How to Run Java Program Automatically on Tomcat Startup

如何在启动tomcat时候，自动启动一个jar程序。
觉得这个应该在打包tomcat web服务为一个独立程序的时候应该有点作用。原文博客特别不错。
原文地址：https://crunchify.com/how-to-run-java-program-automatically-on-tomcat-startup/


Recently I wanted to start my standalone Java Application on Tomcat Startup. Also found so many other related questions on net. i.e.I need to run an application that can run automatically that when the tomcat starts..? any suggestions…?
how can I start my application by default on tomcat server start/restart?
Is it possible to 

edit

 tomcat startup services?
How to Start a service 

automatically

 when the tomcat starts
To run java program automatically on tomcat startup, need to use Servletand this Servlet initialized on tomcat startup automatically.To execute a program, you have to use 

Servlet

 and Servlet should define in deployment descriptor 

web.xml

 file under 

WEB-INF

 folder.web.xml file contain tags 

<load-on-startup>

 and 

<servlet>

 tag. Servlet tag keeps information of Servlet class. When tomcat starts, all Servlet loads in web container and init method of Servlet loaded first. Any java statement in 

init method

 of Servlet can be executed on running tomcat startup batch or shell.In init method we can define our scripts which have to be executed e.g. sending emails, sending newsletters, starting scheduler, etc..

Below is a simple trick to run your java program automatically on Tomcat Startup.

Step-1

Modify Web.xml file with below information. Where 

CrunchifyServletExample

 is a class name and 

crunchify.com.tutorials

 is a package name.Modify these values as per your need.web.xml

<servlet>    <servlet-name>CrunchifyTutorials</servlet-name>    <servlet-class>crunchify.com.tutorials.CrunchifyServletExample</servlet-class>    <load-on-startup>1</load-on-startup></servlet>

This is my complete 

web.xml

 filecomplete 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" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0">  <display-name>CrunchifyTutorials</display-name>  <welcome-file-list>    <welcome-file>index.html</welcome-file>    <welcome-file>index.htm</welcome-file>    <welcome-file>index.jsp</welcome-file>    <welcome-file>default.html</welcome-file>    <welcome-file>default.htm</welcome-file>    <welcome-file>default.jsp</welcome-file>  </welcome-file-list>  <servlet>    <servlet-name>CrunchifyTutorials</servlet-name>    <servlet-class>crunchify.com.tutorials.CrunchifyServletExample</servlet-class>    <load-on-startup>1</load-on-startup></servlet></web-app>

Step-2

CrunchifyServletExample.javaJava

package crunchify.com.tutorials; import javax.servlet.*;import javax.servlet.http.HttpServlet; /** * @author Crunchify.com */ @SuppressWarnings("serial")public class CrunchifyServletExample extends HttpServlet{     public void init() throws ServletException    {          System.out.println("----------");          System.out.println("---------- CrunchifyServletExample Initialized successfully ----------");          System.out.println("----------");    }}

Step-3

Now Clean your project using Maven or 

Project Menu

 -> 

Clean

Step-4

Deploy your project to Tomcat
Start Tomcat
Check your 

system out logs

 and you should see output like this
Console Output

-------------------- CrunchifyServletExample Initialized successfully --------------------

Enjoy and Happy Coding..