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Android - general exception catcher

I'm trying to integrate Facebook into my app so I followed all the instructions. When running it, after onResume event finishes, I get an exception that I can't catch from my code.
Is there a way to set a general exception catcher so no matter what, it will catch it?
The emulator does not throw any exception at all so I can't use it for this
Update: I found it here: Using Global Exception Handling on android
The error came from Facebook itself and it is related to working with proguard

try this solution:
create a class that implement Thread.UncaughtExceptionHandler (this
class going to handle with the uncaughtExceptions), lets call this
class ExceptionHandler.
create a class that extends Application,
lets call this class App, and don't forget to declare this in the
manifest file under application tag: android:name="your_package_path.App"
in your App class override the method onCreate(), and add this line: Thread.setDefaultUncaughtExceptionHandler(new ExceptionHandler(this));

The Throwable class is the superclass of all errors and exceptions in the Java language.
If you catch a throwable you can catch all kind of errors and exceptions.
try {
// code
} catch(Throwable e) {
// handle throwable
}
However this is strongly not recommended and bad practise/design. You should never catch generic errors and exceptions. You should analyse your specific exception and solve the problem instead of simply ignoring it with try/catch!

There is a base Exception class. So if you do like this:
try {
...anything...
}catch(Exception e) {
e.printStackTrace();
}
you'll catch any exception that is thrown by any method called from within the try block.
But remember that exceptions aren't always thrown. Sometimes there's just no result to return, or something.

Correctly setting up Java exception handling

I've been attempting to write Java exception handlers for a while now, have tried multiple methods and have even visited/read through Oracle's "The Java Tutorials" and I still cannot get it straight. I'm unsure what I am doing wrong. I have a given class (TooLowException) for the exception that I am trying to use. In the method I am attempting to use it in I am using an argument that I need to catch if it is less than zero.
public int func(int num) throws TooLowException {
int blah = num + 1;
if ( blah < 0) {
return blah;
}
else {
String error = "Input is too low.";
throw new TooLowException(error);
}
}
This is the exception class:
public class TooLowException extends Exception {
public TooLowException(String response) {
super(response);
}
}
I'm getting the error in Oracle "Unhandled Exception type TooLowException". I've also attempted the try-catch method as well, but it also doesn't work for me. Hopefully this is enough information for someone to point out what I'm doing incorrectly. I need to be set right in my ways of exception handling.

Taken from what info you've given, it seems that you need to have a try/catch block somewhere in your code. Basically somewhere in your application that func(int) method is being called, or needs to be called if you're running into a compiler error telling you the "Unhandled Exception type TooLowException." General rule for exceptions is Handle/Catch or Declare. This can be broken down like this:
Handle/Catch: If you choose to handle the exception, then the "throws" declaration should be removed from the method signature ("public int func(int num) throws TooLowException" becomes "public int func(int num)"). The idea behind this approach is that you as the programmer intend to handle this type of exception because it's specific enough to the method that you don't want external code to have to worry about handling the exception outside of the scope of the method. This requires that you "handle" the exception yourself, by using a try/catch block.
Declare: This is the method you went with. You are stating that whatever class uses this function has the burden of handling the exception with the try/catch block. This would be used if the method you wrote is generic enough that many different applications can use it and that handling the exception should be application specific, i.e., it's up to other developers to handle it in their own way. Some people like to just log things, others like to have a different control flow execute upon receiving certain exceptions.
Here's what works, sorry if it basically answers an exercise you needed to do, but it's in the interest of helping you! Please take time to understand what is happening here:
public class YourClassThisStuffIsIn {
public static int func(int num) throws TooLowException {
int blah = num + 1;
if ( blah < 0) {
return blah;
}
else {
String error = "Input is too low.";
throw new Exception(error);
}
}
public static void main(String[] commandlineArgument){
try {
YourClassThisStuffIsIn.func(3);
} catch (TooLowException tle){
System.out.println("Caught " + e);
}
}
}
When you click run in your IDE, or you run through the console, the JVM looks for the main method with the correct signature. In this case it finds it, and it executes the main method. First line is a try, meaning the JVM has to prepare itself for the possibility of a problem in the application, allowing it to recover in case an exception is thrown. In this case, the only exception that can be thrown is a TooLowException, which you have written how to handle it inside the catch block. Your way of handling it is simply printing the stack trace out, which is fine I think in this situation.
I've changed your example slightly, making your method static just so it's quicker to write. I also suspect that the intent is that the commandLineArgument is meant to be the number passed into the func(int) method, so in that case you're looking at the func method to look like func(Integer.parseInt(commandlineArgument[0])).
Bonus points for you is noticing that parseInt throws a NumberFormatException too, but you will of course remember that java.lang.RuntimeException and its subclasses aren't checked exceptions so there is no requirement to catch them, though it is good practice!

