我正在尝试使用 JavaMailSender 在我的 Spring MVC Web 应用程序和 Tomcat 7 中发送注册确认电子邮件，但它始终返回 NullPointerException。谁能帮我找出为什么我得到空指针？以下是我的配置设置：

网页.xml

<!-- jndi mail session -->
<resource-ref>
    <description>
        Resource reference to a factory for javax.mail.Session
        instances that may be used for sending electronic mail
        messages, preconfigured to connect to the appropriate
        SMTP server.
    </description>
    <res-ref-name>mail/Session</res-ref-name>
    <res-type>javax.mail.Session</res-type>
    <res-auth>Container</res-auth>
</resource-ref>

应用程序-servlet.xml

    <!-- Mail Sender bean definition -->

<bean id="smtpSession" class="org.springframework.jndi.JndiObjectFactoryBean">
        <property name="jndiName" value="java:comp/env/mail/session"/>
</bean>

<bean id="mailSender" class="org.springframework.mail.javamail.JavaMailSenderImpl">
    <property name="session" ref="smtpSession"/>
     <!--
    <property name="host" value="smtp.gmail.com" />
    <property name="port" value="465" />
    <property name="username" …

我从其他片段开始一个片段时得到NullPointerException.我试图在动态启动片段后调用第二个片段中的方法.

这是我的logcat:

05-20 09:58:31.907: E/AndroidRuntime(2585): FATAL EXCEPTION: main
05-20 09:58:31.907: E/AndroidRuntime(2585): java.lang.NullPointerException
05-20 09:58:31.907: E/AndroidRuntime(2585):     at com.exercise.FragmentTest.MyFragment3.setImage(MyFragment3.java:22)
05-20 09:58:31.907: E/AndroidRuntime(2585):     at com.exercise.FragmentTest.FragmentTestActivity$1.onClick(FragmentTestActivity.java:48)
05-20 09:58:31.907: E/AndroidRuntime(2585):     at android.view.View.performClick(View.java:4204)
05-20 09:58:31.907: E/AndroidRuntime(2585):     at android.view.View$PerformClick.run(View.java:17355)
05-20 09:58:31.907: E/AndroidRuntime(2585):     at android.os.Handler.handleCallback(Handler.java:725)
05-20 09:58:31.907: E/AndroidRuntime(2585):     at android.os.Handler.dispatchMessage(Handler.java:92)
05-20 09:58:31.907: E/AndroidRuntime(2585):     at android.os.Looper.loop(Looper.java:137)
05-20 09:58:31.907: E/AndroidRuntime(2585):     at android.app.ActivityThread.main(ActivityThread.java:5041)
05-20 09:58:31.907: E/AndroidRuntime(2585):     at java.lang.reflect.Method.invokeNative(Native Method)
05-20 09:58:31.907: E/AndroidRuntime(2585):     at java.lang.reflect.Method.invoke(Method.java:511)
05-20 09:58:31.907: E/AndroidRuntime(2585):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
05-20 09:58:31.907: E/AndroidRuntime(2585):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
05-20 09:58:31.907: E/AndroidRuntime(2585):     at dalvik.system.NativeStart.main(Native Method)

和我的主要活动代码: …

由于某种原因,我的String部分由PrintWriter编写.结果我在我的文件中得到了部分文本.这是方法:

    public void new_file_with_text(String text, String fname) {
        File f = null;
        try {
            f = new File(fname);
            f.createNewFile();
            System.out.println(text);           
            PrintWriter out = new PrintWriter(f, "UTF-8");
            out.print(text);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

在我将文本打印到控制台的地方,我可以看到数据全部存在,没有任何遗失,但是当PrintWriter完成其工作时,显然部分文本会丢失...我很无能为力......

