java使用RSA加密字符串

Java中使用RSA加密字符串的步骤如下：

1. 生成RSA密钥对

KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
keyPairGenerator.initialize(2048);
KeyPair keyPair = keyPairGenerator.generateKeyPair();

2. 获取公钥和私钥

PublicKey publicKey = keyPair.getPublic();
PrivateKey privateKey = keyPair.getPrivate();

3. 使用公钥加密字符串

Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.ENCRYPT_MODE, publicKey);
byte[] encryptedBytes = cipher.doFinal(plainText.getBytes());

4. 使用私钥解密字符串

cipher.init(Cipher.DECRYPT_MODE, privateKey);
byte[] decryptedBytes = cipher.doFinal(encryptedBytes);
String decryptedText = new String(decryptedBytes);

完整代码示例：

import java.security.*;
import javax.crypto.*;

public class RSAEncryptionExample {
    public static void main(String[] args) throws Exception {
        String plainText = "Hello, world!";

        // 生成RSA密钥对
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
        keyPairGenerator.initialize(2048);
        KeyPair keyPair = keyPairGenerator.generateKeyPair();

        // 获取公钥和私钥
        PublicKey publicKey = keyPair.getPublic();
        PrivateKey privateKey = keyPair.getPrivate();

        // 使用公钥加密字符串
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
        byte[] encryptedBytes = cipher.doFinal(plainText.getBytes());

        // 使用私钥解密字符串
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
        byte[] decryptedBytes = cipher.doFinal(encryptedBytes);
        String decryptedText = new String(decryptedBytes);

        System.out.println("Plain Text: " + plainText);
        System.out.println("Encrypted Text: " + new String(encryptedBytes));
        System.out.println("Decrypted Text: " + decryptedText);
    }
}

注意：RSA加密算法是一种非常耗时的加密算法，因此在加密大量数据时会影响性能。建议使用对称加密算法来加密大量数据。