4.x: Static content from classpath improvements

[tomas-langer]

Currently we generate temporary files for extracted jar entries as ws-****.je

A few improvements could be done:

• use helidon- (or helidon-ws) prefix to clearly bind them to Helidon
• add configuration option to cache in-memory only (probably to a certain size), to avoid creating the files altogether

[hrstoyanov]

Is it possible to process the files as they are extracted from the class path? For example, CSS files may have comments, that I might not want to serve to the client , and would like to strip off.

[tomas-langer]

Is it possible to process the files as they are extracted from the class path? For example, CSS files may have comments, that I might not want to serve to the client , and would like to strip off.

I think this should be done at build time and your deployment should contain the files you want to serve (minified css, javascript etc.).

Also Helidon does not have such a feature, as we need to work with the content length of the file (i.e. when a range is requested, to correctly provide Content-Length header etc.). Such operations would introduce quite an overhead (I can imagine this being implemented, but I would rather not)

[tomas-langer]

The PR will have the following updates:

• support for configuration based setup of static content (currently only possible through API)
• introduces static content server feature to do so (can be used programmaticaly and through config)
• introduces more configurable temporary storage (enabled, location, prefix, suffix), shared by all handlers, with possibility to customize per handler
• introduces more configurable memory storage (enabled, maximal size in bytes), shared by all handlers, with possibility to customize per handler
• when using classpath, if cached in memory, no temporary file gets created
• when using classpath, when using temporary files, we have a shutdown hook to delete them
• when using classpath, when temporary storage is disabled, files are served directly from jar input stream

Example of a configuration:

server:
  features:
    # the new static content feature, automatically discovered
    static-content:
      # (optional) configuration of temporary storage
      temporary-storage:
        directory: "./target/helidon/tmp"
        file-prefix: "helidon-custom"
        file-suffix: ".cache"
        # delete-on-exit: false
      # classpath handlers (context to serve on webserver and location on classpath)
      classpath:
        - context: "/classpath"
          location: "web"
        - context: "/singleclasspath"
          location: "web/resource.txt"
      # file system handlers (context to serve on webserver and location on file system)
      path:
        - context: "/path"
          location: "./src/test/resources/web"
        - context: "/singlepath"
          location: "./src/test/resources/web/resource.txt"