org.diet4j.core

Class ModuleClassLoader

java.lang.Object

java.lang.ClassLoader

org.diet4j.core.ModuleClassLoader

Direct Known Subclasses:

ToplevelClassLoader

public class ModuleClassLoader
extends ClassLoader

This is a ClassLoader that knows how to load the code for a Module. It first looks for code in its own JAR, and then delegates to the ModuleClassLoaders of the Modules that this Module depends on.

This used to inherit from URLClassLoader, but the URLClassLoader did mysterious things (it suddenly added additional JARs to itself and I have no idea where they came from), so I did it myself.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	ModuleClassLoader.CompoundIterator<T> Compound iterator helper class.

Field Summary

Fields

Modifier and Type	Field and Description
protected static Object	CANNOT_FIND_OBJECT Marker object to be inserted into the cannotFindTable.
protected HashMap<String,Object>	cannotFindTable This map maps names of resources that we know for sure we can't load to a marker object, so we stop attempting to load here and not delegate.
protected ModuleClassLoader[]	theDependencyClassLoaders The set of ModuleClassLoaders from the dependent Modules.
protected String[]	theDoNotLoadClassPrefixes Always load classes with these prefixes through the default ClassLoader.
protected Module	theModule The Module whose classes this ClassLoader is responsible for loading.
protected URLStreamHandler	theStreamHandler Our StreamHandler, allocated as needed.

Constructor Summary

Constructors

Constructor and Description
ModuleClassLoader(Module mod, ClassLoader parent, ModuleClassLoader[] dependencyClassLoaders, String[] doNotLoadClassPrefixes) Construct one with the Module whose classes this ModuleClassLoader is supposed to load, the parent/system ClassLoader, and the ClassLoaders of dependent Modules.

Method Summary

Modifier and Type	Method and Description
void	addModuleJarUrls(Set<URL> set) Add, to the provided set, all URLs to Module JARs, of this ModuleClassLoader and all dependent ClassLoaders.
protected Package	definePackage(String name, Manifest man, URL url) Verbatim copy from JDK's URLClassLoader.
URL	findResource(String name) Find a URL.
protected Package	getAndVerifyPackage(String pkgname, Manifest man, URL url) Verbatim copy from JDK's URLClassLoader.
ModuleClassLoader[]	getDependencyClassLoaders() Obtain the ClassLoaders from dependent Modules.
Module	getModule() Obtain the Module whose classes this ModuleClassLoader loads.
ModuleRegistry	getModuleRegistry() Convenience method to obtain the ModuleRegistry in use.
URL	getResource(String name) Find a resource through this ClassLoader.
Enumeration<URL>	getResources(String name) Obtain an Enumeration of Resources.
Class	loadClass(String name, boolean resolve) Override loadClass() per comment above.
protected static byte[]	slurpJarEntry(JarFile file, JarEntry entry) Helper method to read a byte array from a JarEntry.
String	toString() Convert to a string representation for debugging.

Methods inherited from class java.lang.ClassLoader

clearAssertionStatus, defineClass, defineClass, defineClass, defineClass, definePackage, findClass, findLibrary, findLoadedClass, findResources, findSystemClass, getClassLoadingLock, getPackage, getPackages, getParent, getResourceAsStream, getSystemClassLoader, getSystemResource, getSystemResourceAsStream, getSystemResources, 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

theModule

protected Module theModule

The Module whose classes this ClassLoader is responsible for loading.

theDependencyClassLoaders

protected ModuleClassLoader[] theDependencyClassLoaders

The set of ModuleClassLoaders from the dependent Modules. Allocated as needed.

theStreamHandler

protected URLStreamHandler theStreamHandler

Our StreamHandler, allocated as needed.

theDoNotLoadClassPrefixes

protected String[] theDoNotLoadClassPrefixes

Always load classes with these prefixes through the default ClassLoader.

cannotFindTable

protected HashMap<String,Object> cannotFindTable

This map maps names of resources that we know for sure we can't load to a marker object, so we stop attempting to load here and not delegate.

CANNOT_FIND_OBJECT

protected static final Object CANNOT_FIND_OBJECT

Marker object to be inserted into the cannotFindTable.

