Jetty:将对象从main方法传递给servlet

Question

我有两个类Server(使用main方法,启动服务器)和StartPageServletServlet.

代码中最重要的部分是:

public class Server {
    public static void main(String[] args) throws Exception {
        // some code

        // I want to pass "anObject" to every Servlet.
        Object anObject = new Object();

        Server server = new Server(4000);
        ServletContextHandler context = 
            new ServletContextHandler(ServletContextHandler.SESSIONS);
        context.addServlet(StartPageServlet.class, "/");
        // more code
}

和StartPageServlet:

public class StartPageServlet extends HttpServlet {

    @Override
    public void doGet(HttpServletRequest request,
                      HttpServletResponse response)
            throws ServletException, IOException
    {
        // Here I want to access "anObject"
    }

我该怎么做呢？

Answer 1

嵌入式Jetty在这里非常精彩.

你有几个常见的选择:

1. 直接实例化servlet,使用构造函数或setter,然后通过它将其交给Jetty ServletHolder(可以是任何值或对象类型)
2. 将其添加到ServletContext主文件中,然后通过ServletContext应用程序中的文件访问它(可以是任何值或对象类型).

例子:

package jetty;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.servlet.ServletContextHandler;
import org.eclipse.jetty.servlet.ServletHolder;

public class ObjectPassingExample
{
    public static void main(String args[]) throws Exception
    {
        Server server = new Server(8080);

        ServletContextHandler context = new ServletContextHandler();
        context.setContextPath("/");

        // Option 1: Direct servlet instantiation and ServletHolder
        HelloServlet hello = new HelloServlet("everyone");
        ServletHolder helloHolder = new ServletHolder(hello);
        context.addServlet(helloHolder, "/hello/*");

        // Option 2: Using ServletContext attribute
        context.setAttribute("my.greeting", "you");
        context.addServlet(GreetingServlet.class, "/greetings/*");

        server.setHandler(context);
        server.start();
        server.join();
    }

    public static class HelloServlet extends HttpServlet
    {
        private final String hello;

        public HelloServlet(String greeting)
        {
            this.hello = greeting;
        }

        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException
        {
            resp.setContentType("text/plain");
            resp.getWriter().println("Hello " + this.hello);
        }
    }

    public static class GreetingServlet extends HttpServlet
    {
        private String greeting;

        @Override
        public void init() throws ServletException
        {
            this.greeting = (String) getServletContext().getAttribute("my.greeting");
        }

        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException
        {
            resp.setContentType("text/plain");
            resp.getWriter().println("Greetings to " + this.greeting);
        }
    }
}