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Posted to issues@maven.apache.org by GitBox <gi...@apache.org> on 2022/11/15 12:57:53 UTC
[GitHub] [maven-site] elharo commented on a diff in pull request #338: [MNG-5771] Document all classloaders used in Maven
elharo commented on code in PR #338:
URL: https://github.com/apache/maven-site/pull/338#discussion_r1022745807
##########
content/apt/guides/mini/guide-maven-classloading.apt:
##########
@@ -30,55 +30,89 @@
Guide to Maven Classloading
This is a description of the classloader hierarchy in Maven.
-
+
+%{toc|section=1|fromDepth=2}
+
* Overview
- * System Classloader
+ Maven uses the {{{https://codehaus-plexus.github.io/plexus-classworlds/}Plexus Classworlds}} classloading framework with which we
Review Comment:
"with which we
create our" --> to create the
##########
content/apt/guides/mini/guide-maven-classloading.apt:
##########
@@ -30,55 +30,89 @@
Guide to Maven Classloading
This is a description of the classloader hierarchy in Maven.
-
+
+%{toc|section=1|fromDepth=2}
+
* Overview
- * System Classloader
+ Maven uses the {{{https://codehaus-plexus.github.io/plexus-classworlds/}Plexus Classworlds}} classloading framework with which we
+ create our classloader graph. If you look in your <<<$\{maven.home\}/boot>>> directory you will see a single JAR
+ which is the Classworlds JAR we use to boot the classloader graph. The Classworlds JAR is the only element of
+ the Java <<<CLASSPATH>>> and Classworlds then builds the other classloaders or realms in Classworlds terminology.
- * Core Classloader
+ Each realm exposes
- * Plugin Classloaders
+ [[1]] optionally some classes imported from 0..n other classloaders
- * Custom Classloaders
-
- []
+ [[2]] optionally some classes from a directory or JAR
+
+ [[3]] one parent classloader
+ []
-* 1. {System Classloader}
+ The search order is always as given above.
- Maven uses the {{{https://codehaus-plexus.github.io/plexus-classworlds/}Plexus Classworlds}} classloading framework with which we
- create our classloader graph. If you look in your <<<$\{maven.home\}/boot>>> directory you will see a single JAR
- which is the Classworlds JAR we use to boot the classloader graph. The Classworlds JAR is the only element of
- the Java <<<CLASSPATH>>> and Classworlds then builds the other classloaders or realms in Classworlds terminology.
+* {Platform Classloader}
+
+ This is the classloader exposing all JRE classes.
+
+* {System Classloader}
- An Ant script like this will show the contents of the system classloader:
+ An Ant script like this will show the contents of the system/bootstrap classloader:
Review Comment:
why are we talking about ant? Please delete this.
##########
content/apt/guides/mini/guide-maven-classloading.apt:
##########
@@ -30,55 +30,89 @@
Guide to Maven Classloading
This is a description of the classloader hierarchy in Maven.
-
+
+%{toc|section=1|fromDepth=2}
+
* Overview
- * System Classloader
+ Maven uses the {{{https://codehaus-plexus.github.io/plexus-classworlds/}Plexus Classworlds}} classloading framework with which we
+ create our classloader graph. If you look in your <<<$\{maven.home\}/boot>>> directory you will see a single JAR
Review Comment:
comma after directory
##########
content/apt/guides/mini/guide-maven-classloading.apt:
##########
@@ -30,55 +30,89 @@
Guide to Maven Classloading
This is a description of the classloader hierarchy in Maven.
-
+
+%{toc|section=1|fromDepth=2}
+
* Overview
- * System Classloader
+ Maven uses the {{{https://codehaus-plexus.github.io/plexus-classworlds/}Plexus Classworlds}} classloading framework with which we
+ create our classloader graph. If you look in your <<<$\{maven.home\}/boot>>> directory you will see a single JAR
+ which is the Classworlds JAR we use to boot the classloader graph. The Classworlds JAR is the only element of
+ the Java <<<CLASSPATH>>> and Classworlds then builds the other classloaders or realms in Classworlds terminology.
- * Core Classloader
+ Each realm exposes
- * Plugin Classloaders
+ [[1]] optionally some classes imported from 0..n other classloaders
- * Custom Classloaders
-
- []
+ [[2]] optionally some classes from a directory or JAR
+
+ [[3]] one parent classloader
+ []
-* 1. {System Classloader}
+ The search order is always as given above.
- Maven uses the {{{https://codehaus-plexus.github.io/plexus-classworlds/}Plexus Classworlds}} classloading framework with which we
- create our classloader graph. If you look in your <<<$\{maven.home\}/boot>>> directory you will see a single JAR
- which is the Classworlds JAR we use to boot the classloader graph. The Classworlds JAR is the only element of
- the Java <<<CLASSPATH>>> and Classworlds then builds the other classloaders or realms in Classworlds terminology.
