Now we'll convert the tutorial that we created to a web application. The web part of it is done in JSP and is intentionally primitive from the UI perspective, to concentrate on Cayenne integration aspect. There may be some specifics depending on the web framework used (JSP, Struts, JSF, Click, WebWork, Tapestry, etc.), still the procedure outlined here is quite universal as it relies on the J2EE servlet specification.

To run the web application from Eclipse, we will use JettyLauncher plugin. If you are using something else (e.g. a Tomcat plugin) it should probably work as well.

The following is the contents of web.xml. All the DataContext magic described above is achieved by WebApplicationContextFilter.

web.xml

<?xml version="1.0" encoding="utf-8"?>
 <!DOCTYPE web-app
   PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
   "http://java.sun.com/dtd/web-app_2_3.dtd">
<web-app>
    <display-name>Cayenne Tutorial</display-name>
    <filter>
        <filter-name>CayenneFilter</filter-name>
        <filter-class>org.apache.cayenne.conf.WebApplicationContextFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>CayenneFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
    <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
</web-app>

webapp/index.jsp

<%@ page language="java" contentType="text/html" %>
<%@ page import="cayenne.tutorial.*" %>
<%@ page import="org.apache.cayenne.*" %>
<%@ page import="org.apache.cayenne.query.*" %>
<%@ page import="org.apache.cayenne.exp.*" %>
<%@ page import="org.apache.cayenne.access.*" %>
<%@ page import="java.util.*" %>

<% 
    SelectQuery query = new SelectQuery(Artist.class);
    query.addOrdering(Artist.NAME_PROPERTY, true);

    DataContext context = DataContext.getThreadDataContext();
    List artists = context.performQuery(query);
%>
<html>
    <head>
        <title>Main</title>
    </head>
    <body>
        <h2>Artists:</h2>
        
        <% if(artists.isEmpty()) {%>
        <p>No artists found</p>
        <% } else { 
            Iterator it = artists.iterator();
            while(it.hasNext()) {
                Artist a = (Artist) it.next();
        %>
        <p><a href="detail.jsp?id=<%=DataObjectUtils.intPKForObject(a)%>"> <%=a.getName()%> </a></p>
        <%
            }
            } %>
        <hr>
        <p><a href="detail.jsp">Create new artist...</a></p>
    </body>	
</html>

webapp/detail.jsp

<%@ page language="java" contentType="text/html" %>
<%@ page import="cayenne.tutorial.*" %>
<%@ page import="org.apache.cayenne.*" %>
<%@ page import="org.apache.cayenne.access.*" %>
<%@ page import="java.util.*" %>
<%@ page import="java.text.*" %>

<% 
    DataContext context = DataContext.getThreadDataContext();
    String id = request.getParameter("id");

    // find artist for id
    Artist artist = null;
    if(id != null && id.trim().length() > 0) {
        artist = (Artist) DataObjectUtils.objectForPK(context, Artist.class, Integer.parseInt(id));
    }

    if("POST".equals(request.getMethod())) {
        // if no id is saved in the hidden field, we are dealing with
        // create new artist request
        if(artist == null) {
            artist = (Artist) context.newObject(Artist.class);
        }

        // note that in a real application we would so dome validation ...
        // here we just hope the input is correct
        artist.setName(request.getParameter("name"));
        artist.setDateOfBirthString(request.getParameter("dateOfBirth"));

        context.commitChanges();

        response.sendRedirect("index.jsp");
    }

    if(artist == null) {
        // create transient artist for the form response rendering
        artist = new Artist();
    }

    String name = artist.getName() == null ? "" : artist.getName();
    String dob = artist.getDateOfBirth() == null
            ? "" : new SimpleDateFormat("yyyyMMdd").format(artist.getDateOfBirth());
%>
<html>
    <head>
        <title>Artist Details</title>
    </head>
    <body>
        <h2>Artists Details</h2>
        <form name="EditArtist" action="detail.jsp" method="POST">
            <input type="hidden" name="id" value="<%= id != null ? id : "" %>" />
            <table border="0">
                <tr>
                    <td>Name:</td>
                    <td><input type="text" name="name" value="<%= name %>"/></td>
                </tr>
                <tr>
                    <td>Date of Birth (yyyyMMdd):</td>
                    <td><input type="text" name="dateOfBirth" value="<%= dob %>"/></td>
                </tr>
                <tr>
                    <td></td>
                    <td align="right"><input type="submit" value="Save" /></td>
                </tr>  
            </table>
        </form>
    </body>	
</html>

INFO  QueryLogger: --- will run 1 query.
INFO  QueryLogger: Opening connection: jdbc:derby:/Users/andrus/Desktop/testdb;create=true
	Login: null
	Password: *******
INFO  QueryLogger: +++ Connecting: SUCCESS.
INFO  QueryLogger: --- transaction started.
INFO  QueryLogger: Detected and installed adapter: org.apache.cayenne.dba.derby.DerbyAdapter
INFO  QueryLogger: SELECT t0.DATE_OF_BIRTH, t0.NAME, t0.ID FROM ARTIST t0 ORDER BY t0.NAME - prepared in 32 ms.
INFO  QueryLogger: === returned 0 rows. - took 461 ms.
INFO  QueryLogger: +++ transaction committed.