HDDS-15808. Replace json-simple with Jackson in httpfsgateway

[smengcl]

Generated-by: Claude Code (Opus 4.8)

What changes were proposed in this pull request?

The hadoop-ozone/httpfsgateway module was the only remaining consumer of com.googlecode.json-simple:json-simple (1.1.1), a library that has been unmaintained since 2012. Jackson (jackson-databind) is already a compile dependency of the module, so json-simple was redundant and carried needless maintenance and supply chain risk.

This PR migrates all JSON serialization in httpfsgateway from json-simple to Jackson, then removes the dependency:

• JSONMapProvider now serializes the response Map with a shared ObjectMapper. AUTO_CLOSE_TARGET is disabled so the underlying response stream stays open for the trailing newline and container managed close, matching the previous behavior.
• JSONProvider, whose only purpose was serializing json-simple JSONStreamAware entities, is removed. JAX-RS providers are registered by Jersey package scanning via jersey.config.server.provider.packages, so deleting the class is sufficient to unregister it.
• In InstrumentationService, the Timer, VariableHolder, and Sampler snapshot types no longer implement JSONAware/JSONStreamAware. Their getJSON() methods return a LinkedHashMap annotated with @JsonValue, so Jackson serializes each object as that map and produces the same JSON.
• FSOperations and HttpFSServer use Map/List (LinkedHashMap/ArrayList) in place of JSONObject/JSONArray, and reuse the module local JsonUtil.toJsonString helper.
• The dependency is removed from the module pom, and the version property plus the dependencyManagement entry are removed from the root pom. The com.googlecode.json-simple:json-simple entries in the distribution bin/LICENSE.txt and the generated jar-report.txt inventory are removed accordingly. The module also declares jackson-core and jackson-annotations explicitly, since the code now references JsonGenerator and @JsonValue directly rather than only transitively through jackson-databind.

The wire format is preserved. Both libraries emit standard JSON, AtomicLong serializes as a bare number in both, and switching from HashMap to LinkedHashMap only makes key order deterministic, which WebHDFS clients (which parse by key) are unaffected by. The replaceAll("\\\\", "") call in FSCreateSnapshot, originally there to undo json-simple's forward slash escaping (\/), is removed. Jackson does not escape slashes, and stripping all backslashes could corrupt legitimately escaped values.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-15808

How was this patch tested?

Two focused unit tests were added to the module (which previously had almost no coverage for these paths):

• TestInstrumentationSerialization verifies the @JsonValue serialization of Timer, VariableHolder, and Sampler produces the expected JSON keys and values.
• TestJSONMapProvider verifies the provider emits compact JSON followed by a trailing newline and does not close the underlying stream.

Verified locally: the module compiles, all module unit tests pass (2 existing + 5 new), checkstyle.sh is clean, and rat.sh reports 0 unknown licenses.

[Copilot]

Pull request overview

This PR migrates the hadoop-ozone/httpfsgateway module off the unmaintained json-simple library by switching JSON serialization to Jackson (already present as a dependency), and then removing json-simple from the build and distribution inventories.

Changes:

• Replaced json-simple-based JAX-RS JSON serialization with Jackson in providers and response-building code paths.
• Updated httpfsgateway JSON-producing server operations to build Map/List structures instead of JSONObject/JSONArray.
• Added focused unit tests for the new Jackson serialization behavior and removed json-simple from module and distro license inventories.

