Add getStructured default method, add empty StructuredConfigProperties

[jack-berg]

Add StructuredConfigProperties.getStructured(String, StructuredConfigProperties) method to assist with walking trees without null checking. Originated from this conversation.

[codecov]

Codecov Report

Attention: Patch coverage is 92.85714% with 1 line in your changes missing coverage. Please review.

Project coverage is 90.02%. Comparing base (361f035) to head (6d4891a).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
.../spi/internal/EmptyStructuredConfigProperties.java	90.90%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #6759   +/-   ##
=========================================
  Coverage     90.02%   90.02%           
- Complexity     6475     6488   +13     
=========================================
  Files           718      719    +1     
  Lines         19573    19587   +14     
  Branches       1931     1931           
=========================================
+ Hits          17621    17634   +13     
- Misses         1353     1354    +1     
  Partials        599      599           

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[trask]

can you give an example of how you see this method being used?

[jack-berg]

There's a demonstration here in the unit test:

    // Validate common pattern of walking down tree path which is not defined
    // Access string at .foo.bar.baz without null checking and without exception.
    assertThat(
            structuredConfigProps
                .getStructured("foo", empty())
                .getStructured("bar", empty())
                .getString("baz"))
        .isNull();

I give the same example in the javadoc for the new empty() method, but should probably copy it here as well.

[trask]

Sorry, I meant specifically the list method, it's not clear to me if that variant is needed

[jack-berg]

Ah sorry for misunderstanding.

At that point, it was just for completeness. Every other accessor has a "get or default" variant, and so it feels out of place for this one omission. Its true that it doesn't have utility for tree walking, but that doesn't mean it doesn't have utility at all. For example, this code for interpreting OTLP headers could be simplified to:

config.getStructuredList("headers", List.of()).forEach(header -> {
    String name = header.getString("name");
    String value = header.getString("value");
    if (name != null && value != null) {
      addHeader.accept(name, value);
    }
});

[trask]

Every other accessor has a "get or default" variant

good point, I hadn't thought about the existing methods already having the default variant