+* {Platform Classloader}
+
+ This is the classloader exposing all JRE classes.
+
+* {System Classloader}
- An Ant script like this will show the contents of the system classloader:
+ An Ant script like this will show the contents of the system/bootstrap classloader:
+---+
<target name="info">
<echo>java.class.path=${java.class.path}</echo>
</target>
+---+
+ It imports the platform classloader.
-* 2. {Core Classloader}
+* {Core Classloader}
- The second classloader down the graph contains the core requirements of Maven. More precisely, the core classloader
- has the libraries in <<<$\{maven.home\}/lib>>>. In general these are just Maven libraries, e.g. instances of
+ The second classloader down the graph contains the core requirements of Maven. <<It is only used by Maven internally but not by Plugins>>.
+ The core classloader has the libraries in <<<$\{maven.home\}/lib>>>. In general these are just Maven libraries, e.g. instances of
<<<{{{/ref/current/apidocs/org/apache/maven/project/MavenProject.html}MavenProject}}>>>
belong to this classloader.
- We hope to further separate these in the future to just be Maven APIs and have
- the implementations selected at runtime as required by the system.
You can add elements to this classloader by {{{/ref/current/maven-model/maven.html#class_extension}extensions}}.
These are loaded into the same place as <<<$\{maven.home\}/lib>>> and hence are available
- to the Maven core and all plugins for the current project and subsequent projects (in future, we
- plan to remove it from subsequent projects).
+ to the Maven core and all plugins for the current project (through the API classloader).
+ More information available in {{{./guide-using-extensions.html}Core Extension}}.
+
+* {API Classloader}
+
+ This exposes a filtered view of the Core Classloader by only exposing the exported packages from all Core Extensions.
+ The main API is listed in {{{https://maven.apache.org/ref/3-LATEST/maven-core/core-extensions.html}Maven Core Extensions Reference}}.
+
+ This has been introduced with Maven 3.3.1 ({{{https://issues.apache.org/jira/browse/MNG-5771}MNG-5771}}).
+
+* {Build Extension Classloaders}
-
-* 3. {Plugin Classloaders}
+[../../buildExtensionClassRealm.svg] Build Extension Class Realm
- After that, each plugin has its own classloader that is a child of Maven's core classloader.
- The classes in this classloader are taken from the dependencies in the plugin's dependency list.
+ For every plugin which is marked with <<<\<extensions\>true\</extensions\>>>> or a build extension listed in the according section of the POM there is
Review Comment:
comma after POM
##########
content/apt/guides/mini/guide-maven-classloading.apt:
##########
@@ -30,55 +30,89 @@
Guide to Maven Classloading
This is a description of the classloader hierarchy in Maven.
-
+
+%{toc|section=1|fromDepth=2}
+
* Overview
- * System Classloader
+ Maven uses the {{{https://codehaus-plexus.github.io/plexus-classworlds/}Plexus Classworlds}} classloading framework with which we
+ create our classloader graph. If you look in your <<<$\{maven.home\}/boot>>> directory you will see a single JAR
+ which is the Classworlds JAR we use to boot the classloader graph. The Classworlds JAR is the only element of
+ the Java <<<CLASSPATH>>> and Classworlds then builds the other classloaders or realms in Classworlds terminology.
- * Core Classloader
+ Each realm exposes
- * Plugin Classloaders
+ [[1]] optionally some classes imported from 0..n other classloaders
- * Custom Classloaders
-
- []
+ [[2]] optionally some classes from a directory or JAR
+
+ [[3]] one parent classloader
+ []
-* 1. {System Classloader}
+ The search order is always as given above.
- Maven uses the {{{https://codehaus-plexus.github.io/plexus-classworlds/}Plexus Classworlds}} classloading framework with which we
- create our classloader graph. If you look in your <<<$\{maven.home\}/boot>>> directory you will see a single JAR
- which is the Classworlds JAR we use to boot the classloader graph. The Classworlds JAR is the only element of
- the Java <<<CLASSPATH>>> and Classworlds then builds the other classloaders or realms in Classworlds terminology.
+* {Platform Classloader}
+
+ This is the classloader exposing all JRE classes.
+
+* {System Classloader}
- An Ant script like this will show the contents of the system classloader:
+ An Ant script like this will show the contents of the system/bootstrap classloader:
+---+
<target name="info">
<echo>java.class.path=${java.class.path}</echo>
</target>
+---+
+ It imports the platform classloader.
