INTERNET PROTOCOLS (lập TRÌNH MẠNG cơ bản SLIDE)

Uniform Resource Locator: URL Hierarchy of Classes  Methods of the Class  Examples of Using the Class... String getContentType; String getContentLength; long getLastModified;... Forma

INTERNET PROTOCOLS

Uniform Resource Locator: URL

 Hierarchy of Classes

 Methods of the Class

 Examples of Using the Class

Hierarchy of Classes

URL Class

 Class URL is a description of a resource location on the Internet

 Complete URL: http://www.cs.joensuu.fi:1547/~john/pub/index.html

Methods of URL Class

MalformedURLException).

Methods of URL Class

instantiated

• An InputStream object is returned and permits to retrieve information specifed

into the URL

• If the connection fails, the exception IOException is raised.

String getContentType();

String getContentLength();

long getLastModified();

Creating a URL Instance

 The following statement creates a Java URL object:

 You can also build a URL by setting each part individually:

URL u = new URL(“http”, www.cs.rpi.edu,80,”/~hollingd/”);

Retrieving Remote Files

Rather than reading the fle from the local system, this example reads the fle from a Web server

private void showFile() {

URL url = null;

Retrieving a Resource with the URL Class

import java.net.*;

import java.io.*;

public class FtpUrls {

public static void main(String[] args) throws IOException {

// URL url = new URL("ftp://pvtinh:Tinh7570@192.168.1.6/t.txt");

URL url = new URL("http://192.168.1.2/cackhoa.html");

InputStream uin = url.openStream();

BufferedReader in = new BufferedReader(new

SMTP

Format of an email

Commands and response

Command

Response

Response (con)

Status code

 The Server responds with a 3 digit code that may be followed by text info

 2## - Success

 3## - Command can be accepted with more information

 4## - Command was rejected, but error condition is temporary

 5## - Command rejected, Bad User!

Connection establishment

F Message transfer

FConnection termination

After connection, we can type the SMTP commands and then receive the responses as shown below We have shown the commands in black and the responses in color Note that we have added for clarification some comment lines, designated by the “=” sign These lines are not part of the email procedure.

Example

============= Connection Termination===============

250 Message received: adelphia.net@mail.adelphia.net

QUIT

221 mta13.adelphia.net SMTP server closing connection

Connection closed by foreign host.

Example

SMTP & Sending E-Mail

Simple Mail Transfer Protocol - RFC 821

 To send e-mail, you make a socket connection to port 25 , the SMTP port SMTP is the Simple Mail Transport Protocol that describes the format for e-mail messages.

 Open a socket to your host.

Socket s = new Socket("mail.yourserver.com", 25);

PrintWriter out = new PrintWriter(s.getOutputStream());

 Send the following information to the print stream:

HELO sending host # Domain name

MAIL FROM:< sender email address >

RCPT TO:< recipient email address >

Sending E-Mail

private BufferedReader in;

private PrintWriter out;

private JTextField from;

private JTextField to;

private JTextArea message;

……….

public void sendMail() {

try {

Socket s = new Socket(smtpServer.getText(), 25);

out = new PrintWriter(s.getOutputStream());

public void receive() throws IOException {

String line = in.readLine();

if (line != null) {

………

}

}

Limitations in SMTP

 Only uses NVT 7 bit ASCII format

 How to represent other data types?

 No authentication mechanisms

 Messages are sent un-encrypted

 Susceptible to misuse (Spamming,

faking sender address)

POP3

Receive E-Mail – POP3 (RFC 1939)

 // Login by sending USER and PASS commands