REST tutorial

[Ong Vua]

I need to call a REST service and I want to use Java JDK.

Below is login info from the 3rd party vendor given to me.

URL: http://servername/rest/user/login
HTTP Request Type: POST
Parameters: username, password
Cookie Required: False

The response will be a JSON-encoded object.

How do I call this REST service and parse the response back? Do you have any tutorial that I can review? I'm new to REST.

Thanks.

[Surender Suri]

A simple java call with java.net.URL and HttpURLConnection will do (or) use httpclient jar. Example Rest Java Client Example.
To parse jason objects too there are bunch of thrid party apis like google-gson or you can write your own simple parser.

Here is a good tutorial to understand rest : REST Tutorial , it's easy then you think.

[Ong Vua]

Below is my code

String urlParameters = "username=" + URLEncoder.encode("user1", "UTF-8") + "&password=" + URLEncoder.encode("password1", "UTF-8");

URL url = new URL("http://servername/rest/user/login");
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setDoOutput(true);
connection.setDoInput(true);
connection.setInstanceFollowRedirects(false);
connection.setRequestMethod("POST");
connection.setRequestProperty("charset", "utf-8");
connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
connection.setRequestProperty("Content-Length", "" + Integer.toString(urlParameters.getBytes().length));
connection.setUseCaches (false);

DataOutputStream wr = new DataOutputStream(connection.getOutputStream ());
wr.writeBytes(urlParameters);

// Get the response
BufferedReader rd = new BufferedReader(new InputStreamReader(connection.getInputStream()));
String line;
line = rd.readLine();
while (line != null) {
System.out.println(line);
line = rd.readLine();
}

wr.flush();
wr.close();
connection.disconnect();

But I got the below errors back

java.io.IOException: Server returned HTTP response code: 401 for URL: http://servername/rest/user/login
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1436)
at client.Class1.login(Class1.java:31)
at client.Class1.main(Class1.java:130)


Do you have any idea?

Thanks

[Surender Suri]

401 error is generally due to authentication failure, looks like the url you are trying to access needs basic authentication to access the url. Find out the credentials and see below code to send those in http header.

String userPassword = username + ":" + password; 
String encoding = new sun.misc.BASE64Encoder().encode(userPassword.getBytes()); 
URLConnection uc = url.openConnection(); 
uc.setRequestProperty("Authorization", "Basic " + encoding); 

[Ong Vua]

Thanks. I got past the security thing and now I got the 406 error. Below is my code. For some reason, it does not recognize the JSON object returned. Do you have any ideas? Thanks

        URL url = new URL("http://servername/rest/user/login");
        HttpURLConnection conn = (HttpURLConnection) url.openConnection(); 
        
        conn.setRequestMethod("POST");
        conn.setDoOutput(true);
        conn.setDoInput(true);
        conn.setUseCaches(false);
        
        //Set basic authentication in the header
        String userPassword = "admin:password123";    
        String encoding = new sun.misc.BASE64Encoder().encode(userPassword.getBytes()); 
        conn.setRequestProperty("Authorization", "Basic " + encoding);
        
        //Submit user and password.  A JSON object will return that contains session name and session id for this user
        String formParameters = "username=" + URLEncoder.encode("user1", "UTF-8") + "&password=" + URLEncoder.encode("user1password", "UTF-8");
                         
        conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded"); 
        conn.setRequestProperty("Content-Length", Integer.toString(formParameters.length()));
        conn.setRequestProperty("Accept", "application/json");
        
        DataOutputStream out = new DataOutputStream(conn.getOutputStream());
        
        out.writeBytes(formParameters);
        out.flush();
        out.close();
        
        System.out.println(conn.getResponseCode());

[Ong Vua]

I got the below error message back. Do you have any ideas?

HTTP/1.1 406 Not Acceptable: Unsupported request content type application/x-www-form-urlencoded

[Ashish Agre]

hey ong i'm also trying to implement the same please guide how to approach this problem.

[Surender Suri]

Can you try with "text/xml" instead of "application/x-www-form-urlencoded" in below line.

  conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");  

Also, here is a nice article on these issue. Hope it helps : RESTful HTTP in practice

[Ong Vua]

Thanks. I tried changing it but still got 406 error. The application/x-www-form-urlencoded is for POST since I'm posting the username and password parameters in the form.

Thanks for the article. I read that article before also and everything I put in my code follows it but still no luck