use own sound recorder android library in unity

I want record and save audio in unity3d with my own library (without unity classes); so I write a library and export jar and then import it to unity

library :

import java.io.File; import java.io.IOException;

 import android.media.MediaMuxer.OutputFormat;
 import android.media.MediaRecorder;
 import android.media.MediaRecorder.AudioEncoder;
 import android.media.MediaRecorder.AudioSource;
 import android.os.Environment;
 import android.util.Log;
 
 public class SoundRecorder {
     MediaRecorder mediaRecorder;
     String soundName;
     String diractory;
     File soundFile;
     File directoryFile;
     String lastError = "";
     boolean isInRecord = false;
     
     void init(String directory, String soundName)
     {
         this.soundName = soundName;
         this.diractory = directory;
         directoryFile = new File(directory);
         if(!directoryFile.exists())
         {
             directoryFile.mkdirs();
         }
         soundFile = new File(directoryFile, soundName);    
         Log.i("Unity", "@#$%^&#$@$@#$@");
     }
     
     void prepareSound()
     {
         try
         {
             mediaRecorder = new MediaRecorder();
             mediaRecorder.setAudioSource(AudioSource.MIC);
             mediaRecorder.setOutputFormat(MediaRecorder.OutputFormat.AMR_NB);
             mediaRecorder.setAudioEncoder(AudioEncoder.AMR_NB);
             mediaRecorder.setOutputFile(soundFile.getAbsolutePath());
             mediaRecorder.prepare();
         }
         catch (Exception e)
         {
             e.printStackTrace();
             lastError = e.getMessage();
            
         }
     }
 
     public void startStopRecording()
     {
  
         if (isInRecord)
         {
             if(mediaRecorder != null)
             {
                 mediaRecorder.reset();
             }
         } else
         {
             prepareSound();
             mediaRecorder.start();
         }
         isInRecord = !isInRecord;
     }
     
     public String getLastError()
     {
         return lastError;
     }
     
     boolean getIsInRecord()
     {
         
         return isInRecord;
     }
     
     public String getSoundName()
     {
         return soundName;
     }
     public String getSoundDirectory()
     {
         return diractory;
     }
     
     public String getExternalStoragePath()
     {
         return Environment.getExternalStorageDirectory().getAbsolutePath();
     }   
 }

and the unity script :

using UnityEngine; using System.Collections; using System.Collections.Generic; using System.IO; using System;

 public class SoundRecorder : MonoBehaviour
 {
 
     AndroidJavaObject soundRecorder;
 
     void Start()
     {
         Application.RequestUserAuthorization(UserAuthorization.Microphone);
         soundRecorder = new AndroidJavaObject("com.tafavotco.soundrecorder.SoundRecorder");
         
         object[] args =
             {
                 soundRecorder.Call<String>("getExternalStoragePath")+"/aaa",
                 "abc.amr"
             };
         soundRecorder.Call("init", args);
         Debug.Log("Error : " + soundRecorder.Call<String>("getLastError"));
     }
 
     // Update is called once per frame
     void Update()
     {
 
     }
 
     void OnGUI()
     {
         if(GUI.Button(new Rect(0, 0, 200, 90), soundRecorder.Call<bool>("getIsInRecord") ? "stop" : "start"))
         {
             soundRecorder.Call("startStopRecording");
             Debug.Log("Error : " + soundRecorder.Call<String>("getLastError"));
         }
   
 
     }
 
 
 }

but it doesn't work and log in the log cat :

 08-17 10:01:58.134: I/Unity(32673): @#$%^&#$@$@#$@
 08-17 10:01:58.134: I/Unity(32673): Error : 
 08-17 10:01:58.134: I/Unity(32673):  
 08-17 10:01:58.134: I/Unity(32673): (Filename: ./artifacts/generated/common/runtime/UnityEngineDebugBindings.gen.cpp Line: 65)
 08-17 10:01:59.614: I/Unity(32673): AndroidJavaException: java.lang.IllegalStateException
 08-17 10:01:59.614: I/Unity(32673):   at UnityEngine.AndroidJNISafe.CheckException () [0x00000] in <filename unknown>:0 
 08-17 10:01:59.614: I/Unity(32673):   at UnityEngine.AndroidJNISafe.CallVoidMethod (IntPtr obj, IntPtr methodID, UnityEngine.jvalue[] args) [0x00000] in <filename unknown>:0 
 08-17 10:01:59.614: I/Unity(32673):   at UnityEngine.AndroidJavaObject._Call (System.String methodName, System.Object[] args) [0x00000] in <filename unknown>:0 
 08-17 10:01:59.614: I/Unity(32673):   at UnityEngine.AndroidJavaObject.Call (System.String methodName, System.Object[] args) [0x00000] in <filename unknown>:0 
 08-17 10:01:59.614: I/Unity(32673):   at SoundRecorder.OnGUI () [0x00000] in <filename unknown>:0 
 08-17 10:01:59.614: I/Unity(32673):  
 08-17 10:01:59.614: I/Unity(32673): (Filename:  Line: -1)

what's the problem ?

UPDATE :

the "lastError" after click on gui button is : "setAudioSource failed."