How To Access Data With Java

The following Java code example demonstrates how to configure a connection to download data from an Earthdata Login enabled server. Note that you will need a secure way to configure the Earthdata Login username and password.

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.CookieHandler;
import java.net.CookieManager;
import java.net.CookiePolicy;
import java.net.URL;
import java.net.HttpURLConnection;
import java.util.Base64;

public class test
{
    /*
     * Prefix used to identify redirects to URS for the purpose of
     * adding authentication headers. For test, this should be:
     * https://uat.urs.earthdata.nasa.gov for test
     */
    static String URS = "https://urs.earthdata.nasa.gov";


    /*
     * Simple test.
     */
    public static void main( String[] args )
    {
        String resource = "<url of resource>";
        String username = "<URS user ID>";
        String password = "<URS user password>";
        System.out.println("Accessing resource " + resource);
        try
        {
            /*
             * Set up a cookie handler to maintain session cookies. A custom
             * CookiePolicy could be used to limit cookies to just the resource
             * server and URS.
             */
            CookieHandler.setDefault(
                new CookieManager(null, CookiePolicy.ACCEPT_ALL));

            /* Retreve a stream for the resource */
            InputStream in = getResource(resource, username, password);
            /* Dump the resource out (not a good idea for binary data) */
            BufferedReader bin = new BufferedReader(
                new InputStreamReader(in));
            String line;
            while( (line = bin.readLine()) != null)
            {
                System.out.println(line);
            }
            bin.close();
        }
        catch( Exception t)
        {
            System.out.println("ERROR: Failed to retrieve resource");
            System.out.println(t.getMessage());
            t.printStackTrace();
        }
    }


    /*
     * Returns an input stream for a designated resource on a URS
     * authenticated remote server.
     *
     */
    public static InputStream getResource(
        String resource, String username, String password) throws Exception
    {
        int redirects = 0;
        /* Place an upper limit on the number of redirects we will follow */
        while( redirects < 10 )
        {
            ++redirects;
            /*
             * Configure a connection to the resource server and submit the
             * request for our resource.
             */
            URL url = new URL(resource);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("GET");
            connection.setInstanceFollowRedirects(false);
            connection.setUseCaches(false);
            connection.setDoInput(true);

            /*
             * If this is the URS server, add in the authentication header.
             */
            if( resource.startsWith(URS) )
            {
                connection.setDoOutput(true);
                connection.setRequestProperty(
                    "Authorization",
                    "Basic " + Base64.getEncoder().encodeToString(
                        (username + ":" + password).getBytes()));
            }

            /*
             * Execute the request and get the response status code.
             * A return status of 200 means is good - it means that we
             * have got our resource. We can return the input stream
             * so it can be read (may want to return additional header
             * information, such as the mime type or size ).
             */
            int status = connection.getResponseCode();
            if( status == 200 )
            {
                return connection.getInputStream();
            }

            /*
             * Any value other than 302 (a redirect) will need some custom
             * handling. A 401 from URS means that the credentials
             * are invalid, while a 403 means that the user has not authorized
             * the application.
             */
            if( status != 302 )
            {
                throw new Exception(
                    "Invalid response from server - status " + status);
            }

            /*
             * Get the redirection location and continue. This should really
             * have a null check, just in case.
             */
            resource = connection.getHeaderField("Location");
        }

        /*
         * If we get here, we exceeded our redirect limit. This is most likely
         * a configuration problem somewhere in the remote server.
         */
        throw new Exception("Redirection limit exceeded");
    }
}