Errata

New Atlanta Communication haven't been bought by Unify Corp.

You can look at:

http://www.servletexec.com/rescission/rescission.jsp

FastCGI *does* support multiple concurrent requests per process, contrary to the description on this page. It uses a capability protocol to ask each application whether it is capable of handling concurrent requests.

The code, as written, does not make use of the local_count variable. I
believe the author's intent was to create a "small as possible"
synchronization scope. I believe the author intended the code to be:

int local_count;
synchronized(this) {
local_count = ++count;
}
if(count % 10 ==0) saveState();

out.println("......"); // etc., etc.

First, in the while loop towards the bottom of the page, null checks are
performed e.g. if (name == null) name = "Unknown user";
The problem is that these will never be performed because what's returned if
a user types in no information is an empty string, which is not the same as
a null in java. So each of these lines should be
if (name.equals("")) name = "Unknown user";
the other problem is in the email null check it is listed as
if (name == null) email = "Unknown email";
The problem is the email should be checked not the name so this should be
if (email.equals("")) name = "Unknown email";
This whole issue is not very serious though because it's an empty string and
not a null so there are no null pointer problems to worry about. This only
make's sure that something is printed if the user doesn't enter anything,
which was the authors intention.

text reads, "...or the servlet's SessionContext that we'll learn...

There is no SessionContext class or interface in the Servlet API. Perhaps this was
meant to be a reference to the ServletContext.

out.println("<I>Error accessing " + req.getRequestURI() + "</I>");

This line does not return the output I would expect as a user, as a programmer I can
see why this happens though.

The output from this line, when I try an access
http://localhost:8080/learn/readme.night is:

Error accessing /learn/servlet/ErrorDisplay

as a user would expect this to read:

Error accessing /learn/readme.night

I think this is because it is a separate http request and it simply looses the URI as
it has been redirected to this servlet. Therefore the code is actually displaying
accurate information its just its usefullness to a user is removed. Some might say
that this is a security risk as it unvails your directory structure. I am aware this
is an example in a book and not production code.

I used this config to run the web-app:

<?xml version="1.0" encoding="ISO-8859-1"?>

<!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>
<servlet>
<servlet-name>ed</servlet-name>
<servlet-class>ErrorDisplay</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>ed</servlet-name>
<url-pattern>/ed.html</url-pattern>
</servlet-mapping>
<error-page>
<error-code>
404
</error-code>
<location>/ed.html</location>
</error-page>
</web-app>

This error has already been posted but I would like to point out that changing:

req.getRequestURI() to
req.getAttribute("javax.servlet.error.request_uri")

(with a check for the attribute being null) would fix the problem.

out.println("<I>Error accessing " + req.getRequestURI() + "</I>");

it should read

out.println("<I>Error accessing " +
request.getAttribute("javax.servlet.forward.request_uri") + "</I>");

The text:

"For example, .foo.com is valid and matches www.foo.com and upload.foo.com but
not www.upload.foo.com."

should read:

"For example, .foo.com is valid and matched www.foo.com and
www.upload.foo.com, but not foo.com."

According to Netscape's cookie specification and RFC 2109, the domain pattern
.foo.com does match www.upload.foo.com. From the links off of Jason Hunter's
servlets.com website:

http://wp.netscape.com/newsref/std/cookie_spec.html :
"A domain attribute of 'acme.com' would match host names 'anvil.acme.com' as
well as 'shipping.crate.acme.com'."

http://www.servlets.com/rfcs/rfc2109.html
"Note that domain-match is not a commutative operation: a.b.c.com
domain-matches .c.com, but not the reverse."

Finally, ... a servlet can retrieve the client's certificates (plural) as a
request attribute:

java.security.cert.X509Certificate[] certs =
(java.security.cert.X509Certificate[])
reg.getAttribute("javax.servlet.request.X509Certificate");

For any server ... will return a security.cert.X509Certificate[]
(array) object ...

Example 8-13 is ok !

The description seems to be simply copied from addDateHeader