How to send HTTP request in Java?

java

http-client

http-request

http-response

byAnton Shumikhin·Sep 15, 2024

Make a speed-run HTTP GET request with HttpClient:

var client = HttpClient.newHttpClient();
var request = HttpRequest.newBuilder(URI.create("http://example.com")).GET().build();
var response = client.send(request, HttpResponse.BodyHandlers.ofString());

System.out.println(response.body());  // Ta-da! That was fast!

Fetching content from http://example.com made easy! Fancy POST? Replace .GET() with .POST(HttpRequest.BodyPublishers.ofString("your-data")).

Mastering the request details

Picture a request as a puzzle with several pieces:

Kick-off using HttpClient.
Piece together the HttpRequest jigsaw - URL, HTTP method, headers, and body.
Send the masterpiece and await a HttpResponse award!
Unwrap the server response gift; savor the status codes and response data goodies.

Even the notorious try-with-resources can't resist this charm:

HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder()
        .uri(URI.create("http://example.com"))
        .header("Content-Type", "application/json")
        .POST(HttpRequest.BodyPublishers.ofString("{\"example\":\"data\"}"))
        .build();

try {
    HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());
    // Engage response handling gears
} catch (IOException | InterruptedException e) {  // These exceptions can't stop us!
    e.printStackTrace();
}

Tackling complexity

Like peeling an onion! External libraries, such as Apache HttpClient, peel off HTTP request complexity, leaving a fresh request ready for authentication, cookie handling, and more:

CloseableHttpClient httpClient = HttpClients.createDefault();
HttpPost httpPost = new HttpPost("http://example.com");
httpPost.setEntity(new StringEntity("Post data"));
CloseableHttpResponse response = httpClient.execute(httpPost);

try {
    System.out.println(EntityUtils.toString(response.getEntity()));  // Enjoy the clear aroma!
} finally {
    response.close();  // Bye-bye, response! You've served well.
}

Overcoming stumbling blocks

Timeouts, redirects, JSON data, stream management - solved with a dash of code flavor!

How to escape a hanging connection

Set timeout values to shoot those lagging connections:

con.setConnectTimeout(5000);
con.setReadTimeout(5000);  // No time for dilly-dallying!

Chasing redirects

Redirects can't outrun setInstanceFollowRedirects():

con.setInstanceFollowRedirects(true);  // Redirects, we've got your number!

Sending JSON data that's pure gold

Set Content-Type and employ OutputStream for fun JSON sending:

con.setRequestProperty("Content-Type", "application/json; utf-8");
try (OutputStream os = con.getOutputStream()) {
    byte[] input = "{\"name\":\"mkyong\"}".getBytes(StandardCharsets.UTF_8);
    os.write(input, 0, input.length);           
}

Stream affairs handled with elegance

Guarantee streams are closed to avoid memory leaks:

try(BufferedReader br = new BufferedReader(
    new InputStreamReader(con.getInputStream(), StandardCharsets.UTF_8))) {
    // Read response like an old-timey letter
}