apache/beam

[Feature Request]: Add a native Logging transform to Java SDK

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#38528 opened on May 18, 2026

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 (3 comments) (0 reactions) (1 assignee)Java (7,313 stars) (4,097 forks)batch import
P2good first issuejavanew feature

Description

What would you like to happen?

AFAIK the Java SDK doesn't have an easy utility to print/log the outputs of a PCollection. I've always had to hack something together like:

    rows.apply(MapElements.into(strings()).via(row -> {
      System.out.println("row: " + row);
      return "";
    }));

Would be nice to have an easy utility that can be used like:

    rows.apply(Log.info());

The Python SDK has something like this: https://github.com/apache/beam/blob/26c6ec7cb749d60455c9895aa1be49d5cf552a75/sdks/python/apache_beam/transforms/util.py#L2183-L2197

Issue Priority

Priority: 2 (default / most feature requests should be filed as P2)

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Contributor guide

Tech stack
java
Domain
backendobservability
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
JavaApache Beam basicsBeam PTransform understanding
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60
Research direction
Examine the Python SDK's Log transform implementation at https://github.com/apache/beam/blob/26c6ec7cb749d60455c9895aa1be49d5cf552a75/sdks/python/apache beam/transforms/util.py#L2183 L2197. Identify the appropriate location for a Java equivalent, likely in sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/. Review existing PTransform patterns like MapElements. Implement a Log class with static methods like Log.info(). Ensure it uses the standard logging framework (SLF4J). Add unit tests.