如何用Java加密或解密文件？

您只是混淆了文件。如您所链接的文章中所述，此代码使用从openssl生成的DER文件工作：

    FileEncryption secure = new FileEncryption();    // Encrypt pre    {        File encryptFile = new File("encrypt.data");        File publicKeyData = new File("public.der");        File originalFile = new File("sys_data.db");        File secureFile = new File("secure.data");        // create AES key        secure.makeKey();        // save AES key using public key        secure.saveKey(encryptFile, publicKeyData);        // save original file securely         secure.encrypt(originalFile, secureFile);    }    // Decrypt pre    {        File encryptFile = new File("encrypt.data");        File privateKeyFile = new File("private.der");        File secureFile = new File("secure.data");        File unencryptedFile = new File("unencryptedFile");        // load AES key        secure.loadKey(encryptFile, privateKeyFile);        // decrypt file        secure.decrypt(secureFile, unencryptedFile);    }