Reviewed changes

Copilot reviewed 8 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
hadoop-ozone/httpfsgateway/src/test/java/org/apache/ozone/lib/wsrs/TestJSONMapProvider.java	Adds tests validating JSON framing (newline) and stream-close behavior for JSONMapProvider.
hadoop-ozone/httpfsgateway/src/test/java/org/apache/ozone/lib/service/instrumentation/TestInstrumentationSerialization.java	Adds tests validating @JsonValue-driven Jackson serialization shape for instrumentation snapshots.
hadoop-ozone/httpfsgateway/src/main/java/org/apache/ozone/lib/wsrs/JSONProvider.java	Removes the json-simple JSONStreamAware writer provider.
hadoop-ozone/httpfsgateway/src/main/java/org/apache/ozone/lib/wsrs/JSONMapProvider.java	Switches map serialization from json-simple to Jackson with stream-close behavior preserved.
hadoop-ozone/httpfsgateway/src/main/java/org/apache/ozone/lib/service/instrumentation/InstrumentationService.java	Removes json-simple interfaces and uses @JsonValue to serialize snapshot types as maps.
hadoop-ozone/httpfsgateway/src/main/java/org/apache/ozone/fs/http/server/HttpFSServer.java	Updates endpoints to return Map-backed JSON payloads instead of JSONObject.
hadoop-ozone/httpfsgateway/src/main/java/org/apache/ozone/fs/http/server/FSOperations.java	Replaces JSONObject/JSONArray construction with Map/List and uses JsonUtil for serialization.
hadoop-ozone/httpfsgateway/pom.xml	Removes the json-simple dependency from the httpfsgateway module.
hadoop-ozone/dist/src/main/license/jar-report.txt	Removes json-simple.jar from the distribution jar inventory.
hadoop-ozone/dist/src/main/license/bin/LICENSE.txt	Removes com.googlecode.json-simple:json-simple from the distribution LICENSE inventory.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

Pull request overview

Copilot reviewed 8 out of 10 changed files in this pull request and generated 3 comments.

[adoroszlai]

Thanks @smengcl for the patch. There are some PMD failures:

PMD Failure: org.apache.ozone.lib.service.instrumentation.Timer:251 Rule:UnusedPrivateMethod Priority:3 Avoid unused private methods such as 'getJSON()'..
PMD Failure: org.apache.ozone.lib.service.instrumentation.VariableHolder:298 Rule:UnusedPrivateMethod Priority:3 Avoid unused private methods such as 'getJSON()'..
PMD Failure: org.apache.ozone.lib.service.instrumentation.Sampler:342 Rule:UnusedPrivateMethod Priority:3 Avoid unused private methods such as 'getJSON()'..

Oh, I see already fixed.

[Copilot]

Pull request overview

Copilot reviewed 8 out of 10 changed files in this pull request and generated 4 comments.

[Copilot]

Pull request overview

Copilot reviewed 8 out of 10 changed files in this pull request and generated 2 comments.

Comments suppressed due to low confidence (1)

hadoop-ozone/httpfsgateway/pom.xml:52

• The PR description says the json-simple version property and dependencyManagement entry were removed from the root pom.xml, but they are still present (eg pom.xml:121 and pom.xml:459-463). If json-simple is truly no longer used anywhere, please remove those root-pom entries as well (or update the PR description/dist license inventory accordingly) so the dependency is fully eliminated.

    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-databind</artifactId>
    </dependency>
    <dependency>
      <groupId>jakarta.ws.rs</groupId>
      <artifactId>jakarta.ws.rs-api</artifactId>
    </dependency>

[Copilot]

Pull request overview

Copilot reviewed 8 out of 10 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (1)

hadoop-ozone/httpfsgateway/pom.xml:52

• The module dependency on json-simple is removed here, but the repository root pom.xml still defines <json-simple.version> and a dependencyManagement entry for com.googlecode.json-simple:json-simple (eg pom.xml:121 and pom.xml:459-463). This contradicts the PR description’s claim that the root pom cleanup is included, and it leaves stale dependency metadata behind. Please remove those root pom entries (and any other remaining references) to complete the migration/removal.

    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-databind</artifactId>
    </dependency>
    <dependency>
      <groupId>jakarta.ws.rs</groupId>
      <artifactId>jakarta.ws.rs-api</artifactId>
    </dependency>

[Copilot]

Pull request overview

Copilot reviewed 9 out of 11 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 9 out of 11 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 9 out of 11 changed files in this pull request and generated no new comments.

[adoroszlai]

Thanks @smengcl for the patch.

[smengcl]

Thanks @adoroszlai for the review and merging this.