Java: ConnectException/Cannot find or load Main-Class

Question

So in a nutshell, I'm just trying to get a small working skeleton program that I can use to sort of learn about Http communication and "feel" my way around to figure out what I will eventually need for a bigger program I am working on. This particular code here is actually just a chopped up version of an example from the Apache libraries. I could compile the examples listed on the Apache website, but they didn't run properly, giving a "java.net.ConnectException". I figured it had to do with Windows c-blocking a program like this from making a connection, and that I would need to run it as an administrator. I then tried taking the code and throwing it into an executable jar file, but I get a Cannot-find-or-load-main-class error. Am I an idiot or is the Apache library a little outdated/not fit for Win 8/something else?

Code below:

package NewProject;


import java.net.Socket;

import org.apache.http.ConnectionReuseStrategy;
import org.apache.http.HttpHost;
import org.apache.http.HttpResponse;
import org.apache.http.impl.DefaultBHttpClientConnection;
import org.apache.http.impl.DefaultConnectionReuseStrategy;
import org.apache.http.message.BasicHttpRequest;
import org.apache.http.protocol.HttpCoreContext;
import org.apache.http.protocol.HttpProcessor;
import org.apache.http.protocol.HttpProcessorBuilder;
import org.apache.http.protocol.HttpRequestExecutor;
import org.apache.http.protocol.RequestConnControl;
import org.apache.http.protocol.RequestContent;
import org.apache.http.protocol.RequestExpectContinue;
import org.apache.http.protocol.RequestTargetHost;
import org.apache.http.protocol.RequestUserAgent;
import org.apache.http.util.EntityUtils;

class NewProject
{
    public static void main(String[] args) throws Exception
    {
        HttpProcessor httpproc = HttpProcessorBuilder.create()
            .add(new RequestContent())
            .add(new RequestTargetHost())
            .add(new RequestConnControl())
            .add(new RequestUserAgent("Test/1.1"))
            .add(new RequestExpectContinue(true)).build();

        HttpRequestExecutor httpexecutor = new HttpRequestExecutor();

        HttpCoreContext coreContext = HttpCoreContext.create();
        HttpHost host = new HttpHost("localhost", 8080);
        coreContext.setTargetHost(host);

        Out os = new Out("TestOut.txt");

        DefaultBHttpClientConnection conn = new DefaultBHttpClientConnection(8 * 1024);
        ConnectionReuseStrategy connStrategy = DefaultConnectionReuseStrategy.INSTANCE;

        try 
        {

            String[] targets = 
            {
                "http://www.google.com/"
            };

            for (int i = 0; i < targets.length; i++) 
            {
                if (!conn.isOpen()) 
                {
                    Socket socket = new Socket(host.getHostName(), host.getPort());
                    conn.bind(socket);
                }
                BasicHttpRequest request = new BasicHttpRequest("GET", targets[i]);
                os.println(">> Request URI: " + request.getRequestLine().getUri());

                httpexecutor.preProcess(request, httpproc, coreContext);
                HttpResponse response = httpexecutor.execute(request, conn, coreContext);
                httpexecutor.postProcess(response, httpproc, coreContext);

                os.println("<< Response: " + response.getStatusLine());
                os.println(EntityUtils.toString(response.getEntity()));
                os.println("==============");

                if (!connStrategy.keepAlive(response, coreContext)) 
                {
                    conn.close();
                }
                else 
                {
                    os.println("Connection kept alive...");
                }
            }
        }
        catch (IndexOutOfBoundsException iob)
        {
            os.println("What happened here?");
        }
        finally
        {
            conn.close();
        }

        return;
    }
}

Answer 1

The code you posted seems a little low level (e.g. interacting directly with Socket connections). The code posted below should give you what it sounds like you are looking for. The classes used also give you a lot of inroads into setting and getting http parameters (e.g. headers, time-outs, etc).

package org.yaorma.example.http.client;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.HttpURLConnection;
import java.net.URL;

public class HttpClientExample {

    public static void main(String[] args) throws Exception {
        String response;
        response = get("http://www.google.com");
        System.out.println("RESPONSE FROM GET -----------------------------------------");
        System.out.println(response);
        response = post("http://httpbin.org/post", "This is the message I posted to httpbin.org/post");
        System.out.println("RESPONSE FROM POST -----------------------------------------");
        System.out.println(response);
    }

    /**
     * Method to post a request to a given URL.
     */
    public static String post(String urlString, String message) {
        try {
            // get a connection
            URL url = new URL(urlString);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            // set the parameters
            conn.setRequestMethod("POST");
            conn.setDoOutput(true);
            // send the message
            OutputStream os = conn.getOutputStream();
            BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(os, "UTF-8"));
            writer.write(message);
            writer.flush();
            writer.close();
            os.close();
            // get the response
            conn.connect();
            InputStream content = (InputStream) conn.getInputStream();
            // read the response
            BufferedReader in = new BufferedReader(new InputStreamReader(content));
            String rtn = "";
            String line;
            while ((line = in.readLine()) != null) {
                rtn += line + "\n";
            }
            return rtn;
        } catch (Exception exp) {
            throw new RuntimeException(exp);
        }
    }

    /**
     * Method to do a get from a given URL.
     */
    public static String get(String urlString) {
        try {
            // get a connection
            URL url = new URL(urlString);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            // set the parameters
            conn.setRequestMethod("GET");
            conn.setDoOutput(true);
            // get the response
            conn.connect();
            InputStream content = (InputStream) conn.getInputStream();
            // read the response
            BufferedReader in = new BufferedReader(new InputStreamReader(content));
            String rtn = "";
            String line;
            while ((line = in.readLine()) != null) {
                rtn += line + "\n";
            }
            return rtn;
        } catch (Exception exp) {
            throw new RuntimeException(exp);
        }
    }

}

Answer 2

... they didn't run properly, giving a "java.net.ConnectException"

That could be caused by lots of things. There are clues in the exception message ... which you chose not to share with us.

... "Cannot find or load Main-Class"

Again multiple possible causes, and there are clues in the exception message ... which you chose not to share with us.

But the fact that you have created a JAR file plus the "Main-Class" hint in the error message fragment you provided suggest that you made a mistake in the creation of the JAR file; i.e. you used the wrong name for the "Main-Class" attribute.

Given that source code, the "Main-Class" attribute should be "NewProject.NewProject". I suspect you set it to something else.

A second possibility is that you haven't handled the dependency on the Apache library correctly. The Apache classes need to be on the classpath specified by the JAR file. (You can't use a -cp argument or $CLASSPATH when you launch with java -jar.)

---

Am I an idiot or is the Apache library a little outdated/not fit for Win 8/something else?

There is nothing wrong with the Apache library.