alma.acs.classloading

Class AcsSystemClassLoader

java.lang.Object

java.lang.ClassLoader

java.security.SecureClassLoader

java.net.URLClassLoader

alma.acs.classloading.AcsSystemClassLoader

All Implemented Interfaces:

java.io.Closeable, java.lang.AutoCloseable

public class AcsSystemClassLoader
extends java.net.URLClassLoader

Custom class loader which correctly handles multiple occurrences of identical jar files in "overlayed" directories. These directories would typically be ../lib, INTROOT/lib, ACSROOT/lib and ORB dirs.

The main purpose is to cut down the very long classpath produced otherwise by the ACS start scripts. Only the jar file that contains this class loader must be supplied to the JVM using the "-classpath" option. The JVM must be started with property definitions similar to:

• -Djava.system.class.loader=alma.acs.classloading.AcsSystemClassLoader.
• -Dacs.system.classpath.jardirs=../lib/:$INTROOT/lib:$ACSROOT/lib. If an operating system has a native style path separator different from ":", it can optionally be used instead.

Notes on the classloader hierarchies:

• Don't confuse the inheritance hierarchy and the delegation hierarchy. Both this CL as well as its delegation-parent inherit from URLClassLoader.
• This classloader is meant to be registered with the JVM using the property java.system.class.loader.
• Instead of using the real system classloader (sun.misc.Launcher$AppClassLoader) as the parent, since ACS 6.0 this CL takes over the functionality of the direct parent, and uses the original grandparent CL for parent-delegation. Circumventing the original parent CL after copying its CLASSPATH entries, removes the distinction between the CLASSPATH entries and the jar files from the acs.system.classpath.jardirs directories.
  • The effect is that we can add jar files to the CLASSPATH, which use classes from the normal pool of jar files. One use case for this is testing component implementation classes outside of containers: the jar files under ../lib/ACScomponents are not picked up by the classloader unless we add them to the CLASSPATH, e.g. using acsStartJava -addToClasspath.
  • The CL hierarchy becomes (1) Bootstrap CL, (2) Extention CL, (3) AcsSystemClassLoader, [(4) optional component CL etc]
• The method ClassLoader.getSystemClassLoader() "tricks" the caller and returns this class loader, even though it thinks that the real system CL is our circumvented sibling, the sun.misc.Launcher$AppClassLoader. This allows JUnit tests run, since the JUnit framework sets up their own classloader to be a child of the system classloader, shortcutting any "regular" child class loaders in between.

Author:

hsommer created Sep 13, 2004 6:31:32 PM

Field Summary

Fields

Modifier and Type	Field and Description
static java.lang.String	PROPERTY_CLASSLOADERVERBOSE
static java.lang.String	PROPERTY_JARDIRS
static java.lang.String	PROPERTY_TOPJARSONLY

Constructor Summary

Constructors

Constructor and Description
AcsSystemClassLoader(java.lang.ClassLoader parent) Constructor will be called by the JVM.

Method Summary

Modifier and Type	Method and Description
protected java.lang.Class<?>	findClass(java.lang.String name) Delegates to base class implementation.
protected java.lang.Class<?>	loadClass(java.lang.String name, boolean resolve)

Methods inherited from class java.net.URLClassLoader

addURL, close, definePackage, 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, findLibrary, findLoadedClass, findSystemClass, getClassLoadingLock, getPackage, getPackages, getParent, getResource, getResources, 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, toString, wait, wait, wait

Field Detail

PROPERTY_JARDIRS

public static final java.lang.String PROPERTY_JARDIRS

See Also:

Constant Field Values

PROPERTY_TOPJARSONLY

public static final java.lang.String PROPERTY_TOPJARSONLY

See Also:

Constant Field Values

PROPERTY_CLASSLOADERVERBOSE

public static final java.lang.String PROPERTY_CLASSLOADERVERBOSE

See Also:

Constant Field Values

Constructor Detail

AcsSystemClassLoader

public AcsSystemClassLoader(java.lang.ClassLoader parent)

Constructor will be called by the JVM. The standard system class loader (instance of sun.misc.Launcher$AppClassLoader is expected to be the parent parameter, although no such assumption is made in the code.

In the ctor, the directories given in acs.system.classpath.jardirs are searched for JAR files, which are fed as URLs into the classpath maintained by the URLClassLoader base class.

See Also:

AcsJarFileFinder

Method Detail

loadClass

protected java.lang.Class<?> loadClass(java.lang.String name,
                                       boolean resolve)
                                throws java.lang.ClassNotFoundException

Overrides:

loadClass in class java.lang.ClassLoader

Throws:

java.lang.ClassNotFoundException

findClass

protected java.lang.Class<?> findClass(java.lang.String name)
                                throws java.lang.ClassNotFoundException

Delegates to base class implementation.

Discards requests to load classes from certain sub-packages of sun. or com.sun. by throwing a ClassNotFoundException. The JDK libs try to search (e.g. during ACS container startup) for some optional system classes such as sun.text.resources.DateFormatZoneData_en_US or sun.util.logging.resources.logging_en. We know that ALMA jar files do not contain any classes in those packages, and can thus speed up the applications, in cases where those classes have already been searched unsuccessfully by any parent class loaders, which as the last step desparately would ask this class loader, which would cause a search through all jar files. sun.awt.resources. com.sun.swing.internal.plaf.

Overrides:

findClass in class java.net.URLClassLoader

Throws:

java.lang.ClassNotFoundException