andygrove opened a new pull request, #32:
URL: https://github.com/apache/datafusion-java/pull/32
## Which issue does this PR close?
- Closes #.
## Rationale for this change
The repository lacks runnable end-to-end examples. Code snippets in the docs
are easy to drift out of sync with the API: there is no build step that fails
when a public method is renamed or removed.
Adding an `examples/` Maven module that depends on the library lets the
reactor compile every example on each build, so they cannot fall behind the
API. Doing this requires the repo to be a multi-module Maven project; while
we're there, the parent POM gets shared `dependencyManagement` and plugin
versions so child modules stay terse.
## What changes are included in this PR?
**Multi-module restructure:**
- Root `pom.xml` becomes the parent (`datafusion-java-parent`,
`packaging=pom`) with `dependencyManagement` for arrow, protobuf, junit, and
the library itself.
- `core/` is a new directory holding the existing library
(`datafusion-java`). `src/` moves to `core/src/`.
- `examples/` is a new module (`datafusion-java-examples`) depending on the
library via `${project.version}`. It wires `exec-maven-plugin` so each example
launches with the right `java.library.path` and `--add-opens` flags.
- `native/`, `proto/`, `Makefile`, and `mvnw` stay at the repo root
unchanged.
- Surefire's `java.library.path` now uses
`${maven.multiModuleProjectDirectory}` so it resolves under the reactor
regardless of which module Maven is invoked from.
- `apache-rat-plugin` runs only at the root
(`<inherited>false</inherited>`); the rat exclude list is unchanged.
**Three runnable examples** under
`examples/src/main/java/org/apache/datafusion/examples/`:
- `SqlQueryExample` — `registerCsv` + a SQL `GROUP BY` aggregation.
- `DataFrameExample` — `readCsv` → `filter` / `select` / `withColumnRenamed`
/ `distinct` → `writeParquet(singleFileOutput)` → `readParquet` round-trip.
- `ProtoPlanExample` — build a `LogicalPlanNode` directly via the generated
protobuf classes and execute it through `SessionContext.fromProto`.
Each example creates its own throwaway data in a temp dir and cleans up, so
no external fixtures (TPC-H, etc.) are required.
**Docs:** `docs/source/contributor-guide/development.md` is updated with the
new repo layout and a "Running an example" section that documents the `./mvnw
install -DskipTests` + `exec:exec` flow.
## Are these changes tested?
- The full JVM test suite (`./mvnw test`) still passes against the relocated
`core/src/test/` sources — 61 tests run, 0 failures (12 skipped, same skip
pattern as `main` when TPC-H data is absent).
- Each example was executed end-to-end via `./mvnw -pl
:datafusion-java-examples exec:exec` and produces expected output:
- `SqlQueryExample` prints `HIGH 3 215 / MEDIUM 1 60 / LOW 1 25`.
- `DataFrameExample` prints a 3-row deduped table and `Round-tripped row
count: 3`.
- `ProtoPlanExample` prints `42 7`.
- `spotless:check` and the reactor build are clean across all three modules.
## Are there any user-facing changes?
- The published library artifact (`org.apache.datafusion:datafusion-java`)
is unchanged — same `groupId`, `artifactId`, `version`, and package contents.
- The repo layout changes: source paths move from `src/main/java/...` to
`core/src/main/java/...`. IDE projects pointing at the old location need to
re-import.
- New `datafusion-java-examples` artifact exists but is marked
`maven.install.skip=true` / `maven.deploy.skip=true` and is not intended for
distribution.
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