How to retrieve an entity through REST for Dummies

Support
#1

hi out there, I am absolute beginner when it comes to REST. Following the documentation I tried to load an entity with the following code:

    String url = "http://localhost:8080/rest/entities/bookstore_EHC_Q_KFZA/" + getEditedEntity().getId() ;
    try {
        ResponseEntity<String> response = restTemplate.getForEntity(url, String.class);
        String body = response.getBody();
        MediaType contentType = response.getHeaders().getContentType();
        HttpStatus statusCode = response.getStatusCode();
        System.out.println("Erfolgreicher REST-Aufruf");
        System.out.println("MediaType:" + contentType.toString());
        System.out.println("HttpStatus:" + statusCode.toString());
        System.out.println("Body:" + body.toString());
        // Process the response...
    } catch (RestClientException e) {
        // Handle the exception...
        System.out.println(e.getMessage());
        System.out.println(e.getStackTrace());
    }

I receive an error code 401 stating: “{“error”:“unauthorized”,“error_description”:“Full authentication is required to access this resource”}”.

I understood, that I have to POST an authorization request prior to this GET request. Do you have a code sample to do this? The curl-sample in the documentation does not work for me.

Thx for any assistance

Michael

#2

Hi Michael,

You need to authenticate first and then use the obtained token in API requests.

This is how you can authenticate using Java code:

public void test() {
    authenticate("client", "secret", "admin", "admin");
}

private String authenticate(String client, String secret, String username, String password) {
    HttpClient httpClient = HttpClient.newHttpClient();
    HttpRequest request = HttpRequest.newBuilder()
            .uri(URI.create("http://localhost:8080/oauth/token"))
            .header("Authorization", getBasicAuthHeader(client, secret))
            .header("Content-Type", "application/x-www-form-urlencoded")
            .POST(HttpRequest.BodyPublishers.ofString(getAuthRequestBody(username, password)))
            .build();
    try {
        HttpResponse<String> response = httpClient.send(request, HttpResponse.BodyHandlers.ofString());
        if (response.statusCode() == HttpStatus.OK.value()) {
            String responseText = response.body();
            System.out.println("Response: " + responseText);
            // Using Jackson to convert JSON responce to a map:
            Map<String, Object> map = new ObjectMapper().readValue(responseText, Map.class);
            String accessToken = (String) map.get("access_token");
            System.out.println("Access token: " + accessToken);
            return accessToken;
        } else {
            System.out.println("Error: " + response.statusCode());
        }
    } catch (IOException | InterruptedException e) {
        e.printStackTrace();
    }
}

private String getBasicAuthHeader(String client, String secret) {
    String str = client + ":" + secret;
    return "Basic " + Base64.getEncoder().encodeToString(str.getBytes());
}

private String getAuthRequestBody(String username, String password) {
    return "grant_type=password&username=" + username + "&password=" + password;
}
1 Like
#3

Thank you Konstantin, that worked!

Now I can move on further.

best regards,

Michael