LoanApplication

public class LoanApplication {

    private long applicationNo;
    private long amount;
    private String email;
    private String contact;
    private boolean approved;

    public LoanApplication() {
        applicationNo = LoanHandler.getNextId();
    }

    public long getAmount() {
        return amount;
    }

    public void setAmount(long amount) {
        this.amount = amount;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public long getApplicationNo() {
        return applicationNo;
    }

    public void setApplicationNo(long applicationNo) {
        this.applicationNo = applicationNo;
    }

    public void approve() {
        setApproved(true);
    }

    public boolean isApproved() {
        return approved;
    }

    public void setApproved(boolean approved) {
        this.approved = approved;
    }

    public void setContact(String who) {
        this.contact = who;
    }

    public String getContact() {
        return contact;
    }
}

LoanHandler

import java.io.File;
import java.io.FileFilter;
import java.io.IOException;
import java.io.PrintWriter;

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

import org.eclipse.jetty.server.Request;
import org.eclipse.jetty.server.handler.AbstractHandler;

import com.google.gson.Gson;

public class LoanHandler extends AbstractHandler {
    public static final String APPLICATION = "apply";
    public static final String FETCH = "fetch";
    public static final String TICKET_ID = "ticketId";
    public static final String APPROVE = "approve";

    @Override
    public void handle(String target, Request baseRequest, HttpServletRequest request, HttpServletResponse response)
            throws IOException, ServletException {
        response.setContentType("application/json;charset=utf-8");
        response.setStatus(HttpServletResponse.SC_OK);
        baseRequest.setHandled(true);
        PrintWriter writer = response.getWriter();
        try {
            if (isApplication(request)) {
                LoanApplication application = new LoanApplication();
                application.setAmount(amountFrom(request));
                application.setContact(contactFrom(request));
                Ticket ticket = LoanRepository.store(application);
                writer.println(new Gson().toJson(ticket));
            } else if (isStatusRequest(request) && idSpecified(request)) {
                writer.println(fetchLoanInfo(request.getParameter(TICKET_ID)));
            } else if (isApproval(request) && idSpecified(request)) {
                writer.println(approveLoan(request.getParameter(TICKET_ID)));
            } else {
                writer.println("Incorrect parameters provided");
            }
        } catch (ApplicationException e) {
            writer.println("Uh oh! Problem occured: " + e.getMessage());
        }
    }

    private String contactFrom(HttpServletRequest request) {
        return request.getParameter("contact");
    }

    private long amountFrom(HttpServletRequest request) {
        return Long.parseLong(request.getParameter("amount"));
    }

    private String approveLoan(String parameter) {
        return new Gson().toJson(LoanRepository.approve(parameter));
    }

    private boolean isApproval(HttpServletRequest request) {
        return APPROVE.equals(request.getParameter("action"));
    }

    private boolean idSpecified(HttpServletRequest request) {
        return request.getParameter(TICKET_ID) != null && validId(request) >= 0;
    }

    private long validId(HttpServletRequest request) {
        String ticketId = request.getParameter(TICKET_ID);
        try {
            return Long.parseLong(ticketId);
        } catch (NumberFormatException e) {
            return -1L;
        }
    }

    private boolean isStatusRequest(HttpServletRequest request) {
        return FETCH.equals(request.getParameter("action"));
    }

    private boolean isApplication(HttpServletRequest request) {
        return APPLICATION.equals(request.getParameter("action"));
    }

    private String fetchLoanInfo(String ticketId) {
        LoanApplication formerApplication = LoanRepository.fetch(ticketId);
        return new Gson().toJson(formerApplication);
    }

    public static long getNextId() {
        File file = new File(LoanRepository.REPOSITORY_ROOT);
        File[] files = file.listFiles(new FileFilter() {
            @Override
            public boolean accept(File pathname) {
                return pathname.getName().endsWith(LoanRepository.FILE_EXTENSION);
            }
        });

        return files == null ? 0 : files.length + 1;
    }

}

LoanRepository

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Scanner;

import com.google.gson.Gson;

public class LoanRepository {

    public final static String FILE_EXTENSION = ".loan";
    public final static String REPOSITORY_ROOT = System.getProperty("user.home") + "/loan";

    public static LoanApplication fetch(String ticketId) {
        return fetch(Long.parseLong(ticketId));
    }

    public static LoanApplication fetch(long ticketId) {
        File file = fileFromApplication(ticketId);
        try {
            String output = new Scanner(file).useDelimiter("\\Z").next();
            return new Gson().fromJson(output, LoanApplication.class);
        } catch (FileNotFoundException e) {
            throw new ApplicationException("Ticket not found", e);
        }
    }

    public static Ticket store(LoanApplication application) {
        try {
            new File(REPOSITORY_ROOT).mkdirs();
            FileOutputStream fileOutputStream = new FileOutputStream(
                    fileFromApplication(application.getApplicationNo()));
            fileOutputStream.write(new Gson().toJson(application).getBytes());
            fileOutputStream.close();
            return new Ticket(application.getApplicationNo());
        } catch (FileNotFoundException e) {
            throw new ApplicationException("Could not store application", e);
        } catch (IOException e) {
            throw new ApplicationException("Could not store application", e);
        }
    }

    private static File fileFromApplication(long applicationNo) {
        return new File(REPOSITORY_ROOT + "/" + applicationNo + FILE_EXTENSION);
    }

    public static Ticket approve(String ticketId) {
        LoanApplication application = fetch(ticketId);
        application.approve();
        store(application);
        return new Ticket(application.getApplicationNo());
    }

}

LoanServer

import org.eclipse.jetty.server.Server;

public class LoanServer {
    public static void main(String[] args) throws Exception {
        Server server = new Server(8080);
        server.setHandler(new LoanHandler());
        server.start();
        server.join();
    }
}

Ticket

public class Ticket {
    private long id;

    public Ticket(long applicationNo) {
        id = applicationNo;
    }

    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }
}