使用epubLibrary时出现空指针异常。 Appplicaion仅在主要活动中退出

Question

我正在尝试阅读教程http://www.siegmann.nl/epublib/android和其他堆栈溢出链接之后的epub文件。但我仍然得到空指针异常。

我已下载这些jar，放在libs文件夹中并添加到构建路径：

1)epub-lib-core-latest.jar
2)slf4j-android-1.6.1-RC1.jar
3)slf4j-api.jar.zip

以下是例外情况：

01-12 13:11:39.968: W/dalvikvm(27889): threadid=1: thread exiting with uncaught exception (group=0x41712700)
01-12 13:11:39.968: E/AndroidRuntime(27889): FATAL EXCEPTION: main
01-12 13:11:39.968: E/AndroidRuntime(27889): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.bookreaderwithlogger/com.example.bookreaderwithlogger.MainActivity}: java.lang.NullPointerException
01-12 13:11:39.968: E/AndroidRuntime(27889):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
01-12 13:11:39.968: E/AndroidRuntime(27889):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
01-12 13:11:39.968: E/AndroidRuntime(27889):    at android.app.ActivityThread.access$600(ActivityThread.java:141)
01-12 13:11:39.968: E/AndroidRuntime(27889):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
01-12 13:11:39.968: E/AndroidRuntime(27889):    at android.os.Handler.dispatchMessage(Handler.java:99)
01-12 13:11:39.968: E/AndroidRuntime(27889):    at android.os.Looper.loop(Looper.java:137)
01-12 13:11:39.968: E/AndroidRuntime(27889):    at android.app.ActivityThread.main(ActivityThread.java:5103)
01-12 13:11:39.968: E/AndroidRuntime(27889):    at java.lang.reflect.Method.invokeNative(Native Method)
01-12 13:11:39.968: E/AndroidRuntime(27889):    at java.lang.reflect.Method.invoke(Method.java:525)
01-12 13:11:39.968: E/AndroidRuntime(27889):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
01-12 13:11:39.968: E/AndroidRuntime(27889):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
01-12 13:11:39.968: E/AndroidRuntime(27889):    at dalvik.system.NativeStart.main(Native Method)
01-12 13:11:39.968: E/AndroidRuntime(27889): Caused by: java.lang.NullPointerException
01-12 13:11:39.968: E/AndroidRuntime(27889):    at com.example.bookreaderwithlogger.MainActivity.onCreate(MainActivity.java:37)
01-12 13:11:39.968: E/AndroidRuntime(27889):    at android.app.Activity.performCreate(Activity.java:5133)
01-12 13:11:39.968: E/AndroidRuntime(27889):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
01-12 13:11:39.968: E/AndroidRuntime(27889):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
01-12 13:11:39.968: E/AndroidRuntime(27889):    ... 11 more
01-12 13:16:40.321: I/Process(27889): Sending signal. PID: 27889 SIG: 9

MainActivity.java

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        AssetManager assetManager = getAssets();

        try{
            //find input Stream for book
            InputStream epubInputStream = assetManager.open("oliver_twist.epub");

            //Load book from input stream
            Book book = (new EpubReader()).readEpub(epubInputStream);

            Log.i("epublib", "title: "+book.getTitle());

            //Log the book's cover image property
            Bitmap coverImage = BitmapFactory.decodeStream(book.getCoverImage().getInputStream());

            Log.i("epublib", "CoverImage is" + coverImage.getWidth()+" by "+coverImage.getHeight()+" pixels");

            //Log the tales of contents
            logTableOfContents(book.getTableOfContents().getTocReferences(),0);
        }
        catch(IOException e){
            Log.e("epublib", e.getMessage());
        }

    }

    private void logTableOfContents(List<TOCReference> tocReferences, int depth){

        if(tocReferences == null){
            return;
        }

        for(TOCReference tocReference:tocReferences){

            StringBuilder tocString = new StringBuilder();

            for(int i=0;i<depth;i++){
                tocString.append("\t");
            }

            tocString.append(tocReference.getTitle());
            Log.i("epulib", tocString.toString());

            logTableOfContents(tocReference.getChildren(), depth+1);
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

}