public int getBlockSize() {
        return blockSize;
    }
Returns the block cipher's block size to be used when constructing
{@link javax.crypto.Cipher Cipher} transformation string or {@code 0} if the JCA Provider default block size
for the specified {@link #getAlgorithmName() algorithm} should be used.
<p/>
This attribute is used <em>only</em> when constructing the transformation string for block (byte array)
operations ({@link #encrypt(byte[], byte[])} and {@link #decrypt(byte[], byte[])}).  The
{@link #getStreamingBlockSize() streamingBlockSize} attribute is used when the block cipher is used for
streaming operations.
<p/>
The default value is {@code 0} which retains the JCA Provider default.

@return the block cipher block size to be used when constructing the
        {@link javax.crypto.Cipher Cipher} transformation string, or {@code 0} if the JCA Provider default
        block size for the specified {@link #getAlgorithmName() algorithm} should be used.
src/main/java/org/apache/shiro/crypto/cipher/DefaultBlockCipherService.java