This documentation is for an old GraalVM version. See the latest version.

URL Protocols in Native Image

URL Protocols in Native Image can be divided into three classes:

  • supported and enabled by default
  • supported and disabled by default
  • HTTPS support

Supported and Enabled by Default #

These are protocols that are enabled by default and added to every generated native image. Currently, file and resource are the only supported URL protocols, enabled by default.

Supported and Disabled by Default #

These are protocols that are supported but not enabled by default when building a native image. They must be enabled during the native image building by adding --enable-url-protocols=<protocols> to the native-image command. The option accepts a list of comma-separated protocols.

The rationale behind enabling protocols on-demand is that you can start with a minimal image and add features as you need them. This way your image will only include the features you use, which helps keep the overall size small. Currently http and https are the only URL protocols that are supported and can be enabled on demand. They can be enabled using the --enable-http and --enable-https options.

HTTPS Support #

Support for the https URL protocol relies on the Java Cryptography Architecture (JCA) framework. Thus enabling https will add to the generated image the code required by the JCA, including statically linking native libraries that the JCA may depend on. See the documentation on security services for more details.

Not Tested #

No other URL protocols are currently tested. They can still be enabled using --enable-url-protocols=<protocols>, however they might not work as expected.

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