Query Parameters and Path Parameters in Undertow

Query parameters and path parameters are fairly straightforward in Undertow. There is some slight boilerplate because, technically, query and path params can have multiple values. We are using some helper functions (PathParameters.java and QueryParameters.java).

Path Parameter and Query Parameter RoutingHandler

Fairly standard path param syntax. Undertow uses {param}, though you may be used to :param from other frameworks.

private static final HttpHandler ROUTES = new RoutingHandler()
    .get("/hello", ParametersServer::queryParam)
    .get("/hello/{name}/{num}", ParametersServer::pathParam)
    .get("/users/{userId}", ParametersServer::obfuscatedIdRoute)
;

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Path Parameter and Query Parameter HttpHandlers

These should be straightforward. Once again, we are using the following helpers — PathParameters.java and QueryParameters.java

private static void queryParam(HttpServerExchange exchange) {
    String name = Exchange.queryParams().queryParam(exchange, "name").orElse("world");
    int num = Exchange.queryParams().queryParamAsInteger(exchange, "num").orElse(1);
    Exchange.body().sendText(exchange, "Hello " + name + Strings.repeat("!", num));
}

private static void pathParam(HttpServerExchange exchange) {
    String name = Exchange.pathParams().pathParam(exchange, "name").orElse("world");
    int num = Exchange.pathParams().pathParamAsInteger(exchange, "num").orElse(1);
    Exchange.body().sendText(exchange, "Hello " + name + Strings.repeat("!", num));
}

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Server

public static void main(String[] args) {
    // Just some examples for obfuscated parameters.
    LongStream.range(100_000_000, 100_000_003).forEach( id -> {
       log.debug("id: " + id + " hashed: " + HashIds.encode(id));
    });
    SimpleServer server = SimpleServer.simpleServer(ROUTES);
    server.start();
}

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Output

curl localhost:8080/hello
Hello world!

curl localhost:8080/hello?name=bill
Hello bill!

curl 'localhost:8080/hello?name=bill&num=5'
Hello bill!!!!!

curl 'localhost:8080/hello/bill/5'
Hello bill!!!!!

Best Practices

Although it's not very hard to call params in this way, we recommend extracting the logic out even further. Take a look at Request Utilities. Here, you define the string literals and defaults once and only once. Everywhere else in the code that references this param is called just like UserRequests.email(exchange). This way, if you change the param name or even the type of param, it updates all of your code at once. Sharing defaults is also incredibly useful. Another feature of this is that you can cache values on the HttpServerExchange so you can use expensive calls in multiple routes with the cached values.

Obfuscating Sequential Ids

Sometimes you may want to obfuscate sequential ids to reduce the possibility of giving away some information. A quick example can be found at Obfuscating and Shortening Sequential ids with HashIds.