android获得公钥的有甚么方法

在Android中获得公钥的方法有以下几种：

1. 通过KeyStore获得：Android提供了KeyStore类来管理密钥和证书。可使用KeyStore来获得已存储的公钥。以下是一个示例代码：

KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore");
keyStore.load(null);
Certificate cert = keyStore.getCertificate(alias);
PublicKey publicKey = cert.getPublicKey();

2. 通过文件获得：如果有公钥的PEM文件或其他格式的文件，可使用相应的类来读取文件并获得公钥。以下是一个示例代码：

String publicKeyStr = "-----BEGIN PUBLIC KEY-----
" +
        "MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA3r3A8C1M8tY7f0zYVjFy
" +
        "lQIDAQAB
" +
        "-----END PUBLIC KEY-----";
byte[] publicKeyBytes = Base64.decode(publicKeyStr, Base64.DEFAULT);
X509EncodedKeySpec spec = new X509EncodedKeySpec(publicKeyBytes);
KeyFactory keyFactory = KeyFactory.getInstance("RSA");
PublicKey publicKey = keyFactory.generatePublic(spec);

3. 通过URL获得：如果公钥存储在远程服务器上，可以通过URL获得公钥。以下是一个示例代码：

URL url = new URL("http://example.com/publicKey.pem");
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
InputStream inputStream = conn.getInputStream();
byte[] publicKeyBytes = new byte[inputStream.available()];
inputStream.read(publicKeyBytes);
X509EncodedKeySpec spec = new X509EncodedKeySpec(publicKeyBytes);
KeyFactory keyFactory = KeyFactory.getInstance("RSA");
PublicKey publicKey = keyFactory.generatePublic(spec);

这些方法可以根据具体的情况选择适合的方式来获得公钥。