CS 596: Client-Server Programming
Spring Semester, 1997
Doc 19, CGI and Java

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San Diego State University -- This page last updated Apr 3, 1997

Contents of Doc 19, CGI and Java

CGI and Java	slide # 1
...Problems with all CGI Programs	slide # 1
...Problems Using Java in CGI Programs	slide # 2
...Solutions to Java and CGI problems	slide # 3
......Strawman SimpleWrapper	slide # 4
...Problems with SimpleWrapper	slide # 7
......Solution 1 - Other Libraries	slide # 7
......Solution 2 - One Wrapper fits all	slide # 8
......Solution 3 System.properties	slide # 10
...The Final Wrapper	slide # 11
...A C Equivalent of Wrapper	slide # 12

Doc 19, CGI and Java Slide # 1

CGI and Java

Problems with all CGI Programs

1. Since CGI programs are run by the web server, all files, programs and directories involved in the CGI program must be accessable by the web server!!!!!!!!!!!!!!!!!!!!!!!

All directories must be readable and executable by everyone (chmod o+rx) or (chmod a+rx)

All executables must be readable and executable by everyone (chmod o+rx) or (chmod a+rx)

All files must be readable by everyone (chmod o+r)

2. Data automatically available when a CGI program is run is not automatically available when you run the program without the broswer

Environment variables, other input

3. When the CGI program is run by the Web server there is at least one program between you and the CGI program

Doc 19, CGI and Java Slide # 2

Problems Using Java in CGI Programs

1. Java can not read environment variables

CGI requires access to environment variables

2. Java programs are started with a two word command:

java className

All methods of calling CGI programs (in Unix) only allow a one word command to start the program

3. Java uses the CLASSPATH environment variable to find classes

CGI programs are run by the web server, not you

Your environment is not used when your CGI program is run

Doc 19, CGI and Java Slide # 3

Solutions to Java and CGI problems

Use a wrapper program

Use the following java program as an example:

class HiMom
     {
     public  static  void  main( String  args[] ) throws Exception
          {
          System.out.print("Content-type: text/plain\n\n");
          System.out.println("Hi Mom");
          }
     }

Assume java program is in file HiMom.java in directory:

/net/www/www-eli/cgi-bin/cgiExamples

where /cgi-bin is the cgi bin directory for the web server:

www.eli.sdsu.edu

Doc 19, CGI and Java Slide # 4

Strawman SimpleWrapper

Put the following shell program in the file simpleWrapper in the directory:

/net/www/www-eli/cgi-bin/cgiExamples

The Shell program:


#!/bin/sh

JAVA="/opt/java/bin"
$JAVA  HiMom

Make HiMom.class and simpleWrapper world accessable:


chmod a+rx simpleWrapper
chmod a+r HiMom.class

Doc 19, CGI and Java Slide # 5
Testing SimpleWrapper

Command line test:


/net/www/www-eli -> simpleWrapper
Content-type: text/plain

Hi Mom
/net/www/www-eli ->

Browserless http Test:


/net/www/www-eli -> telnet www.eli.sdsu.edu 80
Trying 130.191.226.80...
Connected to www.eli.sdsu.edu.
Escape character is '^]'.
GET /cgi-bin/cgiExamples/simpleWrapper HTTP/1.0

HTTP/1.0 200 OK
Server: Netscape-Commerce/1.12
Date: Sunday, 30-Mar-97 17:38:36 GMT
Content-type: text/plain

Hi Mom
Connection closed by foreign host.
/net/www/www-eli ->

Doc 19, CGI and Java Slide # 6

Testing SimpleWrapper

Browser Test Access the URL:


http://www.eli.sdsu.edu/cgi-bin/cgiExamples/simpleWrapper

Result:


Hi Mom

Doc 19, CGI and Java Slide # 7

Problems with SimpleWrapper

1. No environment varaibles

2. Can't use SDSU java library or other libraries not part of standard Java distribution

3. Each CGI program requires it's own modified SimpleWrapper program

Solution 1 - Other Libraries

The Shell program:

#!/bin/sh

JAVA="/opt/java/bin"
CLASSPATH=".:/opt/java/classes:/usr/local/lib/java"

$JAVA -classpath $CLASSPATH  HiMom

Doc 19, CGI and Java Slide # 8

Solution 2 - One Wrapper fits all

Use basename and dirname

betterWrapper:

#!/bin/sh

JAVA="/opt/java/bin"
BASENAME="/usr/bin/basename"
DIRNAME="/usr/bin/dirname"