-* 2. {Core Classloader}
+* {Core Classloader}
- The second classloader down the graph contains the core requirements of Maven. More precisely, the core classloader
- has the libraries in <<<$\{maven.home\}/lib>>>. In general these are just Maven libraries, e.g. instances of
+ The second classloader down the graph contains the core requirements of Maven. <<It is only used by Maven internally but not by Plugins>>.
+ The core classloader has the libraries in <<<$\{maven.home\}/lib>>>. In general these are just Maven libraries, e.g. instances of
<<<{{{/ref/current/apidocs/org/apache/maven/project/MavenProject.html}MavenProject}}>>>
belong to this classloader.
- We hope to further separate these in the future to just be Maven APIs and have
- the implementations selected at runtime as required by the system.
You can add elements to this classloader by {{{/ref/current/maven-model/maven.html#class_extension}extensions}}.
These are loaded into the same place as <<<$\{maven.home\}/lib>>> and hence are available
- to the Maven core and all plugins for the current project and subsequent projects (in future, we
- plan to remove it from subsequent projects).
+ to the Maven core and all plugins for the current project (through the API classloader).
+ More information available in {{{./guide-using-extensions.html}Core Extension}}.
+
+* {API Classloader}
+
+ This exposes a filtered view of the Core Classloader by only exposing the exported packages from all Core Extensions.
+ The main API is listed in {{{https://maven.apache.org/ref/3-LATEST/maven-core/core-extensions.html}Maven Core Extensions Reference}}.
+
+ This has been introduced with Maven 3.3.1 ({{{https://issues.apache.org/jira/browse/MNG-5771}MNG-5771}}).
+
+* {Build Extension Classloaders}
-
-* 3. {Plugin Classloaders}
+[../../buildExtensionClassRealm.svg] Build Extension Class Realm
- After that, each plugin has its own classloader that is a child of Maven's core classloader.
- The classes in this classloader are taken from the dependencies in the plugin's dependency list.
+ For every plugin which is marked with <<<\<extensions\>true\</extensions\>>>> or a build extension listed in the according section of the POM there is
+ a dedicated classloader. Those are isolated (i.e. one build extension does not have access to other build extensions).
Review Comment:
Those are isolated (i.e. -->
Those are isolated. That is,
##########
content/apt/guides/mini/guide-maven-classloading.apt:
##########
@@ -118,7 +152,7 @@ Guide to Maven Classloading
When a build plugin is executed, the thread's context classloader is set to the plugin classloader.
-* 4. {Custom Classloaders}
+* {Custom Classloaders}
Plugins are free to create further classloaders on their discretion. For example, a plugin might want to create a
Review Comment:
delete "on their discretion"
##########
content/apt/guides/mini/guide-using-extensions.apt:
##########
@@ -40,10 +41,12 @@ Using Extensions
* Loading Extensions
- There are different means of loading extensions. They can be distinguished into <<early>> and <<late>> loading behaviour. Some extensions require early loading.
- Please refer to the extension's documentation whether early loading is required.
+ There are different means of loading extensions depending on the type. There are <core extensions> which are loaded <<early>>
+ and build extensions which are loaded <<late>>.
+ Some extensions require early loading as they fundamentally change Maven behaviour.
+ Please refer to the extension's documentation whether they provide a core or a build extension.
Review Comment:
"Please refer to the extension's documentation whether they provide a core or a build extension." --> An extension's documentation should indicate whether it provide a core or a build extension.
##########
content/apt/guides/mini/guide-maven-classloading.apt:
##########
@@ -30,55 +30,89 @@
Guide to Maven Classloading
This is a description of the classloader hierarchy in Maven.
-
+
+%{toc|section=1|fromDepth=2}
+
* Overview
- * System Classloader
+ Maven uses the {{{https://codehaus-plexus.github.io/plexus-classworlds/}Plexus Classworlds}} classloading framework with which we
+ create our classloader graph. If you look in your <<<$\{maven.home\}/boot>>> directory you will see a single JAR
+ which is the Classworlds JAR we use to boot the classloader graph. The Classworlds JAR is the only element of
+ the Java <<<CLASSPATH>>> and Classworlds then builds the other classloaders or realms in Classworlds terminology.
- * Core Classloader
+ Each realm exposes
- * Plugin Classloaders
+ [[1]] optionally some classes imported from 0..n other classloaders
- * Custom Classloaders
-
- []
+ [[2]] optionally some classes from a directory or JAR
+
+ [[3]] one parent classloader
+ []
-* 1. {System Classloader}
+ The search order is always as given above.
- Maven uses the {{{https://codehaus-plexus.github.io/plexus-classworlds/}Plexus Classworlds}} classloading framework with which we
- create our classloader graph. If you look in your <<<$\{maven.home\}/boot>>> directory you will see a single JAR
- which is the Classworlds JAR we use to boot the classloader graph. The Classworlds JAR is the only element of
- the Java <<<CLASSPATH>>> and Classworlds then builds the other classloaders or realms in Classworlds terminology.
