My java web server works in eclipse but it crashes every time if ran through the command line

Question

I have a VERY simple web server that does accepts client connections, retrieves static web pages and services servlets.

I wrote the web server in Java and I'm using the tomcat library for servlets. I tested all my code by running it in the eclipse IDE and everything works fine, but when I run my code through the command line it starts the main correctly, but as soon as I try to access a web page through the browser (http://localhost/hello.html) then the application crashes, here is a sample output:

p1>java p1Solution.WebServer 80
Waiting for a connection.
Servicing the connection.
Closing the connection and shutting down the executor.
Exception in thread "main" java.lang.NoClassDefFoundError: javax/servlet/Servlet
Exception
        at p1Solution.WebServer.main(WebServer.java:54)
Caused by: java.lang.ClassNotFoundException: javax.servlet.ServletException
        at java.net.URLClassLoader$1.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClassInternal(Unknown Source)
        ... 1 more

Here is my WebServer

public class WebServer {
    private static final ExecutorService executor = Executors.newCachedThreadPool();

    public static void main(String[] args) throws Exception {
        int port = (args.length > 0) ? Integer.parseInt(args[0]) : 80;

        // listen for clients on the port specified as a command line argument
        ServerSocket serverSocket = new ServerSocket(port);
        Socket connection = null;
        try {
            while (true) {
                try {
                    System.out.println("Waiting for a connection.");
                    // Wait for an in bound client connection
                    connection = serverSocket.accept();

                    System.out.println("Servicing the connection.");
                    // Handle the client connection in a separate thread
                    executor.execute(new ConnectionHandler(connection));
                } catch (Exception e) {
                    // Never crash the server
                    e.printStackTrace();
                }
            }
        }finally {
            System.out.println("Closing the connection and shutting down the executor.");
            connection = null;
            serverSocket.close();
            executor.shutdown();
            executor.awaitTermination(3, TimeUnit.SECONDS);
        }
    }
}

I've been googling my exception and some people have been mentioning things about the classpath, but I have not found a definitive answer yet. When I run the program in eclipse everything works fine!

Here is the directory of my project (where my project resides):

p1>ls
.classpath  bin           hello.html  p1Solution.jar
.project    coreservlets  p1Solution  testsuite

Here is the directory contents of my p1Solution (where the code resides):

p1>ls p1Solution
ConnectionHandler.class           MyHttpServletRequest.class
ConnectionHandler.java            MyHttpServletRequest.java
HttpServletRequestAdapter.class   MyHttpServletResponse.class
HttpServletRequestAdapter.java    MyHttpServletResponse.java
HttpServletResponseAdapter.class  WebServer.class
HttpServletResponseAdapter.java   WebServer.java

Can anybody help me resolve this issue? Has anybody seen this problem before?

P.S. And yes, I do have the 'ls' command in Windows and it's not magic! Google "ls for windows" if you don't believe me.

Answer 1

You have a satisfied compile time dependency on javax.servlet.Servlet which is however not there at runtime, hence the NoClassDefFoundError. So you need to put an implementation of this class on the classpath (provided by Tomcat's servlet-api.jar). To do so, the recommended way would be to use the -cp option:

p1>java -cp c:\path\to\servlet-api.jar;. p1Solution.WebServer 80

Don't forget the "." (the current directory) in "-cp C:\path\to\servlet-api.jar;.". Also note that I'm not sure how spaces in path names are handled (I'm not under windows, can't test). So either use Windows short names 8.3 (like C:\PROGRA~1\) or don't use spaces in path names or move this library somewhere else.

Answer 2

Use the "Export -> Runnable Jar" facility to create a jar file with dependent libraries included underneath and properly referenced (as you do not have servlet.jar in your runtime classpath). Then you can just run

java -jar p1solution.jar