[jira] [Assigned] (HDDS-15808) Replace json-simple with Jackson in httpfsgateway

["Siyao Meng (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HDDS-15808?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Siyao Meng reassigned HDDS-15808:
---------------------------------

    Assignee: Siyao Meng

> Replace json-simple with Jackson in httpfsgateway
> -------------------------------------------------
>
>                 Key: HDDS-15808
>                 URL: https://issues.apache.org/jira/browse/HDDS-15808
>             Project: Apache Ozone
>          Issue Type: Improvement
>          Components: HttpFS GateWay
>            Reporter: Siyao Meng
>            Assignee: Siyao Meng
>            Priority: Major
>              Labels: pull-request-available
>
> h3. Problem
> The {{hadoop-ozone/httpfsgateway}} module is the only remaining consumer of {{com.googlecode.json-simple:json-simple}} (1.1.1), a library unmaintained since 2012. Jackson ({{jackson-databind}}) is already a compile dependency of the module, so json-simple is redundant.
> h3. Approach
> Migrate all JSON serialization in httpfsgateway from json-simple to Jackson, then drop the dependency:
> * {{JSONMapProvider}} 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.
> * {{JSONProvider}} (which only served to serialize json-simple {{JSONStreamAware}} entities) is removed. Providers are registered by Jersey package scanning via {{jersey.config.server.provider.packages}}, so deleting the class unregisters 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 dependencyManagement entry are removed from the root pom. The json-simple entries in the distribution {{bin/LICENSE.txt}} and the generated {{jar-report.txt}} inventory are removed accordingly.
> h3. Compatibility
> 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 parsing by key are unaffected by. The {{replaceAll}} call in {{FSCreateSnapshot}}, originally undoing json-simple forward slash escaping, becomes a harmless no-op since Jackson does not escape slashes.
> h3. Testing
> Added two focused unit tests in the module:
> * {{TestInstrumentationSerialization}} verifies the {{@JsonValue}} serialization of {{Timer}}, {{VariableHolder}}, and {{Sampler}}.
> * {{TestJSONMapProvider}} verifies the provider emits compact JSON followed by a trailing newline and does not close the underlying stream.
> Module build, checkstyle, and rat pass; all module unit tests pass.



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