How to sign string as well sign request body with public key using Java

Below is a code snippet which will sign your request using Public key.

package com.pkm.src;

import Base64OutputStream;
import IOUtil;

import javax.crypto.Cipher;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.security.MessageDigest;
import java.security.cert.CertificateFactory;
import java.security.cert.X509Certificate;

/**
 * Created by pritom on 24/05/2017.
 */
public class SignatureSigner {
    public static void main(String[] args) throws Exception {
        String certificateFile = ".....\\publickey.cer";
        String requestBody = "Param1=Value_Of_Param1&Param2=Value_Of_param2";
        String signature = encodeRSASHA1(certificateFile, requestBody);
        System.out.println("Signature=" + signature);
    }

    protected static String encodeRSASHA1(String certificateFile, String requestBody) throws Exception {
        FileInputStream certIn1 = new FileInputStream(certificateFile);
        CertificateFactory e = CertificateFactory.getInstance("X509");
        X509Certificate myCertificate = (X509Certificate) e.generateCertificate(certIn1);

        MessageDigest hashGen = MessageDigest.getInstance("SHA1");
        byte[] hash = hashGen.digest(requestBody.getBytes("UTF-8"));
        Cipher rsa = Cipher.getInstance("RSA/ECB/PKCS1Padding");
        rsa.init(1, myCertificate);
        byte[] signature = rsa.doFinal(hash);

        ByteArrayInputStream sigIn = new ByteArrayInputStream(signature);
        ByteArrayOutputStream sigOut = new ByteArrayOutputStream();
        Base64OutputStream base64Out = new Base64OutputStream(sigOut, "");
        IOUtil.copy(sigIn, base64Out);
        base64Out.close();
        return new String(sigOut.toByteArray(), "US-ASCII");
    }
}

Which will output as below:

Signature=7GNccit4cY+rs4t/S0WBv.........+w1rYdiEO8PxuR3SQ=