i.e., information associated to the page). The type of the content that will be generated by the JSP page The page that will be shown if some error occurs during the execution of the JSP page The library that defines certain actions used in the page The name of a file that contains a page header and which should be included as a header of the resulting page... 9

11 Introduction to web applications with Java. 2.6 JSP pages. Directives Directives (2) Syntax directive-name [attrib1="val1" attrib2="val2"...]%> Types JSP defines three standard directives: page include taglib 10

12 Introduction to web applications with Java. 2.6 JSP pages. Directives Page directive page [attribute1="value1" attribute2="value2"...%> The page directive specifies some attributes that apply to the page as a whole Examples: info: It gives some textual information on the purpose of the page. <%@ page info="page to upload files into a server" %> contenttype: The type of content that will be generated by the JSP page. <%@ page contenttype="text/html" %> 11

13 Introduction to web applications with Java. 2.6 JSP pages. Directives errorpage: The page that will be displayed if an exception occurs during the execution of a JSP page. <%@ page errorpage="errorhandler.jsp" %> iserrorpage: True if this is the error page activated as a result of an error caused by another page. For instance, the page errorhandler.jsp would contain the following directive: <%@ page iserrorpage="true" %> import: It imports java packages which are used by the java code contained in the page (scriptlets or expressions). <%@ page import="java.text.*" %> session: It informs whether the page needs an http session or not. <%@ page session="true" %> 12

14 Introduction to web applications with Java. 2.6 JSP pages. Directives Include directive It merges the contents of another file with the JSP page. This merging takes place before the translation of the JSP page into a servlet. It may be used to include common header pages or procedures. <%@ include file="commonheader.html" %> It is different from the standard tag action <jsp:include> 13

15 Introduction to web applications with Java. 2.6 JSP pages. Directives Taglib directive It declares a tag action library so that it can be used in the JSP page. <%@ taglib uri="taglibraryuri" prefix="tagprefix"%> (See Introduction to tag libraries) 14

16 Introduction to web applications with Java. 2.6 JSP pages. Expressions Expressions Expressions containing java variables may be accessed in a JSP page in the following way: <%= java-expression %> Examples: <%= %> Current time is <%= new java.util.date() %> 15

17 Introduction to web applications with Java. 2.6 JSP pages. Scriptlets Scriptlets A scriptlet is a sequence of one or various java sentences which are included in the JSP page. These sentences provide the dynamic behaviour of the page. They are executed each time that the page is requested. The JSP container includes the contents of the scriptlet verbatim into the method jspservice() of the servlet into which the JSP page has been translated. <% sentence1; sentence2;... %> 16

18 Introduction to web applications with Java. 2.6 JSP pages. Example 1 Example: Pesetas to euros conversion Example location: introapweb/examples/ex6.1 <%@ page import="java.text.*" %> <html> <table border=1 cellpadding=3> <tr> <th>pesetas</th> <th>euros</th> </tr> <% String es=""; double e; int p; NumberFormat fmt= new DecimalFormat("###.00"); for (p=100; p<=1000; p+=50){ e=(double)p/ ; es=fmt.format(e); %> <tr> <td align="right"><%= p %></td> <td align="right"><%= es %></td> </tr> <% } %> </table> </html> 17

19 Introduction to web applications with Java. 2.6 JSP pages. Declarations Declarations Declarations are similar to scriptlets: They are sequences of one or various java sentences which are included in the JSP page. The difference with scriptlets is the following: The JSP container includes the contents of the declaration verbatim out of the method jspservice() of the servlet into which the JSP page has been translated. <%! sentence1; sentence2;... %> Declarations are used to declare classes, methods or variables 18

20 Introduction to web applications with Java. 2.6 JSP pages. Implicit objects Implicit objects There are several implicit objects that can be used in scriptlets and expressions (however, not in declarations). These implicit objects are created implicitly when the JSP page is translated into a servlet. 19

21 Introduction to web applications with Java. 2.6 JSP pages. Implicit objects Implicit objects (2) Variable name Value request The instance of the class HttpServletRequest which is being served response The instance of the class HttpServletResponse which will receive html code that has been generated by the servlet pagecontext The instance of the class PageContext which provides access to the page attributes, request, response, exception (if any) and t all namespaces session The instance of the class HttpSession that is being used by the JSP page (if any) application The instance of the class ServletContext that encapsulates the web application to which this JSP belongs to out The output stream that is being used in order to generate the resulting html exception The exception that is responsible for the raising of an error JSP page (only for pages with the directive iserrorpage= true ) 20

