The target audience for this guide is the Web Component provider, i.e. the person in charge of developing the web components on the server side.
The content of this guide is the following:
A Web Component is a generic term which denotes both JSP pages and
Servlets. Web components are packaged in a .war
file and can be
deployed in a JOnAS server via the web service. Web components can be
integrated in a J2EE application by packing the .war
file in an
.ear
file (refer to the J2EE
Application Programmer's Guide).
The JOnAS distribution includes a Web application example: The EarSample example.
The directory structure of this application is the following:
etc/xml | contains the web.xml file describing the web application |
etc/resources/web | contains html pages and images; JSP pages can also be placed here. |
src/org/objectweb/earsample/servlets | servlet sources |
src/org/objectweb/earsample/beans | beans sources |
The bean directory is not needed if beans coming from another application will be used.
Java Server Pages (JSP) is a technology that allows regular, static HTML, to be mixed with dynamically-generated HTML written in Java programming language for encapsulating the logic that generates the content for the page. Refer to the Java Server PagesTM and the Quickstart guide for more details.
The following example shows a sample JSP page that lists the content of a cart.
<!-- Get the session --> <%@ page session="true" %> <!-- The import to use --> <%@ page import="java.util.Enumeration" %> <%@ page import="java.util.Vector" %> <html> <body bgcolor="white"> <h1>Content of your cart</h1><br> <table> <!-- The header of the table --> <tr bgcolor="black"> <td><font color="lightgreen">Product Reference</font></td> <td><font color="lightgreen">Product Name</font></td> <td><font color="lightgreen">Product Price</font></td> </tr> <!-- Each iteration of the loop display a line of the table --> <% Cart cart = (Cart) session.getAttribute("cart"); Vector products = cart.getProducts(); Enumeration enum = products.elements(); // loop through the enumeration while (enum.hasMoreElements()) { Product prod = (Product) enum.nextElement(); %> <tr> <td><%=prod.getReference()%></td> <td><%=prod.getName()%></td> <td><%=prod.getPrice()%></td> </tr> <% } // end loop %> </table> </body> </html>
It is a good idea to hide all the mechanisms for accessing EJBs from JSP
pages by using a proxy java bean, referenced in the JSP page by the
usebean
special tag. This technique is shown in the alarm
example, where the .jsp files communicate with the EJB via a proxy java
bean ViewProxy.java.
Servlets are modules of Java code that run in an application server for answering client requests. Servlets are not tied to a specific client-server protocol. However, they are most commonly used with HTTP, and the word "Servlet" is often used as referring to an "HTTP Servlet."
Servlets make use of the Java standard extension classes in the packages
javax.servlet
(the basic Servlet framework) and
javax.servlet.http
(extensions of the Servlet framework for
Servlets that answer HTTP requests).
Typical uses for HTTP Servlets include:
For more details refer to the JavaTM Servlet Technology and the Servlets tutorial.
The following example is a sample of a Servlet that lists the content of a
cart.
This example is the servlet version of the previous JSP page example.
import java.util.Enumeration; import java.util.Vector; import java.io.PrintWriter; import java.io.IOException; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import javax.servlet.http.HttpSession; public class GetCartServlet extends HttpServlet { protected void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { res.setContentType("text/html"); PrintWriter out = res.getWriter(); out.println("<html><head><title>Your cart</title></head>"); out.println("<body>"); out.println("<h1>Content of your cart</h1><br>"); out.println("<table>"); // The header of the table out.println("<tr>"); out.println("<td><font color="lightgreen">Product Reference</font></td>"); out.println("<td><font color="lightgreen">Product Name</font></td>"); out.println("<td><font color="lightgreen">Product Price</font></td>"); out.println("</tr>"); // Each iteration of the loop display a line of the table HttpSession session = req.getSession(true); Cart cart = (Cart) session.getAttribute("cart"); Vector products = cart.getProducts(); Enumeration enum = products.elements(); while (enum.hasMoreElements()) { Product prod = (Product) enum.nextElement(); int prodId = prod.getReference(); String prodName = prod.getName(); float prodPrice = prod.getPrice(); out.println("<tr>"); out.println("<td>" + prodId + </td>); out.println("<td>" + prodName + </td>); out.println("<td>" + prodPrice + </td>); out.println("</tr>"); } out.println("</table>"); out.println("</body>"); out.println("</html>"); out.close(); } }
The following sections describe:
import javax.naming.Context; import javax.naming.InitialContext; //remote interface import org.objectweb.earsample.beans.secusb.Op; import org.objectweb.earsample.beans.secusb.OpHome; Context initialContext = null; try { initialContext = new InitialContext(); } catch (Exception e) { out.print("<li>Cannot get initial context for JNDI: "); out.println(e + "</li>"); return; } // Connecting to OpHome thru JNDI OpHome opHome = null; try { opHome = (OpHome) PortableRemoteObject.narrow(initialContext.lookup("java:comp/env/ejb/Op"), OpHome.class); } catch (Exception e) { out.println("<li>Cannot lookup java:comp/env/ejb/Op: " + e + "</li>"); return; } // OpBean creation Op op = null; try { op = opHome.create("User1"); } catch (Exception e) { out.println("<li>Cannot create OpBean: " + e + "</li>"); return; }Note that the following elements must be set in the
web.xml
file
tied to this web application:
<ejb-ref> <ejb-ref-name>ejb/Op</ejb-ref-name> <ejb-ref-type>Session</ejb-ref-type> <home>org.objectweb.earsample.beans.secusb.OpHome</home> <remote>org.objectweb.earsample.beans.secusb.Op</remote> <ejb-link>secusb.jar#Op</ejb-link> </ejb-ref>
//local interfaces import org.objectweb.earsample.beans.secusb.OpLocal; import org.objectweb.earsample.beans.secusb.OpLocalHome; // Connecting to OpLocalHome thru JNDI OpLocalHome opLocalHome = null; try { opLocalHome = (OpLocalHome) initialContext.lookup("java:comp/env/ejb/OpLocal"); } catch (Exception e) { out.println("<li>Cannot lookup java:comp/env/ejb/OpLocal: " + e + "</li>"); return; }This is found in the
web.xml
file:
<ejb-local-ref> <ejb-ref-name>ejb/OpLocal</ejb-ref-name> <ejb-ref-type>Session</ejb-ref-type> <local-home>org.objectweb.earsample.beans.secusb.OpLocalHome</local-home> <local>org.objectweb.earsample.beans.secusb.OpLocal</local> <ejb-link>secusb.jar#Op</ejb-link> </ejb-local-ref>
String envEntry = null; try { envEntry = (String) initialContext.lookup("java:comp/env/envEntryString"); } catch (Exception e) { out.println("<li>Cannot get env-entry on JNDI " + e + "</li>"); return; }This is the corresponding part of the
web.xml
file:
<env-entry> <env-entry-name>envEntryString</env-entry-name> <env-entry-value>This is a string from the env-entry</env-entry-value> <env-entry-type>java.lang.String</env-entry-type> </env-entry>
import javax.transaction.UserTransaction; // We want to start transactions from client: get UserTransaction UserTransaction utx = null; try { utx = (UserTransaction) initialContext.lookup("java:comp/UserTransaction"); } catch (Exception e) { out.println("<li>Cannot lookup java:comp/UserTransaction: " + e + "</li>"); return; } try { utx.begin(); opLocal.buy(10); opLocal.buy(20); utx.commit(); } catch (Exception e) { out.println("<li>exception during 1st Tx: " + e + "</li>"); return; }