A document has been updated:
http://cocoon.zones.apache.org/daisy/documentation/681.html
Document ID: 681
Branch: main
Language: default
Name: Creating a Reader (unchanged)
Document Type: Document (unchanged)
Updated on: 8/25/05 7:44:05 PM
Updated by: Berin Loritsch
A new version has been created, state: publish
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</pre>
<p>Now we are going to override the <tt>service()</tt> method and implement
the
--- <tt>dispose()</tt> method to get and cleanup after ourselves.</p>
+++ <tt>dispose()</tt> method to get and cleanup after ourselves. First lets
start
+++ with getting the DataSourceComponent. Because Cocoon is configured to deal
with
+++ multiple databases, you will need to use a ServiceSelector to choose the
+++ DataSourceComponent corresponding to your desired database.</p>
+++ <pre> @Override
+++ public void service(ServiceManager services) throws ServiceException
+++ {
+++ super.service(services);
+++
+++ dbselector = (ServiceSelector)
manager.lookup(DataSourceComponent.ROLE + "Selector");
+++ datasource = (DataSourceComponent)
dbselector.select(DB_RESOURCE_NAME);
+++ }
+++ </pre>
+++
+++ <p class="note">The <tt>@Override</tt> annotation above is used by the Java
+++ compiler to ensure that you are overriding a parent class's method. It only
+++ works in Java 5. If you are developing against an earlier version of Java
+++ remove that line so that you can compile the class. That goes for every
time
+++ you see it.</p>
+++
+++ <p>We ensured that we called the superclass's <tt>service()</tt> method so
that
+++ we didn't upset the expectations of anyone wanting to extend our class.
Keeping
+++ the user's expectations in mind always helps to produce a good product--and
in
+++ this case the user is a developer. Next, we retrieved the selector for the
+++ DataSourceComponent and stored it in the class field we created earlier.
Then
+++ we did the same for the actual DataSouceComponent itself. Now we have
access to
+++ the component when we need it. We didn't get an actual connection yet
because
+++ the connections are pooled. If we held onto a connection for the life of
the
+++ component then we would run out and the application would come to a
screaching
+++ halt waiting for a connection to become available.</p>
+++
+++ <p>Since we are still dealing with managing the component itself, let's do
the
+++ cleanup code next. The Avalon framework uses the
<tt>Disposable.dispose()</tt>
+++ callback method to let the component know when it is safe to release all the
+++ components it is using and perform other cleanup.</p>
+++
+++ <pre> public void dispose()
+++ {
+++ dbselector.release(datasource);
+++ manager.release(dbselector);
+++ datasource = null;
+++ manager = null;
+++ }
+++ </pre>
+++
+++ <p>While setting the fields to <tt>null</tt> might not be necessary with
modern
+++ day garbage collectors, it still doesn't hurt. By releasing those
components we
+++ ensure that Cocoon can shut down nicely and safely when it is time.</p>
+++
+++ <h3>Make sure PDFs Work</h3>
+++
+++ <p>Since we expect to have PDF documents in our database alongside pictures
and
+++ other types of documents, we need to make sure they display properly.
Since the
+++ bug in the IE Acrobat Reader plugin wasn't fixed until version 7 we need to
make
+++ sure the content length is returned. There is some overhead with this as
Cocoon
+++ has to cache the results to get the content length, but because we are
going to
+++ cache it anyway there is little difference on when it gets sent to the
cache.
+++ This is how we do it:</p>
+++
+++ <pre> @Override
+++ public boolean shouldSetContentLength()
+++ {
+++ return true;
+++ }
+++ </pre>
+++
+++ <h3>Setting up for the Read (Cache directives, finding the resource,
etc.)</h3>
+++
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