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Breaking the Android ClassLoader Zac Sweers @pandanomic Photo by Vitalis Hirschmann on Unsplash

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ClassLoader

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class ClassLoader

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class ClassLoader {a Class> loadClass(String name); Class> findClass(String name); Class> defineClass(...); URL getResource(String name); // A few others }a

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class ClassLoader {a Class> loadClass(String name); Class> findClass(String name); Class> defineClass(...); URL getResource(String name); // A few others }a

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class URLClassLoader {a Class> loadClass(String name) { // Go fetch them from a jar }a }a

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class URLClassLoader {a Class> loadClass(String name) { // Go fetch them from a jar }a }a

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class URLClassLoader {a Class> loadClass(String name) { // Go fetch them from a jar }a }a

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class URLClassLoader {a // ClassLoader parent Class> loadClass(String name) }a

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class URLClassLoader {a // ClassLoader parent Class> loadClass(String name) }a

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Class> loadClass(String name)

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package example; class Foo { private Bar bar; }a

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package example; class Foo { private Bar bar; }a loadClass("example.Foo")

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package example; class Foo { private Bar bar; }a loadClass("example.Foo") Foo.class.getClassLoader().loadClass("example.Bar")

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class PathClassLoader

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class PathClassLoader class DexClassLoader

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class PathClassLoader extends BaseDexClassLoader class DexClassLoader extends BaseDexClassLoader

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class BaseDexClassLoader {a DexPathList pathList }a

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class BaseDexClassLoader {a DexPathList pathList // --> DexFile, etc }a

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class BaseDexClassLoader {a DexPathList pathList // --> DexFile, etc }a

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Story time!

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PathClassLoader classLoader = new PathClassLoader( context.getApplicationInfo().sourceDir, /* parent */ null );

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class CustomClassLoader extends PathClassLoader

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class CustomClassLoader extends PathClassLoader { @Override public Class> loadClass(String name) { Log.d("ClLoading", "Loading " + name); return super.loadClass(name); } }

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CustomClassLoader cl = new CustomClassLoader(...);

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CustomClassLoader cl = new CustomClassLoader(...); // set java.lang.ClassLoader$SystemClassLoader.loader

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CustomClassLoader cl = new CustomClassLoader(...); // set java.lang.ClassLoader$SystemClassLoader.loader Thread.currentThread().setContextClassLoader(cl)

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CustomClassLoader cl = new CustomClassLoader(...); // set java.lang.ClassLoader$SystemClassLoader.loader Thread.currentThread().setContextClassLoader(cl) ContextImpl

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CustomClassLoader cl = new CustomClassLoader(...); // set java.lang.ClassLoader$SystemClassLoader.loader Thread.currentThread().setContextClassLoader(cl) ContextImpl.mClassLoader

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CustomClassLoader cl = new CustomClassLoader(...); // set java.lang.ClassLoader$SystemClassLoader.loader Thread.currentThread().setContextClassLoader(cl) ContextImpl

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CustomClassLoader cl = new CustomClassLoader(...); // set java.lang.ClassLoader$SystemClassLoader.loader Thread.currentThread().setContextClassLoader(cl) ContextImpl.mPackageInfo

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CustomClassLoader cl = new CustomClassLoader(...); // set java.lang.ClassLoader$SystemClassLoader.loader Thread.currentThread().setContextClassLoader(cl) ContextImpl.mPackageInfo.mClassLoader

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BlackM irro r

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Demo time!

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github.com/hzsweers/ blackmirror

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Final notes

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Harder in Pie g.co/dev/appcompat

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Be mindful

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github.com/hzsweers/ blackmirror Zac Sweers @pandanomic