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DelegateLastClassLoader

public final class DelegateLastClassLoader
extends PathClassLoader

java.lang.Object
   ↳ java.lang.ClassLoader
     ↳ dalvik.system.BaseDexClassLoader
       ↳ dalvik.system.PathClassLoader
         ↳ dalvik.system.DelegateLastClassLoader


A ClassLoader implementation that implements a delegate last lookup policy. For every class or resource this loader is requested to load, the following lookup order is employed:

  • The boot classpath is always searched first
  • Then, the list of dex files associated with this classloaders's dexPath is searched.
  • Finally, this classloader will delegate to the specified parent.

Summary

Public constructors

DelegateLastClassLoader(String dexPath, ClassLoader parent)

Equivalent to calling DelegateLastClassLoader(String, String, ClassLoader) with librarySearchPath = null.

DelegateLastClassLoader(String dexPath, String librarySearchPath, ClassLoader parent)

Creates a DelegateLastClassLoader that operates on a given dexPath and a librarySearchPath.

Public methods

URL getResource(String name)

Finds the resource with the given name.

Enumeration<URL> getResources(String name)

Finds all the resources with the given name.

Protected methods

Class<?> loadClass(String name, boolean resolve)

Loads the class with the specified binary name.

Inherited methods

Public constructors

DelegateLastClassLoader

added in API level 27
public DelegateLastClassLoader (String dexPath, 
                ClassLoader parent)

Equivalent to calling DelegateLastClassLoader(String, String, ClassLoader) with librarySearchPath = null.

Parameters
dexPath String

parent ClassLoader

DelegateLastClassLoader

added in API level 27
public DelegateLastClassLoader (String dexPath, 
                String librarySearchPath, 
                ClassLoader parent)

Creates a DelegateLastClassLoader that operates on a given dexPath and a librarySearchPath. The dexPath should consist of one or more of the following, separated by File.pathSeparator, which is ":" on Android.

  • JAR/ZIP/APK files, possibly containing a "classes.dex" file as well as arbitrary resources.
  • Raw ".dex" files (not inside a zip file).
Unlike PathClassLoader, this classloader will attempt to locate classes (or resources) using the following lookup order.
  • The boot classpath is always searched first.
  • Then, the list of dex files contained in dexPath is searched./li>
  • Lastly, this classloader will delegate to the specified parent.
Note that this is in contrast to other standard classloaders that follow the delegation model. In those classloaders, the parent is always searched first. librarySearchPath specifies one more directories containing native library files, separated by File.pathSeparator.

Parameters
dexPath String: the list of jar/apk files containing classes and resources, delimited by File.pathSeparator, which defaults to ":" on Android.

librarySearchPath String: the list of directories containing native libraries, delimited by File.pathSeparator; may be null.

parent ClassLoader: the parent class loader

Public methods

getResource

added in API level 27
public URL getResource (String name)

Finds the resource with the given name. A resource is some data (images, audio, text, etc) that can be accessed by class code in a way that is independent of the location of the code.

The name of a resource is a '/'-separated path name that identifies the resource.

This method will first search the parent class loader for the resource; if the parent is null the path of the class loader built-in to the virtual machine is searched. That failing, this method will invoke findResource(String) to find the resource.

Parameters
name String: The resource name

Returns
URL A URL object for reading the resource, or null if the resource could not be found or the invoker doesn't have adequate privileges to get the resource.

getResources

added in API level 27
public Enumeration<URL> getResources (String name)

Finds all the resources with the given name. A resource is some data (images, audio, text, etc) that can be accessed by class code in a way that is independent of the location of the code.

The name of a resource is a /-separated path name that identifies the resource.

The search order is described in the documentation for getResource(String).

Parameters
name String: The resource name

Returns
Enumeration<URL> An enumeration of URL objects for the resource. If no resources could be found, the enumeration will be empty. Resources that the class loader doesn't have access to will not be in the enumeration.

Throws
IOException

Protected methods

loadClass

added in API level 27
protected Class<?> loadClass (String name, 
                boolean resolve)

Loads the class with the specified binary name. The default implementation of this method searches for classes in the following order:

  1. Invoke findLoadedClass(String) to check if the class has already been loaded.

  2. Invoke the loadClass method on the parent class loader. If the parent is null the class loader built-in to the virtual machine is used, instead.

  3. Invoke the findClass(String) method to find the class.

If the class was found using the above steps, and the resolve flag is true, this method will then invoke the resolveClass(Class) method on the resulting Class object.

Subclasses of ClassLoader are encouraged to override findClass(String), rather than this method.

Parameters
name String: The binary name of the class

resolve boolean: If true then resolve the class

Returns
Class<?> The resulting Class object

Throws
ClassNotFoundException