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 specifies both JSP pages and Servlets.
Web components are packaged in a .war
file and may be
deployed in a JOnAS server via the web service. Web components may be integrated
in a J2EE application by packing the .war
file in a .ear
file
(see J2EE Application Programmer's Guide).
You can find a Web application exemple in the JOnAS distribution: The EarSample example
The directory structure of this application looks like this:
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 |
In case your beans come from another application, you don't need the bean directory.
Java Server Pages (JSP) is a technology that lets you mix regular, static HTML, with dynamically-generated HTML written in Java programming language to encapsulate the logic that generates the content for the page. For more details see Java Server PagesTM and Quickstart guide.
The following example shows a sample JSP page which 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 could be a good idea to hide all the mechanisms to access EJBs from JSP pages by using
a proxy java bean, refered in the JSP page by the usebean
special tag. This technique is
shown in the alarm example.
Just look at one of the .jsp files. A proxy java bean
ViewProxy.java
has been used to contain the glue necessary to access EJB.
Servlets are modules of Java code that run in an application server to answer client requests. Servlets are not tied to a specific client-server protocol but they are most commonly used with HTTP and the word "Servlet" is often used in the meaning of "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 see JavaTM Servlet Technology and Servlets tutorial.
The following example shows a sample of a Servlet which 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(); } }
Here we show :
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 you have to set in the
web.xml
file tied to this web application the
following elements:
<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; }Here you will find 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; }Here is the corresponding part of
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; }