Just make a java class and call it in your jsp-page (or better struts-action).
If you are using this or older java versions than "JavaTM 2 SDK v 1.4", you can download the "JavaTM Cryptography Extension (JCE)".
In newer versions, these classes are already inside, see Java security classes
This is a code snippet randomly taken from the java API documentation:
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Cipher aesCipher;
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// Create the cipher
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aesCipher = Cipher.getInstance("AES/ECB/PKCS5Padding");
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We use the generated aesKey from above to initialize the Cipher object for encryption:
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// Initialize the cipher for encryption
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aesCipher.init(Cipher.ENCRYPT_MODE, aesKey);
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// Our cleartext
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byte[] cleartext = "This is just an example".getBytes();
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// Encrypt the cleartext
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byte[] ciphertext = aesCipher.doFinal(cleartext);
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// Initialize the same cipher for decryption
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aesCipher.init(Cipher.DECRYPT_MODE, aesKey);
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// Decrypt the ciphertext
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byte[] cleartext1 = aesCipher.doFinal(ciphertext);
