我就不講原理了

直接開擼程式碼

祕鑰對生成，專案根目錄生成一個檔案。
也可直接取打印出來的私鑰和公鑰

import java.io.FileOutputStream;
import java.io.ObjectOutputStream;
import java.security.Key;
import java.security.KeyPair;
import java.security.KeyPairGenerator;

import sun.misc.BASE64Encoder;//jdk1.8報黃不影響使用
/**
     * 指定加密演算法為RSA
     */
    private
 
 static final String ALGORITHM = "RSA";
    /**
     * 金鑰長度，用來初始化
     */
    private static final int KEYSIZE = 1024;
    /**
     * 指定公鑰存放檔案
     */
    private static String PUBLIC_KEY_FILE = "PublicKey";
    /**
     * 指定私鑰存放檔案
     */
    private static String PRIVATE_KEY_FILE = "PrivateKey";
    

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

    /**
     * 本系統生成金鑰對
     *
     * @throws Exception
     */
    private static void generateKeyPair() throws Exception {

        /** RSA演算法要求有一個可信任的隨機數源 */
        /** 為RSA演算法建立一個KeyPairGenerator物件 */
        KeyPairGenerator keyPairGenerator =
 
 KeyPairGenerator.getInstance(ALGORITHM);

        /** 利用上面的隨機資料來源初始化這個KeyPairGenerator物件 */
        keyPairGenerator.initialize(KEYSIZE);

        /** 生成密匙對 */
        KeyPair keyPair = keyPairGenerator.generateKeyPair();

        /** 得到公鑰 */
        Key publicKey = keyPair.getPublic();

        /** 得到私鑰 */
        Key privateKey = keyPair.getPrivate();
        
        byte[] publicKeyBytes = publicKey.getEncoded();
        byte[] privateKeyBytes = privateKey.getEncoded();

        String publicKeyBase64 = new BASE64Encoder().encode(publicKeyBytes);
        String privateKeyBase64 = new BASE64Encoder().encode(privateKeyBytes);

        System.out.println("系統公鑰長度:" + publicKeyBase64.length());
        System.out.println("系統公鑰:" + publicKeyBase64);

        System.out.println("系統私鑰長度:" + privateKeyBase64.length());
        System.out.println("系統私鑰:" + privateKeyBase64);
        
        ObjectOutputStream oos1 = null;
        ObjectOutputStream oos2 = null;
        try {
            /** 用物件流將生成的金鑰寫入檔案 */
            oos1 = new ObjectOutputStream(new FileOutputStream(PUBLIC_KEY_FILE));
            oos2 = new ObjectOutputStream(new FileOutputStream(PRIVATE_KEY_FILE));
            oos1.writeObject(publicKey);
            oos2.writeObject(privateKey);
        } catch (Exception e) {
            throw e;
        } finally {
            /** 清空快取，關閉檔案輸出流 */
            oos1.close();
            oos2.close();
        }
    }

資料長度過長會報錯，這是需使用分段式加密

import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.security.Key;
import javax.crypto.Cipher;
import sun.misc.BASE64Decoder;
import sun.misc.BASE64Encoder;

public class RSAUtil {
	/** 指定加密演算法為RSA */
    private static final String ALGORITHM = "RSA";
    /** 指定公鑰存放檔案 */
    private static String PUBLIC_KEY_FILE = "PublicKey";
    /** 指定私鑰存放檔案 */
    private static String PRIVATE_KEY_FILE = "PrivateKey";
    /** 
     * RSA最大加密明文大小
     */
    private static final int MAX_ENCRYPT_BLOCK = 117;
    
    /** *//**
     * RSA最大解密密文大小
     */
    private static final int MAX_DECRYPT_BLOCK = 128;
    
 	//正常加密
	public static String encryptOne(String source) throws Exception {
		/** 獲得公鑰 */
        Key publicKey = getKey(PUBLIC_KEY_FILE);

