Networking with Java for Computer Science and MCA students

What is port?

• It is a logical connection place and uses the internet protocol TCP/IP the way a client program specifies a particular server program on a computer in a network.
• The higher level applications use the TCP/IP such as the web protocol, hypertext transfer protocol that have the ports with preassigned numbers. They are well known as well known ports.
• The processes are given port numbers dynamically for each connection.
• Porting means to move an application program from an operating system environment in which it was developed to another operating system environment so it can be run there.
• Porting implies some work, but not nearly as much as redeveloping the program in the new environment.
• When the Java ES installer requests a port number, the installer performs a runtime check on the ports in use and displays an appropriate default value. If the default port number is being used by another component or by another instance of the same product component, the installer presents an alternative value.

What is URL?

• URL is known as Uniform Resource Locator. It is a standard way of locating resources on the Internet.
• Class URL represents a Uniform Resource Locator, a pointer to a "resource" on the World Wide Web. A resource can be something as simple as a file or a directory, or it can be a reference to a more complicated object, such as a query to a database or to a search engine.

• Protocol name: http/file/mailto etc.
• Host: www.hotmail.com
• Port: It is an optional attribute that is specified after the host name. e.g. www.hotmail.com:80
• File: It is the name of the file that is to be accessed. e.g. www.hotmail.com/index.html
• Reference: It is the name of the named reference within the page (i.e. cs) e.g. www.hotmail.com/index.html#cs

• Lets assume there is a document called "foobar.txt"; and itt sits on an anonymous ftp server called "ftp.careerride.com" in directory "/pub/files". The URL for this file is then:
file://ftp.careerride.com/pub/files/foobar.txt
• The toplevel directory of this FTP server will be:
file://ftp.careerride.com/
• The "pub" directory of this FTP server will be:
file://ftp.careerride.com/pub

• They are a little more complicated than file URLs, as they are a little tricker to deal with than FTP servers. To visit a particular gopher server, use this URL:
gopher://gopher.careerride.com/
• There are some gopher servers may reside on unusual network ports on their host machines. (The default gopher port number is 70.) If you know that the gopher server on the machine "gopher.banzai.edu" is on port 1234 instead of port 70, then the corresponding URL would be:
gopher://gopher.careerride.edu:1234/

• For pointing to a Usenet newsgroup, the URL is:
news : rec.java
• Currently, the network clients like Mosaic don't allow to specify a news server like it is normally expected it is being planned but in the meantime the local news server is to be specified via some other method.

• HTTP stands for HyperText Transport Protocol. They are commonly used for serving hypertext documents, as HTTP is an extremely low-overhead protocol that capitalizes on the fact that navigation information can be embedded in such documents directly and thus the protocol itself doesn't have to support full navigation features like the FTP and Gopher protocols do. They can be any normal URL that we use everyday.

• Once a document is viewed located somewhere on the network, the partial URL can be used to point to another file in the same directory, on the same machine, being served by the same server software. For example, if another file exists in that same directory called "anotherfile.html", then anotherfile.html is a valid partial URL at that point. It provides an easy way to build sets of hypertext documents.