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Servlet Packages And Task In Java
Servlet provides a component-based, platform-independent method for building Web-based applications , without the performance limitations of CGI programs. Servlets have access to the entire family of Java APIs, including the JDBC API to access enterprise databases.
Java Servlets are programs that run on a Web or Application server and act as a middle layer between a request coming from a Web browser or other HTTP client and databases or applications on the HTTP server.
Using Servlets, we can collect input from users through web page forms, present records from a database or another source, and create web pages dynamically.
Java Servlets often serve Advanced java training in bangalore the same purpose as programs implemented using the Common Gateway Interface (CGI). But Servlets offer several advantages in comparison with the CGI.Performance is significantly better.
Features Of Servlet :
- Servlets execute within the address space of a Web server . It is not necessary to create a separate process to handle each client request .
- Servlets are platform-independent ...
... because they are written in Java .
- Java security manager on the server enforces a set of restrictions to protect the resources on a server machine. So servlets are trusted.
- The full functionality of the Java class libraries is available to a servlet. It can communicate with applets, databases, java/j2ee classes bangalore or other software via the sockets and RMI mechanisms that you have seen already.
Servlets perform the following major tasks:
- Read the explicit data sent by the clients (browsers). This includes an HTML form on a Web page or it could also come from an applet or a custom HTTP client program.
- Read the implicit HTTP request data sent by the clients (browsers). This includes cookies, media types and compression schemes the browser understands, and so forth.
- Process the data and generate the results. This process may require talking to a database, executing an RMI or CORBA call, invoking a Web service, or computing the response directly. Java training center bangalore
- Send the explicit data (i.e., the document) to the clients (browsers). This document can be sent in a variety of formats, including text (HTML or XML), binary (GIF images), Excel, etc.
- Send the implicit HTTP response to the clients (browsers). This includes telling the browsers or other clients what type of document is being returned (e.g., HTML), setting cookies and caching parameters, and other such tasks.
Java Servlets are Java classes run by a web server that has an interpreter that supports the Java Servlet specification.
Servlets can be created using the javax.servlet and javax.servlet.http packages , which are a standard part of the Java's enterprise edition, java course in bangalore an expanded version of the Java class library that supports large-scale development projects.
Servlet Life Cycle :
A servlet life cycle can be defined as the entire process from its creation till the destruction. The following are the paths followed by a servlet
-The servlet is initialized by calling the init () method.
-The servlet calls service() method to process a client's request.
-The servlet is terminated by calling the destroy() method.
- Finally, servlet is garbage collected by the garbage collector of the JVM.
The init() method :
The init method is designed to be called only once. It is called when the servlet is first created, and not called again for each user request. Best core java training in bangalore So, it is used for one-time initializations, just as with the init method of applets.
The service() method :
The service() method is the main method to perform the actual task. The servlet container (i.e. web server) calls the service() method to handle requests coming from the client( browsers) and to write the formatted response back to the client.
Each time the server receives a request for a servlet, the server spawns a new thread and calls service. The service() method checks the HTTP request type (GET, POST, PUT, DELETE, etc.) and calls doGet, doPost, doPut, doDelete, etc. methods as appropriate.
The destroy() method :
The destroy() method is called only once at the end of the life cycle of a servlet. This method gives servlet a Advanced java training in bangalore chance to close database connections, halt background threads, write cookie lists or hit counts to disk, and perform other such cleanup activities.
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