Constructor Detail

ModuleClassLoader

public ModuleClassLoader(Module mod,
                         ClassLoader parent,
                         ModuleClassLoader[] dependencyClassLoaders,
                         String[] doNotLoadClassPrefixes)

Construct one with the Module whose classes this ModuleClassLoader is supposed to load, the parent/system ClassLoader, and the ClassLoaders of dependent Modules.

Parameters:

mod - the Module whose classes this ClassLoader will load

parent - the parent ClassLoader of this ClassLoader

dependencyClassLoaders - the ModuleClassLoaders of the Module's dependent Modules

doNotLoadClassPrefixes - prefixes of classes always to be loaded through the system class loader, not this one

Method Detail

getModule

public Module getModule()

Obtain the Module whose classes this ModuleClassLoader loads.

Returns:

the Module for whose classes this ModuleClassLoader loads

getModuleRegistry

public ModuleRegistry getModuleRegistry()

Convenience method to obtain the ModuleRegistry in use.

Returns:

the ModuleRegistry

addModuleJarUrls

public void addModuleJarUrls(Set<URL> set)
                      throws MalformedURLException

Add, to the provided set, all URLs to Module JARs, of this ModuleClassLoader and all dependent ClassLoaders. This is a method required to make Jasper and other JSP technologies happy.

Parameters:

set - the set to add

Throws:

MalformedURLException - thrown if a URL was invalid

getResource

public URL getResource(String name)

Find a resource through this ClassLoader. First look for a resource locally to this ClassLoader, then in the ClassLoaders of our dependent Modules.

Overrides:

getResource in class ClassLoader

Parameters:

name - name of the resource to find

Returns:

URL to the resource

getResources

public Enumeration<URL> getResources(String name)
                              throws IOException

Obtain an Enumeration of Resources.

Overrides:

getResources in class ClassLoader

Parameters:

name - the name of the Resource

Returns:

the Enumeration

Throws:

IOException - thrown if an I/O error occurred

loadClass

public Class loadClass(String name,
                       boolean resolve)
                throws ClassNotFoundException

Override loadClass() per comment above.

Overrides:

loadClass in class ClassLoader

Parameters:

name - name of the to-be-loaded class

resolve - do we also resolve the class

Returns:

the loaded class

Throws:

ClassNotFoundException - loading the class failed, it could not be found

findResource

public URL findResource(String name)

Find a URL.

Overrides:

findResource in class ClassLoader

Parameters:

name - the name of the resource

Returns:

the URL of the resource, if found

slurpJarEntry

protected static byte[] slurpJarEntry(JarFile file,
                                      JarEntry entry)
                               throws IOException

Helper method to read a byte array from a JarEntry.

Parameters:

file - the JarFile from which to read the JarEntry

entry - the JarEntry to read. If null, return null

Returns:

the found byte array

Throws:

IOException - thrown if an I/O error occurred

getDependencyClassLoaders

public ModuleClassLoader[] getDependencyClassLoaders()

Obtain the ClassLoaders from dependent Modules.

Returns:

the ClassLoaders from dependent Modules

toString

public String toString()

Convert to a string representation for debugging.

Overrides:

toString in class Object

Returns:

string representation of this object

getAndVerifyPackage

protected Package getAndVerifyPackage(String pkgname,
                                      Manifest man,
                                      URL url)

Verbatim copy from JDK's URLClassLoader. Retrieve the package using the specified package name. If non-null, verify the package using the specified code source and manifest.

Parameters:

pkgname - the name of the package

man - the applicable Manifest

url - the URL

definePackage

protected Package definePackage(String name,
                                Manifest man,
                                URL url)
                         throws IllegalArgumentException

Verbatim copy from JDK's URLClassLoader. Defines a new package by name in this ClassLoader. The attributes contained in the specified Manifest will be used to obtain package version and sealing information. For sealed packages, the additional URL specifies the code source URL from which the package was loaded.

Parameters:

name - the package name

man - the Manifest containing package version and sealing information

url - the code source url for the package, or null if none

Returns:

the newly defined Package object

Throws:

IllegalArgumentException - if the package name duplicates an existing package either in this class loader or one of its ancestors