Executing Java CGI Program and Returning Result to Browser

Question

Hi all, I'm an experienced ASP/PHP/JS programmer but completely new to Java. I'm building a site where I need to execute the same piece of code in every language I can manage, and I'm onto Java. For the purpose of illustration, my goal is to replicate the following PHP code as Java code:
<?php echo($_GET['message']); ?>I've written and compiled a "Hello World!" application and uploaded it to my server (Dreamhost shared hosting, Linux platform with JDK installed). Using this line form telnet, the application prints "Hello World!" to the screen:
java -classpath . helloworld.classSo, following a very old tutorial I found online, I created a CGI script and CHMOD'd it to 755 containing the following:
#!/usr/sh /usr/bin/java -classpath . regex.classBut this returns a 500 "Internal server error". After a few unsuccessful alterations I tried to emulate the CGI script in PHP like so:
<?php exec('java -classpath . regex', $output); echo(join($output, '<br />')); ?>But all I get back from that is "Error occurred during initialization of VM. Could not reserve enough space for code cache".
Any advice would be very much appreciated. I can learn the Java language - there's plenty of resources available for that, but I'm struggling to get started because I can't get the application to run as CGI.
Many Thanks,
-William

Answer 1

wwarby wrote:
Hi, and thanks for the responses.
paulcw, my ultimate goal is obviously a little more ambitious than printing "Hello World!" to the browser but for simplicity's sake I thought I'd start there. I tried this in a .cgi file:
#!/bin/sh
/usr/local/dh/java -version...and I still get a 500 internal server error. I have uploaded the script in ASCII mode and CHMOD'd it to 755, and checked with my host that I have the Java path correct (I've also tried just "java" and "/usr/bin/java" which do the same thing).Well that's because you're confusing running Java generally vs running it as a CGI vs running ANYTHING as a CGI. The web server expects CGI scripts to send certain content to standard output, and in a certain format. Generally speaking it's headers, then a blank line, then other content.
Furthermore, I think you might be confusing executing arbitrary code from PHP vs executing a CGI script. I'm not familiar with PHP but the way you called exec suggests to me that it can run arbitrary code and doesn't expect the output to necessarily be in CGI format.
You've got to do things one step at a time here.
spoon_, the #!/usr/sh" thing was a mistake on the forum post - in the script it is "#!/bin/sh" and it is on a line of it's own. The full .cgi file is now:
{code}#!/bin/sh
/usr/local/dh/java -classpath . hello{code}
And the .java file is now:
{code}class hello {
     public static void main(String args[]) {
          System.out.println("Content-type: text/html");
          System.out.println();
          System.out.println("Hello World!");
}{code}
as per your instructions. I compliled it on the server using javac, and when I run:
{code}java -classpath . hello{code}
in telnet, it returns:
{code}Content-type: text/html
Hello World!{code}
to the telnet window. Unfortunately when run from the CGI script I still get the 500 Internal server error.Have you checked your web server logs?
I'm going to guess here that your web server doesn't have permission to run the JVM executable.
That's an interesting path: "/usr/local/dh". What does "dh" stand for?
My server definitely supports Java (version 1.5.0_02) and CGI - it says so on their Wiki and specifically mentions Java as one of the languages that CGI scripts can use. What am I doing wrong?
Edited by: wwarby on Dec 25, 2007 1:30 AMCheck your web server logs. There should be both an access log and an errors log. The errors log will probably contain more information.