Uri selectedUri = Uri.fromFile(selected.getAbsoluteFile());
String fileExtension = MimeTypeMap.getFileExtensionFromUrl(selectedUri.toString());
String mimeType = MimeTypeMap.getSingleton().getMimeTypeFromExtension(fileExtension);

Intent intent = new Intent(Intent.ACTION_VIEW);
intent.setDataAndType(selectedUri, mimeType);
Intent chooser = Intent.createChooser(intent, "Open File...");
startActivity(chooser);

此代码始终有效,这意味着即使没有找到任何活动来处理意图,选择器对话框仍然会出现这样的情况.现在,如果没有找到填充选择器对话框的活动,此代码将抛出NullPointerException(版本4.3).有没有其他人经历过这个或知道我可能做错了什么？

logcat的:

02-25 17:03:24.260: E/AndroidRuntime(13502): FATAL EXCEPTION: main
02-25 17:03:24.260: E/AndroidRuntime(13502): java.lang.RuntimeException: Unable to start activity ComponentInfo{android/com.android.internal.app.ChooserActivity}: java.lang.NullPointerException
02-25 17:03:24.260: E/AndroidRuntime(13502):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2517)
02-25 17:03:24.260: E/AndroidRuntime(13502):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2574)
02-25 17:03:24.260: E/AndroidRuntime(13502):    at android.app.ActivityThread.access$600(ActivityThread.java:162)
02-25 17:03:24.260: E/AndroidRuntime(13502):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1413)
02-25 17:03:24.260: E/AndroidRuntime(13502):    at android.os.Handler.dispatchMessage(Handler.java:99)
02-25 17:03:24.260: E/AndroidRuntime(13502):    at android.os.Looper.loop(Looper.java:158)
02-25 17:03:24.260: E/AndroidRuntime(13502):    at android.app.ActivityThread.main(ActivityThread.java:5789)
02-25 …

在Java中,我看到了很多代码,如下所示.我想知道的是,仅显示错误消息是否足够？

我是Java新手.我想学的是如何有效地处理错误,并了解错误处理的最佳实践.一般来说,我应该怎么做catch块？

示例1:printStackTrace()

} catch (SomeException e) {
    e.printStackTrace();
}

示例2:getMessage

} catch (SomeException e) {
    e.getMessage();
}

示例3:显示自定义错误消息

} catch (IOException E) {
    System.out.println("Error occured. Please try again.");
}

大家好我想在我的谷歌地图上实现叠加.但是我在运行时收到致命错误,似乎是某种NullPointerException.当我删除"overlayList = mapView.getOverlays();"时,应用程序正常运行 和"overlayList.add(t);" 代码行.任何帮助是极大的赞赏!

主要活动:

public class CSActivity extends MapActivity implements LocationListener  {

 MapController mapController;
 MapView mapView;
 LocationManager locationManager;

MyLocationOverlay myLocationOverlay;
MyLocationOverlay compass;

private Button click_but;
private Button exit_but;
long start;
long stop;
int x,y;
GeoPoint touchedPoint;
Drawable d;
List<Overlay> overlayList;
String towers;
int lat;
int lng;

public void onCreate(Bundle bundle) {
    super.onCreate(bundle);
    setContentView(R.layout.main); // bind the layout to the activity

    click_but = new Button(this);
    click_but = (Button)findViewById(R.id.clickBtn);
    exit_but = new Button(this);
    exit_but = (Button)findViewById(R.id.exitBtn);

    d = getResources().getDrawable(R.drawable.markerblue);
    Touchy …

//System.out.println("hii");'\uxxx'

println语句已注释，但unicode未注释。为什么？

我spring4gwt在我的项目中使用.

我有以下登录服务实现:

@Service("loginService")
public class LoginServiceImpl extends RemoteServiceServlet implements LoginService {

    @Override
    @Transactional(propagation = Propagation.REQUIRED, rollbackFor = Exception.class)
    public UserBean checkUser(String userName, String password) throws Exception {

        HttpSession httpSession = getThreadLocalRequest().getSession();

    }
}

当我调用loginService.checkUser("test","test")(在托管模式下)时,我得到一个NullPointerException,因为getThreadLocalRequest()返回NULL而不是实际的会话.

