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javatomcatclassloader

Tomcat Java Servlet - Initialize Class on Application Startup

I have a class that takes a bit of time to start up (makes some JNI calls and what not), so it is not feasable to initialize this class everytime a page loads. Is it possible to initialize this class on application startup, then access its methods as pages are being served up?

For Example:

I have MyClass. When the application (tomcat) starts up I would like it to initialze my calss as follows:

MyClass myClassInstance = new MyClass("arg1", "arg2");

Then when a page is called, say /testpage, I would like to make calls to myClassInstance:

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import MyClass;

public class TestPage extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException
    {
        String myResult = myClassInstance.getResult("whatever");

        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        out.println("<html>");
        out.println("<head>");
        out.println("<title>Test</title>");
        out.println("</head>");
        out.println("<body>");
        out.println("<h1>" +myResult +"</h1>");
        out.println("</body>");
        out.println("</html>");
    }
}

Is this possible?

Solution

  • You have two choices:

    1. Initialize your class in servlet's init() method. You may add <load-on-startup> attribute to make sure your servlet is created at application startup and not on first access.

    2. Add ServletContextListener and use contextInitialized() callback method. Use ServletContext#setAttribute to store created object for future use.