File Upload in Jersey Restful service

About:

There are many blogs which discuss on how to do file transfer in JAX-RS /Restful service all this blogs discuss using the Multipartformdata i.e. FormDataParam as the input Stream.
In this Blog, I will  be discussing on one of the way about how to create a service which will accept the File Object as input for the method which it consumes in the form XML.


Code: 

Bean Class

package model;
import java.io.InputStream;
import javax.activation.DataHandler;
import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
public class FileData {
    public FileData() {
        super();
    }
    
    String fileName;
    byte[] fileInfo;


    public void setFileName(String fileName) {
        this.fileName = fileName;
    }

    public String getFileName() {
        return fileName;
    }


    public void setFileInfo(byte[] fileInfo) {
        this.fileInfo = fileInfo;
    }

    public byte[] getFileInfo() {
        return fileInfo;
    }

}

Service Class

package model;


import java.io.ByteArrayInputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.FileOutputStream;

import javax.ws.rs.Consumes;
import javax.ws.rs.POST;
import javax.ws.rs.Path;

@Path("model")
public class FileService {
    public FileService() {
        super();
    }


    @POST
    @Consumes("application/xml")
    public void uploadFile(FileData fd) {
        try {
            OutputStream os = new FileOutputStream("" + fd.getFileName());
            InputStream is = new ByteArrayInputStream(fd.getFileInfo());
             
            byte[] buffer = new byte[1024];
            int bytesRead;
            //read from is to buffer
            while ((bytesRead = is.read(buffer)) != -1) {
                os.write(buffer, 0, bytesRead);
            }
            is.close();
            //flush OutputStream to write any buffered data to file
            os.flush();
            os.close();


        } catch (Exception e) {
            System.out.println("Inside the Service"+e);
        }

    }

}

For Client :

I will explain in another blog on how to consume this in REST DataControl / URL DataControl 

How to pass complex Input Parameters to WSDC (WebServiceDataControl)

About :

One of the most common usecases in WS is passing complex Input parameters, but incase if the user wants to pass the multiple occurence of the same complex Input parameter type, how to achieve this in WSDC ?.

This blog explains about passing the multiple complex Employee records to the WebService from the WSDC via the Backing Bean.

Implementation :

Let us Consider an ADFBC Component which contains an Employees Entity, now the user can select multiple employee records from the page containing list of Employee records and post it to the WebService.

1. Create an Web Service which takes the Input Argument as ArrayList of Employee Object  and returns the ArrayList .

The Sample SOAP Request/Response looks like as shown below , here we can observe that the the occurence of the "emp" object is dynamic which contains different employee records with three attributes (empEmail, empId, empName).

SOAP Request

<ns1:addEmp>
    <emp>
 <empEmail>SLROCK</empEmail>
        <empId>101</empId>
        <empName>ShawnRock</empName>
    </emp>
    
 <emp>
        <empEmail>OKOKHLO</empEmail>
        <empId>202</empId>
        <empName>OnkBank</empName>
    </emp>
</ns1:addEmp>

SOAP Response

<ns2:addEmpResponse xmlns:ns2="http://project1/">
 <return>
        <empEmail>SLROCK</empEmail>
        <empId>101</empId>
        <empName>ShawnRock</empName>
    </return>
    <return>
        <empEmail>OKOKHLO</empEmail>
        <empId>202</empId>
        <empName>OnkBank</empName>
    </return>
</ns2:addEmpResponse>

2. Create Business Components from Employee Table.

3. Drag and Drop the EmployeesView1 node from the DC palette onto the page1.jspx as ADF Table, Ensure that the page1.jspx is bounded to a Backing Bean.

4. Create a WSDC using the WSDL url of the service deployed to the server

5. Create a Command Button in page1.jspx and bound it to an Action Listener method in the Backing Bean . The Method is used to retrieve the records selected by the user from the page1.jspx and post it to the WS.

BindingContainer bindings = getBindings();
//From the Table exposed in the Backing Bean 
RowKeySet selectedEmps = getT1().getSelectedRowKeys();   
Iterator selectedEmpIter = selectedEmps.iterator();
DCBindingContainer bx =  (DCBindingContainer) getBindings();
DCIteratorBinding empIter = bx.findIteratorBinding("EmployeesView1Iterator");
RowSetIterator empRSIter = empIter.getRowSetIterator();

This is Achieved by marshalling the selected data as an Employee Objects and adding them to an ArrayList.