+* {Platform Classloader}
+
+ This is the classloader exposing all JRE classes.
+
+* {System Classloader}
- An Ant script like this will show the contents of the system classloader:
+ An Ant script like this will show the contents of the system/bootstrap classloader:
+---+
<target name="info">
<echo>java.class.path=${java.class.path}</echo>
</target>
+---+
+ It imports the platform classloader.
-* 2. {Core Classloader}
+* {Core Classloader}
- The second classloader down the graph contains the core requirements of Maven. More precisely, the core classloader
- has the libraries in <<<$\{maven.home\}/lib>>>. In general these are just Maven libraries, e.g. instances of
+ The second classloader down the graph contains the core requirements of Maven. <<It is only used by Maven internally but not by Plugins>>.
+ The core classloader has the libraries in <<<$\{maven.home\}/lib>>>. In general these are just Maven libraries, e.g. instances of
<<<{{{/ref/current/apidocs/org/apache/maven/project/MavenProject.html}MavenProject}}>>>
belong to this classloader.
- We hope to further separate these in the future to just be Maven APIs and have
- the implementations selected at runtime as required by the system.
You can add elements to this classloader by {{{/ref/current/maven-model/maven.html#class_extension}extensions}}.
These are loaded into the same place as <<<$\{maven.home\}/lib>>> and hence are available
- to the Maven core and all plugins for the current project and subsequent projects (in future, we
- plan to remove it from subsequent projects).
+ to the Maven core and all plugins for the current project (through the API classloader).
+ More information available in {{{./guide-using-extensions.html}Core Extension}}.
+
+* {API Classloader}
+
+ This exposes a filtered view of the Core Classloader by only exposing the exported packages from all Core Extensions.
Review Comment:
This --> The API classloader
only exposing the --> exposing only the
##########
content/apt/guides/mini/guide-maven-classloading.apt:
##########
@@ -30,55 +30,89 @@
Guide to Maven Classloading
This is a description of the classloader hierarchy in Maven.
-
+
+%{toc|section=1|fromDepth=2}
+
* Overview
- * System Classloader
+ Maven uses the {{{https://codehaus-plexus.github.io/plexus-classworlds/}Plexus Classworlds}} classloading framework with which we
+ create our classloader graph. If you look in your <<<$\{maven.home\}/boot>>> directory you will see a single JAR
+ which is the Classworlds JAR we use to boot the classloader graph. The Classworlds JAR is the only element of
+ the Java <<<CLASSPATH>>> and Classworlds then builds the other classloaders or realms in Classworlds terminology.
- * Core Classloader
+ Each realm exposes
- * Plugin Classloaders
+ [[1]] optionally some classes imported from 0..n other classloaders
- * Custom Classloaders
-
- []
+ [[2]] optionally some classes from a directory or JAR
+
+ [[3]] one parent classloader
+ []
-* 1. {System Classloader}
+ The search order is always as given above.
- Maven uses the {{{https://codehaus-plexus.github.io/plexus-classworlds/}Plexus Classworlds}} classloading framework with which we
- create our classloader graph. If you look in your <<<$\{maven.home\}/boot>>> directory you will see a single JAR
- which is the Classworlds JAR we use to boot the classloader graph. The Classworlds JAR is the only element of
- the Java <<<CLASSPATH>>> and Classworlds then builds the other classloaders or realms in Classworlds terminology.
+* {Platform Classloader}
+
+ This is the classloader exposing all JRE classes.
+
+* {System Classloader}
- An Ant script like this will show the contents of the system classloader:
+ An Ant script like this will show the contents of the system/bootstrap classloader:
+---+
<target name="info">
<echo>java.class.path=${java.class.path}</echo>
</target>
+---+
+ It imports the platform classloader.
-* 2. {Core Classloader}
+* {Core Classloader}
- The second classloader down the graph contains the core requirements of Maven. More precisely, the core classloader
- has the libraries in <<<$\{maven.home\}/lib>>>. In general these are just Maven libraries, e.g. instances of
+ The second classloader down the graph contains the core requirements of Maven. <<It is only used by Maven internally but not by Plugins>>.
+ The core classloader has the libraries in <<<$\{maven.home\}/lib>>>. In general these are just Maven libraries, e.g. instances of
Review Comment:
, e.g. -> . For example,
##########
content/apt/guides/mini/guide-maven-classloading.apt:
##########
@@ -30,55 +30,89 @@
Guide to Maven Classloading
This is a description of the classloader hierarchy in Maven.
