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jclasslocator

Java library for analyzing the classpath of an application, e.g., used to determine dynamic class hierarchies (simply add a jar with additional classes in packages that the ClassLister monitors and they are automatically located).

Used by ADAMS.

Class hierarchies

Defining class hierarchies is very easy. Just supply a java.util.Properties object to the ClassLister.setPackages(Properties) method that lists for each superclass (or interface) the packages that need inspecting.

Here is the basic format:

class.name=package1,package2,...

Blacklisting

Blacklisting of classes is extremely easy. You just need to supply a java.util.Properties object to the ClassLister.setBlacklist(Properties) method that lists a comma-separated list of regular expressions for matching class names to exclude. The simplest is to use the full class name of the class to exclude.

Here is the basic format:

class.name=regexp1,regexp2,...

Example (manual setup)

The following code is taken from nz.ac.waikato.cms.locator.example.ClassListerExample:

import nz.ac.waikato.cms.locator.ClassLister;
import java.util.Properties;

// configuring the class hierarchies
Properties pkgs = new Properties();
pkgs.put(AbstractAncestor.class.getName(), "nz.ac.waikato.cms.locator.example.pkgA,nz.ac.waikato.cms.locator.example.pkgB");
pkgs.put(SomeInterface.class.getName(), "nz.ac.waikato.cms.locator.example.pkgA,nz.ac.waikato.cms.locator.example.pkgB");

// blacklisted classes
Properties black = new Properties();
black.put(AbstractAncestor.class.getName(), ".*C");  // anything that ends with a capital "C"
black.put(SomeInterface.class.getName(), "nz.ac.waikato.cms.locator.example.pkgB.InterfaceImplInternal");  // specific class

// initialize
ClassLister lister = ClassLister.getSingleton();
lister.setPackages(pkgs);
lister.setBlacklist(black);
lister.initialize();

Class[] classes;
// abstract class
System.out.println("\nAbstract super class: " + AbstractAncestor.class.getName());
classes = lister.getClasses(AbstractAncestor.class);
for (Class cls: classes)
  System.out.println("- " + cls.getName());
// interface
System.out.println("\nInterface: " + SomeInterface.class.getName());
classes = lister.getClasses(SomeInterface.class);
for (Class cls: classes)
  System.out.println("- " + cls.getName());

Generates this output:

Abstract super class: nz.ac.waikato.cms.locator.example.AbstractAncestor
- nz.ac.waikato.cms.locator.example.pkgA.ConcreteClassA
- nz.ac.waikato.cms.locator.example.pkgA.ConcreteClassB

Interface: nz.ac.waikato.cms.locator.example.SomeInterface
- nz.ac.waikato.cms.locator.example.pkgA.InterfaceImplA
- nz.ac.waikato.cms.locator.example.pkgB.InterfaceImplB
- nz.ac.waikato.cms.locator.example.pkgB.InterfaceImplC

Example (using .props files)

Instead of manually creating java.util.Properties objects, you can also use .props files and load them instead.

Listing packages (ClassLister.props):

nz.ac.waikato.cms.locator.example.AbstractAncestor=\
  nz.ac.waikato.cms.locator.example.pkgA,\
  nz.ac.waikato.cms.locator.example.pkgB

nz.ac.waikato.cms.locator.example.SomeInterface=\
  nz.ac.waikato.cms.locator.example.pkgA,\
  nz.ac.waikato.cms.locator.example.pkgB

Blacklisting classes (ClassLister.blacklist)

nz.ac.waikato.cms.locator.example.AbstractAncestor=.*C

nz.ac.waikato.cms.locator.example.SomeInterface=nz.ac.waikato.cms.locator.example.pkgB.InterfaceImplInternal
import nz.ac.waikato.cms.locator.ClassLister;
import java.util.Properties;

// loading the props files (path might need adjusting)
Properties pkgs = ClassLister.load("ClassLister.props");
Properties black = ClassLister.load("ClassLister.blacklist");

// initialize
ClassLister lister = ClassLister.getSingleton();
lister.setPackages(pkgs);
lister.setBlacklist(black);
lister.initialize();

Class[] classes;
// abstract class
System.out.println("\nAbstract super class: " + AbstractAncestor.class.getName());
classes = lister.getClasses(AbstractAncestor.class);
for (Class cls: classes)
  System.out.println("- " + cls.getName());
// interface
System.out.println("\nInterface: " + SomeInterface.class.getName());
classes = lister.getClasses(SomeInterface.class);
for (Class cls: classes)
  System.out.println("- " + cls.getName());

Logging

Logging is by default restricted to WARNING or higher (like SEVERE). However, you can enable logging for debugging purposes via environment variables:

  • nz.ac.waikato.cms.locator.ClassCache.LOGLEVEL
  • nz.ac.waikato.cms.locator.ClassLister.LOGLEVEL
  • nz.ac.waikato.cms.locator.ClassLocator.LOGLEVEL
  • nz.ac.waikato.cms.locator.ClassPathTraversal.LOGLEVEL

These environment variables can take the following values:

{OFF|SEVERE|WARNING|INFO|CONFIG|FINE|FINER|FINEST}

No classpath

Fixed list of classnames

In case the classpath is empty, i.e., System.getProperty("java.class.path") returns an empty string, you can initialize the ClassCache instance with a fixed list of class names. For that you need to provide an instance of the FixedClassListTraversal class to the ClassLister.getSingleton(ClassTraversal) method. FixedClassListTraversal can be instantiated either with a java.util.List<String> that lists all class names or with an java.io.InputStream object, from which to read the class names. Empty lines and lines starting with # get automatically skipped.

The example classes could be stored in the file nz/ac/waikato/cms/locator/example/fixed.classes like this:

# first package
nz.ac.waikato.cms.locator.example.pkgA.ConcreteClassA
nz.ac.waikato.cms.locator.example.pkgA.ConcreteClassB
nz.ac.waikato.cms.locator.example.pkgA.InterfaceImplA

# second package
nz.ac.waikato.cms.locator.example.pkgB.ConcreteClassC
nz.ac.waikato.cms.locator.example.pkgB.InterfaceImplB
nz.ac.waikato.cms.locator.example.pkgB.InterfaceImplC
nz.ac.waikato.cms.locator.example.pkgB.InterfaceImplInternal

The code therefore looks like this for initializing the ClassLister:

FixedClassListTraversal fixed = new FixedClassListTraversal(
  ClassLoader.getSystemResourceAsStream("nz/ac/waikato/cms/locator/example/fixed.classes"));
ClassLister lister = ClassLister.getSingleton(fixed);

The above code is taken from nz.ac.waikato.cms.locator.example.ClassListerExampleFixedClassList.

Classnames from properties

Example nz.ac.waikato.cms.locator.example.ClassListerExamplePropertiesBasedClassList shows how to initialize from a java.utils.Properties object. Each of the properties contains a comma-separated list of classnames.

Other useful methods

  • ClassLister.toProperties() - returns the class hierarchies as a java.util.Properties object. The key of a property is the superclass name and the associated value is the comma-separated list of classnames.
  • ClassLister.toPackages() - returns the class hierarchies as a java.util.Properties object. The key of a property is the superclass name and the associated value is the comma-separated list of packages.

Maven

Add the following dependency to your pom.xml:

    <dependency>
      <groupId>com.github.waikato</groupId>
      <artifactId>jclasslocator</artifactId>
      <version>0.0.22</version>
    </dependency>