ArrayList<employee> al = new ArrayList<employee>();
while(selectedEmpIter.hasNext()){
Key key = (Key)((List)selectedEmpIter.next()).get(0);
Row currentRow = empRSIter.getRow(key);                
al.add(new Employee((String)currentRow.getAttribute("FirstName"),(Integer)currentRow.getAttribute("EmployeeId"),(String)currentRow.getAttribute("Email")));

This ArrayList is then passed onto the Params Map of the WSDC method as shown below

OperationBinding operationBinding =  bindings.getOperationBinding("addEmp");
operationBinding.getParamsMap().put("emp",al);
operationBinding.execute();

6. In page2.jspx, Drag and Drop the Return type of the WSDC method as ADF Table

7. Run the Page1.jspx, select the list of Employee records and click on the post to webservice button

8. In the Next Page we can observe that the selected 4 records are posted to the WebService

Passing Header parameters in WebService Data Control

About

In this blog, I will be explaining on how to pass header parameters in WebServiceDataControl

Implementation:

In this example, i have webservice where based on the Header parameter value the system will greet the user such as any value other than John will be treated as USER.

import java.util.List;
import java.util.Map;
import javax.annotation.Resource;
import javax.jws.WebService;
import javax.xml.ws.WebServiceContext;
import javax.xml.ws.handler.MessageContext;

@WebService(serviceName = "HeaderService")
public class HeaderService {
    public HeaderService() {
        super();
    }
    @Resource
    WebServiceContext ctx ;

    public String greetUser() {
        try{
        String tenantID = null;
        MessageContext context = ctx.getMessageContext();
        Map requestHeaders =
            ((Map)context.get(MessageContext.HTTP_REQUEST_HEADERS));
        if (requestHeaders != null && requestHeaders.get("TenentID") != null) {
            tenantID =
                    ((List)requestHeaders.get("TenentID")).get(0).toString();
        }
        if (tenantID.equalsIgnoreCase("John")) {
            tenantID = "ADMIN";
        } else {
            tenantID = "USER";
        }
            return "Hello " + tenantID;
        }catch(Exception e)
        {
        e.printStackTrace();
        }
       return null;
    }
}

In JDeveloper, create a New Fusion Web Application and Invoke the WebService DataControl from the New Gallery

Provide the WSDL of the above service deployed and click on Next. In the DataControl Operations page select the method to exposed in our case the greetUser and select the Include Http Headers Check box.

Click on finish and complete the wizard. Now Expand the DC palette we can observe that the method exposes  the Http Header Parameter (Map Type) as input parameter for the method and the output as String.

In the ViewController project create a jspx page with bacing bean or you can also create java class and associate it to the page.I will go with the latter approach as it is easy

Now open the Backing Bean java Class and add a Map variable with getters and setters. Then set the value for the Map field and initialize in the setf1 method as it is executed when the page loads.

 private Map httpheadermap;
public void setHttpheadermap(Map httpheadermap) {
        this.httpheadermap = httpheadermap;
    }

public Map getHttpheadermap() {
        return httpheadermap;
    }
// Here we are setting the value to the Map , you can also set in //the setters of the Map

public void setF1(RichForm f1) {
        this.f1 = f1;
        setHttpheadermap(new HashMap());
        httpheadermap.put("TenentID", "John");
    }

After creating the jspx page, Drag and Drop the method from the DC palette onto the page as ADF parameter form

On dropping it you will get the Edit Form Fields dialog where delete the HttpHeader Field that is exposed

In  the Edit Action Binding Dialog for the Http Header Parameter bind it to  the Map defined in the Backing bean 

Now Run the page.  Click on the GreetUser, we can see that it says as Hello ADMIN as we have set the value as JOHN in  the backing bean

Accessing a Twitter GET API in URLDC which is secured with OAuth 1.0

About :

In this Blog, I will be explaining about how to access Twitter GET Resource API from URLDC by passing the OAuth Access token. This can be used as model to the same for other Resource API secured with OAuth 1.0

OAuth Support in Twitter:

Twitter uses the OAuth authentication for the external applications to access its resources.  We need to create an API in Twitter which the external application will access and through which the resources will be shared by twitter to the external application. 