Is there a way to make Runnable's run() throw an exception?

A method I am calling in run() in a class that implements Runnable) is designed to be throwing an exception.
But the Java compiler won't let me do that and suggests that I surround it with try/catch.
The problem is that by surrounding it with a try/catch I make that particular run() useless. I do want to throw that exception.
If I specify throws for run() itself, the compiler complains that Exception is not compatible with throws clause in Runnable.run().
Ordinarily I'm totally fine with not letting run() throw an exception. But I have unique situation in which I must have that functionality.
How to I work around this limitation?

You can use a Callable instead, submitting it to an ExecutorService and waiting for result with FutureTask.isDone() returned by the ExecutorService.submit().
When isDone() returns true you call FutureTask.get(). Now, if your Callable has thrown an Exception then FutureTask.get() wiill throw an Exception too and the original Exception you will be able to access using Exception.getCause().

If you want to pass a class that implements Runnable into the Thread framework, then you have to play by that framework's rules, see Ernest Friedman-Hill's answer why doing it otherwise is a bad idea.
I have a hunch, though, that you want to call run method directly in your code, so your calling code can process the exception.
The answer to this problem is easy. Do not use Runnable interface from Thread library, but instead create your own interface with the modified signature that allows checked exception to be thrown, e.g.
public interface MyRunnable
{
void myRun ( ) throws MyException;
}
You may even create an adapter that converts this interface to real Runnable ( by handling checked exception ) suitable for use in Thread framework.

If run() threw a checked exception, what would catch it? There's no way for you to enclose that run() call in a handler, since you don't write the code that invokes it.
You can catch your checked exception in the run() method, and throw an unchekced exception (i.e., RuntimeException) in its place. This will terminate the thread with a stack trace; perhaps that's what you're after.
If instead you want your run() method to report the error somewhere, then you can just provide a callback method for the run() method's catch block to call; that method could store the exception object somewhere, and then your interested thread could find the object in that location.

Yes, there is a way to throw a checked exception from the run() method, but it's so terrible I won't share it.
Here's what you can do instead; it uses the same mechanism that a runtime exception would exercise:
#Override
public void run() {
try {
/* Do your thing. */
...
} catch (Exception ex) {
Thread t = Thread.currentThread();
t.getUncaughtExceptionHandler().uncaughtException(t, ex);
}
}
As others have noted, if your run() method is really the target of a Thread, there's no point in throwing an exception because it is unobservable; throwing an exception has the same effect as not throwing an exception (none).
If it's not a Thread target, don't use Runnable. For example, perhaps Callable is a better fit.

#FunctionalInterface
public interface CheckedRunnable<E extends Exception> extends Runnable {
#Override
default void run() throws RuntimeException {
try {
runThrows();
}
catch (Exception ex) {
throw new RuntimeException(ex);
}
}
void runThrows() throws E;
}

