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How to load class from byte array in android?

Firstly, I saw Download Java bytecode at runtime , and it was useful since I came to me in the same place where I was stuck at the moment.

I am trying to load a class from an array of bytes to avoid storing the file on disk. For testing purposes, in this example, I just read the .class file into an array of bytes, so obviously the file is still stored on disk, but it's just to see if the code can work.

I take this byte array and then use my own ClassLoader with the loadClass method to load the class, but it does not work.

    byte[] bytearray = null;
    try{    
    RandomAccessFile f = new RandomAccessFile("/sdcard/ClassToGet.dex", "r");
    bytearray = new byte[(int) f.length()];
    f.read(bytearray);

    MyClassLoader classloader = new MyClassLoader();
    classloader.setBuffer(bytearray); 
    classloader.loadClass("com.pack.ClassIWant");
    }

Here is the implementation of ClassLoader:

public class MyClassLoader extends DexClassLoader {

 private byte[] buffer;

  @Override
    public Class findClass(String className){
    byte[] b = getBuffer();
    return this.defineClass(className, b, 0, b.length);
    }

public void setBuffer(byte[] b){
    buffer = b;
}
public byte[] getBuffer(){
    return buffer;
}

And the error I get is this:

java.lang.UnsupportedOperationException: java.lang.VMClassLoader.defineClass( )

.class, .dex,.apk,.jar .. , " " , . . .

+5
3

, .dex Dalvik dx, Java .class. .dex, .dex; .jar ZIP , classes.dex.

Dalvik . , . DexMaker generateAndLoad:

    byte[] dex = ...

    /*
     * This implementation currently dumps the dex to the filesystem. It
     * jars the emitted .dex for the benefit of Gingerbread and earlier
     * devices, which can't load .dex files directly.
     *
     * TODO: load the dex from memory where supported.
     */
    File result = File.createTempFile("Generated", ".jar", dexCache);
    result.deleteOnExit();
    JarOutputStream jarOut = new JarOutputStream(new FileOutputStream(result));
    jarOut.putNextEntry(new JarEntry(DexFormat.DEX_IN_JAR_NAME));
    jarOut.write(dex);
    jarOut.closeEntry();
    jarOut.close();
    try {
        return (ClassLoader) Class.forName("dalvik.system.DexClassLoader")
                .getConstructor(String.class, String.class, String.class, ClassLoader.class)
                .newInstance(result.getPath(), dexCache.getAbsolutePath(), null, parent);
    } catch (ClassNotFoundException e) {
        throw new UnsupportedOperationException("load() requires a Dalvik VM", e);
    } catch (InvocationTargetException e) {
        throw new RuntimeException(e.getCause());
    } catch (InstantiationException e) {
        throw new AssertionError();
    } catch (NoSuchMethodException e) {
        throw new AssertionError();
    } catch (IllegalAccessException e) {
        throw new AssertionError();
    }
+1

, .

, " ", .

"/dalvik/vm/native/java_lang_VMClassLoader.cpp", "defineClass", . (: ICS)

, , .dex .

-, .dex ? ( )

/*
 * static Class defineClass(ClassLoader cl, String name,
 *     byte[] data, int offset, int len)
 *     throws ClassFormatError
 *
 * Convert an array of bytes to a Class object.
 */
static void Dalvik_java_lang_VMClassLoader_defineClass(const u4* args, JValue* pResult)
{
    Object* loader = (Object*) args[0];
    StringObject* nameObj = (StringObject*) args[1];
    const u1* data = (const u1*) args[2];
    int offset = args[3];
    int len = args[4];
    char* name = NULL;

    name = dvmCreateCstrFromString(nameObj);
    ALOGE("ERROR: defineClass(%p, %s, %p, %d, %d)",
        loader, name, data, offset, len);
    dvmThrowUnsupportedOperationException(
        "can't load this type of class file");

    free(name);
    RETURN_VOID();
}

/*
 * static Class defineClass(ClassLoader cl, byte[] data, int offset,
 *     int len)
 *     throws ClassFormatError
 *
 * Convert an array of bytes to a Class object. Deprecated version of
 * previous method, lacks name parameter.
 */
static void Dalvik_java_lang_VMClassLoader_defineClass2(const u4* args, JValue* pResult)
{
    Object* loader = (Object*) args[0];
    const u1* data = (const u1*) args[1];
    int offset = args[2];
    int len = args[3];

    ALOGE("ERROR: defineClass(%p, %p, %d, %d)",
        loader, data, offset, len);
    dvmThrowUnsupportedOperationException(
        "can't load this type of class file");

    RETURN_VOID();
}
+2

Android - JVM, - Dalvik. , defineClass()

context.setOptimizationLevel(-1);
0
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