-
+
+%{toc|section=1|fromDepth=2}
+
* Overview
- * System Classloader
+ Maven uses the {{{https://codehaus-plexus.github.io/plexus-classworlds/}Plexus Classworlds}} classloading framework with which we
+ create our classloader graph. If you look in your <<<$\{maven.home\}/boot>>> directory you will see a single JAR
+ which is the Classworlds JAR we use to boot the classloader graph. The Classworlds JAR is the only element of
+ the Java <<<CLASSPATH>>> and Classworlds then builds the other classloaders or realms in Classworlds terminology.
Review Comment:
"The Classworlds JAR is the only element of
the Java <<<CLASSPATH>>> and Classworlds then builds the other classloaders or realms in Classworlds terminology." is awkward. perhaps something like
Classworlds uses this jar to bootstrap the other classloaders ("realms" in Classworlds terminology).
##########
content/apt/guides/mini/guide-maven-classloading.apt:
##########
@@ -30,55 +30,89 @@
Guide to Maven Classloading
This is a description of the classloader hierarchy in Maven.
-
+
+%{toc|section=1|fromDepth=2}
+
* Overview
- * System Classloader
+ Maven uses the {{{https://codehaus-plexus.github.io/plexus-classworlds/}Plexus Classworlds}} classloading framework with which we
+ create our classloader graph. If you look in your <<<$\{maven.home\}/boot>>> directory you will see a single JAR
+ which is the Classworlds JAR we use to boot the classloader graph. The Classworlds JAR is the only element of
+ the Java <<<CLASSPATH>>> and Classworlds then builds the other classloaders or realms in Classworlds terminology.
- * Core Classloader
+ Each realm exposes
- * Plugin Classloaders
+ [[1]] optionally some classes imported from 0..n other classloaders
- * Custom Classloaders
-
- []
+ [[2]] optionally some classes from a directory or JAR
+
+ [[3]] one parent classloader
+ []
-* 1. {System Classloader}
+ The search order is always as given above.
- Maven uses the {{{https://codehaus-plexus.github.io/plexus-classworlds/}Plexus Classworlds}} classloading framework with which we
- create our classloader graph. If you look in your <<<$\{maven.home\}/boot>>> directory you will see a single JAR
- which is the Classworlds JAR we use to boot the classloader graph. The Classworlds JAR is the only element of
- the Java <<<CLASSPATH>>> and Classworlds then builds the other classloaders or realms in Classworlds terminology.
+* {Platform Classloader}
+
+ This is the classloader exposing all JRE classes.
+
+* {System Classloader}
- An Ant script like this will show the contents of the system classloader:
+ An Ant script like this will show the contents of the system/bootstrap classloader:
+---+
<target name="info">
<echo>java.class.path=${java.class.path}</echo>
</target>
+---+
+ It imports the platform classloader.
-* 2. {Core Classloader}
+* {Core Classloader}
- The second classloader down the graph contains the core requirements of Maven. More precisely, the core classloader
- has the libraries in <<<$\{maven.home\}/lib>>>. In general these are just Maven libraries, e.g. instances of
+ The second classloader down the graph contains the core requirements of Maven. <<It is only used by Maven internally but not by Plugins>>.
+ The core classloader has the libraries in <<<$\{maven.home\}/lib>>>. In general these are just Maven libraries, e.g. instances of
<<<{{{/ref/current/apidocs/org/apache/maven/project/MavenProject.html}MavenProject}}>>>
belong to this classloader.
- We hope to further separate these in the future to just be Maven APIs and have
- the implementations selected at runtime as required by the system.
You can add elements to this classloader by {{{/ref/current/maven-model/maven.html#class_extension}extensions}}.
These are loaded into the same place as <<<$\{maven.home\}/lib>>> and hence are available
- to the Maven core and all plugins for the current project and subsequent projects (in future, we
- plan to remove it from subsequent projects).
+ to the Maven core and all plugins for the current project (through the API classloader).
+ More information available in {{{./guide-using-extensions.html}Core Extension}}.
Review Comment:
is available
##########
content/apt/guides/mini/guide-using-extensions.apt:
##########
@@ -28,7 +28,8 @@
Using Extensions
- Extensions are a way to add classes to {{{./guide-maven-classloading.html#Core_Classloader}Core Classloader}}.
+ Extensions are a way to add classes to either the {{{./guide-maven-classloading.html#Core_Classloader}Core Classloader}} (Core Extensions)
+ or the {{{./guide-maven-classloading.html#Project_Classloaders}Project Classloader}} (Build Extensions).
This is necessary for adjusting Maven in a way that affects more than just one plug-in.
The mechanism allows to either replace default {{{https://www.eclipse.org/sisu/}Sisu components}} with custom ones or add
Review Comment:
allows who?
