Internet

1
Internet Communications

• Server-side programming for
• the WWW (lecture 9)
• CGI Programming Calling Java programs

2
CGI Programs

• A few lectures back we introduced CGI.
• Can run programs in any language as a CGI
  program.
• Weve used shell scripts - but rather limited.
• Most common to use PERL - A simple scripting
  language.
• But also possible to call Java programs.

3
CGI and Java

• We can write a Java program to write out HTML (or
  just text)
• Compile this, make executable by all then..

public class test public static void
main(String argv) System.out.println(
Content-type text/plain\n)
System.out.println(Hello World!)
4
CGI and Java

• Now write a tiny shell script just to run your
  Java program
• Lets say its called testjava and executable by
  others..
• Now use URLwww. macs./cgi-bin/cgiwrap/yourlogin
  /testjava

!/bin/sh java test
5
Using Java to Handle Form Data

• Remember that data from an HTML form is available
  in the QUERY_STRING variable, e.g.,
• namealisonaddressEdinburgh
• We can pass that data to Java prog as follows
• Our Java can then write out this data

!/bin/sh java -Dquery.stringQUERY_STRING test
String data System.getProperty(query.string)
System.out.println(Data data)
6
Can also write out data to a file
FileWriter file2 new FileWriter(data) PrintWr
iter outputFile new PrintWriter(file2) outputFi
le.println(Data data)
7
Example
public class test public static void
main(String argv) throws IOException
FileWriter file1 new FileWriter("mydata")
PrintWriter outputFile new PrintWriter(file1)
System.out.println("Content-type
text/plain\n" ) String s System.getProperty(
"query") System.out.println("Your data "
s) outputFile.println("Your data " s)
outputFile.close()
Download script
Try It
Download java
8
Java and Form Data

• Want to break query string into useful parts..
• Use a class CGI to do this (provided)
• Can then get hold of values from our form
• Would get address, as vector of lines of text

import java.util. public class test
public static void main(String argv)
System.out.println(Content-type
text/plain\n) CGI cgi new CGI()
Vector v cgi.getValues(address)
9
Writing out data..

• We can now write out the users address.
• Note that the data is in a vector - but usually
  youll just want the first element.

• import java.util.
• public class test
• public static void main(String argv)
• System.out.println(Content-type
  text/plain\n)
• CGI cgi new CGI()
• Vector v cgi.getValues(address)
• System.out.println(Your address is)
• System.out.println(v.elementAt(0))

Try It
Download
Download Script
10
Incorporating CGI class

• We provide CGI.java
• To compile your program so that the CGI class is
  available use
• javac CGI.java Yourfile.java
• Yourfile.class will now contain what you want.

11
Writing it all out..

• Can write out all the form data

CGI cgi new CGI() Enumeration e
cgi.getNames() while(e.hasMoreElements())
String name (String) e.nextElement() Vector
v cgi.getValues(name) System.out.println(nam
e v.elementAt(0))
Example
Download
12
Writing out HTML response page

• We can of course write out HTML

System.out.println(Content-type
text/html\n) CGI cgi new CGI()
Vector v cgi.getValues(address)
System.out.println(lthtmlgtltheadgt lt/headgt
ltbodygt) System.out.println(lth1gt
Addresslt/h1gt) System.out.println(v.elementA
t(0)) System.out.println(lt/bodygt
lt/htmlgt)
13
Testing CGI

• You dont need to load a web page to test a CGI
  program - just try running your script.
• It may not have all the form data there, but
  something like following should be output
• Content-type text/plainYour address is

14
Activities

• Try and get the Java examples in this handout
  working.
• Link it to your form - try to create a response
  page which says, say Thanks Alison. Your
  order will be delivered to 13 Nosuchstreet
  Edinburgh any day now.

15
Summary CGI

• CGI programs can be written in any language.
• Perversely, we choose Java.
• Call java program from tiny shell script.
• Java can contain code to get at different parts
  of the HTML form data.
• This can be saved to file, or incorporated into
  response page.

16
Comparison CGI vs servlets

• Coding Java CGI vs Java Servlets is probably
  about the same complexity.
• Java CGI needs launching via script.
• In both we can use special methods to access
  input data from forms.
• In both we need to take care in compilation.
• CGI is a little more robust - doesnt depend on
  Tomcat server being up.
• Servlets are a little more efficient.
• JSP is easier for small examples, but awkward
  when amount of code is significant.