Aes decrypt file java with base64 data encoding

I referred this and trying to do file decryption with base64 decoding

My requirement is to encode data with base64 during encryption and decode data with base64 during decryption.

But im facing below error:

javax.crypto.IllegalBlockSizeException: Input length must be multiple of 16 when decrypting with padded cipher
	at java.base/com.sun.crypto.provider.CipherCore.doFinal(Unknown Source)
	at java.base/com.sun.crypto.provider.CipherCore.doFinal(Unknown Source)
	at java.base/com.sun.crypto.provider.AESCipher.engineDoFinal(Unknown Source)
	at java.base/javax.crypto.Cipher.doFinal(Unknown Source)
	at aes.DecryptNew.decryptNew(DecryptNew.java:124)
	at aes.DecryptNew.main(DecryptNew.java:32)

Also im confused on how to perform decryption in chunks.
Please suggest me issues in this code.

import javax.crypto.Cipher;
import javax.crypto.CipherOutputStream;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

import java.io.BufferedWriter;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.security.*;
import java.util.Arrays;
import java.util.Base64;

public class DecryptNew {
    public static void main(String[] args) {
        String plaintextFilename = "D:\\\\plaintext.txt";
        String ciphertextFilename = "D:\\\\plaintext.txt.crypt";
        String decryptedtextFilename = "D:\\\\plaintextDecrypted.txt";
        String password = "testpass";

        writeToFile();
        String ciphertext = encryptfile(plaintextFilename, password);
        System.out.println("ciphertext: " + ciphertext);
        decryptNew(ciphertextFilename, password, decryptedtextFilename);
    }

    static void writeToFile() {
    	BufferedWriter writer = null;
    	try
    	{
    	    writer = new BufferedWriter( new FileWriter("D:\\\\plaintext.txt"));
    	    byte[] data = Base64.getEncoder().encode("hello\r\nhello".getBytes(StandardCharsets.UTF_8));
    	    writer.write(new String(data)); 
    	}
    	catch ( IOException e)
    	{
    	}
    	finally
    	{
    	    try
    	    {
    	        if ( writer != null)
    	        writer.close( );
    	    }
    	    catch ( IOException e)
    	    {
    	    }
    	}
    }
    
    public static String encryptfile(String path, String password) {
        try {
            FileInputStream fis = new FileInputStream(path);
            FileOutputStream fos = new FileOutputStream(path.concat(".crypt"));
            final byte[] pass = Base64.getEncoder().encode(password.getBytes());
            final byte[] salt = (new SecureRandom()).generateSeed(8);
            fos.write(Base64.getEncoder().encode("Salted__".getBytes()));
            fos.write(salt);
            final byte[] passAndSalt = concatenateByteArrays(pass, salt);
            byte[] hash = new byte[0];
            byte[] keyAndIv = new byte[0];
            for (int i = 0; i < 3 && keyAndIv.length < 48; i++) {
                final byte[] hashData = concatenateByteArrays(hash, passAndSalt);
                final MessageDigest md = MessageDigest.getInstance("SHA-1");
                hash = md.digest(hashData);
                keyAndIv = concatenateByteArrays(keyAndIv, hash);
            }
            final byte[] keyValue = Arrays.copyOfRange(keyAndIv, 0, 32);
            final byte[] iv = Arrays.copyOfRange(keyAndIv, 32, 48);
            final SecretKeySpec key = new SecretKeySpec(keyValue, "AES");
            final Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
            cipher.init(Cipher.ENCRYPT_MODE, key, new IvParameterSpec(iv));
            CipherOutputStream cos = new CipherOutputStream(fos, cipher);
            int b;
            byte[] d = new byte[8];
            while ((b = fis.read(d)) != -1) {
                cos.write(d, 0, b);
            }
            cos.flush();
            cos.close();
            fis.close();
            System.out.println("encrypt done " + path);
        } catch (IOException | NoSuchAlgorithmException | NoSuchPaddingException | InvalidKeyException | InvalidAlgorithmParameterException e) {
            e.printStackTrace();
        }
        return path;
    }