22 Introduction to web applications with Java. 2.6 JSP pages. Example 2 Example 2: Form reader (exemple2) Example location: introapweb/examples/ex6.2 This example does the following: 1. Shows an html form 2. Submits it to the server (i.e., sends a request to the server with the attributes provided in the form) 3. Sends back to the client all the information contained in the original request in the format that it has been obtained by the server Different methods (GET/POST) and parameter codification (query string/multipart) are used to submit the form leading to different request formats. However, the use of the object request of the class HttpServletRequest makes it possible to abstract these different formats. 21

23 Introduction to web applications with Java. 2.6 JSP pages. Example 2 Example 2: Form reader. Code <%@ page import="java.io.* " %> <%@ page import="java.net.* " %> <%@ page import="java.util.* " %> <html> <body bgcolor="white"> <h1> Contents of an http request </h1> <pre> <% String controlline=new String(""); Enumeration enum; String st=new String(""); try { %> <b>1. Request line </b> <br><br> Method:<%=request.getMethod()%> <br> Request URL:<%=request.getRequestURL()%> <br> Query string:<%= request.getquerystring()%><br>; <b>2. Request header</b> <br><br> <% enum=request.getheadernames(); while(enum.hasmoreelements()) { st=(string) enum.nextelement(); %> <%=st+" : "+request.getheader(st)%> <% } %> 22

24 Introduction to web applications with Java. 2.6 JSP pages. Example 2 <b>3. Request body:</b> <br><br> <% java.io.bufferedreader br=request.getreader(); String temp=br.readline(); while (temp!=null) { out.println(temp); temp=br.readline(); } br.close(); out.println("end HTTP REQUEST"); } catch (Exception io_e) {out.println("exception:"+io_e); io_e.printstacktrace(); } %> </pre> </body> </html> 23

25 Introduction to web applications with Java. 2.6 JSP pages. Example 3 Example 3: Form reader: parameters retrieval (exemple3) Example location: introapweb/examples/ex6.3 In example 2, we showed the http request in the way that it had arrived to the server. Example 3 shows how to obtain the parameters that constitute the request In particular, the methods getparameternames() and getparametervalues(...) on the implicit object request are used 24

26 Introduction to web applications with Java. 2.6 JSP pages. Example 3 Example 3: Form reader: parameters retrieval (exemple3). Code <%@ page import="java.io.* " %> <%@ page import="java.util.* " %> <html> <table border="1" cellpadding="3" cellspacing="1" width="600"> <tr> <td colspan="2" align="center" class="header"> Valors dels parametres del formulari: </td> </tr> (cont...) 25

27 Introduction to web applications with Java. 2.6 JSP pages. Example 3 (cont...) <tr><th> Nom </th><th> Valor</th></tr> <% int fileraact=0; Enumeration nompars= request.getparameternames(); while(nompars.hasmoreelements()){ String nom= (String) nompars.nextelement(); String[] valors=request.getparametervalues(nom); for (int i=0; i<valors.length; i++) { String valor=valors[i]; %> <tr valign= "top"> <td align="right" ><B><%= nom%></b></td> <td align="left" ><%= valor%></td> </tr> <% } } java.io.bufferedreader br=request.getreader(); String st=br.readline(); %> <tr valign= "top"> <td align="right"><b>dades</b></td> <td align="left"><%= st %></td> </tr> </table> </html> 26

28 Introduction to web applications with Java. 2.6 JSP pages. Example 4 Example 4: Character file reader Example location: introapweb/examples/ex6.4 This example reads a char file from a form sent by the client and shows its contents back to the client Notice: To send a file, the request method POST and codification multipart/formdata should be used Currently the class HttpServletRequest does not offer any automatic way to get the file contents. Therefore, the request body must be parsed manually We use the method getreader() (class ServletRequest) which gets the request body as a char stream In those cases in which the request parameters are sent in the request body (POST method), reading the body directly via getinputstream() or getreader() can interfere with request.getparameter(). For this reason, in this case all request parameters are read directly from the body instead of using the getparameter() method Control line gives us the end flag 27

29 Introduction to web applications with Java. 2.6 JSP pages. Example 4 Example 4: Character file reader (exemple4). Code <%@ page import="java.io.* " %> <%@ page import="java.net.* " %> <%@ page import="java.util.* " %> <html> <h1> Upload of a character file </h1> <pre> <% String controlline=new String(""); try { out.println("input start:"); java.io.bufferedreader br=request.getreader(); String filename=""; StringBuffer filebody=new StringBuffer(1000); String temp=br.readline(); while (! temp.startswith(" ") ) { temp=br.readline(); } controlline=new String(temp); //Per definicio de readline(), temp no conte <cr>, <lf> (cont...) 28

