Bitnets

MVC Pattern

Pattern-It means it resolve's some problem,it follows some set of rules

The MVC (Model-View-Controller) architecture the client request is first intercepted by a servlet referred as controller servlet. this servlet handles the initial processing of the request and determines which JSP page to display next. Here the controller servlet is the single point of entry, there is a clear sepration of business logic, presentation output and request processing. MCV architecture is a way of decomposing an application into three parts:

The model maintains the state and data that the application represents.
The view allows the display of information about the model to the user.
The controller allows the user to manipulate the application.
the model, the view and the controller.

MVC was originally applied in the graphical user interaction model of input, processing and output.

In Struts, the view is handled by JSPs and presentation components, the model is represented by Java Beans and the controller uses Servlets to perform its action.

Model
A model represents an application’s data and contains the logic for accessing and manipulating that data. Any data that is part of the persistent state of the application should reside in the model objects. The business objects update the application state. ActionForm bean represents the Model state at a session or request level, and not at a persistent level. Model services are accessed by the controller for either querying or effecting a change in the model state. The model notifies the view when a state change occurs in the model.The JSP file reads information from the ActionForm bean using JSP tags.

View
The view is responsible for rendering the state of the model. The presentation semantics are encapsulated within the view, therefore model data can be adapted for several different kinds of clients.The view modifies itself when a change in the model is communicated to the view. A view forwards user input to the controller.The view is simply a JSP or HTML file. There is no flow logic, no business logic, and no model information -- just tags. Tags are one of the things that make Struts unique compared to other frameworks like Velocity.

Controller
The controller is responsible for intercepting and translating user input into actions to
be performed by the model. The controller is responsible for selecting the next view based on user input and the outcome of model operations.The Controller receives the request from the browser, and makes the decision where to send the request. With Struts, the Controller is a command design pattern implemented as a servlet. The struts-config.xml file configures the Controller.

20 File Transfer Protocol (Data)

The File Transfer protocol provides a mechanism for transferring specific files between network connected computer systems (usually a Linux or UNIX based system). Transfer is typically performed using the ftp client which provides a range of commands used to connect to a remote server for the purpose of uploading or downloading files. Most modern web browsers also have the ability to browse and download files located on a remote FTP server. FTP uses TCP (rather than UDP) to transfer files so is considered to be a highly reliable transport mechanism. FTP does not encrypt data and is not considered to be a secure file transfer protocol. The use of Secure Copy Protocol (SCP) and Secure File Transfer Protocol (SFTP) is strongly recommended in place of FTP.

21 FTP File Transfer (Control)

Traditionally FTP has two ports assigned (port 20 and port 21). Port 20 was originally conisidered the data transfer port, while port 21 was assigned to communicate control information. In modern implementations port 20 is now rarely used, with all communication taking place on port 21.

22 SSH Secure Shell

The Secure Shell is used to provide a secure, encypted, remote logon session to a remote host over a TCP/IP network. The original mechanism for remote access was the Telnet protocol. Because Telnet transmits data in plain text its use is now strongly discouraged in favor of the secure shell, which encrypts all communications, including log-in and password credentials. SSH also provides the mechanism by which files can be securely trandferred using the Secure Copy Protocol (SCP), and is also the basis for the Secure File Transfer Protocol (SFTP). SSH also replaces both the rsh and rlogin clients.

23 Telnet Telnet

Telnet is a terminal emulation protocol that provides the ability to log into a remote system over a TCP/IP connection. The access is text based allowing the user to type into a command prompt on the remote host and text displayed by the remote host is displayed on the local Telnet client. Telnet encrypts neither the password nor the text communicated between the client and server. As such, the use of telnet is strongly discouragaed. Most modern systems will have port 23 closed and the telnet service disabled to prevent its use. SSH should be used in place of Telnet.

25 SMTP Simple mail Transfer Protocol

SMTP defines the mechanism by which email messages are sent from one network host to another. SMTP is a very simple protocol and requires that the mail service always be available at the receiving host. Typically the receiving host will store incoming messages in a spool for subsequent access by the recipient using the POP3 or IMAP protocols. SMTP uses the TCP transport protocol to ensure error free message delivery.

53 DNS Domain Name Server - The service used by TCP/IP networks to translate host names and Fully Qualified Domain Names (FQDN) to IP addresses.

69 TFTP Trivial File Transfer Protocol

TFTP is a strpped down version of the File Transfer Protocol (FTP). It has a reduced command-set and lacks authentication. The most significant feature of TFTP is that it uses UDP to transfer data. This results in extremely fast transfer speeds but, consequently, lacks data reliability. TFTP is typically used in network based booting for diskless workstations.

80 HTTP Hypertext Text Transfer Protocol

HTTP is the protocol used to download text, graphics and multimedia from a web server and to a web browser. Essentially it defines the command and control mechanism between the browser and server defining client requests and server responses. HTTP is based on the TCP transport protocol and, as such, is a connection-oriented protocol.

110 POP3 Post Office Protocol

The POP3 protocol is a mechanism for storage and retrieval of incoming email messages from a server. In most corporate environments incoming email is stored on an email server and then downloaded to an email client running on the user's desktop or laptop when the user checks email. POP3 downloads all new messages to the client, and does not provide the user the option of choosing which messages to download, view headers, or download only parts of messages. It is for this reason the IMAP protocol is increasingly being used in place of POP3.

119 NNTP Network News Transfer Protocol

The protocol responsible for posting and retrieving messages to and from Usenet News Servers (i.e newsgroups and discussion forums hosted on remote servers). NNTP operates at the Application layer of the OSI stack and uses TCP to ensure error free message retrieval and transmission.

123 NTP Network Time Protocol

A protocol designed to synchronize computer clocks with an external time source. Using this protocol an operating system or application can request the current time from a remote NTP server. The remote NTP server is usually based on the time provided by a nuclear clock. NTP is useful for ensuring that all systems in a network are set to the same, accurate time of day. This is of particular importance in security situations when, for example, the time a file was accessed or modified on a client or server is in question.

143 IMAP4 Internet Message Access Protocol, Version 4

IMAP4 is an advanced and secure email retrieval protocol. IMAP is similar to POP3 in that it provides a mechanism for users to access email messages stored on an email server, although IMAP includes many additional features such as the ability to selectively download messages, view message headers, search messages and download part of a message. IMAP4 uses authentication and fully supports Kerberos authentication.

161 SNMP Simple Network Management Protocol

Provides a mechanism whereby network administrators are able to collect information about the devices (such as hubs, bridges, routers and switches) on a network. The SNMP protocol enables agents running on network devices to communicate their status to a central manager and, in turn, enables the manager to send new configuration parameters to the device agent. The agents can further be configured to notify the manager when certains events, known as traps, occur. SNMP uses UDP to send and receive data.

443 HTTPS Hypertext Transfer Protocol Secure

The standard HTTP (non-secure) protocol transfers data in clear text (i.e with no encryption and visible to anyone who might intercept the traffic). Whilst this is acceptable for most web browsing purposes it poses a serious security risk when confidential information such as credit card details need to be transmitted from the browser to the web server. HTTPS addresses this by using the Secure Sockets Layer (SSL) to send encypted data between the client and server.

2049 NFS Network File System

Originally developed by Sun Microsystems and subsequently widely adopted throughout the industry, NFS allows a file system on a remote system to be accessed over the network by another system as if the file system were on a local disk drive. NFS is widely used on UNIX and LINUX based systems. Later versions of Microsoft Windows possess the ability to also access NFS shared file systems on UNIX and LINUX based systems.

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