Twitter uses the HMAC-SHA1 Signature method to create the Authorization requests. So we will be needing the following HMACUtil java class to sign our OAuth Request calls

import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.Random;
import java.util.TreeMap;
import java.util.regex.Pattern;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
import org.apache.commons.codec.binary.Base64;

public class HMACSHAUtil {
    private static final String TIMESTAMP = "oauth_timestamp";
    private static final String SIGN_METHOD = "oauth_signature_method";
    private static final String SIGNATURE = "oauth_signature";
    private static final String CONSUMER_KEY = "oauth_consumer_key";
    private static final String VERSION = "oauth_version";
    private static final String NONCE = "oauth_nonce";
    private static final String TOKEN = "oauth_token";
    private static final String VERIFIER = "oauth_verifier";
    private static String CHARSET = "UTF-8";
    private static Timer timer = new Timer();
    private static final String EMPTY_STRING = "";
    private static final Map ENCODING_RULES;
    private static final String AMPERSAND_SEPARATED_STRING = "%s&%s&%s";
    private static final String HMAC_SHA1 = "HmacSHA1";
    private static final String CARRIAGE_RETURN = "\r\n";

    static {
        Map rules = new HashMap();
        rules.put("*", "%2A");
        rules.put("+", "%20");
        rules.put("%7E", "~");
        ENCODING_RULES = Collections.unmodifiableMap(rules);
    }

    public HMACSHAUtil() {
        super();
    }

 public   static String OAUTH1Header(String oauth_token, String consumer_key,  String httpMethod,
                                      String url, String consumerSecret, String oauth_token_secret,String verifier) throws Exception {
        Map oauthParameters = new TreeMap();
        oauthParameters.put(TOKEN, oauth_token);
        oauthParameters.put(TIMESTAMP, getTimestampInSeconds());
        oauthParameters.put(NONCE, getNonce());
        oauthParameters.put(CONSUMER_KEY, consumer_key);
        oauthParameters.put(SIGN_METHOD, "HMAC-SHA1");
        oauthParameters.put(VERSION, "1.0");/**/
        if(verifier!=null && !verifier.isEmpty())
        {
          oauthParameters.put(VERIFIER, verifier);
        }
        oauthParameters.put(VERSION, "1.0");


        String params = encode(asFormUrlEncodedString(oauthParameters));
        String baseString =
            String.format(AMPERSAND_SEPARATED_STRING, encode(httpMethod), encode(getSanitizedUrl(url)), params);
        String signature = doSign(baseString, encode(consumerSecret) + '&' + encode(oauth_token_secret));

        oauthParameters.put(SIGNATURE, signature);
        return generateOAuth1Header(oauthParameters);
    }

    private static String generateOAuth1Header(Map parameters) {
        StringBuffer header = new StringBuffer(parameters.size() * 20);
        header.append("OAuth ");
        for (String key : parameters.keySet()) {
            if (header.length() > "OAuth ".length()) {
                header.append(", ");
            }
            header.append(String.format("%s=\"%s\"", key, encode(parameters.get(key))));
        }
        return header.toString();
    }

    private static String doSign(String toSign, String keyString) throws Exception {
        SecretKeySpec key = new SecretKeySpec((keyString).getBytes(CHARSET), HMAC_SHA1);
        Mac mac = Mac.getInstance(HMAC_SHA1);
        mac.init(key);
        byte[] bytes = mac.doFinal(toSign.getBytes(CHARSET));
        return new String(Base64.encodeBase64(bytes)).replace(CARRIAGE_RETURN, EMPTY_STRING);
    }

    static class Timer {
        Long getMilis() {
            return System.currentTimeMillis();
        }


        Integer getRandomInteger() {
            return new Random().nextInt();
        }
    }

    private static String getNonce() {
        Long ts = getTs();
        return String.valueOf(ts + timer.getRandomInteger());
    }

    private static String getTimestampInSeconds() {
        return String.valueOf(getTs());
    }

    private static String getSanitizedUrl(String url) {
        return url.replaceAll("\\?.*", "").replace("\\:\\d{4}", "");
    }

    private static Long getTs() {
        return timer.getMilis() / 1000;
    }

    private static String asFormUrlEncodedString(Map oauthParameters) {
        if (oauthParameters.size() == 0)
            return EMPTY_STRING;

