[DO NOT MERGE] Prototype JSON representation for attribute collections

[pellared]

Prototypes open-telemetry/opentelemetry-specification#5149 in Java.

This complements the existing Go prototypes:

• [DO NOT MERGE] attribute: add String method for KeyValue opentelemetry-go#8205
• attribute: add Set.String opentelemetry-go#8347

What this prototypes

• Override the built-in Attributes implementation's toString() to encode the collection as a compact JSON object.
• Reuse the existing internal JSON encoder behind Value.asString(), including its handling of nested arrays/maps, bytes, empty values, non-finite doubles, and JSON escaping.
• Exercise the representation through existing diagnostic consumers, notably LoggingSpanExporter and SystemOutLogRecordExporter.

For example, diagnostic output changes from:

{animal="cat", bytes=ValueBytes{AQID}, empty=ValueEmpty{}}

to:

{"animal":"cat","bytes":"AQID","empty":null}

Scope and merge status

This is intentionally a draft and marked DO NOT MERGE while the specification change is pending.

No public API or dependency is added. The repository documents toString() output as unstable. The logging/stdout exporter formats also remain diagnostic and unspecified; their updated tests demonstrate that the proposed common representation works in real exporters, not that the surrounding exporter format is now guaranteed.

This PR prototypes the Attribute Collection representation section. Java does not expose a standalone Attribute pair type, so this does not add public API solely to prototype the single-attribute section.

AI assistance

This prototype was prepared with (a huge) assistance from OpenAI Codex. 😉

[opentelemetry-pr-dashboard]

Pull request dashboard status

Waiting on the author · refreshed 2026-09-02 21:38 UTC

Move out of draft to request review.

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[codecov]

Codecov Report

❌ Patch coverage is 92.85714% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 91.30%. Comparing base (e2efec5) to head (4e14bc0).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...pentelemetry/api/common/ArrayBackedAttributes.java	75.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #8768      +/-   ##
============================================
+ Coverage     91.29%   91.30%   +0.01%     
- Complexity    10498    10502       +4     
============================================
  Files          1006     1006              
  Lines         28338    28351      +13     
  Branches       3581     3583       +2     
============================================
+ Hits          25870    25885      +15     
+ Misses         1675     1672       -3     
- Partials        793      794       +1     

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[jack-berg]

The tension here is that the current format is the idiomatic toString() implementation in java.

Its meant for debugging, not machine readability. Actually, not being reliably machine readable is strength here since it reduces the likelihood of someone depending on the structure of toString and crying "breaking change!" when we change it.