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我正在从 assets 文件夹中访问 epub 文件以读取 epub内容。我一步一步地跟随siegmann 。它在抛出 nulpointer 异常

      Book book = (new EpubReader()).readEpub(epubInputStream);

我的代码片段是

public class MainActivity extends Activity {
  /** Called when the activity is first created. */
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    AssetManager assetManager = getAssets();
    System.err.println("assetManager>>"+assetManager);
    try {
      // find InputStream for book
      InputStream epubInputStream = assetManager.open("ww.epub");

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

      // Log the book's authors
      Log.i("epublib", "author(s): " + book.getMetadata().getAuthors());

      // Log the book's title
      Log.i("epublib", "title: " + book.getTitle());

      // Log the book's coverimage property
      Bitmap coverImage = BitmapFactory.decodeStream(book.getCoverImage().getInputStream());
     Log.i("epublib", "Coverimage is " + coverImage.getWidth() + " by " + coverImage.getHeight() + " pixels");

      // Log the tale 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("epublib", tocString.toString());

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

ww.epub是我简单地保存在资产文件夹中的文件。谁能告诉我如何解决这个空指针异常？

Logcat 显示

02-04 13:22:57.189: W/System.err(22968): 1915 [main] ERROR nl.siegmann.epublib.epub.NCXDocument - null
02-04 13:22:57.189: W/System.err(22968): java.lang.NullPointerException
02-04 13:22:57.189: W/System.err(22968):    at nl.siegmann.epublib.epub.NCXDocument.read(NCXDocument.java:92)
02-04 13:22:57.189: W/System.err(22968):    at nl.siegmann.epublib.epub.EpubReader.processNcxResource(EpubReader.java:113)
02-04 13:22:57.189: W/System.err(22968):    at nl.siegmann.epublib.epub.EpubReader.readEpub(EpubReader.java:99)
02-04 13:22:57.189: W/System.err(22968):    at nl.siegmann.epublib.epub.EpubReader.readEpub(EpubReader.java:53)
02-04 13:22:57.189: W/System.err(22968):    at nl.siegmann.epublib.epub.EpubReader.readEpub(EpubReader.java:37)
02-04 13:22:57.189: W/System.err(22968):    at com.example.epub.MainActivity.onCreate(MainActivity.java:36)
02-04 13:22:57.189: W/System.err(22968):    at android.app.Activity.performCreate(Activity.java:5104)
02-04 13:22:57.189: W/System.err(22968):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
02-04 13:22:57.189: W/System.err(22968):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
02-04 13:22:57.189: W/System.err(22968):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
02-04 13:22:57.189: W/System.err(22968):    at android.app.ActivityThread.access$600(ActivityThread.java:141)
02-04 13:22:57.189: W/System.err(22968):    at  android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
02-04 13:22:57.189: W/System.err(22968):    at android.os.Handler.dispatchMessage(Handler.java:99)
02-04 13:22:57.189: W/System.err(22968):    at android.os.Looper.loop(Looper.java:137)
02-04 13:22:57.189: W/System.err(22968):    at android.app.ActivityThread.main(ActivityThread.java:5039)
02-04 13:22:57.189: W/System.err(22968):    at java.lang.reflect.Method.invokeNative(Native Method)
02-04 13:22:57.189: W/System.err(22968):    at java.lang.reflect.Method.invoke(Method.java:511)
02-04 13:22:57.189: W/System.err(22968):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
02-04 13:22:57.189: W/System.err(22968):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
02-04 13:22:57.189: W/System.err(22968):    at dalvik.system.NativeStart.main(Native Method)
02-04 13:22:57.189: I/epublib(22968): author(s): [Melville, Herman]
02-04 13:22:57.189: I/epublib(22968): title: Moby-Dick
02-04 13:22:57.189: D/AndroidRuntime(22968): Shutting down VM
02-04 13:22:57.189: W/dalvikvm(22968): threadid=1: thread exiting with uncaught exception (group=0x41e99930)
02-04 13:22:57.189: E/AndroidRuntime(22968): FATAL EXCEPTION: main
02-04 13:22:57.189: E/AndroidRuntime(22968): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.epub/com.example.epub.MainActivity}: java.lang.NullPointerException
02-04 13:22:57.189: E/AndroidRuntime(22968):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
02-04 13:22:57.189: E/AndroidRuntime(22968):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
02-04 13:22:57.189: E/AndroidRuntime(22968):    at android.app.ActivityThread.access$600(ActivityThread.java:141)
02-04 13:22:57.189: E/AndroidRuntime(22968):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
02-04 13:22:57.189: E/AndroidRuntime(22968):    at android.os.Handler.dispatchMessage(Handler.java:99)
02-04 13:22:57.189: E/AndroidRuntime(22968):    at android.os.Looper.loop(Looper.java:137)
02-04 13:22:57.189: E/AndroidRuntime(22968):    at android.app.ActivityThread.main(ActivityThread.java:5039)
02-04 13:22:57.189: E/AndroidRuntime(22968):    at java.lang.reflect.Method.invokeNative(Native Method)
02-04 13:22:57.189: E/AndroidRuntime(22968):    at java.lang.reflect.Method.invoke(Method.java:511)
02-04 13:22:57.189: E/AndroidRuntime(22968):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
02-04 13:22:57.189: E/AndroidRuntime(22968):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
02-04 13:22:57.189: E/AndroidRuntime(22968):    at dalvik.system.NativeStart.main(Native Method)
02-04 13:22:57.189: E/AndroidRuntime(22968): Caused by: java.lang.NullPointerException
02-04 13:22:57.189: E/AndroidRuntime(22968):    at com.example.epub.MainActivity.onCreate(MainActivity.java:45)
02-04 13:22:57.189: E/AndroidRuntime(22968):    at android.app.Activity.performCreate(Activity.java:5104)
02-04 13:22:57.189: E/AndroidRuntime(22968):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
02-04 13:22:57.189: E/AndroidRuntime(22968):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
02-04 13:22:57.189: E/AndroidRuntime(22968):    ... 11 more
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1 回答 1

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空指针异常基本上是由于部分加载了 sl4j 和 epublib 等类。为此，您必须将 slf4-api 和 slf4-simple 等 slf4-android 的依赖项导入 libs 文件夹并将其放入构建路径。

于 2013-02-05T06:07:25.663 回答