Support output_stream in declarative config of otlp_file/development

[robintra]

Fixes #8675.

The OTLP file exporter builders already accept an arbitrary OutputStream and the generated config model already carries output_stream, but the declarative configuration component providers never read it so only stdout was reachable without writing code. The support table in opentelemetry-configuration reports Java as not_implemented for this option, while C++ and PHP report supported.

This wires the option through for spans, metrics and logs:

• stdout sets System.out explicitly, rather than relying on the default installed by the static builder() factory. Matching is case-insensitive, like the sibling options parsed in the same create() call.
• A file URI is resolved through java.net.URI, so both file:///path and the authority-less file:/path are accepted, with any scheme casing. Missing parent directories are created, the file is opened with CREATE + APPEND and the stream is wrapped in a BufferedOutputStream. StreamJsonWriter flushes after every record so buffering does not delay output.
• Anything else fails with a ConfigurationException, distinguishing an unusable value from a file that could not be opened.

Two choices worth confirming:

• Append rather than truncate follows the "Streaming appending" section of the file exporter spec, which does not state it outright.
• Creating missing parent directories avoids taking the whole application down at startup when the directory is created by another process, but it is a behaviour the spec does not mention.

Tests are added to AbstractOtlpStdoutExporterTest so they run for all three signals: stdout, a plain file:// URI producing the expected JSON, the authority-less and upper case URI form, parent directory creation, an unrecognized value, and a path that cannot be opened.

DeclarativeConfigurationCreateTest.parseAndCreate_Examples needed one adjustment. The ExperimentalOtlpFile*_file.yaml snippets write to file:///var/log/*.jsonl, which is not writable in tests. The test already rewrites ca_file, key_file and cert_file to temp files for the same reason so output_stream is rewritten the same way.

Two limitations are left as-is, since addressing either would go beyond wiring up the option. I am happy to follow up if maintainers want them handled here:

• Pointing several signals at the same path opens one stream per signal and StreamJsonWriter does not synchronize so concurrent writes can interleave.
• The handle is held for the exporter's lifetime so external log rotation is not picked up.

Verification

./gradlew :exporters:logging-otlp:check and ./gradlew :sdk-extensions:declarative-config:check pass. jApiCmp reports no API change since the new class lives in an internal package so docs/apidiffs is unchanged.

Also verified end to end with a throwaway test that runs DeclarativeConfiguration.parseAndCreate on:

file_format: "1.0"
tracer_provider:
  processors:
    - simple:
        exporter:
          otlp_file/development:
            output_stream: file:///tmp/traces.jsonl

and confirms the span is written as one JSON line to the file with nothing on stdout.

[linux-foundation-easycla]

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• ✅ login: robintra / name: robintra (b3ab6ed)

[codecov]

Codecov Report

❌ Patch coverage is 96.42857% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 91.48%. Comparing base (bc956bc) to head (054525a).

Files with missing lines	Patch %	Lines
.../logging/otlp/internal/OutputStreamConfigUtil.java	96.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #8676      +/-   ##
============================================
+ Coverage     91.47%   91.48%   +0.01%     
- Complexity    10465    10471       +6     
============================================
  Files          1021     1022       +1     
  Lines         27694    27722      +28     
  Branches       3247     3251       +4     
============================================
+ Hits          25333    25362      +29     
+ Misses         1617     1615       -2     
- Partials        744      745       +1     

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Waiting on reviewers · refreshed 2026-07-31 19:39 UTC

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