##########
content/apt/guides/mini/guide-maven-classloading.apt:
##########
@@ -30,55 +30,89 @@
Guide to Maven Classloading
This is a description of the classloader hierarchy in Maven.
-
+
+%{toc|section=1|fromDepth=2}
+
* Overview
- * System Classloader
+ Maven uses the {{{https://codehaus-plexus.github.io/plexus-classworlds/}Plexus Classworlds}} classloading framework with which we
+ create our classloader graph. If you look in your <<<$\{maven.home\}/boot>>> directory you will see a single JAR
+ which is the Classworlds JAR we use to boot the classloader graph. The Classworlds JAR is the only element of
+ the Java <<<CLASSPATH>>> and Classworlds then builds the other classloaders or realms in Classworlds terminology.
- * Core Classloader
+ Each realm exposes
- * Plugin Classloaders
+ [[1]] optionally some classes imported from 0..n other classloaders
- * Custom Classloaders
-
- []
+ [[2]] optionally some classes from a directory or JAR
+
+ [[3]] one parent classloader
+ []
-* 1. {System Classloader}
+ The search order is always as given above.
- Maven uses the {{{https://codehaus-plexus.github.io/plexus-classworlds/}Plexus Classworlds}} classloading framework with which we
- create our classloader graph. If you look in your <<<$\{maven.home\}/boot>>> directory you will see a single JAR
- which is the Classworlds JAR we use to boot the classloader graph. The Classworlds JAR is the only element of
- the Java <<<CLASSPATH>>> and Classworlds then builds the other classloaders or realms in Classworlds terminology.
+* {Platform Classloader}
+
+ This is the classloader exposing all JRE classes.
+
+* {System Classloader}
- An Ant script like this will show the contents of the system classloader:
+ An Ant script like this will show the contents of the system/bootstrap classloader:
+---+
<target name="info">
<echo>java.class.path=${java.class.path}</echo>
</target>
+---+
+ It imports the platform classloader.
-* 2. {Core Classloader}
+* {Core Classloader}
- The second classloader down the graph contains the core requirements of Maven. More precisely, the core classloader
- has the libraries in <<<$\{maven.home\}/lib>>>. In general these are just Maven libraries, e.g. instances of
+ The second classloader down the graph contains the core requirements of Maven. <<It is only used by Maven internally but not by Plugins>>.
Review Comment:
delete only, lower case plugins
##########
content/apt/guides/mini/guide-maven-classloading.apt:
##########
@@ -30,55 +30,89 @@
Guide to Maven Classloading
This is a description of the classloader hierarchy in Maven.
-
+
+%{toc|section=1|fromDepth=2}
+
* Overview
- * System Classloader
+ Maven uses the {{{https://codehaus-plexus.github.io/plexus-classworlds/}Plexus Classworlds}} classloading framework with which we
+ create our classloader graph. If you look in your <<<$\{maven.home\}/boot>>> directory you will see a single JAR
+ which is the Classworlds JAR we use to boot the classloader graph. The Classworlds JAR is the only element of
+ the Java <<<CLASSPATH>>> and Classworlds then builds the other classloaders or realms in Classworlds terminology.
- * Core Classloader
+ Each realm exposes
- * Plugin Classloaders
+ [[1]] optionally some classes imported from 0..n other classloaders
- * Custom Classloaders
-
- []
+ [[2]] optionally some classes from a directory or JAR
+
+ [[3]] one parent classloader
+ []
-* 1. {System Classloader}
+ The search order is always as given above.
- Maven uses the {{{https://codehaus-plexus.github.io/plexus-classworlds/}Plexus Classworlds}} classloading framework with which we
- create our classloader graph. If you look in your <<<$\{maven.home\}/boot>>> directory you will see a single JAR
- which is the Classworlds JAR we use to boot the classloader graph. The Classworlds JAR is the only element of
- the Java <<<CLASSPATH>>> and Classworlds then builds the other classloaders or realms in Classworlds terminology.
+* {Platform Classloader}
+
+ This is the classloader exposing all JRE classes.
+
+* {System Classloader}
- An Ant script like this will show the contents of the system classloader:
+ An Ant script like this will show the contents of the system/bootstrap classloader:
+---+
<target name="info">
<echo>java.class.path=${java.class.path}</echo>
</target>
+---+
+ It imports the platform classloader.
-* 2. {Core Classloader}
+* {Core Classloader}
- The second classloader down the graph contains the core requirements of Maven. More precisely, the core classloader
- has the libraries in <<<$\{maven.home\}/lib>>>. In general these are just Maven libraries, e.g. instances of
+ The second classloader down the graph contains the core requirements of Maven. <<It is only used by Maven internally but not by Plugins>>.