Some people try to convince you that you have to play by the rules. Listen, but whether you obey, you should decide yourself depending on your situation. The reality is "you SHOULD play by the rules" (not "you MUST play by the rules"). Just be aware that if you do not play by the rules, there might be consequences.
The situation not only applies in the situation of Runnable, but with Java 8 also very frequently in the context of Streams and other places where functional interfaces have been introduced without the possibility to deal with checked exceptions. For example, Consumer, Supplier, Function, BiFunction and so on have all been declared without facilities to deal with checked exceptions.
So what are the situations and options?
In the below text, Runnable is representative of any functional interface that doesn't declare exceptions, or declares exceptions too limited for the use case at hand.
You've declared Runnable somewhere yourself, and could replace Runnable with something else.
Consider replacing Runnable with Callable<Void>. Basically the same thing, but allowed to throw exceptions; and has to return null in the end, which is a mild annoyance.
Consider replacing Runnable with your own custom #FunctionalInterface that can throw exactly those exceptions that you want.
You've used an API, and alternatives are available. For example, some Java APIs are overloaded so you could use Callable<Void> instead of Runnable.
You've used an API, and there are no alternatives. In that case, you're still not out of options.
You can wrap the exception in RuntimeException.
You can hack the exception into a RuntimeException by using an unchecked cast.
You can try the following. It's a bit of a hack, but sometimes a hack is what we need. Because, whether an exception should be checked or unchecked is defined by its type, but practically should actually be defined by the situation.
#FunctionalInterface
public interface ThrowingRunnable extends Runnable {
#Override
default void run() {
try {
tryRun();
} catch (final Throwable t) {
throwUnchecked(t);
}
}
private static <E extends RuntimeException> void throwUnchecked(Throwable t) {
throw (E) t;
}
void tryRun() throws Throwable;
}
I prefer this over new RuntimeException(t) because it has a shorter stack trace.
You can now do:
executorService.submit((ThrowingRunnable) () -> {throw new Exception()});
Disclaimer: The ability to perform unchecked casts in this way might actually be removed in future versions of Java, when generics type information is processed not only at compile time, but also at runtime.

Your requirement doesn't make any sense. If you want to notify the called of the thread about an exception that happened, you could do that through a call back mechanism. This can be through a Handler or a broadcast or whatever else you can think of.

I think a listener pattern might help you with this scenario. In case of an exception happening in your run() method, use a try-catch block and in the catch send a notification of an exception event. And then handle your notification event. I think this would be a cleaner approach. This SO link gives you a helpful pointer to that direction.

Yes, you can throw checked exceptions from the run() method. It can be done with generics by tricking the compiler. Look at this code:
public static void main(String[] args) {
new Main().throwException();
}
public void throwException() {
Runnable runnable = () -> throwAs(new Exception());
new Thread(runnable).start();
}
private <T extends Throwable> void throwAs(Throwable t) throws T {
throw ( T ) t;
}
This might be helpful if you want to throw checked exceptions from the run() method of Runnable

The easiest way is to define your own exception object which extend the RuntimeException class instead of the Exception class.

relax exception catch necessity

Is there a possibility in Java to get rid of the necessity to catch non-RuntimeException exceptions? Maybe compiler flags?
I know the reason why the catching is promoted, but want to do simple and straight tools that enforce their requirements. So if something can went wrong I don't like to catch up but exit the application, crashing with a meaningful exception. Usually this ends up like:
try {
connection.close();
} catch (IOException e) {
throw new RuntimeException(e);
}
which introduces 4 lines of code mess, and introduces the wrapping RuntimeException mess on error output. Sometimes it even motivate people to wrap large try ... catch (Throwable ..) blocks around anything, which is the likely cause for our beloved 'Unknown error occured' alert boxes...

you can use throws keyword with method prototype to avoid try-catch block. which eventually throws the exception to JVM's Default Exception handler which halts the application if no catch block's are specified in your code to handle the exception raised.

