*.cer文件通常仅包含证书，而不包含对APK进行签名所需的私钥.

*.cer files usually only contain certificates, not the private key needed to sign an APK.

列出密钥库的内容:

keytool -list -v -keystore my_keystore.keystore

，然后查找Entry type:行(用于相应的别名).该值必须是PrivateKeyEntry，而不是trustedCertEntry

And look for the Entry type: line (for the corresponding alias). The value must be PrivateKeyEntry, not trustedCertEntry