public class

DexClassLoader

extends ClassLoader
java.lang.Object
   ↳ java.lang.ClassLoader
     ↳ dalvik.system.DexClassLoader

Class Overview

Provides a simple ClassLoader implementation that operates on a list of jar/apk files with classes.dex entries. The directory that holds the optimized form of the files is specified explicitly. This can be used to execute code not installed as part of an application. The best place to put the optimized DEX files is in app-specific storage, so that removal of the app will automatically remove the optimized DEX files. If other storage is used (e.g. /sdcard), the app may not have an opportunity to remove them.

Summary

Public Constructors
DexClassLoader(String dexPath, String dexOutputDir, String libPath, ClassLoader parent)
Creates a DexClassLoader that finds interpreted and native code.
Protected Methods
Class<?> findClass(String name)
Finds a class.
String findLibrary(String libname)
Finds a native library.
URL findResource(String name)
Finds a resource.
Package getPackage(String name)
Returns package information for the given package.
[Expand]
Inherited Methods
From class java.lang.ClassLoader
From class java.lang.Object

Public Constructors

public DexClassLoader (String dexPath, String dexOutputDir, String libPath, ClassLoader parent)

Since: API Level 3

Creates a DexClassLoader that finds interpreted and native code. Interpreted classes are found in a set of DEX files contained in Jar or APK files. The path lists are separated using the character specified by the "path.separator" system property, which defaults to ":".

Parameters
dexPath the list of jar/apk files containing classes and resources
dexOutputDir directory where optimized DEX files should be written
libPath the list of directories containing native libraries; may be null
parent the parent class loader

Protected Methods

protected Class<?> findClass (String name)

Since: API Level 3

Finds a class. This method is called by loadClass() after the parent ClassLoader has failed to find a loaded class of the same name.

Parameters
name The name of the class to search for, in a human-readable form like "java.lang.String" or "java.net.URLClassLoader$3$1".
Returns
  • the Class object representing the class
Throws
ClassNotFoundException if the class cannot be found

protected String findLibrary (String libname)

Since: API Level 3

Finds a native library. This method is called after the parent ClassLoader has failed to find a native library of the same name.

Parameters
libname The name of the library to find
Returns
  • the complete path of the library, or null if the library is not found.

protected URL findResource (String name)

Since: API Level 3

Finds a resource. This method is called by getResource() after the parent ClassLoader has failed to find a loaded resource of the same name.

Parameters
name The name of the resource to find
Returns
  • the location of the resource as a URL, or null if the resource is not found.

protected Package getPackage (String name)

Since: API Level 3

Returns package information for the given package. Unfortunately, the DexClassLoader doesn't really have this information, and as a non-secure ClassLoader, it isn't even required to, according to the spec. Yet, we want to provide it, in order to make all those hopeful callers of myClass.getPackage().getName() happy. Thus we construct a Package object the first time it is being requested and fill most of the fields with dummy values. The Package object is then put into the ClassLoader's Package cache, so we see the same one next time. We don't create Package objects for null arguments or for the default package.

There a limited chance that we end up with multiple Package objects representing the same package: It can happen when when a package is scattered across different JAR files being loaded by different ClassLoaders. Rather unlikely, and given that this whole thing is more or less a workaround, probably not worth the effort.

Parameters
name the name of the class
Returns
  • the package information for the class, or null if there is not package information available for it