org.apache.nifi.nar

Class NarClassLoader

java.lang.Object

java.lang.ClassLoader

java.security.SecureClassLoader

java.net.URLClassLoader

org.apache.nifi.nar.NarClassLoader

All Implemented Interfaces:

Closeable, AutoCloseable

public class NarClassLoader
extends URLClassLoader

A ClassLoader for loading NARs (NiFi archives). NARs are designed to allow isolating bundles of code (comprising one-or-more NiFi FlowFileProcessors, FlowFileComparators and their dependencies) from other such bundles; this allows for dependencies and processors that require conflicting, incompatible versions of the same dependency to run in a single instance of NiFi.

NarClassLoader follows the delegation model described in ClassLoader.findClass(...); classes are first loaded from the parent ClassLoader, and only if they cannot be found there does the NarClassLoader provide a definition. Specifically, this means that resources are loaded from NiFi's conf and lib directories first, and if they cannot be found there, are loaded from the NAR.

The packaging of a NAR is such that it is a ZIP file with the following directory structure:

   +META-INF/
   +-- bundled-dependencies/
   +-- <JAR files>
   +-- MANIFEST.MF
 

The MANIFEST.MF file contains the same information as a typical JAR file but also includes two additional NiFi properties: Nar-Id and Nar-Dependency-Id.

The Nar-Id provides a unique identifier for this NAR.

The Nar-Dependency-Id is optional. If provided, it indicates that this NAR should inherit all of the dependencies of the NAR with the provided ID. Often times, the NAR that is depended upon is referred to as the Parent. This is because its ClassLoader will be the parent ClassLoader of the dependent NAR.

If a NAR is built using NiFi's Maven NAR Plugin, the Nar-Id property will be set to the artifactId of the NAR. The Nar-Dependency-Id will be set to the artifactId of the NAR that is depended upon. For example, if NAR A is defined as such:

 ...
 <artifactId>nar-a</artifactId>
 <packaging>nar</packaging>
 ...
 <dependencies>
   <dependency>
     <groupId>group</groupId>
     <artifactId>nar-z</artifactId>
     <type>nar</type>
   </dependency>
 </dependencies>
 

Then the MANIFEST.MF file that is created for NAR A will have the following properties set:

• Nar-Id: nar-a
• Nar-Dependency-Id: nar-z

Note, above, that the type of the dependency is set to nar.

If the NAR has more than one dependency of type nar, then the Maven NAR plugin will fail to build the NAR.

Field Summary

Fields

Modifier and Type	Field and Description
private static FileFilter	JAR_FILTER
private static org.slf4j.Logger	LOGGER
private File	narWorkingDirectory The NAR for which this ClassLoader is responsible.

Constructor Summary

Constructors

Constructor and Description
NarClassLoader(File narWorkingDirectory) Construct a nar class loader.
NarClassLoader(File narWorkingDirectory, ClassLoader parentClassLoader) Construct a nar class loader with the specific parent.

Method Summary

Methods

Modifier and Type	Method and Description
protected String	findLibrary(String libname)
File	getWorkingDirectory()
String	toString()
private void	updateClasspath(File root) Adds URLs for the resources unpacked from this NAR: the root: for classes, META-INF, etc. META-INF/dependencies: for config files, .sos, etc. META-INF/dependencies/*.jar: for dependent libraries

Methods inherited from class java.net.URLClassLoader

addURL, close, definePackage, findClass, findResource, findResources, getPermissions, getResourceAsStream, getURLs, newInstance, newInstance

Methods inherited from class java.security.SecureClassLoader

defineClass, defineClass

Methods inherited from class java.lang.ClassLoader

clearAssertionStatus, defineClass, defineClass, defineClass, defineClass, definePackage, findLoadedClass, findSystemClass, getClassLoadingLock, getPackage, getPackages, getParent, getResource, getResources, getSystemClassLoader, getSystemResource, getSystemResourceAsStream, getSystemResources, loadClass, loadClass, registerAsParallelCapable, resolveClass, setClassAssertionStatus, setDefaultAssertionStatus, setPackageAssertionStatus, setSigners

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

LOGGER

private static final org.slf4j.Logger LOGGER

JAR_FILTER

private static final FileFilter JAR_FILTER

narWorkingDirectory

private final File narWorkingDirectory

The NAR for which this ClassLoader is responsible.

Constructor Detail

NarClassLoader

public NarClassLoader(File narWorkingDirectory)
               throws ClassNotFoundException,
                      IOException

Construct a nar class loader.

Parameters:

narWorkingDirectory - directory to explode nar contents to

Throws:

IllegalArgumentException - if the NAR is missing the Java Services API file for FlowFileProcessor implementations.

ClassNotFoundException - if any of the FlowFileProcessor implementations defined by the Java Services API cannot be loaded.

IOException - if an error occurs while loading the NAR.

NarClassLoader

public NarClassLoader(File narWorkingDirectory,
              ClassLoader parentClassLoader)
               throws ClassNotFoundException,
                      IOException

Construct a nar class loader with the specific parent.

Parameters:

narWorkingDirectory - directory to explode nar contents to

parentClassLoader - parent class loader of this nar

Throws:

IllegalArgumentException - if the NAR is missing the Java Services API file for FlowFileProcessor implementations.

ClassNotFoundException - if any of the FlowFileProcessor implementations defined by the Java Services API cannot be loaded.

IOException - if an error occurs while loading the NAR.

Method Detail

getWorkingDirectory

public File getWorkingDirectory()

updateClasspath

private void updateClasspath(File root)
                      throws IOException

Adds URLs for the resources unpacked from this NAR:

• the root: for classes, META-INF, etc.
• META-INF/dependencies: for config files, .sos, etc.
• META-INF/dependencies/*.jar: for dependent libraries

Parameters:

root - the root directory of the unpacked NAR.

Throws:

IOException - if the URL list could not be updated.

findLibrary

protected String findLibrary(String libname)

Overrides:

findLibrary in class ClassLoader

toString

public String toString()

Overrides:

toString in class Object