CGISUFFIX=".cgi"

CLASSPATH=".:/opt/java/classes:/usr/local/lib/java"

CLASS=`$BASENAME $0 $CGISUFFIX`
DIR=`$DIRNAME $0`

cd $DIR
$JAVA -classpath $CLASSPATH  $CLASS

Doc 19, CGI and Java Slide # 9
Using betterWrapper

Put betterWrapper into file:


/net/www/www-eli/bin/betterWrapper

Make it world accessable and executable

Goto cgi bin directory( in my case)


/net/www/www-eli/cgi-bin/cgiExamples

Link CGI program to betterWrapper


ln -s ../../bin/betterWrapper HiMom

Recall that HiMom.class in is this directory

Now access the URL:


http://www.eli.sdsu.edu/cgi-bin/cgiExamples/HiMom

Doc 19, CGI and Java Slide # 10

Solution 3 System.properties

In Java command line arguments of the form:


-Dname=value

Are added to the System property object

Properties is a subclass of Hashtable

Given the class Test below, the command line:


java Test -Dname=Roger  -Dclass=cs596

will produce the output:


Roger
cs595

class Test
     {
     public  static  void  main( String  args[] ) throws Exception
          {
          String theName = System.getProperty( "name");
          Properties systemStuff = System.getProperties();
          
          System.out.print( theName );
          System.out.println( systemStuff.get( "class" ) );
          }
     }

Doc 19, CGI and Java Slide # 11

The Final Wrapper

#!/bin/sh
# Java-Wrapper Version 1.1
# Copyright (C) 1996 by Marc Balmer, CH-4055 Basel, marc@msys.ch.
# This wrapper executes java binaries as CGI programs
# Modified by Roger Whitney, added suffix, DIR, Classpath, sorted and added some env variables

BASENAME="/usr/bin/basename"
DIRNAME="/usr/bin/dirname"
JAVA="/opt/java/bin"
CLASSPATH=".:/opt/java/classes:/usr/local/lib/java"
CGISUFFIX=".cgi"

CLASS=`$BASENAME $0 $CGISUFFIX`
DIR=`$DIRNAME $0`

cd $DIR

if [ -f $CLASS.class ] ; then
     $JAVA  -classpath $CLASSPATH \
     -DAUTH_TYPE=$AUTH_TYPE \
     -DCONTENT_LENGTH=$CONTENT_LENGTH \
     -DCONTENT_TYPE=$CONTENT_TYPE \
     -DDOCUMENT_ROOT=$DOCUMENT_ROOT \
     -DGATEWAY_INTERFACE=$GATEWAY_INTERFACE \
     -DHTTP_ACCEPT="$HTTP_ACCEPT" \
     -DHTTP_CONNECTION=$HTTP_CONNECTION \
     -DHTTP_HOST=$HTTP_HOST \
     -DHTTP_USER_AGENT="$HTTP_USER_AGENT" \
     -DPATH_INFO=$PATH_INFO \
     -DPATH_TRANSLATED=$PATH_TRANSLATED \
     -DQUERY_STRING=$QUERY_STRING \
     -DREMOTE_ADDR=$REMOTE_ADDR \
     -DREMOTE_HOST=$REMOTE_HOST \
     -DREMOTE_IDENT=$REMOTE_IDENT \
     -DREMOTE_USER=$REMOTE_USER \
     -DREQUEST_METHOD=$REQUEST_METHOD \
     -DSCRIPT_NAME=$SCRIPT_NAME \
     -DSERVER_NAME=$SERVER_NAME \
     -DSERVER_PORT=$SERVER_PORT \
     -DSERVER_PROTOCOL=$SERVER_PROTOCOL \
     -DSERVER_SOFTWARE=$SERVER_SOFTWARE \
     $CLASS
else
     echo Content-type: text/html
     echo
     echo \<head\>\<title\>Java-Wrapper Error\</title\>\</head\>
     echo \<body\>
     echo \<h1\>Java-Wrapper error\</h1\>
     echo The requested java class file \<b\>$CLASS.class\</b\>
     echo was not found on this server.
     echo \</body\>
fi

Doc 19, CGI and Java Slide # 12

A C Equivalent of Wrapper

A C program written by Andrew that does a bit more than wrapper can be found at:

http://www.eli.sdsu.edu/java-SDSU/examples/net/jcgi.c

jcgi.c is slightly more general. It will send all environment variables that starts with "HTTP_"

This difference is will not affect assignment 5.

CS 596: Client-Server Programming Spring Semester, 1997 Doc 19, CGI and Java