        StringBuilder builder = new StringBuilder();
        for (String p : oauthParameters.keySet()) {
            builder.append('&').append(encode(p).concat("=").concat(encode(oauthParameters.get(p))));
        }
        return builder.toString().substring(1);
    }

    private static String applyRule(String encoded, String toReplace, String replacement) {
        return encoded.replaceAll(Pattern.quote(toReplace), replacement);
    }

    private static String encode(String plain) {
        String encoded = "";
        try {
            encoded = URLEncoder.encode(plain, CHARSET);
        } catch (UnsupportedEncodingException uee) {
            throw new RuntimeException("Charset not found while encoding string: " + CHARSET, uee);
        }
        for (Map.Entry rule : ENCODING_RULES.entrySet()) {
            encoded = applyRule(encoded, rule.getKey(), rule.getValue());
        }
        return encoded;
    }


}

Pre requisites:

1. Obtain the Consumer key and Secret for the application created in twitter

2. The HMACSHA utility java class was used to created the encoded authorized value from the parameters provided.

3. Any Jdev Versions with Http Header Parameter support in URL DataControl 

Steps in JDeveloper :

1. Create a jspx page e.g index page with backing bean, in the backing bean create a method in which URLConnection is used to access the http://api.twitter.com/oauth/request_token and the authorization parameters are set to the URL before connecting. HMACSHAUtil.OAUTH1Header method is used to create the Authorization value using the Consumer key and Consumer Secret obtained while creating the application in Twitter .

Code Snippet of backing bean method :

String requestToken = HMACSHAUtil.OAUTH1Header("",this.getConsumer_key(),"POST","http://api.twitter.com/oauth/request_token", this.getConsumer_secret(),"","");
URL  url = new URL( "http://api.twitter.com/oauth/request_token" );
URLConnection  myURLConnection = url.openConnection();
HttpURLConnection conn = (HttpURLConnection)myURLConnection;
conn.setRequestMethod("POST");
conn.setRequestProperty("Authorization", requestToken);
conn.connect();
 

2. Once the Connection is successful read the content of the response. Twitter sends the response stream in two different ways randomly; they are normal UTF-8 Input Stream and encoded GZIPInput Stream so ensure that your code handles both the types of response

3. Read the Temporary oauth token and oauth secret value from the response streams and set them to the session scope as we will need them later.

4. Now navigate to the following URL https://api.twitter.com/oauth/authorize?oauth_token=”Value obtained in the previous step”.

5. The User will be prompted with a login screen to provide their twitter username and password to authorize the application to read their tweets.

6. Once the Authorization is successful, twitter redirects the request to the call back URL provided in the API, and along with it sends the oauth verifier as a parameter.

7. In the jspx e.g redirect page to which twitter redirects, retrieve the oauth verifier from the URL  and set in an bean.

8. In the same page using the Client and Server listener, call a method in the backing bean in which the URL connection is again used to connect to the following
URL :  http://api.twitter.com/oauth/access_token with the appropriate authorization parameters to get the permanent access token as shown below.

Code Snippet 

String requestToken = HMACSHAUtil.OAUTH1Header(oauh_token,consumKey,"POST","http://api.twitter.com/oauth/access_token",consumSec,oauth_secret,oauth_verifier);  
URL url = new URL( "http://api.twitter.com/oauth/access_token" );
myURLConnection = url.openConnection();
conn = (HttpURLConnection)myURLConnection;
conn.setRequestMethod("POST");
conn.setRequestProperty("Authorization", requestToken);
conn.connect();

Here consumSec is the consumer secret obtained after registering the application in Twitter.

9. Read the response stream the same way as mentioned in the step 2, now from the response stream get the permanent oauth token and permanent oauth secret.

10. Using the utility class create an Authorization parameter which will be used to fetch the tweets from twitter as shown in the code snippet below.

Code Snippet 

String HeaderToken = HMACSHAUtil.OAUTH1Header(perm_oauth_token,consumkey,"GET","http://api.twitter.com/1/statuses/friends_timeline.xml",consumSec,perm_oauth_secret,null);

The URL which will be used to fetch the tweets and along with the operation type (GET) is passed as parameters to the Utility method so that this authorization parameter allows twitter to recognize the user requesting for the appropriate operation.

