我对此并不陌生,但是我正在编写一个应用程序,并且不断收到此错误,导致该应用程序在启动时崩溃。
java.lang.NullPointerException: Attempt to invoke virtual method 'void java.io.BufferedWriter.close()' on a null object reference
导致该错误的代码在下面的类中,在此行旁边有一个HERE注释。
public class FileOptions extends Activity{
public void createFile(String title, String storeValue){
BufferedWriter bufferWriter = null;
try {
FileOutputStream fileOutputStream = openFileOutput(title, Context.MODE_PRIVATE);
bufferWriter = new BufferedWriter(new OutputStreamWriter(fileOutputStream));
String content = storeValue;
bufferWriter.write(content);
} catch (FileNotFoundException e) {
e.printStackTrace();
}
catch (IOException e) { //Cannot be removed
e.printStackTrace();
}
finally {
try {
/**HERE*/ bufferWriter.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
//More unimportant stuff
}
这是我从中调用方法的代码。
public class MainActivity extends ActionBarActivity {
Context context = this;
boolean debug = true;
FileOptions file = new FileOptions();
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Boolean isFirstRun = getSharedPreferences("PREFERENCE", MODE_PRIVATE)
.getBoolean("isfirstrun", true);
if(isFirstRun) {
file.createFile("userInfo", "");
getSharedPreferences("PREFERENCE", MODE_PRIVATE).edit()
.putBoolean("isfirstrun", false).commit();
}
if(file.readFile("userInfo") != "")
{
if(debug){alerter(file.readFile("userInfo"));alerter("true");}
switchToHome();
}else{
if(debug){alerter("false");}
}
}
}
这是堆栈跟踪。
08-27 22:44:35.830 13089-13089/? I/libpersona﹕ KNOX_SDCARD checking this for 10247
08-27 22:44:35.830 13089-13089/? I/libpersona﹕ KNOX_SDCARD not a persona
08-27 22:44:35.830 13089-13089/? E/Zygote﹕ MountEmulatedStorage()
08-27 22:44:35.830 13089-13089/? E/Zygote﹕ v2
08-27 22:44:35.830 13089-13089/? I/SELinux﹕ Function: selinux_compare_spd_ram, SPD-policy is existed. and_ver=SEPF_SM-N910V_5.0.1 ver=27
08-27 22:44:35.830 13089-13089/? I/SELinux﹕ Function: selinux_compare_spd_ram , priority [1] , priority version is VE=SEPF_SM-N910V_5.0.1_0027
08-27 22:44:35.830 13089-13089/? E/SELinux﹕ [DEBUG] get_category: variable seinfo: default sensitivity: NULL, cateogry: NULL
08-27 22:44:35.830 13089-13089/? I/art﹕ Late-enabling -Xcheck:jni
08-27 22:44:35.870 13089-13089/? D/TimaKeyStoreProvider﹕ TimaSignature is unavailable
08-27 22:44:35.870 13089-13089/? D/ActivityThread﹕ Added TimaKeyStore provider
08-27 22:44:35.920 13089-13089/? D/ResourcesManager﹕ creating new AssetManager
and set to /data/app/preventioninnovations.preventapp-2/base.apk
08-27 22:44:36.050 13089-13089/? D/AndroidRuntime﹕ Shutting down VM
08-27 22:44:36.050 13089-13089/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: preventioninnovations.preventapp, PID: 13089
java.lang.RuntimeException: Unable to start activity ComponentInfo{preventioninnovations.preventapp/preventioninnovations.preventapp.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void java.io.BufferedWriter.close()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2712)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2777)
at android.app.ActivityThread.access$900(ActivityThread.java:179)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1462)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:5972)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void java.io.BufferedWriter.close()' on a null object reference
at preventioninnovations.preventapp.FileOptions.createFile(FileOptions.java:37)
at preventioninnovations.preventapp.MainActivity.onCreate(MainActivity.java:38)
at android.app.Activity.performCreate(Activity.java:6289)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2777)
at android.app.ActivityThread.access$900(ActivityThread.java:179)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1462)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:5972)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
谢谢你的帮助。
最佳答案
当您的openFileOutput()
方法引发异常时,会发生这种情况。
由于引发了异常,因此bufferWriter
未初始化为有效对象。
并且该异常导致执行跳过了try块的其余部分,以赶上catch块,然后最终执行block。
因此,当它到达finally块时,bufferWriter
是null
。
finally {
try {
if (bufferWriter != null)
bufferWriter.close();
} catch (IOException e) {
e.printStackTrace();
}
}
要解决此问题,请在
null
中调用close之前检查bufferWriter
。还是更好地使用资源。
try(BufferedWriter = new BufferedWriter(
new OutputStreamWriter(
openFileOutput(title, Context.MODE_PRIVATE)))) {}