    static void decryptNew(String path,String password, String outPath) {
        byte[] SALTED_MAGIC = Base64.getEncoder().encode("Salted__".getBytes());
        try{
            FileInputStream fis = new FileInputStream(path);
            FileOutputStream fos = new FileOutputStream(outPath);
            final byte[] pass = password.getBytes(StandardCharsets.US_ASCII);
            final byte[] inBytes = Files.readAllBytes(Paths.get(path));
            final byte[] shouldBeMagic = Arrays.copyOfRange(inBytes, 0, SALTED_MAGIC.length);
            if (!Arrays.equals(shouldBeMagic, SALTED_MAGIC)) {
                throw new IllegalArgumentException("Initial bytes from input do not match OpenSSL SALTED_MAGIC salt value.");
            }
            final byte[] salt = Arrays.copyOfRange(inBytes, SALTED_MAGIC.length, SALTED_MAGIC.length + 8);
            final byte[] passAndSalt = concatenateByteArrays(pass, salt);
            byte[] hash = new byte[0];
            byte[] keyAndIv = new byte[0];
            for (int i = 0; i < 3 && keyAndIv.length < 48; i++) {
                final byte[] hashData = concatenateByteArrays(hash, passAndSalt);
                MessageDigest md = null;
                md = MessageDigest.getInstance("SHA-1");
                hash = md.digest(hashData);
                keyAndIv = concatenateByteArrays(keyAndIv, hash);
            }
            final byte[] keyValue = Arrays.copyOfRange(keyAndIv, 0, 32);
            final SecretKeySpec key = new SecretKeySpec(keyValue, "AES");
            final byte[] iv = Arrays.copyOfRange(keyAndIv, 32, 48);
            final Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
            cipher.init(Cipher.DECRYPT_MODE, key, new IvParameterSpec(iv));
            final byte[] clear = cipher.doFinal(inBytes, 16, inBytes.length - 16);
            String contentDecoded = new String(Base64.getDecoder().decode(clear));
            fos.write(contentDecoded.getBytes());
            fos.close();
            System.out.println("Decrypt is completed");
        }catch(Exception e){
            e.printStackTrace();
        }
    }
    

    public static byte[] concatenateByteArrays(byte[] a, byte[] b) {
        return ByteBuffer
                .allocate(a.length + b.length)
                .put(a).put(b)
                .array();
    }
}

As mentioned in my first comment: Encryption and decryption use different encodings for the password (Base64 in encryption, ASCII in decryption).<br>
In addition the prefix is Base64 encoded in both encryption and decryption, so prefix plus salt are larger than one block (16 bytes), and therefore the subsequent length determination of the ciphertext during decryption fails, as it is assumed that the ciphertext starts with the 2nd block.<br>
Both issues can be solved if the same encoding is used for the password in encryption and decryption (e.g. ASCII) and the prefix is ASCII encoded, e.g. for encryption:

...
byte[] pass = password.getBytes(StandardCharsets.US_ASCII);
byte[] SALTED_MAGIC = "Salted__".getBytes(StandardCharsets.US_ASCII);
byte[] salt = (new SecureRandom()).generateSeed(8);
fos.write(SALTED_MAGIC);
fos.write(salt);
...

and for decryption:

...
byte[] pass = password.getBytes(StandardCharsets.US_ASCII);
byte[] SALTED_MAGIC = "Salted__".getBytes(StandardCharsets.US_ASCII);
byte[] prefix = fis.readNBytes(8);
byte[] salt = fis.readNBytes(8);
...

However the current encryption method does not Base64 encode (only the prefix is Base64 encoded which is rather counterproductive, s. above).<br>
Even a Base64 encoded plaintext does not change this, as the ciphertext itself is not Base64 encoded.<br>
Considering your statement My requirement is to encode data with base64 during encryption and decode data with base64 during decryption and the OpenSSL format used, I assume that you want to decrypt a ciphertext that has been encrypted with the -base64 option, analogous to OpenSSL, i.e. with

openssl enc -aes-256-cbc -base64 -pass pass:testpass -p -in sample.txt -out sample.crypt

Here, prefix, salt and ciphertext are concatenated on byte level and the result is then Base64 encoded. To achieve this, your implementation posted in the question could be changed as follows:

static void decrypt(String path, String password, String outPath) {

	try (FileInputStream fis = new FileInputStream(path);
		 Base64InputStream bis = new Base64InputStream(fis, false, 64, "\r\n".getBytes(StandardCharsets.US_ASCII))) { // from Apache Commons Codec
		
		// Read prefix and salt
        byte[] SALTED_MAGIC = "Salted__".getBytes(StandardCharsets.US_ASCII);
		byte[] prefix = bis.readNBytes(8);
		if (!Arrays.equals(prefix, SALTED_MAGIC)) {
			throw new IllegalArgumentException("Initial bytes from input do not match OpenSSL SALTED_MAGIC salt value.");
		}
		byte[] salt = bis.readNBytes(8);

		// Derive key and IV
		byte[] pass = password.getBytes(StandardCharsets.US_ASCII);
		byte[] passAndSalt = concatenateByteArrays(pass, salt);
        byte[] hash = new byte[0];
        byte[] keyAndIv = new byte[0];
        for (int i = 0; i < 3 && keyAndIv.length < 48; i++) {
            byte[] hashData = concatenateByteArrays(hash, passAndSalt);
            MessageDigest md = null;
            md = MessageDigest.getInstance("SHA-1");   // Use digest from encryption
            hash = md.digest(hashData);
            keyAndIv = concatenateByteArrays(keyAndIv, hash);
        }
        byte[] keyValue = Arrays.copyOfRange(keyAndIv, 0, 32);
		SecretKeySpec key = new SecretKeySpec(keyValue, "AES");
		byte[] iv = Arrays.copyOfRange(keyAndIv, 32, 48);