Crashing the application at the first sight of an exception is very bad practice. Especially when some work is unsaved and the application is using some resources that needs to be freed and cleaned before the application terminates execution. Some very popular software used to do that... and instead of "fixing" the issue, they introduced a data recoverability features on application restart. However the trick, this is not good software engineering.
At the very least, your application should not crash on the first exception/error encountered, but recover with a meaningful message. It is being lazy to just wrap everything in a RuntimeException (or even Throwable) and, especially, not do anything with it.
Java does not support flags of any kind because there are 1) a workaround, and 2) better ways to handle this situation. For example :
1. Handle the exception in the calling method
You can add the throws keyword in your method declaration, up to your static public void main method, which, if not handling the exception, will eventually crash the application with a stacktrace.
class Foo {
public void someMethod(....) throws IllegalArgumentException, IOException {
...
}
static public void main(String...args) throws Throwable {
new Foo().someMethod();
}
}
This method does not offer any means of recoverability and will probably make your user unhappy (with a big meaningless stachtrace if they ran the application from a console, or just nothing at all if they launched it from a shortcut or GUI). Also, if you have some acquired resources, you will not be able to clean them when an exception occurs. At the very least, your main should catch (Throwable e) and output something before throwing the exception above. Something like :
class Foo {
public void someMethod(....) throws IllegalArgumentException, IOException {
...
}
static public void main(String...args) {
try {
new Foo().someMethod();
} catch (...) {
// output or log exception here and, optionally, cleanup and exit
}
}
}
** EDIT **
Consider this scenario : a program is initializing some resource for processing some data, then some runtime exception (or error) occurs during processing, the application crash, but the resources are not released or freed. In Java, however, one could do this
public E doSomething() throws RuntimeException {
// declare a bunch of resources
try {
// process resources with unchecked exceptions
} finally {
// free resources
}
// return some result
}
and cleanly exit the method on error or on success, perhaps even logging the runtime error for "posterity".
2. Log the error and return some meaningful value
Logging is a very good practice. You can show your user some message telling them that the operation could not be executed without crashing the whole thing, and giving you some traces of what and where the user were doing. A simplistic logging system could be :
class Foo {
static private final Logger LOG = Logger.getLogger(Foo.class.getName());
public boolean doSomethingImpl(...) {
boolean result = true;
try {
...
} catch (SomeException e) {
LOG.log(Level.SEVERE, "meaningful message why method could not do something!", e);
result = false;
}
return result;
}
public void doSomething() {
if (!doSomethingImpl(...)) {
// handle failure here
}
}
}
By default, the Logger will output everything to the err output stream, but you can add your own handlers :
// loggers are singletons, so you can retrieve any logger at anytime from
// anywhere, as long as you know the logger's name
Logger logger = Logger.getLogger(Foo.class.getName());
logger.setUseParentHandlers(false); // disable output to err
logger.addHandler(new MyHandler()); // MyHandler extends java.util.logging.Handler
Java already ships with some default logging handlers, one of which writes to file.
etc.

Is there a possibility in Java to get rid of the necessity to catch non-RuntimeException exceptions?
For a checked exception, you can chose between catching the exception and declaring it in the method header as thrown.
Maybe compiler flags?
No. There are no compiler flags to relax this. It is a fundamental part of the language design. Relaxing the checked exception rules via a compiler switch would cause serious library interoperability problems.

I don't think that there's any way around this for the JVM. Your best bet is to have your methods re-throw the exception, which gets rid of the "mess" in your code, and then have your main program throw Exception. This should propagate the error up to the top of your program.
Keep in mind, however, that the place where the exception actually happens is a much better place to let the user know what happened (i.e., exactly what it was doing when this particular IOException happened). You'll lose this resolution if all errors are simply propagated up to the top level.

You do have the ability to throw your exceptions up a level. Here's an example
public class Foo {
public Foo() {
super();
}
public void disconnect(connection) throws IOException {
connection.close();
}
}

Use "Throws" to avoid the error..but it will not be good programimg practice

How can I detect when an Exception's been thrown globally in Java?

How can I detect when an Exception has been thrown anywhere in my application?
I'm try to auto-magically send myself an email whenever an exception is thrown anywhere in my Java Desktop Application. I figure this way I can be more proactive.
I know I could just explicitly log and notify myself whenever an exception occurs, but I'd have to do it everywhere and I might(more likely will) miss a couple.
Any suggestions?

