Spring Boot load another file from app.properties - spring

Question

I am new to Spring Boot. I have this emailprop.properties in src/main/resource:
//your private key
mail.smtp.dkim.privatekey=classpath:/emailproperties/private.key.der
But I am getting the error as
classpath:\email properties\private.key.der (The filename, directory
name, or volume label syntax is incorrect)
How do I properly load this file?
Update-1
my java code is
dkimSigner = new DKIMSigner(emailProps.getProperty("mail.smtp.dkim.signingdomain"), emailProps.getProperty("mail.smtp.dkim.selector"),
emailProps.getProperty("mail.smtp.dkim.privatekey"));
its working as "D:\\WorkShop\\MyDemoProj\\EmailService\\src\\main\\resources\\private.key.der"Instead of emailProps.getProperty("mail.smtp.dkim.privatekey")
Update-2
i have tried java code is
String data = "";
ClassPathResource cpr = new ClassPathResource("private.key.der");
try {
byte[] bdata = FileCopyUtils.copyToByteArray(cpr.getInputStream());
data = new String(bdata, StandardCharsets.UTF_8);
} catch (IOException e) {
e.printStackTrace();
}
dkimSigner = new DKIMSigner(emailProps.getProperty("mail.smtp.dkim.signingdomain"), emailProps.getProperty("mail.smtp.dkim.selector"),data);
Error is : java.io.FileNotFoundException: class path resource [classpath:private.key.der] cannot be resolved to URL because it does not exist
Tried Code is :
ClassPathResource resource = new ClassPathResource(emailProps.getProperty("mail.smtp.dkim.privatekey"));
File file = resource.getFile();
String absolutePath = file.getAbsolutePath();
Still same error..
please update the answer..

Answer 1

If you want to load this file runtime then you need to use ResourceLoader please have a look here for the documentation - section 8.4.
Resource resource = resourceLoader.getResource("classpath:/emailproperties/private.key.der");
Now if you want to keep this exact path in properties file you can keep it there and then load it in your Autowired constructor/field like that:
#Value("${mail.smtp.dkim.privatekey}") String pathToPrivateKey
and then pass this to the resource loader.
Full example you can find here. I don't want to copy paste it.

Answer 2

If your file is located here:
"D:\\WorkShop\\MyDemoProj\\EmailService\\src\\main\\resources\\private.key.der"
then it should be:
mail.smtp.dkim.privatekey=classpath:private.key.der
EDIT:
I see now, you are using DKIMSigner, which expects file-path string,
Try changing your code like this:
ClassPathResource resource = new ClassPathResource(emailProps.getProperty("mail.smtp.dkim.privatekey"));
File file = resource.getFile();
String absolutePath = file.getAbsolutePath();
dkimSigner = new DKIMSigner(emailProps.getProperty("mail.smtp.dkim.signingdomain"), emailProps.getProperty("mail.smtp.dkim.selector"),absolutePath
);