sm2算法的pem格式公钥转PublicKey

SM2算法的pem格式公钥可以通过Bouncy Castle库转换为Java的`PublicKey`对象。以下是一个简单的示例代码：

import java.io.BufferedReader;
import java.io.FileReader;
import java.security.PublicKey;
import java.security.Security;

import org.bouncycastle.asn1.pkcs.RSAPublicKey;
import org.bouncycastle.asn1.x509.SubjectPublicKeyInfo;
import org.bouncycastle.cert.X509CertificateHolder;
import org.bouncycastle.crypto.params.ECPublicKeyParameters;
import org.bouncycastle.crypto.util.PublicKeyFactory;
import org.bouncycastle.jce.provider.BouncyCastleProvider;
import org.bouncycastle.util.io.pem.PemObject;
import org.bouncycastle.util.io.pem.PemReader;

public class SM2PublicKeyConverter {
    public static void main(String[] args) {
        try {
            // 加载Bouncy Castle Provider
            Security.addProvider(new BouncyCastleProvider());

            // 读取pem格式公钥
            BufferedReader reader = new BufferedReader(new FileReader("path/to/your/public_key.pem"));
            PemReader pemReader = new PemReader(reader);
            PemObject pemObject = pemReader.readPemObject();
            byte[] publicKeyBytes = pemObject.getContent();

            // 解析公钥
            SubjectPublicKeyInfo subjectPublicKeyInfo = SubjectPublicKeyInfo.getInstance(publicKeyBytes);
            ECPublicKeyParameters ecPublicKeyParameters = (ECPublicKeyParameters) PublicKeyFactory.createKey(subjectPublicKeyInfo);
            PublicKey publicKey = ECKeyUtil.publicKeyFromParameters(ecPublicKeyParameters);

            // 输出公钥信息
            System.out.println("Algorithm: " + publicKey.getAlgorithm());
            System.out.println("Format: " + publicKey.getFormat());
            System.out.println("Encoded: " + Base64.getEncoder().encodeToString(publicKey.getEncoded()));
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

其中，`path/to/your/public_key.pem`是pem格式公钥文件的路径。`publicKey`是SM2公钥，可以通过它获取公钥的各种属性。注意，`ECKeyUtil.publicKeyFromParameters()`方法是自定义的，用于从`ECPublicKeyParameters`对象创建`PublicKey`对象。