        /** 得到Cipher物件來實現對源資料的RSA加密 */
        Cipher cipher = Cipher.getInstance(ALGORITHM);
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
        byte[] b = source.getBytes();
        /** 執行加密操作 */
        byte[] b1 = cipher.doFinal(b);
        BASE64Encoder encoder = new BASE64Encoder();
        return encoder.encode(b1);
    }
   //正常解密
   public static String decrypt(String cryptograph) throws Exception {

        Key privateKey = getKey(PRIVATE_KEY_FILE);

        /** 得到Cipher物件對已用公鑰加密的資料進行RSA解密 */
        Cipher cipher = Cipher.getInstance(ALGORITHM);
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
        BASE64Decoder decoder = new BASE64Decoder();
        byte[] b1 = decoder.decodeBuffer(cryptograph);

        /** 執行解密操作 */
        byte[] b = cipher.doFinal(b1);
        return new String(b);
    }
	//分段加密
	 public static byte[] encrypt(String source) throws Exception {

        Key publicKey = getKey(PUBLIC_KEY_FILE);

        /** 得到Cipher物件來實現對源資料的RSA加密 */
        Cipher cipher = Cipher.getInstance(ALGORITHM);
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
        byte[] b = source.getBytes();
        
        int inputLen = b.length;
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        int offSet = 0;
        byte[] cache;
        int i = 0;
        // 對資料分段加密
        while (inputLen - offSet > 0)
        {
            if ( inputLen - offSet > MAX_ENCRYPT_BLOCK)
            {
                cache = cipher.doFinal( b, offSet, MAX_ENCRYPT_BLOCK);
            }
            else
            {
                cache = cipher.doFinal( b, offSet, inputLen - offSet);
            }
            out.write( cache, 0, cache. length);
            i++;
            offSet = i * MAX_ENCRYPT_BLOCK;
        }
        byte[] encryptedData = out.toByteArray();
        out.close();
        return encryptedData;
    }
    //分段解密
    public static String decryptByPrivateKey( byte[] encryptedData) throws Exception {
    	Key privateKey = getKey(PRIVATE_KEY_FILE);
    	Cipher cipher = Cipher.getInstance(privateKey.getAlgorithm());
        cipher.init(2, privateKey);
        int inputLen = encryptedData.length;
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        int offSet = 0;
        byte[] cache;
        int i = 0;
        while (inputLen - offSet > 0) {
            if (inputLen - offSet > MAX_DECRYPT_BLOCK) {
                cache = cipher.doFinal(encryptedData, offSet, MAX_DECRYPT_BLOCK);
            } else {
                cache = cipher.doFinal(encryptedData, offSet, inputLen - offSet);
            }
            out.write(cache, 0, cache.length);
            i++;
            offSet = i * MAX_DECRYPT_BLOCK;
        }
        byte[] decryptedData = out.toByteArray();
        out.close();
        return new String(decryptedData);
    }
    private static Key getKey(String fileName) throws Exception, IOException {
        Key key;
        ObjectInputStream ois = null;
        try {
            /** 將檔案中的私鑰物件讀出 */
            ois = new ObjectInputStream(new FileInputStream(fileName));
            key = (Key) ois.readObject();
        } catch (Exception e) {
            throw e;
        } finally {
            ois.close();
        }
        return key;
    }
}

問題一：spring boot專案需改下面配置

private static String PUBLIC_KEY_FILE = "PublicKey";

替換為：

private static String PUBLIC_KEY_FILE = "classpath:key/PublicKey.txt";

getKey(String fileName)方法內

ois = new ObjectInputStream(new FileInputStream(fileName));

替換為

ois = new ObjectInputStream(new FileInputStream(ResourceUtils.getFile(fileName)));

不替換本地跑是沒問題的，但是打包放到tomcat裡會找不到你的靜態檔案。
其他專案同理，只需替換靜態檔案路徑即可。

問題二：分段加密返回資料有特殊字元會被轉譯，暫時未解決。