致命异常：main java.lang.NoClassDefFoundError：外部library.jar.class Android Studio

Question

I am developing an android app which process speech and I have speech basic project (dependency for android project) ready on JAVA so I compiled JAVA project in eclipse in JAVA 7 compiler and exported that java project as a runnable jar. I put this jar into my android studio project's libs folder and by right clicking selected AS A library, I got build successful message. But when I try run the android project it gives me error saying,

FATAL EXCEPTION: main Process: in.automator.automator, PID: 4242
java.lang.NoClassDefFoundError: jar_filename.Storage.class_in_jar_file

but the said class is there in the jar file, the only doubtful thing is the mentioned class file looks something like this

import javax.sound.sampled.AudioFileFormat;
import javax.sound.sampled.AudioFormat;
import javax.sound.sampled.AudioFormat.Encoding;
import marf.util.InvalidSampleFormatException;

public class MARFAudioFileFormat extends AudioFileFormat {
....

 ...

....

}

It refers javax.sound.sampled, so possibly that might causing the problem.

I tried searching on the google for the problem but didn't got the solution which can resolve the issue. I tried everything. I am using JRE 7 in android studio and exporting java project in Compiler & itself.

How to resolve this error? Thanks in advance.

Answer 1

You are correct, the problem lies in the fact that the library you're trying to depend on, in turn depends on the javax package hierarchy. Android does not provide javax , so those classes don't exist at runtime (even though they do exist in your computer's JDK, so your compiler doesn't complain - it's basically the same as not having a particular DLL installed that a program on your PC needs).

The NoClassDefFoundError is being thrown on the class that first references the invalid class dependencies, which is probably what's confusing. That class may indeed actually exist in your jar, but it requires classes that don't exist in order to complete its definition - so in effect, your class is not fully defined.

The only way around this is to figure out a way to do whatever you're after, without the javax namespace. I have heard of a few attempts to try to port javax.* into Android, but they never end well - many of the javax classes end up boiling down to native calls, which also won't exist on Android.