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https://issues.apache.org/jira/browse/HADOOP-19951?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18105903#comment-18105903
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ASF GitHub Bot commented on HADOOP-19951:
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pan3793 commented on PR #8654:
URL: https://github.com/apache/hadoop/pull/8654#issuecomment-5342070350
Small observation in `RBFMetrics.getJson` (`RBFMetrics.java:1002`): null
fields are stored as `JSONObject.NULL`. With the old Jetty `JSON.toString`,
that rendered as the string `"null"` (Jetty falls back to `toString()` for
unknown POJOs). With Jackson it becomes `{"explicitNull":false}` (jettison
1.5.4's `Null` exposes a public `explicitNull` field), so null fields switch
from string to object in `getMountTable()` / `getNamenodes()` / `getRouters()`.
Probably fine in practice, but it's an observable JMX-output change for
those attributes. If `JSONObject.NULL` was only there for the jettison path,
plain `null` in `getJson` would keep the field as JSON `null`.
> Drop use of jetty-util-ajax and use jackson instead
> ---------------------------------------------------
>
> Key: HADOOP-19951
> URL: https://issues.apache.org/jira/browse/HADOOP-19951
> Project: Hadoop Common
> Issue Type: Task
> Reporter: PJ Fanning
> Priority: Major
> Labels: pull-request-available
>
> Hadoop uses jetty-util-ajax in a few modules to read and write JSON.
> This is a part of HADOOP-19912 that can be split out and it doesn't cause the
> same issues with worrying about jar compatibilities - it actually simplifies
> the build by removing a direct dependency.
> The aim here is to reduce the number of ways that Hadoop works with JSON and
> Jackson is more commonly used in Hadoop than jetty-util-ajax.
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