如何将PEM格式字符串私钥转换为Java的PrivateKey类型？

我有一个2048位的PEM格式私钥字符串，需要传给getSignedText函数（接收PrivateKey类型参数）来签名数据，但尝试了多种转换方法都失败，问题已经困扰我一个月，求解决。

私钥内容： #

-----BEGIN PRIVATE KEY-----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-----END PRIVATE KEY-----

签名函数代码： #

public static String getSignedText(
        String text, String algorithm, PrivateKey privateKey) 
          throws UnsupportedEncodingException, NoSuchAlgorithmException, InvalidKeyException, SignatureException { 
      byte[] data = text.getBytes("UTF8"); 
      Signature sig = Signature.getInstance(algorithm == null ? "SHA256WITHRSA" : algorithm); 
      sig.initSign(privateKey); 
      sig.update(data); 
      byte[] signatureBytes = sig.sign(); 
      return Base64.getEncoder().encodeToString(signatureBytes); 
}

你的私钥是PKCS#8格式的PEM（从BEGIN PRIVATE KEY标识可判断），Java标准库可直接解析，无需额外依赖。以下是完整的转换实现：

转换工具代码 #

import java.security.KeyFactory;
import java.security.PrivateKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.util.Base64;

public class PrivateKeyConverter {
    public static PrivateKey convertPemToPrivateKey(String pemPrivateKey) throws Exception {
        // 清理PEM格式：移除头部、尾部及所有空白字符
        String cleanPem = pemPrivateKey
                .replace("-----BEGIN PRIVATE KEY-----", "")
                .replace("-----END PRIVATE KEY-----", "")
                .replaceAll("\\s+", "");
        
        // Base64解码得到密钥字节数组
        byte[] keyBytes = Base64.getDecoder().decode(cleanPem);
        
        // 通过PKCS8规范生成PrivateKey实例
        PKCS8EncodedKeySpec spec = new PKCS8EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance("RSA");
        return keyFactory.generatePrivate(spec);
    }
}

使用示例 #

public class Main {
    public static void main(String[] args) {
        String pemKey = "你的PEM私钥字符串";
        try {
            PrivateKey privateKey = PrivateKeyConverter.convertPemToPrivateKey(pemKey);
            String signedText = getSignedText("需要签名的内容", null, privateKey);
            System.out.println("签名结果：" + signedText);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

注意事项 #

• 确保使用Java 8及以上版本（自带Base64类），若为Java 7及以下，可替换为javax.xml.bind.DatatypeConverter.parseBase64Binary()或Apache Commons Codec的Base64工具类。
• 若转换时抛出InvalidKeySpecException，检查私钥字符串是否完整，无多余或缺失字符。
• 你的签名函数默认使用SHA256WITHRSA算法，与RSA私钥完全兼容，无需修改。

内容的提问来源于stack exchange，提问作者nima tehrani