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RsaUtils 是一个RSA工具类，提供生成密钥对、读取和写入公钥/私钥文件的功能。它支持从文件中加载密钥，并将密钥转换为对应的对象，适用于加密解密和身份认证场景。

import java.io.File;
import java.io.IOException;
import java.nio.file.Files;
import java.security.*;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.Base64;public class RsaUtils {private static final int DEFAULT_KEY_SIZE = 2048;/*** 从文件中读取公钥** @param filename 公钥保存路径，相对于classpath* @return 公钥对象* @throws Exception*/public static PublicKey getPublicKey(String filename) throws Exception {byte[] bytes = readFile(filename);return getPublicKey(bytes);}/*** 从文件中读取密钥** @param filename 私钥保存路径，相对于classpath* @return 私钥对象* @throws Exception*/public static PrivateKey getPrivateKey(String filename) throws Exception {byte[] bytes = readFile(filename);return getPrivateKey(bytes);}/*** 获取公钥** @param bytes 公钥的字节形式* @return* @throws Exception*/private static PublicKey getPublicKey(byte[] bytes) throws Exception {bytes = Base64.getDecoder().decode(bytes);X509EncodedKeySpec spec = new X509EncodedKeySpec(bytes);KeyFactory factory = KeyFactory.getInstance("RSA");return factory.generatePublic(spec);}/*** 获取密钥** @param bytes 私钥的字节形式* @return* @throws Exception*/private static PrivateKey getPrivateKey(byte[] bytes) throws NoSuchAlgorithmException, InvalidKeySpecException {bytes = Base64.getDecoder().decode(bytes);PKCS8EncodedKeySpec spec = new PKCS8EncodedKeySpec(bytes);KeyFactory factory = KeyFactory.getInstance("RSA");return factory.generatePrivate(spec);}/*** 根据密文，生存rsa公钥和私钥,并写入指定文件** @param publicKeyFilename  公钥文件路径* @param privateKeyFilename 私钥文件路径* @param secret             生成密钥的密文*/public static void generateKey(String publicKeyFilename, String privateKeyFilename, String secret, int keySize) throws Exception {KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");SecureRandom secureRandom = new SecureRandom(secret.getBytes());keyPairGenerator.initialize(Math.max(keySize, DEFAULT_KEY_SIZE), secureRandom);KeyPair keyPair = keyPairGenerator.genKeyPair();// 获取公钥并写出byte[] publicKeyBytes = keyPair.getPublic().getEncoded();publicKeyBytes = Base64.getEncoder().encode(publicKeyBytes);writeFile(publicKeyFilename, publicKeyBytes);// 获取私钥并写出byte[] privateKeyBytes = keyPair.getPrivate().getEncoded();privateKeyBytes = Base64.getEncoder().encode(privateKeyBytes);writeFile(privateKeyFilename, privateKeyBytes);}private static byte[] readFile(String fileName) throws Exception {return Files.readAllBytes(new File(fileName).toPath());}private static void writeFile(String destPath, byte[] bytes) throws IOException {File dest = new File(destPath);if (!dest.exists()) {dest.createNewFile();}Files.write(dest.toPath(), bytes);}
}