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javaweb-servicesgwt

Calling Web-Service / Website from Java

Writing some additional classes for an existing GWT project. I need to:

  • Request a URL
  • Read in the webpage returned, in order to perform operations on.

The returned page is in very simple HTML, therefore parsing it shouldn't be very difficult, I just need to get the data first.

How do I do this in Java? What packages am I best looking at?

Solution

  • With native Java API, the easiest way to read from an URL is using java.net.URL#openStream(). Here's a basic example:

    try (InputStream response = new URL("https://www.stackoverflow.com").openStream()) {
    String body = new String(input.readAllBytes(), StandardCharsets.UTF_8);
    System.out.println(body);
}

    You could feed the InputStream to any DOM/SAX parser of your taste. The average parser can take (in)directly an InputStream as argument or even a URL. Jsoup is one of the better HTML parsers.

    In case you want a bit more control and/or want a more self-documenting API, then you can since Java 11 use the java.net.http.HttpClient. It only gets verbose quickly when you merely want the response body:

    HttpClient client = HttpClient.newBuilder().build();
HttpRequest request = HttpRequest.newBuilder().GET().uri(URI.create("https://stackoverflow.com")).build();
HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());
String body = response.body();
System.out.println(body);

    See also: