Add ExtensionList#lookupFirst convenience method #3021

daniel-beck · 2017-09-12T00:43:39Z

I find myself typing ExtensionList.lookup(Whatever.class).get(Whatever.class) a lot to get the singleton instance for a registered @Extension.

If I'm not the only one (and haven't missed something obvious), maybe this is useful? @jenkinsci/code-reviewers More to tell me there's an obvious alternative I've missed.

oleg-nenashev

Yes, it is something we really need. Probably makes sense to refactor bits within the core.

A more strict method would be also useful:

public static @CheckForNull <U,T> T lookup(Class<U> extensionType, Class<T> implementationType) {
        return lookup(extensionType).get(implementationType);
 }

oleg-nenashev · 2017-09-14T12:13:23Z

core/src/main/java/hudson/ExtensionList.java

+     *
+     * @param type The type to look up.
+     * @param <U>
+     * @return


Empty param/return should be removed or documented

daniel-beck · 2017-09-14T12:20:15Z

more strict method

But what would you even gain from that? This one simplifies things by getting rid of redundancy. Your proposal saves ~4 characters?

oleg-nenashev · 2017-09-14T17:13:44Z

But what would you even gain from that? This one simplifies things by getting rid of redundancy. Your proposal saves ~4 characters?

It also avoids the "YOLO" mode of lookupFirst (). But probably you could just remove "first" from the method name, because the call guarantees to have only one result IIUC

daniel-beck · 2017-09-14T17:14:46Z

because the call guarantees to have only one result IIUC

No, as I may pass e.g. Builder.class.

oleg-nenashev · 2017-09-15T16:38:59Z

Builder... Uh oh, it should not be stored in the extension implementation list imho. But if it is true now, then the current method naming is correct of course

oleg-nenashev

Javadoc still needs to be fixed

daniel-beck · 2017-09-15T17:14:20Z

@oleg-nenashev

it should not be stored in the extension implementation list imho

Good point, then whatever the Descriptor type for that is, if any. The point is, the list can be any @Extension type, including super types, from a single implementation to e.g. Descriptor. To get a singleton instance, you may lookup(Super).get(Specific) or just lookup(Specific).get(Specific).

Notably, lookup(Super).get(Super) already works and just gets whatever entry first fits.

daniel-beck · 2017-09-28T12:55:44Z

@oleg-nenashev Done

daniel-beck · 2017-09-28T12:58:50Z

This is the kind of change where I expect @jglick to tell me it's stupid and redundant due to something I didn't know about, so asking him for review.

amuniz

👍

jglick

Needs some sample calls, for example of Uptime from AbstractProject._poll.

jglick · 2017-09-29T19:04:07Z

core/src/main/java/hudson/ExtensionList.java

+     *
+     * @since TODO
+     */
+    public static @CheckForNull <U> U lookupFirst(Class<U> type) {


@CheckForNull here more or less defeats the real need for this, which is for cases where you expect that there must be one instance. I would rather say something like

ExtensionList<U> all = lookup(type); if (all.size() != 1) throw new IllegalStateException(…); return all.get(0);

And name it something like lookUpSingleton.

See for example GlobalConfigurationCategory.get, Jenkins.doConfigExecutorsSubmit call to MasterBuildConfiguration, JenkinsLocationConfiguration.get, UserDetailsCache.get, ad nauseam. Basically just Find Usages on ExtensionList.get(Class). If you know that the singleton has been registered, then you expect to be able to load it without null checks. Maybe existing calls in fact just assume that the result is not null, meaning FindBugs would complain if we actually let it.

oleg-nenashev · 2017-10-03T05:54:02Z

core/src/main/java/hudson/ExtensionList.java

+    public static @Nonnull <U> U lookupSingleton(Class<U> type) {
+        ExtensionList<U> all = lookup(type);
+        if (all.size() != 1) {
+            throw new IllegalStateException("Expected 1 instance of " + type.getName() + " but got " + all.size());


Needs to be Javadoced. throws would be also useful.
In the case of this method, I agree that RuntimeException is a right approach.

Javadoced 😄 Love English language.

@oleg-nenashev It's mentioned in https://github.com/jenkinsci/jenkins/pull/3021/files#diff-e3f986a0854b9b724f4e12690cdeeac3R423 and I see no point in adding it to the signature. It's a runtime exception after all.

Still a good practice; helpful for Javadoc viewers.

/** * … * @throws IllegalStateException if there are no instances, or more than one */

oleg-nenashev · 2017-10-03T09:42:33Z

I see no point in adding it to the signature. It's a runtime exception after all.

@daniel-beck The only point of it is to have just another place where the API users are warned about that in IDE. Nothing else

oleg-nenashev

OK though @throws tag in Javadoc exits for a reason. 🐝

jglick · 2017-10-18T21:51:35Z

core/src/main/java/hudson/ExtensionList.java

+    public static @Nonnull <U> U lookupSingleton(Class<U> type) {
+        ExtensionList<U> all = lookup(type);
+        if (all.size() != 1) {
+            throw new IllegalStateException("Expected 1 instance of " + type.getName() + " but got " + all.size());


Still a good practice; helpful for Javadoc viewers.

/** * … * @throws IllegalStateException if there are no instances, or more than one */

jglick · 2017-10-18T21:52:48Z

core/src/main/java/jenkins/model/Jenkins.java

-            if (mbc!=null)
-                mbc.configure(req,json);
+            MasterBuildConfiguration mbc = ExtensionList.lookupSingleton(MasterBuildConfiguration.class);
+            mbc.configure(req,json);


or even inline var

daniel-beck · 2017-10-19T08:41:22Z

Addressed @jglick's review comments (including one identical to one by @oleg-nenashev ), so I think this is ready to go into the next weekly.

oleg-nenashev

🐝 Ready to go.

oleg-nenashev · 2017-10-27T08:31:38Z

retriggering CI

oleg-nenashev · 2017-10-27T14:55:31Z

@daniel-beck Sorry, I've forgotten to reopen it :( Was in my TODO list for the next weekly anyway

oleg-nenashev · 2017-10-27T15:54:30Z

CI hates us :(

oleg-nenashev · 2017-10-28T10:58:45Z

🚢 🇮🇹

Add ExtensionList#lookupFirst convenience method

46b62c6

daniel-beck force-pushed the ExtensionList.lookupFirst branch from bc2b525 to 46b62c6 Compare September 13, 2017 08:59

oleg-nenashev reviewed Sep 14, 2017

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oleg-nenashev added the needs-comments-resolved Comments in the PR need to be addressed before it can be considered for merging label Sep 18, 2017

Fix Javadoc

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daniel-beck removed the needs-comments-resolved Comments in the PR need to be addressed before it can be considered for merging label Sep 28, 2017

daniel-beck added the needs-more-reviews Complex change, which would benefit from more eyes label Sep 28, 2017

daniel-beck requested a review from jglick September 28, 2017 12:58

amuniz approved these changes Sep 29, 2017

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daniel-beck added the work-in-progress The PR is under active development, not ready to the final review label Sep 30, 2017

daniel-beck self-assigned this Sep 30, 2017

Convert to lookupSingleton, which throws unless there's only 1

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daniel-beck removed the work-in-progress The PR is under active development, not ready to the final review label Oct 2, 2017

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oleg-nenashev mentioned this pull request Oct 12, 2017

[JENKINS-27027] Notify the SecurityListener on authentication #3074

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Address review comments

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oleg-nenashev added ready-for-merge The PR is ready to go, and it will be merged soon if there is no negative feedback and removed needs-more-reviews Complex change, which would benefit from more eyes labels Oct 21, 2017

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jglick mentioned this pull request Oct 27, 2017

[JENKINS-31661] Check the root url (Admin monitor + Wizard) #3082

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oleg-nenashev merged commit 671a0ad into jenkinsci:master Oct 28, 2017

jglick mentioned this pull request Mar 14, 2018

Another use of ExtensionList.lookupSingleton #3352

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jglick mentioned this pull request Jan 4, 2019

Suggest ExtensionList.lookupSingleton #3833

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Add ExtensionList#lookupFirst convenience method #3021

Add ExtensionList#lookupFirst convenience method #3021

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Add ExtensionList#lookupFirst convenience method #3021

Add ExtensionList#lookupFirst convenience method #3021

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