I'd like to convert my ed25519 keypair to curve25519 in java (similar as ed2curve in js)

Question

I'd like to ask if there is any API that supports converting ed25519 keypairs to curve25519 ones.

Using ed2curve for node.js now, and if you have any better recommendation, I'd appreciate your suggestions.

also looking for an API that supports curve25519 encryption/decryption.... (I tried tweetnacl's nacl.box and had no idea what nonce was)

So here's what I need

• converting ed25519 to curve25519 (to encrypt/decrypt aes256key) - JAVA api
• curve25519 encryption/decryption (does bouncy castle do that?) - JAVA, Javascript

I'd really appreciate your help. Thanks, have a great day!