Class ClassPath

java.lang.Object

com.google.common.reflect.ClassPath

public final class ClassPath
extends Object

Scans the source of a ClassLoader and finds all loadable classes and resources.

Prefer alternatives to classpath scanning

Runtime classpath scanning is expensive because it traverses the entire transitive classpath, which can cause performance issues such as startup latency regressions. (It also does not support Android.) Before scanning the classpath at runtime, consider whether your use case can be solved with compile-time or static mechanisms:

• Compile-time service registration / annotation processors (e.g., @AutoService)
• Dependency injection (e.g., Dagger, Guice)
• Explicit static registries or configuration
• Compile-time classpath scanning, such as that of ClassGraph, but compile-time scanning is likewise costly, so prefer the other options when possible

Limitations of ClassPath (for those who do need classpath scanning)

• It looks only for files and JARs in URLs available from URLClassLoader instances or the system class loader. This means it does not look for classes in the module path or in other environments. If you need to scan one of those locations, consider ClassGraph.
• Like all of Guava, it is less battle-tested under Windows and other non-Linux systems. We have gotten a report of a specific bug under Windows.
• It returns only one resource for a given path, even if resources with that path appear in multiple jars or directories.
• It uses heuristics to guess at which classes are nested and which are not.

ClassPath and symlinks

In the case of directory classloaders, symlinks are supported but cycles are not traversed. This guarantees discovery of each unique loadable resource. However, not all possible aliases for resources on cyclic paths will be listed.

Since:

14.0

Author:

Ben Yu

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static final class	ClassPath.ClassInfo	Represents a class that can be loaded through ClassPath.ClassInfo.load().
static class	ClassPath.ResourceInfo	Represents a class path resource that can be either a class file or any other resource file loadable from the class path.

Method Summary

Modifier and Type	Method	Description
static ClassPath	from(ClassLoader classloader)	Returns a ClassPath representing all classes and resources loadable from classloader and its ancestor class loaders.
ImmutableSet<ClassPath.ClassInfo>	getAllClasses()	Returns all classes loadable from the current class path.
ImmutableSet<ClassPath.ResourceInfo>	getResources()	Returns all resources loadable from the current class path, including the class files of all loadable classes but excluding the "META-INF/MANIFEST.MF" file.
ImmutableSet<ClassPath.ClassInfo>	getTopLevelClasses()	Returns all top level classes loadable from the current class path.
ImmutableSet<ClassPath.ClassInfo>	getTopLevelClasses(String packageName)	Returns all top level classes whose package name is packageName.
ImmutableSet<ClassPath.ClassInfo>	getTopLevelClassesRecursive(String packageName)	Returns all top level classes whose package name is packageName or starts with packageName followed by a '.'.

Methods inherited from class Object

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

Method Details

from

public static ClassPath from(ClassLoader classloader)
                      throws IOException

Returns a ClassPath representing all classes and resources loadable from classloader and its ancestor class loaders.

Warning: ClassPath can find classes and resources only from:

• URLClassLoader instances' file: URLs
• the system class loader. To search the system class loader even when it is not a URLClassLoader (as in Java 9), ClassPath searches the files from the java.class.path system property.

Throws:

IOException - if the attempt to read class path resources (jar files or directories) failed.

getResources

public ImmutableSet<ClassPath.ResourceInfo> getResources()

Returns all resources loadable from the current class path, including the class files of all loadable classes but excluding the "META-INF/MANIFEST.MF" file.

getAllClasses

public ImmutableSet<ClassPath.ClassInfo> getAllClasses()

Returns all classes loadable from the current class path.

Since:

16.0

getTopLevelClasses

public ImmutableSet<ClassPath.ClassInfo> getTopLevelClasses()

Returns all top level classes loadable from the current class path. Note that "top-level-ness" is determined heuristically by class name (see ClassPath.ClassInfo.isTopLevel()).

getTopLevelClasses

public ImmutableSet<ClassPath.ClassInfo> getTopLevelClasses(String packageName)

Returns all top level classes whose package name is packageName.

getTopLevelClassesRecursive

public ImmutableSet<ClassPath.ClassInfo> getTopLevelClassesRecursive(String packageName)

Returns all top level classes whose package name is packageName or starts with packageName followed by a '.'.