代码如下

import javax.crypto.BadPaddingException;import javax.crypto.Cipher;import javax.crypto.IllegalBlockSizeException;import javax.crypto.NoSuchPaddingException;import java.security.*;import java.security.interfaces.RSAPrivateKey;import java.security.interfaces.RSAPublicKey;import java.security.spec.InvalidKeySpecException;import java.security.spec.PKCS8EncodedKeySpec;import java.security.spec.X509EncodedKeySpec;import java.util.HashMap;import java.util.Map; public class RSADecrypt {  public static Map createKeyPair() throws NoSuchAlgorithmException {    //创建秘钥对生成器    KeyPairGenerator generator = KeyPairGenerator.getInstance("rsa");    //初始化密钥对生成器    generator.initialize(1024);    //生成密钥对    KeyPair keyPair = generator.generateKeyPair();    //获取公钥私钥    RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();    RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();    String publicKeyStr = new String(publicKey.getEncoded());    String privateKeyStr = new String(privateKey.getEncoded());    //公钥私钥存放map    Map keyMap = new HashMap<>();    keyMap.put("publicKey", publicKeyStr);    keyMap.put("privateKey", privateKeyStr);    return keyMap;  }   /**   * 获取公钥   * @param publicKey   * @return   */  public static RSAPublicKey getPublicKey(String publicKey) throws NoSuchAlgorithmException, InvalidKeySpecException {    KeyFactory keyFactory = KeyFactory.getInstance("rsa");    //X509编码    X509EncodedKeySpec x509EncodedKeySpec = new X509EncodedKeySpec(publicKey.getBytes());    RSAPublicKey rsaPublicKey = (RSAPublicKey) keyFactory.generatePublic(x509EncodedKeySpec);    return rsaPublicKey;  }   /**   * 获取私钥   * @param privateKey   * @return   */  public static RSAPrivateKey getPrivateKey(String privateKey) throws NoSuchAlgorithmException, InvalidKeySpecException {    KeyFactory keyFactory = KeyFactory.getInstance("rsa");    //PKCS#8编码    PKCS8EncodedKeySpec pkcs8EncodedKeySpec = new PKCS8EncodedKeySpec(privateKey.getBytes());    RSAPrivateKey rsaPrivateKey = (RSAPrivateKey) keyFactory.generatePrivate(pkcs8EncodedKeySpec);    return rsaPrivateKey;  }   /**   * 公钥加密   * @param src   * @param publicKey   * @return   */  public static byte[] publicEncrypt(String src, RSAPublicKey publicKey) throws NoSuchPaddingException, NoSuchAlgorithmException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException {    Cipher cipher = Cipher.getInstance("rsa");    cipher.init(Cipher.ENCRYPT_MODE,publicKey);    byte[] encryptedData = cipher.doFinal(src.getBytes());    return encryptedData;  }   /**   * 私钥解密   * @param data   * @param privateKey   * @return   * @throws NoSuchPaddingException   * @throws NoSuchAlgorithmException   * @throws InvalidKeyException   * @throws BadPaddingException   * @throws IllegalBlockSizeException   */  public static String privateDecrypt(byte[] data, RSAPrivateKey privateKey) throws NoSuchPaddingException, NoSuchAlgorithmException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException {    Cipher cipher = Cipher.getInstance("rsa");    cipher.init(Cipher.DECRYPT_MODE,privateKey);    byte[] result = cipher.doFinal(data);    return new String(result);  }   public static void main(String[] args) throws NoSuchAlgorithmException, InvalidKeySpecException, IllegalBlockSizeException, InvalidKeyException, BadPaddingException, NoSuchPaddingException {    Map keyPair = createKeyPair();    RSAPublicKey publicKey = getPublicKey(keyPair.get("publicKey"));    RSAPrivateKey privateKey = getPrivateKey(keyPair.get("privateKey"));    String str = "hello world";    /**     * 公钥加密，私钥解密     */    byte[] encryptedData = publicEncrypt(str,publicKey);    String result = privateDecrypt(encryptedData, privateKey);     /**     * 私钥加密，公钥解密     */    byte[] encrypted = privateEncrypt(str, privateKey);    String source = publicDecrypt(encrypted, publicKey);   }   /**   * 私钥加密   * @param src   * @param privateKey   * @return   * @throws NoSuchPaddingException   * @throws NoSuchAlgorithmException   * @throws InvalidKeyException   * @throws BadPaddingException   * @throws IllegalBlockSizeException   */  public static byte[] privateEncrypt(String src, RSAPrivateKey privateKey) throws NoSuchPaddingException, NoSuchAlgorithmException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException {    Cipher cipher = Cipher.getInstance("rsa");    cipher.init(Cipher.DECRYPT_MODE,privateKey);    byte[] result = cipher.doFinal(src.getBytes());    return result;  }   /**   * 公钥解密   * @param data   * @param publicKey   * @return   * @throws NoSuchPaddingException   * @throws NoSuchAlgorithmException   * @throws InvalidKeyException   * @throws BadPaddingException   * @throws IllegalBlockSizeException   */  public static String publicDecrypt(byte[] data, RSAPublicKey publicKey) throws NoSuchPaddingException, NoSuchAlgorithmException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException {    Cipher cipher = Cipher.getInstance("rsa");    cipher.init(Cipher.DECRYPT_MODE,publicKey);    byte[] result = cipher.doFinal(data);    return new String(result);  }}

上面例子使用密钥长度1024，如果想使用2048密钥，只需要在初始化密钥对生成器做一些变动，其他部分可以复用。

generator.initialize(2048);

这个例子只是基本常用的RSA加解密，也可加入base64，签名。