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Escape both reserved characters and curly braces in a URI in Spring Boot

I need to pass URI's that contain special characters, using Spring Boot.  

The characters include spaces, curly braces (`{` and `}`), square braces (`[` and `]`).  

The problem is that Spring Boot wants to expand strings between curly braces.  

I've tried to escape the special characters using `UriComponentsBuilder`:

        val uri = UriComponentsBuilder
            .fromUriString("https://example.com/something")
            .path("/my-path")
            .queryParam("param", "{FOO[bar #3]}")
            .build()
            .toUri()

When I use the above code, the value of `uri` is `https://example.com/something/my-path?param=%7BFOO[bar%20%233]%7D`. It has escaped the curly braces, the space, and the hash sign... but not the square brackets. This is despite the fact that square brackets and hash signs are both reserved characters according to [RFC 3986](https://www.rfc-editor.org/rfc/rfc3986#page-12). They both count as `gen-delims`, which makes it strange that one is escaped and the other is not.

I can add a call to `encode()`, but then the curly braces give trouble:

        val uri = UriComponentsBuilder
            .fromUriString("https://example.com/something")
            .path("/my-path")
            .queryParam("param", "{FOO[bar #3]}")
            .encode()
            .build()
            .toUri()

This results in an error:

> java.lang.IllegalStateException: Could not create URI object: Illegal character in query at index 44: https://example.com/something/my-path?param={FOO[bar #3]}

(Leaving the curly braces out results in the URI having the value `https://example.com/something/my-path?param=FOO%5Bbar%20%233%5D` . It seems the UriComponestBuilder chokes on the curly brace and won't go on after that).

I have also tried using `DefaultUriBuilderFactory`:

        val factory = DefaultUriBuilderFactory("https://example.com/something")
        factory.encodingMode = DefaultUriBuilderFactory.EncodingMode.TEMPLATE_AND_VALUES
        val uri = factory
            .builder()
            .path("/my-path")
            .queryParam("param", "{FOO[bar #3]}")
            .build()

This results in the error message: 
> java.lang.IllegalArgumentException: Not enough variable values available to expand 'FOO[bar #3]'  
It gives the same error for the other EncodingModes (`URI_COMPONENT`, `VALUES_ONLY`, and `NONE`).

I could of course just use `String.replace` to replace all special characters, but that seems a very crude solution.  

Is there a way to tell Spring Boot to escape _all_ reserved characters, and escape the curly braces as well? And to tell Spring Boot to NOT expand what is between the curly braces?