+ The core classloader has the libraries in <<<$\{maven.home\}/lib>>>. In general these are just Maven libraries, e.g. instances of
<<<{{{/ref/current/apidocs/org/apache/maven/project/MavenProject.html}MavenProject}}>>>
belong to this classloader.
- We hope to further separate these in the future to just be Maven APIs and have
- the implementations selected at runtime as required by the system.
You can add elements to this classloader by {{{/ref/current/maven-model/maven.html#class_extension}extensions}}.
These are loaded into the same place as <<<$\{maven.home\}/lib>>> and hence are available
Review Comment:
place is unclear. Is this a classpath?
##########
content/apt/guides/mini/guide-maven-classloading.apt:
##########
@@ -30,55 +30,89 @@
Guide to Maven Classloading
This is a description of the classloader hierarchy in Maven.
-
+
+%{toc|section=1|fromDepth=2}
+
* Overview
- * System Classloader
+ Maven uses the {{{https://codehaus-plexus.github.io/plexus-classworlds/}Plexus Classworlds}} classloading framework with which we
+ create our classloader graph. If you look in your <<<$\{maven.home\}/boot>>> directory you will see a single JAR
+ which is the Classworlds JAR we use to boot the classloader graph. The Classworlds JAR is the only element of
+ the Java <<<CLASSPATH>>> and Classworlds then builds the other classloaders or realms in Classworlds terminology.
- * Core Classloader
+ Each realm exposes
- * Plugin Classloaders
+ [[1]] optionally some classes imported from 0..n other classloaders
- * Custom Classloaders
-
- []
+ [[2]] optionally some classes from a directory or JAR
+
+ [[3]] one parent classloader
+ []
-* 1. {System Classloader}
+ The search order is always as given above.
- Maven uses the {{{https://codehaus-plexus.github.io/plexus-classworlds/}Plexus Classworlds}} classloading framework with which we
- create our classloader graph. If you look in your <<<$\{maven.home\}/boot>>> directory you will see a single JAR
- which is the Classworlds JAR we use to boot the classloader graph. The Classworlds JAR is the only element of
- the Java <<<CLASSPATH>>> and Classworlds then builds the other classloaders or realms in Classworlds terminology.
+* {Platform Classloader}
+
+ This is the classloader exposing all JRE classes.
+
+* {System Classloader}
- An Ant script like this will show the contents of the system classloader:
+ An Ant script like this will show the contents of the system/bootstrap classloader:
+---+
<target name="info">
<echo>java.class.path=${java.class.path}</echo>
</target>
+---+
+ It imports the platform classloader.
-* 2. {Core Classloader}
+* {Core Classloader}
- The second classloader down the graph contains the core requirements of Maven. More precisely, the core classloader
- has the libraries in <<<$\{maven.home\}/lib>>>. In general these are just Maven libraries, e.g. instances of
+ The second classloader down the graph contains the core requirements of Maven. <<It is only used by Maven internally but not by Plugins>>.
+ The core classloader has the libraries in <<<$\{maven.home\}/lib>>>. In general these are just Maven libraries, e.g. instances of
<<<{{{/ref/current/apidocs/org/apache/maven/project/MavenProject.html}MavenProject}}>>>
belong to this classloader.
- We hope to further separate these in the future to just be Maven APIs and have
- the implementations selected at runtime as required by the system.
You can add elements to this classloader by {{{/ref/current/maven-model/maven.html#class_extension}extensions}}.
These are loaded into the same place as <<<$\{maven.home\}/lib>>> and hence are available
- to the Maven core and all plugins for the current project and subsequent projects (in future, we
- plan to remove it from subsequent projects).
+ to the Maven core and all plugins for the current project (through the API classloader).
+ More information available in {{{./guide-using-extensions.html}Core Extension}}.
+
+* {API Classloader}
+
+ This exposes a filtered view of the Core Classloader by only exposing the exported packages from all Core Extensions.
+ The main API is listed in {{{https://maven.apache.org/ref/3-LATEST/maven-core/core-extensions.html}Maven Core Extensions Reference}}.
+
+ This has been introduced with Maven 3.3.1 ({{{https://issues.apache.org/jira/browse/MNG-5771}MNG-5771}}).
+
+* {Build Extension Classloaders}
-
-* 3. {Plugin Classloaders}
+[../../buildExtensionClassRealm.svg] Build Extension Class Realm
- After that, each plugin has its own classloader that is a child of Maven's core classloader.
- The classes in this classloader are taken from the dependencies in the plugin's dependency list.
+ For every plugin which is marked with <<<\<extensions\>true\</extensions\>>>> or a build extension listed in the according section of the POM there is
+ a dedicated classloader. Those are isolated (i.e. one build extension does not have access to other build extensions).
+ It imports everything from API classloader.
