Rest API 可以从 Postman 调用，显示来自 ZD52387880E1EA22831817A27 的 400 个错误请求

Question

I am trying to consume a POST restful service. When I try it on Postman I get succesful response. But when I try it on java with below code I am gettin response code 400. In postman I am pasting the same input with replacing escape characters.

try {

    URL url = new URL("https://localhost/PasswordVault/api/Accounts");
    HttpURLConnection conn = (HttpURLConnection) url.openConnection();
    conn.setRequestMethod("POST");
    conn.setDoOutput(true);

    conn.setRequestProperty("Content-Type", "application/json");
    String input = "{\"qty\":100,\"name\":\"iPad 4\", \"detail\":{\"ver\":\"2020\",\"productionDate\":\"2020\"}}";

    OutputStream os = conn.getOutputStream();
    os.write(input.getBytes());
    os.flush();


    if (conn.getResponseCode() != HttpURLConnection.HTTP_CREATED) {
        throw new RuntimeException("Failed : HTTP error code : "
                + conn.getResponseCode());
    }

    BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream()));

    String output;
    System.out.println("Output from Server .... \n");
    while ((output = br.readLine()) != null) {
        System.out.println(output);
    }

    conn.disconnect();
} catch (Exception e) {
        System.out.println("Exception:- " + e);
}

Answer 1

I would highly recommend that you use a library for this. You can use Jackson, this greatly simplifies and standardizes java interaction with remote HTTP services.

Something along these lines will get you started:

import javax.ws.rs.client.Client;
import javax.ws.rs.client.ClientBuilder;
import javax.ws.rs.client.Entity;
import javax.ws.rs.client.WebTarget;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;

public class ApiClient
{

    private transient Client client;
    protected transient WebTarget apiRoot;

    public ApiClient(String rootUrl) 
    {
        this.client = ClientBuilder.newBuilder().build();
        // The root URL is your API starting point, e.g. https://host/api
        this.apiRoot = client.target(rootUrl);
    }

    public Response doPostToAccounts(String data)
    {
        try 
        {
            // This is where you execute your POST request
            return apiRoot.path("/Accounts")
                .request(MediaType.APPLICATION_JSON)
                .post(Entity.entity(data, MediaType.APPLICATION_JSON));
        } catch (Exception e) {
            throw new IllegalStateException(e);
        }
    }

}

Answer 2

Some ideas:

• Encode your request post data in UTF-8: "post data".getBytes(StandardCharsets.UTF_8)
• Read the response from the server (not just the code) to hopefully get more details on the problem ( connection.getErrorStream() )
• Is there a missing authorization header? (an API token etc.)
• Use single quotes to make your request data string more readable, or use a JSON library to avoid manual mistakes
• also call OutputStream.close() after flush()

Eg

  // handle error code
  if(connection.getResponseCode() != HttpURLConnection.HTTP_OK) {
    // use getErrorStream for non OK statuses (https://stackoverflow.com/questions/613307/read-error-response-body-in-java)
    String errorMessage = "HTTP response code: " + responseCode
        + (responseMessage == null || responseMessage.trim().length() == 0 ? "" : " " + responseMessage);

    InputStream errorStream = connection.getErrorStream();
    if(errorStream != null) {
      String errorString = streamToString(connection.getErrorStream());
      if(errorString.length() > MAX_MSG_LENGTH) {
        errorString = errorString.substring(0, Math.min(MAX_MSG_LENGTH, errorString.length())) + "...";
      }
      errorMessage += ", HTTP response data: " + errorString;
    }

    throw new RuntimeException(errorMessage);
  }

  // handle OK code
  // ...

Answer 3

First, check the request headers that the postman may be sending and your code does not. You may need to add some headers to your request before sending it. Second, I strongly recommend to use some 3d party Http client library instead of coding your HTTP request on your own. Some well known libraries are Apache Http client and OK Http client . I personally use my own Http client that is part of a MgntUtils Open source library. You are welcome to try it as well. Here is simplified code just to demonstrate reading some response from a site:

    try {
        HttpClient client = new HttpClient();
        client.setConnectionUrl("https://www.yahoo.com/");
        String result = client.sendHttpRequest(HttpMethod.GET);
        System.out.println(result);
    } catch (IOException e) {
        System.out.println(TextUtils.getStacktrace(e, "com.mgnt."));
    }
    

But of course you could send POST requests and set Request headers and read textual or binaly response and response headers with this library as well. Here is a link to HttpClient class Javadoc . The library itself is available as Maven artifact and on Github , including Javadoc and source code