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Subscribe NowUnderstanding the Servlet Life Cycle in Java
In Java web development, understanding the life cycle of a Servlet is fundamental. The entire life cycle of a Servlet is managed by the Servlet Container (such as Apache Tomcat) and consists of three core methods: init(), service(), and destroy().
1. Initialization Phase: init()
The init() method is invoked by the container strictly once when the Servlet instance is first loaded and instantiated. This phase initializes necessary resources, configurations, or database connections before handling client requests.
2. Request Processing Phase: service()
Once initialized, the service() method is executed multiple times—each time a client sends a request to the mapped URL pattern. It reads incoming client requests and generates dynamic responses back to the browser.
3. Destruction Phase: destroy()
The destroy() method is called by the container strictly once when the Servlet is taken out of service or the server is shutting down. This allows clean-up operations like closing database connections or releasing system memory.
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ServletInterface Project Dir Structure
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| ServletLifeCycle - Example |
ServletsLifeCycle.java
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 | 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; // Extend HttpServlet class public class ServletsLifeCycle extends HttpServlet { private static final long serialVersionUID = 1L; private int i; public void init() throws ServletException { System.out.println("------------------------------------------------------"); System.out.println(" Init method is called "); System.out.println("------------------------------------------------------"); } public void service( HttpServletRequest request, HttpServletResponse response ) throws ServletException, IOException { ++i; System.out.println(" service method is called "+i+ " time"); // Set response content type response.setContentType("text/html"); // Actual logic goes here. PrintWriter out = response.getWriter(); out.println("<h1>" + " service method is called "+i+ " time" + "</h1>"); } public void destroy() { System.out.println("------------------------------------------------------"); System.out.println(" destroy method is called "); System.out.println("------------------------------------------------------"); } } |
web.xml
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 | <?xml version="1.0" encoding="ISO-8859-1"?> <web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0" metadata-complete="true"> <display-name>ServletsLifeCycle Application</display-name> <description> This is a simple web application with a source code organization based on the recommendations of the Application Developer's Guide. </description> <servlet> <servlet-name>ServletsLifeCycle</servlet-name> <servlet-class>ServletsLifeCycle</servlet-class> </servlet> <servlet-mapping> <servlet-name>ServletsLifeCycle</servlet-name> <url-pattern>/hello</url-pattern> </servlet-mapping> </web-app> |
index.html
1 2 3 4 5 6 7 8 9 10 11 12 13 | <!DOCTYPE HTML><html lang="en"><head> <meta charset="UTF-8"> <title>ServletsLifeCycle</title> </head> <body> <p> <h3>ServletsLifeCycle</H3> <p></p> <ul> <li><a href="hello">ServletsLifeCycle Test</a></li> </ul> </body></html> |
