Running Tomcat on port 80

The typical java web application is fronted by a web server (usually Apache) for a number of reasons. Apache handles static content well, and also is easier to configure to listen on privileged ports (under 1024). I’ve written before about different options for connecting Tomcat and Apache, but there are times when all you need is a servlet engine, and installing Apache is overkill. If you don’t want users to see a nonstandard port in their url (http://foo.com:8080/webapp/), then you have a couple of options.

You can run tomcat as root. This is probably not a good idea, since anyone who can write a jsp can now execute arbitrary commands as root. I don’t know how Tomcat’s security is, but in general, the fewer applications running with super user privileges, the better.

If you share my dislike of Tomcat running as root, here’s an excellent rundown of the options for running Tomcat on port 80. I went the route of jsvc. This seemed to work just fine, though every time we shut down tomcat, we would get an entry in the error log file: jsvc.exec error: Service exit with a return value of 143.

That didn’t start to disturb me until I realized that the destroy method of our servlets weren’t being called. This method cleaned up after the servlet and it was important that it get executed. A bit of googling turned up a discussion of this very problem. The version of jsvc that ships with Tomcat 5.0.27 doesn’t shut down Tomcat very nicely.

I downloaded and compiled subversion, because that’s the version control system that the daemon jakarta project (of which jsvc is a part) used. I then checked out the version of the source tagged daemon-1_0_1 (svn co http://svn.apache.org/repos/asf/jakarta/commons/proper/daemon/tags/daemon-1_0_1/) and rebuilt jsvc. This new version allows tomcat to call the destroy methods of servlets, and everything seems to be happy.


Amazon’s Mechanical Turk

I did some work a long time ago with Amazon Web Services; I gave them an email address and they periodically send me newsletters about their web services. The most recent one contained a link to an article about a new service: Amazon Mechanical Turk. This service provides ‘Artificial Artificial Intelligence’ and lets developers place tasks in front of humans in a scalable, standardized manner. Amazon, with their infrastructure, makes sure that the task is completed and pays the human who completes the task. Right now, I only saw one set of tasks, sponsored by Amazon, so I’m not sure of the uptake. But this is certainly an fascinating idea–an interesting inverse of the normal computer/human relationship.



unescaping a string with PL/SQL

I’ve written about PL/SQL before, but I’ve recently started working on a project that uses it heavily. Given the amount of code written for Oracle databases, I’m rather suprised that there’s not a PL/SQL Cookbook, where, like the Perl Cookbook and the Java Cookbook (more cookbooks from O’Reilly are listed here). There is an Oracle Cookbook, but based on a quick scan of Amazon, it’s is focused, as you’d expect, more on the database design than on PL/SQL programming. (Interestingly, there is a Oracle+PHP cookbook, and a PL/SQL sample code page but neither of those is quite what I’m looking for.)

The reason that I’d like a PL/SQL cookbook is that there are large sets of problems that routinely need to be solved in PL/SQL, but the language is so low level (though they just added some regex support in 10g; bravo!) that doing these routine tasks and making sure they’re correctly implemented can be difficult and tedious. This is especially true when it’s a programmer from a different language who’s used to higher levels of abstraction (like, for example, the good folks who author CPAN modules provide)–it’d be well worth my $70 to make sure that I never had to deal with a problem like, say, unescaping a string.

For that’s the problem I recently had to solve. Essentially, we have a string that looks like this: yellow,apple. This string represents two values, which need to be put in different places by splitting them up into ‘yellow’ and ‘apple’. All well and good until the possiblity of embedded commas arises, for it’s possible that the desired end values were ‘yellow,blue’ and ‘apple,banana’. The answer, of course, is to escape the commas on the way in (turning the second input into something like this: yellow:,blue,apple:,banana, and when processing to unescape those special characters (both the comma and the escape character, which in the example is the colon). That’s what these three functions do. They take a string like the above examples and parse it into a table, to be iterated over at your leisure.

/* ------------------- function splitit ------------------*/
FUNCTION splitit(p_str VARCHAR2, p_del VARCHAR2  := ',',p_idx PLS_INTEGER, p_esc VARCHAR2

:= ':')
RETURN INTEGER
IS
l_idx       PLS_INTEGER;
l_chars_before      VARCHAR2(32767);
l_escape_char       VARCHAR2(1) := p_esc;
l_chars_before_count        PLS_INTEGER := 0;
BEGIN
>
LOOP
l_idx := instr(p_str,p_del, p_idx);
IF l_idx > 0 then
WHILE substr(p_str, l_idx-l_chars_before_count-1, 1) = l_escape_char LOOP
l_chars_before_count := l_chars_before_count +1;
END LOOP;

IF mod(l_chars_before_count, 2) = 0 THEN
-- if chars_before_count is even, then we're at a segment boundary
RETURN l_idx;
ELSE
-- if odd, then we're at an escaped delimiter, want to move past
RETURN splitit(p_str, p_del, l_idx+1, p_esc);
END IF;
l_chars_before_count := 0;
ELSE
RETURN l_idx;
EXIT outer;
END IF;
END LOOP;
END splitit;
/* ------------------- function splitit ------------------*/

/* ------------------- function unescape ------------------*/

FUNCTION unescape(p_str VARCHAR2, p_del VARCHAR2 := ',', p_esc VARCHAR2 := ':')
RETURN VARCHAR2
IS
l_str VARCHAR2(32767);
BEGIN
l_str := replace(p_str, p_esc||p_del, p_del);
l_str := replace(l_str, p_esc||p_esc, p_esc);
RETURN l_str;
END unescape;
/* ------------------- function unescape ------------------*/

/* ------------------- function split ------------------*/

FUNCTION split(p_list VARCHAR2, p_del VARCHAR2 := ',')
RETURN split_tbl
IS
l_idx       PLS_INTEGER;
split_idx   PLS_INTEGER     := 0;
l_list      VARCHAR2(32767) := p_list;
l_chars_before      VARCHAR2(32767);
l_escape_char       VARCHAR2(1) := ':';
l_array split_tbl := split_tbl('','','','','','','','','','');
BEGIN
l_list := p_list;
LOOP
split_idx := split_idx + 1;
IF split_idx > 10 then
EXIT;
END IF;

l_idx := splitit(l_list, p_del, 1, l_escape_char);
IF l_idx > 0 then
l_array(split_idx) := unescape(substr(l_list,1,l_idx-1), p_del,

l_escape_char);
l_list := substr(l_list,l_idx+length(p_del));
ELSE
l_array(split_idx) := l_list;
EXIT;
END IF;
END LOOP;
RETURN l_array;
END split;
/* ------------------- function split ------------------*/

/* in the header file, split_tbl is defined */
TYPE split_tbl IS TABLE of varchar2(32767)

Not all of this code is mine–I built on a solution from a colleague. But I hope this saves one other person from the afternoon I just endured. And if you are a PL/SQL expert and care to critique this solution, please feel free.


Article on open formats

Gervase Markham has written an interesting article about open document formats. I did a bit of lurking on the bugzilla development lists for a while and saw Gervase in action–quite a programmer and also interested in the end user’s experience. I think he raises some important issues–if html had been owned by a company, the internet (as the web is commonly known, even though it’s only a part of the internet) would not be where it is today. If Microsoft Word (or WordPerfect) had opened up their document specification (or worked with other interested parties on a common one), other companies could have competed on features and consumers would have benefited. More on OpenDocument, including a link to a marked up version of a letter from Microsoft regarding the standard.



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