Erro ao executar o ClienteWebService

Olá, tudo bem?

Estou tendo o seguinte erro ao executar o ClienteWebService Exception in thread "main" org.apache.http.client.HttpResponseException: at org.apache.http.impl.client.AbstractResponseHandler.handleResponse(AbstractResponseHandler.java:70) at org.apache.http.client.fluent.Response.handleResponse(Response.java:90) at org.apache.http.client.fluent.Response.returnContent(Response.java:97) at br.com.alura.cliente.ClienteWebService.main(ClienteWebService.java:12)

O cliente WebService esta assim:

package br.com.alura.cliente;

import org.apache.http.client.fluent.Request;

public class ClienteWebService {

    public static void main(String[] args) throws Exception {
        String conteudo = Request
                .Post("http://localhost:8080/gerenciador/empresas")
                .addHeader("accept", "application/xml")
                .execute()
                .returnContent()
                .asString();

        System.out.println(conteudo);

    }

}

Já o empresasService:

package br.com.alura.gerenciador.servlet;

import java.io.IOException;
import java.util.List;

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

import com.google.gson.Gson;
import com.thoughtworks.xstream.XStream;

import br.com.alura.gerenciador.modelo.Banco;
import br.com.alura.gerenciador.modelo.Empresa;

/**
 * Servlet implementation class EmpresasService
 */
@WebServlet("/empresas")
public class EmpresasService extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        List<Empresa> empresas = new Banco().getEmpresas();

        String valor = request.getHeader("accept");
        if(valor.endsWith("xml")) {
            XStream xstream = new XStream();
            xstream.alias("empresa", Empresa.class);
            String xml = xstream.toXML(empresas);    
            response.setContentType("application/xml");
            response.getWriter().print(xml);

        } else if (valor.endsWith("xml")) {
            Gson gson = new Gson();
            String json = gson.toJson(empresas);

            response.setContentType("application/json");
            response.getWriter().print(json);
        } else {
            response.setContentType("application/json");
            response.getWriter().print("{'message:': 'no content'}");
        }


    }

}

Não sei onde estou errando, poderiam me ajudar?