Java - Create anonymous Exception subclass with a certain name

Question

We're using Fabric / Crashlytics for sending non-crash issues to their servers and later checking out the logs and stacktraces.

Unfortunately, the Crashlytics API requires to use a different Exception subclass instance for different issue types. (In the iOS SDK, you can simply use a string for different issue types, but in the Android version, you can't).

public static void craslyticsRecordError(String issueType, String errorMsg)
{
    Exception e = new Exception(issueType + "-" + errorMsg);
    Crashlytics.logException(e);
}

Now we have quite a few different issue types, that we also dynamically define at runtime (build together from string parts). So the questions is, is it possible with some Java Vodoo / Hacks (reflection?) to create a subclass at runtime with a certain name (the name of the string that we use as the issue type) and create and instance from it.

Is this somehow possible?

---

I'm now fiddling with ByteBuddy, trying to get it to work - but I'm stuck at getting my dynamic class call the superclass constructor correctly. Also I'm not quite sure if I'm allowed to cast to Exception later on.

---

Thanks to Rafael Winterhalter I'm one step further into getting this thing to work ;) I've tried exactly the you provided:

public static void craslyticsRecordError(String issueType, String errorMsg)
{
    Class<? extends Exception> dynamicType = new ByteBuddy()
            .subclass(Exception.class)
            .name(issueType)
            .make()
            .load(Fabric.class.getClassLoader(), ClassLoadingStrategy.Default.WRAPPER)
            .getLoaded();
    try
    {
        Exception e = dynamicType.getConstructor(String.class).newInstance(errorMsg);

        GameLog.d("[Fabric] Inner Exception: " + e);
        Crashlytics.logException(e);
    }
    catch (Exception e1)
    {
        Exception e = new Exception(issueType + "-" + errorMsg);
        GameLog.d("[Fabric] ERROR ONE");
        Crashlytics.logException(e);
        e1.printStackTrace();
    }
}

and now I'm facing this runtime exception:

java.lang.NoClassDefFoundError: net.bytebuddy.dynamic.loading.NoOpClassFileTransformer
     at net.bytebuddy.dynamic.loading.ByteArrayClassLoader.<init>(ByteArrayClassLoader.java:136)
     at net.bytebuddy.dynamic.loading.ByteArrayClassLoader.of(ByteArrayClassLoader.java:187)
     at net.bytebuddy.dynamic.loading.ByteArrayClassLoader.load(ByteArrayClassLoader.java:212)
     at net.bytebuddy.dynamic.loading.ClassLoadingStrategy$Default$WrappingDispatcher.load(ClassLoadingStrategy.java:285)
     at net.bytebuddy.dynamic.loading.ClassLoadingStrategy$Default.load(ClassLoadingStrategy.java:120)
     at net.bytebuddy.dynamic.TypeResolutionStrategy$Passive.initialize(TypeResolutionStrategy.java:79)
     at net.bytebuddy.dynamic.DynamicType$Default$Unloaded.load(DynamicType.java:4376)
     at org.utils.Fabric.craslyticsRecordError(Fabric.java:47)
     at android.os.MessageQueue.nativePollOnce(Native Method)
     at android.os.MessageQueue.next(MessageQueue.java:323)
     at android.os.Looper.loop(Looper.java:143)
     at android.app.ActivityThread.main(ActivityThread.java:7224)
     at java.lang.reflect.Method.invoke(Native Method)
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

---

After now using this Android-specific code:

Class<? extends Exception> dynamicType = new ByteBuddy()
        .subclass(Exception.class)
        .name(issueType)
        .make()
        .load(Fabric.class.getClassLoader(), AndroidClassLoadingStrategy.Default.WRAPPER)
        .getLoaded();

and using the Android-specific gradle compile line:

compile 'net.bytebuddy:byte-buddy-android:1.7.3'

I'm still facing the same runtime Exception as before.

Answer 1

By default, Byte Buddy copies the constructors of its super class. In your case, it copies all Exception constructors and you can generate an exception like this:

Class<? extends Exception> dynamicType = new ByteBuddy()
  .subclass(Exception.class)
  .name(issueType)
  .make()
  .load(Fabric.class.getClassLoader(), ClassLoadingStrategy.Default.WRAPPER)
  .getLoaded();

 Exception e = dynamicType.getConstructor(String.class).newInstance(errorMsg);