		// Decrypt
		Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
		cipher.init(Cipher.DECRYPT_MODE, key, new IvParameterSpec(iv));
		try (CipherInputStream cis = new CipherInputStream(bis, cipher);
			 FileOutputStream fos = new FileOutputStream(outPath)) {

			int length;
			byte[] buffer = new byte[1024];
			while ((length = cis.read(buffer)) != -1) {
				fos.write(buffer, 0, length);
			}
		}
		System.out.println("Decrypt is completed");
		
	} catch (Exception e) {
		e.printStackTrace();
	}
}

As I already mentioned in the comments to the linked question, the processing in chunks can easily be implemented with the class CipherInputStream. The Base64 decoding can be achieved with the class Base64InputStream of the Apache Commons Codec, as also addressed by Michael Fehr. This is a convenient way to perform Base64 decoding and decryption together. If the data does not need to be Base64 decoded (e.g. if the -base64 option was not used during encryption) the Base64InputStream class can simply be omitted.

As previously stated in the comments, small files do not need to be processed in chunks. This is only necessary when the files become large relative to the memory. However, since your encryption method processes the data in chunks, it is consistent that the decryption does the same.

Note that the encryption posted in the question is not compatible with the result of the above OpenSSL statement, i.e. the encryption would have to be adapted if necessary (analogous to the decryption posted above).

Edit: The encryptfile() method posted in the question creates a file containing the Base64 encoded prefix, the raw salt and the raw ciphertext. For key derivation the Base64 encoded password is applied. The method is used to encrypt a Base64 encoded plaintext. The following method is the counterpart of encryptfile() and allows the decryption and Base64 decoding of the plaintext:

static void decryptfile(String path, String password, String outPath) {

	try (FileInputStream fis = new FileInputStream(path)) {

		// Read prefix and salt
        byte[] SALTED_MAGIC = Base64.getEncoder().encode("Salted__".getBytes());
		byte[] prefix = new byte[SALTED_MAGIC.length];
		fis.readNBytes(prefix, 0, prefix.length);
		if (!Arrays.equals(prefix, SALTED_MAGIC)) {
			throw new IllegalArgumentException("Initial bytes from input do not match OpenSSL SALTED_MAGIC salt value.");
		}
		byte[] salt = new byte[8];
		fis.readNBytes(salt, 0, salt.length);

		// Derive key and IV
        final byte[] pass = Base64.getEncoder().encode(password.getBytes());
		byte[] passAndSalt = concatenateByteArrays(pass, salt);
        byte[] hash = new byte[0];
        byte[] keyAndIv = new byte[0];
        for (int i = 0; i < 3 && keyAndIv.length < 48; i++) {
            byte[] hashData = concatenateByteArrays(hash, passAndSalt);
            MessageDigest md = null;
            md = MessageDigest.getInstance("SHA-1");   // Use digest from encryption
            hash = md.digest(hashData);
            keyAndIv = concatenateByteArrays(keyAndIv, hash);
        }
        byte[] keyValue = Arrays.copyOfRange(keyAndIv, 0, 32);
		SecretKeySpec key = new SecretKeySpec(keyValue, "AES");
		byte[] iv = Arrays.copyOfRange(keyAndIv, 32, 48);

		// Decrypt
		Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
		cipher.init(Cipher.DECRYPT_MODE, key, new IvParameterSpec(iv));
		try (CipherInputStream cis = new CipherInputStream(fis, cipher);
			 Base64InputStream bis = new Base64InputStream(cis, false, -1, null); // from Apache Commons Codec	
			 FileOutputStream fos = new FileOutputStream(outPath)) {

			int length;
			byte[] buffer = new byte[1024];
			while ((length = bis.read(buffer)) != -1) {
				fos.write(buffer, 0, length);
			}
		}
		System.out.println("Decrypt is completed");
		
	} catch (Exception e) {
		e.printStackTrace();
	}
}

The decryptfile()-method writes the Base64 decoded plaintext to the file in outPath. To get the Base64 encoded plaintext simply remove the Base64InputStream instance from the stream hierarchy.

As already explained in the comment, this method is incompatible to OpenSSL, i.e. it can't decrypt ciphertexts generated with the OpenSSL statement posted above (with or without -base64 option). To decrypt a ciphertext generated with OpenSSL with -base64 option use the decrypt() method.