[ 
https://issues.apache.org/jira/browse/NIFI-2909?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15629252#comment-15629252
 ] 

ASF GitHub Bot commented on NIFI-2909:
--------------------------------------

Github user olegz commented on a diff in the pull request:

    https://github.com/apache/nifi/pull/1156#discussion_r86164431
  
    --- Diff: 
nifi-nar-bundles/nifi-framework-bundle/nifi-framework/nifi-framework-core-api/src/main/java/org/apache/nifi/controller/AbstractConfiguredComponent.java
 ---
    @@ -141,48 +191,64 @@ public void setProperty(final String name, final 
String value) {
          * @return true if removed; false otherwise
          * @throws java.lang.IllegalArgumentException if the name is null
          */
    -    @Override
    -    public boolean removeProperty(final String name) {
    +    private boolean removeProperty(final String name) {
             if (null == name) {
                 throw new IllegalArgumentException();
             }
     
    -        lock.lock();
    -        try {
    -            verifyModifiable();
    -
    -            try (final NarCloseable narCloseable = 
NarCloseable.withComponentNarLoader(component.getClass())) {
    -                final PropertyDescriptor descriptor = 
component.getPropertyDescriptor(name);
    -                String value = null;
    -                if (!descriptor.isRequired() && (value = 
properties.remove(descriptor)) != null) {
    -
    -                    if (descriptor.getControllerServiceDefinition() != 
null) {
    -                        if (value != null) {
    -                            final ControllerServiceNode oldNode = 
serviceProvider.getControllerServiceNode(value);
    -                            if (oldNode != null) {
    -                                oldNode.removeReference(this);
    -                            }
    -                        }
    -                    }
    +        final PropertyDescriptor descriptor = 
component.getPropertyDescriptor(name);
    +        String value = null;
    +        if (!descriptor.isRequired() && (value = 
properties.remove(descriptor)) != null) {
     
    -                    try {
    -                        component.onPropertyModified(descriptor, value, 
null);
    -                    } catch (final Exception e) {
    -                        // nothing really to do here...
    +            if (descriptor.getControllerServiceDefinition() != null) {
    +                if (value != null) {
    +                    final ControllerServiceNode oldNode = 
serviceProvider.getControllerServiceNode(value);
    +                    if (oldNode != null) {
    +                        oldNode.removeReference(this);
                         }
    -
    -                    return true;
                     }
                 }
    -        } finally {
    -            lock.unlock();
    +
    +            try {
    +                component.onPropertyModified(descriptor, value, null);
    +            } catch (final Exception e) {
    +                // nothing really to do here...
    +            }
    +
    +            return true;
             }
    +
             return false;
         }
     
    +    /**
    +     * Adds all of the modules identified by the given module paths to the 
InstanceClassLoader for this component.
    +     *
    +     * @param modulePaths a list of module paths where each entry can be a 
comma-separated list of multiple module paths
    +     */
    +    private void processClasspathModifiers(final Set<String> modulePaths) {
    +        try {
    +            final URL[] urls = 
ClassLoaderUtils.getURLsForClasspath(modulePaths, null, true);
    +
    +            final ClassLoader classLoader = 
Thread.currentThread().getContextClassLoader();
    +            if (!(classLoader instanceof InstanceClassLoader)) {
    +                // Really shouldn't happen, but if we somehow got here and 
don't have an InstanceClassLoader then log a warning and move on
    +                logger.warn("Unable to modify the classpath for {}, 
expected InstanceClassLoader, but found {}",
    +                        new Object[] { name, 
classLoader.getClass().getName()});
    +                return;
    --- End diff --
    
    I am wondering if this should really be a fatal condition. Let's say I have 
a processor that utilizes this mechanism and the additional classpath is a 
required property (e.g., like we have in new JMS). This means it can *only* 
work if such classpath is provided and successfully loaded. Letting it continue 
with simple warning message wil not accomplish anything, right?


> Provide a framework mechanism for loading additional classpath resources
> ------------------------------------------------------------------------
>
>                 Key: NIFI-2909
>                 URL: https://issues.apache.org/jira/browse/NIFI-2909
>             Project: Apache NiFi
>          Issue Type: Improvement
>            Reporter: Bryan Bende
>            Assignee: Bryan Bende
>             Fix For: 1.1.0
>
>
> We currently have several components with a property for specifying 
> additional classpath resources (DBCP connection pool, scripting processors, 
> JMS). Each of these components is responsible for handling this in its own 
> way. 
> The framework should provide a more integrated solution to make it easier for 
> component developers to deal with this scenario. Some requirements that need 
> to be met by this solution:
> - Multiple instances of the same component with different resources added to 
> the classpath and not interfering with each other (i.e. two DBCP connection 
> pools using different drivers)
> - Ability to modify the actual ClassLoader of the component to deal with 
> frameworks that use Class.forName() without passing in a ClassLoader, meaning 
> if a processor loads class A and class A calls Class.forName(classBName), 
> then class B needs to be available in the ClassLoader that loaded the 
> processor's class which in turn loaded class A
> - A component developer should be able to indicate that a given 
> PropertyDescriptor represents a classpath resource and the framework should 
> take care of the ClassLoader manipulation



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