Here is a link to the presentation on ad blocking

Here are links to many of the classes that we will need.
ServerSocket

The second constructor, ServerSocket(int port) creates a server socket, binds it to the local host at the the requested

The other important method that we need is accept. This blocks until a client connects, and then returns a Socket

When you look at the documentation for the constructor, you see this. public ServerSocket() throws IOException

Exceptions are error conditions or other problematic situations

The syntax is

try 
{
   // stuff that could cause exceptions
}
catch (exception1)
{
   // what to do if exception1 occurs
}
catch (exception2)
{
  // what to do if exception2 occurs
}
finally
{
   // things to do even if exceptions occur
}

An uncaught exception will crash your program

Here is a link to the on-line help for Exception

The accept member of ServerSocket returns a Socket. Here is the complete description.

Pay particular attention to the Socket member function getInputStream(). This returns an instance of the class InputStream.. This is an abstract superclass which means that it cannot be instantiated, it can only be used as a base class to derive other classes.

There are two ways to store data, in text or binary, so java has two types, char and byte. Input and output streams are bytes.

To read or write characters, you need the classes reader and writer.

There is a class InputStreamReader which converts an input stream (bytes) to a reader (chars)

A charset is named mapping between sequences of sixteen-bit Unicode code units and sequences of bytes. This class defines methods for creating decoders and encoders and for retrieving the various names associated with a charset. Here are a few.

US-ASCII  Seven-bit ASCII, a.k.a. ISO646-US, a.k.a. the Basic Latin block of the Unicode character set
ISO-8859-1   ISO Latin Alphabet No. 1, a.k.a. ISO-LATIN-1
UTF-8 Eight-bit UCS Transformation Format
UTF-16BE Sixteen-bit UCS Transformation Format, big-endian byte order
UTF-16LE Sixteen-bit UCS Transformation Format, little-endian byte order
UTF-16 Sixteen-bit UCS Transformation Format, byte order identified by an optional byte-order mark

try {
  Socket s = new Socket(``www.cs.rpi.edu'', 80);
  InputStream in = s.getInputStream();
  InputStreamReader isr = new InputStreamReader(in);
  BufferedReader br = new BufferedReader(isr);
  int c;
  while ((c = br.read()) != -1) {
    System.out.print((char) c);
  }
  System.out.println();
}
catch (IOException ex) {
   System.err.println("Error reading from socket");  
}

Here is the code for server.java

Here is the code for a client

To compile and run the server on your laptop, open a command prompt window, cd to the directory where the source code is, and type
javac server.java
It is likely that you will get a message
javac is not recognized as an internal or external command
This means that you need to type the absolute pathname of the compiler. On my system it is
c:\jdk1.3.1_01\bin\javac server.java
. (Use the Windows search function to look for javac.exe)

javac is the java compiler. If you get compiler errors, fix them and try again (my code should not have compiler errors). Once you have a clean compile, there will be a file called server.class in your directory. To run this, type this command
java server 44444
(The last arg is the port.) Like a good server, nothing happens until a client connects.

A threaded server

• create a new class that extends the Thread class.
• put the code for your task in the run method
• create an instance (object) of your subclass in the parent thread
• call the start method to start the thread.
• To pass in arguments, create a constructor for the thread class with the appropriate arguments.

The URL class

In general, a URL can be broken into several parts. Here is a typical url.

http://java.sun.com:80/index.html#chapter1

This has five fields

• The protocol (http)
• The host (java.sun.com)
• The filename (index.html)
• The port (80)
• A fragment (#chapter1)

There is also a member InputStream openStream() which actually opens a connection to this url. this.

Here is a sample program which demonstrates this. Note that it downloads the course web page without the programmer having to create a socket.

Datagram Sockets

Here is code for a datagram socket server