Httpservletrequest get JSON POST data

java

json-deserialization

exception-handling

content-type-check

byAnton Shumikhin·Feb 23, 2025

Snap up that JSON payload from an HttpServletRequest in the blink of an eye:

Scanner scanner = new Scanner(request.getInputStream(), "UTF-8");
String jsonData = scanner.useDelimiter("\\A").next();
scanner.close();

In three brief lines, we snatch up the incoming JSON payload as a single string using Scanner. No loop, no fuss. Our secret is the \\A which is regex for the beginning of the input, so it gobbles up the entire content in a single mouthful. Later, it's over to Newton (as in Jackson) or the Gson-ovi to deserialize this puppy.

Unpacking JSON with Jackson and Gson

Once you have your JSON dressed up as a string, it's time for the deserialization promenade using either Gson or Jackson.

Jackson

ObjectMapper objectMapper = new ObjectMapper();
MyClass myObject = objectMapper.readValue(jsonData, MyClass.class);

Gson

Gson gson = new Gson();
MyClass myObject = gson.fromJson(jsonData, MyClass.class);

And just like that, your JSON string is tossed and turned into a Java object of the type MyClass. From here on out, it's smooth sailing! 🏄

Handling Exceptions: `try` not to `catch` a cold

Crunching numbers in JSON can sometimes run you into an error or two. Good for us, we've got a secret weapon up our sleeve: exception handling.

try {
    JSONObject jsonObject = new JSONObject(jsonData);
    // who knew there was an infinity gauntlet in JSON:
    // jsonObject.getInt(), jsonObject.getString(), etc.
} catch (JSONException e) {
    // Houston, we have a solution, but not for the JSONException
}

So even if your JSON throws a tantrum, your mighty app won't even flinch.

Content-Type Checkpoint

Before you go on that JSON adventure, let's make sure you've got the right map. If the HTTP request's Content-Type header is set to application/json; charset=UTF-8, buckle up, it's turbo time!

if ("application/json; charset=UTF-8".equals(request.getContentType())) {
    // JSON ahoy! Dive right in!
}

This check marks you safe from diving head-first into a data type disaster.

Limitations of `getParameter()`: No `POST` for XML

When it comes to non-JSON content types like application/x-www-form-urlencoded, HttpServletRequest's getParameter() is like a fish out of water. It won't parse JSON, so we bid adieu and take the high road with getReader().

Encoding enigma: Special characters, meet UTF-8

In our wide wide world, special characters shouldn't feel left out. With encoding in UTF-8, nobody gets left behind.

BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream, StandardCharsets.UTF_8));

Special characters, reporting for duty!

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