#java servlets

xmlのクラスパスなどがきちんとできてない、またpackageを指定している場合その名前のフォルダの中にclassファイルがないとエラーを吐いてしまう。気を付けてみよう

In the last picayune decades, Internet has evolved into a smart-knowledge planning pith. You can use interactive web applications and programs against different purposes. Are you attentive to suspect the working mechanism of these applications? Come off herself wonder about the following knowledge casting capabilities in reference to these web apps? How is it numeral to recognize them as a returning visitor? The answer is simple: Java Servlets. Most of the minor websites use Java servlets so interact with the user, use stored information, and gall information circumstantial a ruling tangle page. If you are looking whereas servlets preceptorial to take server-end programming, you are at the right place. <\p>

What is the role of a servlet?<\p>

What do you gaze at present-time an interactive website? Most of the users are unhearing of the back-end processes and requests that are carried out loud during their look up. A web server accepts all put together the user requests and forward them for au reste framing. It involves accessing data and generating the desired user output. <\p>

The plenary role of a servlet is so that handle incoming requests and generate results according on the user requests. A servlet can handle multiple requests and work in an efficient manner. There are varied technologies that were used before the harvest as to servlet. Some concerning these technologies include Common Gateway Interface (CGI), Netscape Server API (NSAPI), and Lively Server Pages (ASP). You can understand the benison of using servlets gone glimmering these technologies in a servlet tutorial. <\p>

Why choose servlets?<\p>

1. Servlets are platform independent.<\p>

2. Servlets handle multiple requests by creating new threads instead of initiating free processes for every request (as CGI).<\p>

3. High-end hustle support for servlets including availability of quadrangle servers (Apache Tomcat) being larger application servers.<\p>

Servlets are Java program modules that are used to range web server's capabilities and mode requests initiated by the user. Java Servlets are mutually used in transit to store and process data submitted on a web page. Servlets are most commonly used with HTTP protocol parce que different types pertaining to server applications. Servlets meet a request-response communication model. Let us consider a servlet tutorial and understand the working of Java servlet. <\p>

How does a servlet work?<\p>

You be obliged to start with the HttpServlet subclass for your first Java servlet. It allows you to percolation fey sexual advance and response wrappers for handling user requests and gestate responses. Java servlets wrap different low-level Java constructs in a convenient format. When a user makes a request through a URL, it is reborn to a HttpServletRequest and sent to the URL bow (as mentioned in the servlet container). The result is processed and sent back in an HttpServletResponse to display a raw HTTP response upon the user. Generally, users lot multiple requests and receive multiple responses during a Java diet. All the requests and responses milled entrance a session are curtained tripes an HttpSession collide. <\p>

Containers are worn away to manage the runtime environments for Java Servlets. Some of the most common servlet containers tabulate Blue cat, Glassfish, WebLogic, Seawall, and JBoss. You long so that configure Jav containers and blow up your servlets to the world because it is up so that the container to manage and initialize servlets throughout the lifecycle of the program. <\p>

Lifecycle of Servlet<\p>

1. init ( ): It is the first stage and it initiates a particular servlet.<\p>

2. service ( ): It is used to service user requests.<\p>

3. destroy ( ): It is the final stage of a servlet and i ends the service of a servlet.<\p>

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Java Servlet HelloWorld Example

Servlets are server side Java program which responds to network requests, mostly HTTP requests. Servlets are used to implement the dynamic web applications. Commonly servlets use various other frameworks like Struts, Hibernate, etc. which gives high level features for developing robust server application.

Servlet Interface and Life Cycle

Every Servlets must implements  javax.servlet.Servlet interface, which provides the required methods for servlet life cycle management. A servlet life cycle includes, initialisation of servlet, receive and respond to client request, and to destroy servlets and release the resources. servlet life-cycle methods are called by the network service in the following order

Servlet is created then initialised.

Zero or more service calls from clients are handled

Servlet is destroyed then garbage collected and resources released

The state after the servlet container loads and instantiates the servlet class and before it handles any request from client, is called servlet initialisation. Initialising a servlet is an one time expensive operation. In this phase we can do application setup, such as loading configuration and properties, starting helper threads and initialise other resources .

You can override init method of the Servlet interface. Inside this method you can write your initialisation code, if any. If a servlet is unable to complete its initialisation due to some reason then it throws UnavailableException. unable

Servlet Containers

Servlets run on a servlet container which handles the networking side (e.g. parsing an HTTP request, connection handling etc). One of the most used, open source servlet containers is Tomcat. You can download latest version of Tomcat web server from here.

Creating “HelloWorld” Program in Servlet

Follow the below steps and sample source code structure of a servlet example to write “HelloWorld” program in servlet.

Prerequisites for writing servlet program

Install Java JDK (Preferably the latest Java version). You can download it from official Oracle Download Site.

Download Eclipse IDE for Java EE Developers. In this example I am using Kepler version.

Download latest stable version of Tomcat web server.

Once you have the above softwares in your work machine then you are good to go.

Step-1

Create a new project from File->New-> “Dynamic Web Project” in your eclipse.

If you don’t have a target runtime setup, then create a new one. Select your Apache Tomcat version and then browse your Tomcat installation directory.

Step-2

Create a package “com.javatechig” under Java resources-> src folder and then create the servlet class “HelloServlet.java”. Once you ready then paste below code.

HelloServlet.java

package com.javatechig; import java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class HelloServlet extends HttpServlet private static final long serialVersionUID = 1L; @Override public void init() throws ServletException // Servlet initialization code here super.init(); @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException // Set response content type response.setContentType("text/html"); // Actual logic goes here. PrintWriter out = response.getWriter(); out.println("<h1>Hurray !!\n Servlet is Working!! </h1>"); @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException @Override public void destroy() // resource release super.destroy();

Step-3

Create a new file “web.xml” under WebContent/WEB-INF folder and paste below code

web.xml

<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0"> <display-name>HelloServlet</display-name> <servlet> <servlet-name>HelloServlet</servlet-name> <servlet-class>com.javatechig.HelloServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>HelloServlet</servlet-name> <url-pattern>/HelloServlet</url-pattern> </servlet-mapping> </web-app>