How to use java.net.URLConnection to fire and handle HTTP requests

java

http-requests

java-8

httpclient

byAnton Shumikhin·Oct 11, 2024

Craving a fast and furious way to HTTP requests? It's simple! Create a URL object for your endpoint. To unleash the payload of a GET request, call openConnection(), then getInputStream() to seize your data. Unchain the power of a POST request, activate setDoOutput(true), add headers or parameters using the getOutputStream(), and finally sweep your victory prize - the response from getInputStream().

GET Request: Quick and dirty!

URL url = new URL("http://example.com"); // Every journey starts with the first step, or URL
InputStream response = url.openConnection().getInputStream(); // Let the force flow through you
// Now, it's time for "response processing", sounds exciting!

POST Request: In and out!

URL url = new URL("http://example.com"); // Same structure, different toppings
URLConnection con = url.openConnection(); // Connection is the key, no Jedi mind tricks here
con.setDoOutput(true); // Activate the superpower! Outputs go brrr
con.setRequestProperty("Content-Type", "application/x-www-form-urlencoded"); // Because everyone likes to speak the same language
con.getOutputStream().write("key=value".getBytes()); // Hello, server! Here's your POSTcard!
InputStream response = con.getInputStream(); // Cash in your response, servers love leaving read messages
// Celebrate the "response processing" victory royale!

Heads-up! Managing Request Headers

Set up HTTP headers using the setRequestProperty method, which is pretty much like choosing your coffee flavors.

con.setRequestProperty("User-Agent", "Mozilla/5.0"); // Don't we all like to pretend being a browser! 
con.setRequestProperty("Accept-Charset", "UTF-8"); // Speak my language, servers love UTF-8
con.setRequestProperty("Content-Type", "application/json; charset=UTF-8"); // All dressed up and ready to go in a JSON tuxedo

For handling server sessions like a Cookie Monster, use CookieManager, it does all the cookie gobbling for you.

CookieManager cookieManager = new CookieManager();
CookieHandler.setDefault(cookieManager); // Announcing the Cookie Manager, all hail!

Setting up the stage for Large File Uploads

Got a large file to upload? Use setFixedLengthStreamingMode or setChunkedStreamingMode for a seamless experience.

con.setFixedLengthStreamingMode(fileLength); // Know your size? Great, let's set it up!
// or con.setChunkedStreamingMode(0); for when you like to take sudden detours

Cutting Open the Response Envelope

Unwrap your server response gift by using getHeaderFields.

Map<String, List<String>> headerFields = con.getHeaderFields(); // Secret map to your treasure

Response: A Surprise Package

After triggering a request, check the server response. Drumrolls, please:

if (((HttpURLConnection) con).getResponseCode() == HttpURLConnection.HTTP_OK) {
    // Hereby, I declare you successful! 
} else {
    // Some error handling magic here or we riot!
}

The Secret Decoder Ring

To paint the response picture, grab the coloring instructions from the "Content-Type" header:

String contentType = con.getHeaderField("Content-Type");
String charset = null;

for (String param : contentType.replace(" ", "").split(";")) {
    if (param.startsWith("charset=")) {
        charset = param.split("=", 2)[1]; // Because surprise gifts are beautiful
        break;
    }
}

if (charset != null) {
    try (BufferedReader reader = new BufferedReader(new InputStreamReader(response, charset))) {
        // ...
    }
}

Alternatives in the HTTP Universe

While java.net.URLConnection shines bright, other stars in the universe like Apache HttpComponents HttpClient or google-http-java-client offer advanced control and flair to your code, making them remarkable contenders.

CloseableHttpClient httpclient = HttpClients.createDefault();
HttpGet httpGet = new HttpGet("http://example.com");
CloseableHttpResponse response1 = httpclient.execute(httpGet);
// BAM! HttpClient enters the chat!

Catching Truths and Dare Timeouts

Set timeouts to avoid waiting forever like a love-sick Romeo beneath a balcony:

con.setConnectTimeout(5000); // Time's up in 5 seconds, no more delays, even for Juliet
con.setReadTimeout(5000); // Time waits for no one, not even server responses

A Souvenir: Server's Error Streams

Be proactive, play Sherlock, and find out from error streams what made the server unhappy:

if (((HttpURLConnection) con).getResponseCode() != HttpURLConnection.HTTP_OK) {
    InputStream error = ((HttpURLConnection) con).getErrorStream(); // Found it! Your clue in the server mystery adventure
    // Time to put on your detective hat and handle the errors
}

Mastering POST Requests using PrintWriter

PrintWriter can make POST request construction easier, especially with text data:

PrintWriter writer = new PrintWriter(con.getOutputStream());
writer.print("param1=value1&param2=value2"); // Easy peasy lemon squeezy, POST body is ready!
writer.close(); // Close the door when you leave, please!

HTTP Handling Simplified

Libraries like kevinsawicki/http-request are no less than superheroes for HTTP request handling – faster, stronger, and easier!

HttpRequest request = HttpRequest.get("http://example.com");
int response = request.code(); // One status code that rules them all!
String body = request.body(); // A parcel from the server, what did you get?
Map<String, String> headers = request.headers(); // Got headers? Get clues!