java如何生成sm2的公钥后生成pem文件

Java可以通过以下步骤生成SM2公钥并将其保存为PEM格式的文件：

1. 使用Bouncy Castle库中的KeyPairGenerator和ECNamedCurveTable类生成SM2密钥对。

KeyPairGenerator generator = KeyPairGenerator.getInstance("EC", "BC");
ECNamedCurveParameterSpec spec = ECNamedCurveTable.getParameterSpec("sm2p256v1");
generator.initialize(spec);
KeyPair keyPair = generator.generateKeyPair();

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

2. 将SM2公钥转换为PEM格式。可以使用Bouncy Castle库中的JcaPEMWriter和PemObject对象来实现。

// 将公钥转换为PEM格式
PemObject pemObject = new PemObject("PUBLIC KEY", publicKey.getEncoded());
StringWriter stringWriter = new StringWriter();
JcaPEMWriter pemWriter = new JcaPEMWriter(stringWriter);
pemWriter.writeObject(pemObject);
pemWriter.close();

// 将PEM格式的公钥保存到文件
FileWriter fileWriter = new FileWriter("public_key.pem");
fileWriter.write(stringWriter.toString());
fileWriter.close();

完整的SM2公钥生成并保存为PEM文件的示例代码如下：

import java.io.FileWriter;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;

import org.bouncycastle.asn1.x9.ECNamedCurveTable;
import org.bouncycastle.asn1.x9.X9ECParameters;
import org.bouncycastle.jcajce.provider.asymmetric.ec.BCECPrivateKey;
import org.bouncycastle.jcajce.provider.asymmetric.ec.BCECPublicKey;
import org.bouncycastle.jce.provider.BouncyCastleProvider;
import org.bouncycastle.openssl.jcajce.JcaPEMWriter;
import org.bouncycastle.util.io.pem.PemObject;

public class SM2KeyPairGenerator {

    public static void main(String[] args) throws Exception {
        // 添加Bouncy Castle作为安全提供程序
        Security.addProvider(new BouncyCastleProvider());

        // 生成SM2密钥对
        KeyPairGenerator generator = KeyPairGenerator.getInstance("EC", "BC");
        X9ECParameters ecParams = ECNamedCurveTable.getByName("sm2p256v1");
        generator.initialize(ecParams);
        KeyPair keyPair = generator.generateKeyPair();

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

        // 将公钥转换为PEM格式
        PemObject pemObject = new PemObject("PUBLIC KEY", publicKey.getEncoded());
        StringWriter stringWriter = new StringWriter();
        JcaPEMWriter pemWriter = new JcaPEMWriter(stringWriter);
        pemWriter.writeObject(pemObject);
        pemWriter.close();

        // 将PEM格式的公钥保存到文件
        FileWriter fileWriter = new FileWriter("public_key.pem");
        fileWriter.write(stringWriter.toString());
        fileWriter.close();
    }

}

注意，上述示例代码中使用了Bouncy Castle库中的类和方法。如果你的项目中没有引入Bouncy Castle库，需要先下载并添加到项目中。