我还没有尝试过网络模式.

为什么我会得到一个空会话？它与spring4gwt有关吗？

这是我的课

public class MessageFrameListener{
private MessageFrame mf;
private User us;
private Contact cn;

private Socket s;
private PrintStream ps;
private BufferedReader br;


public MessageFrameListener(MessageFrame m_f, User u_s, Contact c_n){
    mf = m_f;
    us = u_s;
    cn = c_n;
    m_f.addButtonListener(new SButtonListener());
}

public void init(){
    try {
        s = new Socket(InetAddress.getLocalHost(), 8072);
        PrintStream ps = new PrintStream(s.getOutputStream());
        BufferedReader br = new BufferedReader( new InputStreamReader(s.getInputStream()));
    } catch (UnknownHostException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // …

我正在尝试在shreyaloclistfragment中创建列表搜索视图.我在下面的行中得到NullPointerException

final SearchView searchView = (SearchView) menu.findItem(R.id.menu_search).getActionView();

我的方法是

@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater ) {
    super.onCreateOptionsMenu(menu, inflater);
    inflater.inflate( R.menu.menu_search, menu);
    System.out.println( "inflating menu");

    final SearchView searchView = (SearchView) menu.findItem(R.id.menu_search).getActionView();



    final SearchView.OnQueryTextListener queryTextListener = new SearchView.OnQueryTextListener() {
        @Override
        public boolean onQueryTextChange(String newText) {
            showFilteredItems( newText );
            return true;
        }

        @Override
        public boolean onQueryTextSubmit(String query) {
            return true;
        }
    };

    searchView.setOnQueryTextListener(queryTextListener);

    return;
}

堆栈跟踪

FATAL EXCEPTION: main
java.lang.NullPointerException
at com.sears.syw.FragmentShopsTab.onCreateOptionsMenu(FragmentShopsTab.java:52)
at android.support.v4.app.Watson.onCreatePanelMenu(Watson.java:55)
at  


com.actionbarsherlock.ActionBarSherlock.callbackCreateOptionsMenu(ActionBarSherlock.java:559    )
at   

    com.actionbarsherlock.internal.ActionBarSherlockNative.dispatchCreateOptionsMenu(ActionBarSh    erlockNative.java:65)
at 

我在运行下面的代码时得到一个NullPointerException.我不知道如何解决这些问题.

堆栈跟踪:

 E/AndroidRuntime(1118): FATAL EXCEPTION: main
     E/AndroidRuntime(1118): Process: info.androidhive.googlemapsv2, PID: 1118
     E/AndroidRuntime(1118): java.lang.RuntimeException: Unable to start activity ComponentInfo{info.androidhive.googlemapsv2/info.androidhive.googlemapsv2.MainActivity}: android.view.InflateException: Binary XML file line #6: Error inflating class fragment
     E/AndroidRuntime(1118):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
     E/AndroidRuntime(1118):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
     E/AndroidRuntime(1118):    at android.app.ActivityThread.access$800(ActivityThread.java:135)
     E/AndroidRuntime(1118):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
     E/AndroidRuntime(1118):    at android.os.Handler.dispatchMessage(Handler.java:102)
     E/AndroidRuntime(1118):    at android.os.Looper.loop(Looper.java:136)
     E/AndroidRuntime(1118):    at android.app.ActivityThread.main(ActivityThread.java:5017)
     E/AndroidRuntime(1118):    at java.lang.reflect.Method.invokeNative(Native Method)
     E/AndroidRuntime(1118):    at java.lang.reflect.Method.invoke(Method.java:515)
     E/AndroidRuntime(1118):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
     E/AndroidRuntime(1118):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
     E/AndroidRuntime(1118):    at dalvik.system.NativeStart.main(Native Method)
     E/AndroidRuntime(1118): Caused by: android.view.InflateException: Binary XML file line #6: Error inflating class fragment
     E/AndroidRuntime(1118): …