30 Introduction to web applications with Java. 2.6 JSP pages. Example 4 (cont...) temp=br.readline(); while (temp!=null) { //1. File name reading... if (temp.startswith ("Content-Disposition: form-data;"+ " name=\"file_name\"")) { while (!(temp.equals("")) ) temp=br.readline(); temp=br.readline(); filename=temp; } (cont...) 29

31 Introduction to web applications with Java. 2.6 JSP pages. Example 4 (cont...) //2. File body reading... if (temp.startswith ("Content-Disposition: form-data;"+ "name=\"file_body\";")) { while (!(temp.equals("")) ) temp=br.readline(); temp=br.readline(); while (temp.indexof(controlline)==-1 ) { filebody.append(temp); filebody.append("\n"); temp=br.readline(); } } temp=br.readline(); } br.close(); out.println("end of reading..."); out.println("<br>file "+filename+ " uploaded:<br>"+filebody); } catch (Exception io_e) {out.println("exception:"+io_e); io_e.printstacktrace(); } %> </pre> </body></html> 30

32 Introduction to web applications with Java. 2.6 JSP pages. Example 5 Example 5: Character file upload Example location: introapweb/examples/ex6.5 This example uploads a file of characters into the server and writes it as a new server file Notice: Everything is as in the previous case In addition, we use an object of the class BufferedWriter to contain the file that will be written into the server 31

33 Introduction to web applications with Java. 2.6 JSP pages. Example 6 Example 6: Binary file upload Example location: introapweb/examples/ex6.6 This example uploads a binary file into the server and writes it as a new server file Notice: We use the method getinputstream() (instead of getreader()) which gets the request body as a binary stream In addition, we use an object of the class BufferedOutputStream to contain the file that will be written into the server In those cases in which the request parameters are sent in the request body (POST method), reading the body directly via getinputstream() or getreader() can interfere with request.getparameter(). For this reason, in this case, all request parameters are read directly from the body instead of using the getparameter() method 32

34 Introduction to web applications with Java. 2.6 JSP pages. Example 7 Example 7: Server file manager Example location: introapweb/examples/ex6.7 This example deploys a web application that converts the server into a file manager The web application has the following features: Binary files/folders may be uploaded in (and deleted from) a specific server folder The server root folder is configured in the properties file properties/wapp.properties The client may navigate through server folders The web application welcome file is index.jsp Therefore, the application can be accessed as or simply, as 33

35 Introduction to web applications with Java. 2.6 JSP pages. Example 7 Properties file The contents of wapp.properties is: root.directory = /home/josepma/test/ If the server root directory should be another one, the contents of the properties file should be updated accordingly wapp.properties will be deployed at ex6.7/web-inf/classes/properties/wapp.properties The WEB-INF/classes directory is a part of the web application classpath Therefore: Classes (java beans, servlets...) and properties files located there will be available to the web application servlets/jsp pages 34

36 Introduction to web applications with Java. 2.6 JSP pages. Example 7 A convenient way to access the properties of a properties file from a JSP page/servlet/class is using a ResourceBundle: ResourceBundle prop = ResourceBundle.getBundle("properties/wapp"); String rootdir = prop.getstring("root.directory"); (Recall that the properties file must be located within the web application classpath) There exist other ways to deal with a properties file: Using ServletContext.getResourceAsStream(...) Using a classloader and Class.getResourceAsStream(...) 35

37 Introduction to web applications with Java. 2.6 JSP pages. Example 7 Application welcome file The Welcome file is the application main entry page Its default value is defined at CATALINA HOME/conf/web.xml: <welcome-file-list> <welcome-file>index.html</welcome-file> <welcome-file>index.htm</welcome-file> <welcome-file>index.jsp</welcome-file> </welcome-file-list> This means that if we provide the application with a file called index.html/htm/jsp, that file will be displayed when the application is accessed as: The welcome file can be overwritten at the application web.xml file Caution concerning the example 6.7!!!!: Just a beta-version. Some errors are not controlled 36

38 Introduction to web applications with Java. 2.6 JSP pages. Example 7 References JSP specification: jsr245/index.html JSP API 37

Unit 5 JSP (Java Server Pages)

Unit 5 JSP (Java Server Pages) Java Server Pages (JSP) is a server-side programming technology that enables the creation of dynamic, platform-independent method for building Web-based applications. It focuses more on presentation logic