11.The above steps have to be executed only once to obtain the permanent authorization parameters. Set the HeaderToken(Authorization parameter) value in the Session Scope.

FacesContext facesContext = FacesContext.getCurrentInstance();
facesContext.getExternalContext().getSessionMap().put("FinalHeaderToken",HeaderToken);

12. Now create a new jspx page e.g viewtweets.jspx with a backing bean associated to it.

13. Create URLDC with GET operation type with a dummy url where ensure you select the Include Http Header option and provide the following xsd

14. After creating the DC, Open the DataControl.dcx file and edit the attribute  Source="/1/statuses/friends_timeline.xml" and in Connections.xml update the attribute
url="http://api.twitter.com" of urlconnection field.

15. In the backing bean of the viewtweets.jspx put a Map variable and generate accessors as shown below

private Map httpHeaders = new HashMap();
public void setHttpHeaders(Map httpHeaders) {
        this.httpHeaders = httpHeaders;
    }

public Map getHttpHeaders() {
        return httpHeaders;
    }

16. In the same backing bean, inside the method setF1 which gets called first when the page is rendering as shown below

 public void setF1(RichForm f1) {
        this.f1 = f1;
        String HeaderToken = (String)FacesContext.getCurrentInstance().getExternalContext().getSessionMap().get("FinalHeaderToken");
        System.out.println("Session Header Token:"+HeaderToken);
        httpHeaders.put("Authorization",HeaderToken);
    }

17. Drag and Drop the status from the return type of the method in the DC palette onto the page as ADF Form

18. In the Edit Action Binding,set the map as the value for the Header parameter exposed.

Running the Application :

Before running the application we have to ensure that the HostNameVerifier is set to NONE in the WLS.
When Run  the Index page and click on  the Button the following process takes place which is shown as pictorial representation below

How to read the Request Header parameters in Restful Service

About:

In this blog, I will be explaining on how to create Restful Service where we can read the Http Header Parameters in the Service Class

Code Snippet:

package project1;

import java.util.ArrayList;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.Context;
import javax.ws.rs.core.HttpHeaders;

@Path("project1")
public class TestApp {
    @Context
    private HttpHeaders header;
    public TestApp() {
        super();
       
    }
    
    private ArrayList al = new ArrayList();
    @GET
    @Produces("application/xml")
    public String greet()
    {
        String userAgent =  header.getRequestHeader("UserType").get(0);  
        
        return ""+userAgent+"";
    }
}

In JAX-WS we can use the MessageContext to read the header parameters but in the caseof  Restful services we have to use the @Context parameter to get the Header values

Consuming In Client :

In my other blog i will be explaining on how to pass header parameters to service like above using WebService DataControl in Jdeveloper Link.

Programmatically Accessing the Custom Properties Defined for Attributes in WSDC Sparse XML

About :

Accessing the Custom Properties in a ADFBC Components is little bit straight forward compared to accessing it from the Sparse XML generated for WSDC Accessor.
In this blog, I will provide the code snippet to access the Attributes Custom Properties programmatically from an backing Bean.

DCBindingContainer bc = (DCBindingContainer) BindingContext.getCurrent().getCurrentBindingsEntry();
AttributeDef[] ax = bc.findIteratorBinding("ITERATOR NAME").getAttributeDefs();
AttributeDefImpl attr = (AttributeDefImpl) ax[0];
ax[0].getProperty("Color"); // Gets the Value set Editor in this case it gives blue attr.setProperty("Color",YOUR STRING); //This overrides the Value set in the editor

In ADFBC we can access the Attributes from the ViiewObject's Impl Class directly but in this case we have to get the Iterator Bindings in the Page Definition and then get the Attributes definition 

Using JSON Web Token (JWT) to get OAuth 2.0 Access Token [Server-Server Interaction]

Use-Case

This blog explains about using the JWT [JSON Web Tokens] to request for Access Tokens from the Service Providers who support JWT.

I will showcase this scenario by using Google API


What is this JWT [JSON Web Tokens] .............?
JWTs represent a set of claims as a JSON object that is encoded in a JWS and/or JWE structure.
The JWT Structure is mainly composed of three parts they are Header.ClaimSet.Signature which are BASE64 Url Encoded.

