背景：需要对字符串进行RSA加解密，网上的太多废话。
目的：为了解决你的需求，好抄。

上代码：

package ai.saas.framework.common.util;

import org.apache.commons.codec.binary.Base64;
import sun.misc.BASE64Decoder;

import javax.crypto.Cipher;
import java.security.KeyFactory;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;

/**
 * RSA 加解密
 */
public class RSA {

    /**
     * RSA 公钥和私钥
     * 通过RSA密钥处理器获得，而非自定义字符串  照抄即可
     */
    public final static String pubKey = "MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCxF4tm6qJ00KhfZVkubzgSznFuVAqw5vP3mMULfj33HcP9XjUdtxsmwtDQABgSLdihwCtliGBblsfkobeQxJEtyALECd1u3sU8QJarSGCZZBgD+Y2rNQeTKcmP02qIN8FS3y81jgwL321Scr4rrfRbHA0hax9Ap9f5IUBpLWX+5wIDAQAB";
    public final static String priKey = "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";


    public static void main(String[] args) throws Exception {

        String str = "ABCDEFG"; // 需要操作加解密的字符串

        String encryptionBase64Str = pubKeyEncryption(str); // 加密
        System.out.println("公钥加密，私钥解密 --加密: " + encryptionBase64Str); // RSA加密再base64编码后的字符串

        String decryptionStr = priKeyDecryption(encryptionBase64Str); // 解密
        System.out.println("公钥加密，私钥解密 --解密: " + decryptionStr);
    }


    /**
     * 公钥加密
     *
     * @param str 需要加密操作的字符串
     * @return 结果再Base64加密后的字符串
     * @throws Exception
     */
    public static String pubKeyEncryption(String str) throws Exception {
        // String 转 公钥
        PublicKey rsaPublicKey = getPublicKey(pubKey);
        //公钥加密
        X509EncodedKeySpec x509EncodedKeySpec = new X509EncodedKeySpec(rsaPublicKey.getEncoded());
        KeyFactory keyFactory = KeyFactory.getInstance("RSA");
        PublicKey publicKey = keyFactory.generatePublic(x509EncodedKeySpec);
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
        byte[] result = cipher.doFinal(str.getBytes());
        return Base64.encodeBase64String(result);
    }


    /**
     * 用私钥 解密
     *
     * @param encryptionBase64Str RSA加密后又base64编码后的字符串
     * @return 解密结果
     * @throws Exception
     */
    public static String priKeyDecryption(String encryptionBase64Str) throws Exception {
        // base64 解码
        byte[] base64 = Base64.decodeBase64(encryptionBase64Str);
        // String 转 私钥
        PrivateKey rsaPrivateKey = getPrivateKey(priKey);
        //私钥解密
        PKCS8EncodedKeySpec pkcs8EncodedKeySpec = new PKCS8EncodedKeySpec(rsaPrivateKey.getEncoded());
        KeyFactory keyFactory = KeyFactory.getInstance("RSA");
        PrivateKey privateKey = keyFactory.generatePrivate(pkcs8EncodedKeySpec);
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
        byte[] result = cipher.doFinal(base64);
        return new String(result);
    }


    /**
     * String转公钥PublicKey
     *
     * @param key
     * @return
     * @throws Exception
     */
    public static PublicKey getPublicKey(String key) throws Exception {
        byte[] keyBytes;
        keyBytes = (new BASE64Decoder()).decodeBuffer(key);
        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance("RSA");
        PublicKey publicKey = keyFactory.generatePublic(keySpec);
        return publicKey;
    }

    /**
     * String转私钥PrivateKey
     *
     * @param key
     * @return
     * @throws Exception
     */
    public static PrivateKey getPrivateKey(String key) throws Exception {
        byte[] keyBytes;
        keyBytes = (new BASE64Decoder()).decodeBuffer(key);
        PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance("RSA");
        PrivateKey privateKey = keyFactory.generatePrivate(keySpec);
        return privateKey;
    }

}