Review Comment:
the API
##########
content/apt/guides/mini/guide-maven-classloading.apt:
##########
@@ -30,55 +30,89 @@
Guide to Maven Classloading
This is a description of the classloader hierarchy in Maven.
-
+
+%{toc|section=1|fromDepth=2}
+
* Overview
- * System Classloader
+ Maven uses the {{{https://codehaus-plexus.github.io/plexus-classworlds/}Plexus Classworlds}} classloading framework with which we
+ create our classloader graph. If you look in your <<<$\{maven.home\}/boot>>> directory you will see a single JAR
+ which is the Classworlds JAR we use to boot the classloader graph. The Classworlds JAR is the only element of
+ the Java <<<CLASSPATH>>> and Classworlds then builds the other classloaders or realms in Classworlds terminology.
- * Core Classloader
+ Each realm exposes
- * Plugin Classloaders
+ [[1]] optionally some classes imported from 0..n other classloaders
- * Custom Classloaders
-
- []
+ [[2]] optionally some classes from a directory or JAR
+
+ [[3]] one parent classloader
+ []
-* 1. {System Classloader}
+ The search order is always as given above.
- Maven uses the {{{https://codehaus-plexus.github.io/plexus-classworlds/}Plexus Classworlds}} classloading framework with which we
- create our classloader graph. If you look in your <<<$\{maven.home\}/boot>>> directory you will see a single JAR
- which is the Classworlds JAR we use to boot the classloader graph. The Classworlds JAR is the only element of
- the Java <<<CLASSPATH>>> and Classworlds then builds the other classloaders or realms in Classworlds terminology.
+* {Platform Classloader}
+
+ This is the classloader exposing all JRE classes.
+
+* {System Classloader}
- An Ant script like this will show the contents of the system classloader:
+ An Ant script like this will show the contents of the system/bootstrap classloader:
+---+
<target name="info">
<echo>java.class.path=${java.class.path}</echo>
</target>
+---+
+ It imports the platform classloader.
-* 2. {Core Classloader}
+* {Core Classloader}
- The second classloader down the graph contains the core requirements of Maven. More precisely, the core classloader
- has the libraries in <<<$\{maven.home\}/lib>>>. In general these are just Maven libraries, e.g. instances of
+ The second classloader down the graph contains the core requirements of Maven. <<It is only used by Maven internally but not by Plugins>>.
+ The core classloader has the libraries in <<<$\{maven.home\}/lib>>>. In general these are just Maven libraries, e.g. instances of
<<<{{{/ref/current/apidocs/org/apache/maven/project/MavenProject.html}MavenProject}}>>>
belong to this classloader.
- We hope to further separate these in the future to just be Maven APIs and have
- the implementations selected at runtime as required by the system.
You can add elements to this classloader by {{{/ref/current/maven-model/maven.html#class_extension}extensions}}.
These are loaded into the same place as <<<$\{maven.home\}/lib>>> and hence are available
- to the Maven core and all plugins for the current project and subsequent projects (in future, we
- plan to remove it from subsequent projects).
+ to the Maven core and all plugins for the current project (through the API classloader).
+ More information available in {{{./guide-using-extensions.html}Core Extension}}.
+
+* {API Classloader}
+
+ This exposes a filtered view of the Core Classloader by only exposing the exported packages from all Core Extensions.
+ The main API is listed in {{{https://maven.apache.org/ref/3-LATEST/maven-core/core-extensions.html}Maven Core Extensions Reference}}.
+
+ This has been introduced with Maven 3.3.1 ({{{https://issues.apache.org/jira/browse/MNG-5771}MNG-5771}}).
+
+* {Build Extension Classloaders}
-
-* 3. {Plugin Classloaders}
+[../../buildExtensionClassRealm.svg] Build Extension Class Realm
- After that, each plugin has its own classloader that is a child of Maven's core classloader.
- The classes in this classloader are taken from the dependencies in the plugin's dependency list.
+ For every plugin which is marked with <<<\<extensions\>true\</extensions\>>>> or a build extension listed in the according section of the POM there is
+ a dedicated classloader. Those are isolated (i.e. one build extension does not have access to other build extensions).
+ It imports everything from API classloader.
+ All JSR 330 or Plexus components declared in the underlying JAR are registered as components in the global Plexus container
+ while creating the classloader.
+ In addition all component references in the plugin descriptor are properly wired from the underlying Plexus container.
+ Build extensions have limited effect as they are loaded late.
+
+* {Project Classloaders}
+
+ There is one project classloader per Maven project (identified through its GAV).
Review Comment:
GAV --> coordinates
##########
src/plantuml/buildExtensionClassRealm.puml:
##########
@@ -0,0 +1,46 @@
+/*
Review Comment:
What are these new files doing here? Maybe drawing some sort of diagram or something?
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