For Further Information on JWT theory Refer the following Link : http://tools.ietf.org/html/draft-ietf-oauth-json-web-token-13

Scenario

Create an Client ID by registering in the google apis console  and download the keystore file.
Ensure to save this securely as downloading this again will result in the generation of an new file.

Header Claim:
Since Google uses the RS256 Hashing Mechanism to encrypt the keystore, we are setting the alg to RS256 and the type is set as JWT [JSON web Tokens]

{"alg":"RS256","typ":"JWT"}

Claim Set :

{
"iss":" client_id of the application making the access token request@developer.gserviceaccount.com",
"scope":"https://www.googleapis.com/auth/userinfo.profile",
"aud":"https://accounts.google.com/o/oauth2/token",
"exp":1328554385,
"iat":1328550785
}
The scope given in the claim set basically gives the profile information of the client registered in the Google Apis console, but you can use the other Google developer Services  like Google Cloud Storage or the Google Prediction API etc.

The fields exp and iat are the expiration and issuance time on when the jwt was created
Here the exp and iat play an major role as giving an invalid/outdated values may result in the Authentication failure.

Creating the Signature :

Use the following java code to generate the signature

import org.apache.commons.codec.binary.Base64;
import org.apache.commons.codec.binary.StringUtils;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.UnsupportedEncodingException;

import java.security.GeneralSecurityException;
import java.security.PrivateKey;

public class BlogJavaCode {
public BlogJavaCode() {
        super();
    }
 
private  String headerClaim="{\"alg\":\"RS256\",\"typ\":\"JWT\"}"; //provide the above mentioned header claim
private  String claimSet="{\n" + 
"\"iss\":\" client_id of the application making the access token request@developer.gserviceaccount.com\",\n" + 
"\"scope\":\"https://www.googleapis.com/auth/userinfo.profile\",\n" + 
"\"aud\":\"https://accounts.google.com/o/oauth2/token\",\n" + 
"\"exp\":"+generateEXP()+",\n" + 
"\"iat\":"+generateIAT()+"\n" + 
"}";

    
private  long generateIAT()
{
    long currentTime = System.currentTimeMillis();
    long iat = (currentTime/1000);
    return iat; 
}

private   long generateEXP()
{
    long currentTime = System.currentTimeMillis();
    long exp = (currentTime/1000+3600);
    return exp;
}

/**
     * This Method constructs the JWT token 
     * @return jwt string
     */

public  String generateJWTToken()
{
    String encodedHeaderClaim =null;
    String encodedClaimset=null;
    String tempStr =null;  
    byte[] signature = null;
    String jwtToken= null;
        try {
            //Base64encoding of the Header Claim Set
            encodedHeaderClaim = base64encoding(headerClaim.getBytes("UTF-8"));
            //Base64encoding of the Claim Set
            encodedClaimset=base64encoding(claimSet.trim().getBytes("UTF-8"));
            //Temporary String needed to create the signature 
            tempStr = encodedHeaderClaim+"."+encodedClaimset;
            //Load the key from the keystore file
            PrivateKey serviceAccountPrivateKey = SecurityUtils.loadPrivateKeyFromKeyStore(SecurityUtils.getPkcs12KeyStore(),
                                                         new FileInputStream(""),
                                                         "notasecret", "privatekey", "notasecret");
            //Get the UTF-based bytes for the tempStr as it needs to be signed
            byte[] tempStrBytes = getbytesbasedforUtf8(tempStr);
            //Constructing the Signature
            signature =   SecurityUtils.sign(SecurityUtils.getSha256WithRsaSignatureAlgorithm(), serviceAccountPrivateKey, tempStrBytes);
            //The Final JWT String
            jwtToken = tempStr + "." + base64encoding(signature);
            
        } catch (UnsupportedEncodingException e) {
        } catch (FileNotFoundException e) {
        } catch (GeneralSecurityException | IOException e) {
        }
    return jwtToken;
    }

 

 public static String base64encoding(byte[] binaryData) {
        return Base64.encodeBase64URLSafeString(binaryData);
      }
    
  public static byte[] getbytesbasedforUtf8(String string) {
       return StringUtils.getBytesUtf8(string);
    }
}

Making the Request :

Open an URL Connection append the following parameter along with the signature and make the post call as shown below

grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Ajwt-bearer&assertion=<SignatureObtainedFromtheAboveMethod>.