Client.java

import org.apache.http.HttpEntity;
import org.apache.http.client.methods.HttpUriRequest;
import org.apache.http.client.methods.RequestBuilder;
import org.apache.http.client.protocol.ClientContext;
import org.apache.http.impl.client.BasicCookieStore;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.protocol.BasicHttpContext;
import org.apache.http.protocol.HttpContext;
import org.apache.http.util.EntityUtils;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URI;
import java.net.URISyntaxException;

public class Client {

    private DefaultHttpClient client = new DefaultHttpClient();
    private HttpContext context = new BasicHttpContext();

    public Client() throws URISyntaxException, IOException {
        BasicCookieStore store = new BasicCookieStore();
        context.setAttribute(ClientContext.COOKIE_STORE, store);
    }

    public void logIn(String username, String password) throws URISyntaxException, IOException {
        HttpUriRequest login = RequestBuilder.post()
                .setUri(new URI("http://www.derpforum.nl/?p=login"))
                .addParameter("username", username)
                .addParameter("password", password)
                .addHeader("Referer", "http://www.derpforum.nl/")
                .build();
        EntityUtils.consume(client.execute(login, context).getEntity());
    }

    public String getHomePage() throws URISyntaxException, IOException {
        HttpUriRequest get  = RequestBuilder.get()
                .setUri(new URI("http://www.derpforum.nl"))
                .build();
        HttpEntity entity = client.execute(get, context).getEntity();
        BufferedReader reader = new BufferedReader(new InputStreamReader(entity.getContent()));
        StringBuilder builder = new StringBuilder();
        String line;
        while ((line = reader.readLine()) != null)
            builder.append(line).append('\n');
        EntityUtils.consume(entity);
        return builder.toString();
    }

    public void CreateTopic(int forumId, String title, String content) throws IOException {
        HttpUriRequest post = RequestBuilder.post()
                .setUri("http://www.derpforum.nl/?p=forum/nieuwtopic&id=")
                .addParameter("forum", String.valueOf(forumId))
                .addParameter("title", title)
                .addParameter("message", content)
                .addHeader("Referer", "http://www.derpforum.nl/?p=forum/nieuwtopic")
                .build();
        EntityUtils.consume(client.execute(post, context).getEntity());
    }

    public void PostComment(int postId, String content) throws IOException {
        HttpUriRequest post = RequestBuilder.post()
                .setUri("http://www.derpforum.nl/?p=forum/topic&id=" + postId)
                .addParameter("Reply", content)
                .addHeader("Referer", "http://www.derpforum.nl/?p=forum/topic&id=" + postId)
                .build();
        EntityUtils.consume(client.execute(post, context).getEntity());
    }
}