package net.codejava.networking;
 
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
 
/**
 * This class encapsulates methods for requesting a server via HTTP GET/POST and
 * provides methods for parsing response from the server.
 * 
 * @author www.codejava.net
 * 
 */
public class HttpUtility {
 
    /**
     * Represents an HTTP connection
     */
    private static HttpURLConnection httpConn;
 
    /**
     * Makes an HTTP request using GET method to the specified URL.
     * 
     * @param requestURL
     *            the URL of the remote server
     * @return An HttpURLConnection object
     * @throws IOException
     *             thrown if any I/O error occurred
     */
    public static HttpURLConnection sendGetRequest(String requestURL)
            throws IOException {
        URL url = new URL(requestURL);
        httpConn = (HttpURLConnection) url.openConnection();
        httpConn.setUseCaches(false);
 
        httpConn.setDoInput(true); // true if we want to read server's response
        httpConn.setDoOutput(false); // false indicates this is a GET request
 
        return httpConn;
    }
 
    /**
     * Makes an HTTP request using POST method to the specified URL.
     * 
     * @param requestURL
     *            the URL of the remote server
     * @param params
     *            A map containing POST data in form of key-value pairs
     * @return An HttpURLConnection object
     * @throws IOException
     *             thrown if any I/O error occurred
     */
    public static HttpURLConnection sendPostRequest(String requestURL,
            Map<String, String> params) throws IOException {
        URL url = new URL(requestURL);
        httpConn = (HttpURLConnection) url.openConnection();
        httpConn.setUseCaches(false);
 
        httpConn.setDoInput(true); // true indicates the server returns response
 
        StringBuffer requestParams = new StringBuffer();
 
        if (params != null && params.size() > 0) {
 
            httpConn.setDoOutput(true); // true indicates POST request
 
            // creates the params string, encode them using URLEncoder
            Iterator<String> paramIterator = params.keySet().iterator();
            while (paramIterator.hasNext()) {
                String key = paramIterator.next();
                String value = params.get(key);
                requestParams.append(URLEncoder.encode(key, "UTF-8"));
                requestParams.append("=").append(
                        URLEncoder.encode(value, "UTF-8"));
                requestParams.append("&");
            }
 
            // sends POST data
            OutputStreamWriter writer = new OutputStreamWriter(
                    httpConn.getOutputStream());
            writer.write(requestParams.toString());
            writer.flush();
        }
 
        return httpConn;
    }
 
    /**
     * Returns only one line from the server's response. This method should be
     * used if the server returns only a single line of String.
     * 
     * @return a String of the server's response
     * @throws IOException
     *             thrown if any I/O error occurred
     */
    public static String readSingleLineRespone() throws IOException {
        InputStream inputStream = null;
        if (httpConn != null) {
            inputStream = httpConn.getInputStream();
        } else {
            throw new IOException("Connection is not established.");
        }
        BufferedReader reader = new BufferedReader(new InputStreamReader(
                inputStream));
 
        String response = reader.readLine();
        reader.close();
 
        return response;
    }
 
    /**
     * Returns an array of lines from the server's response. This method should
     * be used if the server returns multiple lines of String.
     * 
     * @return an array of Strings of the server's response
     * @throws IOException
     *             thrown if any I/O error occurred
     */
    public static String[] readMultipleLinesRespone() throws IOException {
        InputStream inputStream = null;
        if (httpConn != null) {
            inputStream = httpConn.getInputStream();
        } else {
            throw new IOException("Connection is not established.");
        }
 
        BufferedReader reader = new BufferedReader(new InputStreamReader(
                inputStream));
        List<String> response = new ArrayList<String>();
 
        String line = "";
        while ((line = reader.readLine()) != null) {
            response.add(line);
        }
        reader.close();
 
        return (String[]) response.toArray(new String[0]);
    }
 
    /**
     * Closes the connection if opened
     */
    public static void disconnect() {
        if (httpConn != null) {
            httpConn.disconnect();
        }
    }
}
 

package net.codejava.networking;
 
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
 
public class HttpUtilityTester {
 
    /**
     * This program uses the HttpUtility class to send a GET request to
     * Google home page; and send a POST request to Gmail login page.
     */
    public static void main(String[] args) {
        // test sending GET request
        String requestURL = "http://www.google.com";
        try {
            HttpUtility.sendGetRequest(requestURL);
            String[] response = HttpUtility.readMultipleLinesRespone();
            for (String line : response) {
                System.out.println(line);
            }
        } catch (IOException ex) {
            ex.printStackTrace();
        }
        HttpUtility.disconnect();
 
 
        System.out.println("=====================================");
 
        // test sending POST request
        Map<String, String> params = new HashMap<String, String>();
        requestURL = "https://accounts.google.com/ServiceLoginAuth";
        params.put("Email", "your_email");
        params.put("Passwd", "your_password");
 
        try {
            HttpUtility.sendPostRequest(requestURL, params);
            String[] response = HttpUtility.readMultipleLinesRespone();
            for (String line : response) {
                System.out.println(line);
            }
        } catch (IOException ex) {
            ex.printStackTrace();
        }
        HttpUtility.disconnect();
    }
}