You probobly don't want to mail on any exception. There are lots of code in the JDK that actaully depend on exceptions to work normally. What I presume you are more inerested in are uncaught exceptions. If you are catching the exceptions you should handle notifications there.
In a desktop app there are two places to worry about this, in the event-dispatch-thread (EDT) and outside of the EDT. Globaly you can register a class implementing java.util.Thread.UncaughtExceptionHandler and register it via java.util.Thread.setDefaultUncaughtExceptionHandler. This will get called if an exception winds down to the bottom of the stack and the thread hasn't had a handler set on the current thread instance on the thread or the ThreadGroup.
The EDT has a different hook for handling exceptions. A system property 'sun.awt.exception.handler' needs to be registerd with the Fully Qualified Class Name of a class with a zero argument constructor. This class needs an instance method handle(Throwable) that does your work. The return type doesn't matter, and since a new instance is created every time, don't count on keeping state.
So if you don't care what thread the exception occurred in a sample may look like this:
class ExceptionHandler implements Thread.UncaughtExceptionHandler {
public void uncaughtException(Thread t, Throwable e) {
handle(e);
}
public void handle(Throwable throwable) {
try {
// insert your e-mail code here
} catch (Throwable t) {
// don't let the exception get thrown out, will cause infinite looping!
}
}
public static void registerExceptionHandler() {
Thread.setDefaultUncaughtExceptionHandler(new ExceptionHandler());
System.setProperty("sun.awt.exception.handler", ExceptionHandler.class.getName());
}
}
Add this class into some random package, and then call the registerExceptionHandler method and you should be ready to go.

The new debugging hooks in Java 1.5 let you do this. It enables e.g. "break on any exception" in debuggers.
Here's the specific Javadoc you need.

Check out Thread.UncaughtExceptionHandler. You can set it per thread or a default one for the entire VM.
This would at least help you catch the ones you miss.

If you're using a web framework such as Spring then you can delegate in your web.xml to a page and then use the controller to send the email. For example:
In web.xml:
<error-page>
<error-code>500</error-code>
<location>/error/500.htm</location>
</error-page>
Then define /error/500.htm as a controller. You can access the exception from the parameter javax.servlet.error.exception:
Exception exception = (Exception) request.getAttribute("javax.servlet.error.exception");
If you're just running a regular Java program, then I would imagine you're stuck with public static void main(String[] args) { try { ... } catch (Exception e) {} }

If you are using java 1.3/1.4, Thread.UncaughtExceptionHandler is not available.
In this case you can use a solution based on AOP to trigger some code when an exception is thrown. Spring and/or aspectJ might be helpful.

In my current project I faced the similar requirement regarding the errors detection. For this purpose I have applied the following approach: I use log4j for logging across my app, and everywhere, where the exception is caught I do the standard thing: log.error("Error's description goes here", e);, where e is the Exception being thrown (see log4j documentation for details regarding the initialization of the "log").
In order to detect the error, I use my own Appender, which extends the log4j AppenderSkeleton class:
import org.apache.log4j.AppenderSkeleton;
import org.apache.log4j.spi.LoggingEvent;
public class ErrorsDetectingAppender extends AppenderSkeleton {
private static boolean errorsOccured = false;
public static boolean errorsOccured() {
return errorsOccured;
}
public ErrorsDetectingAppender() {
super();
}
#Override
public void close() {
// TODO Auto-generated method stub
}
#Override
public boolean requiresLayout() {
return false;
}
#Override
protected void append(LoggingEvent event) {
if (event.getLevel().toString().toLowerCase().equals("error")) {
System.out.println("-----------------Errors detected");
this.errorsOccured = true;
}
}
}
The log4j configuration file has to just contain a definition of the new appender and its attachement to the selected logger (root in my case):
log4j.rootLogger = OTHER_APPENDERS, ED
log4j.appender.ED=com.your.package.ErrorsDetectingAppender
You can either call the errorsOccured() method of the ErrorsDetectingAppender at some significant point in your programs's execution flow or react immidiately by adding functionality to the if block in the append() method. This approach is consistent with the semantics: things that you consider errors and log them as such, are detected. If you will later consider selected errors not so important, you just change the logging level to log.warn() and report will not be sent.

In this case I think your best bet might be to write a custom classloader to handle all classloading in your application, and whenever an exception class is requested you return a class that wraps the requested exception class. This wrapper calls through to the wrapped exception but also logs the exception event.

I assume you don't mean any Exception but rather any uncaught Exception.
If this is the case this article on the Sun Website has some ideas. You need to wrap your top level method in a try-catch block and also do some extra work to handle other Threads.

Sending an email may not be possible if you are getting a runtime exception like OutOfMemoryError or StackOverflow. Most likely you will have to spawn another process and catch any exceptions thrown by it (with the various techniques mentioned above).

There is simply no good reason to be informed of every thrown exception. I guess you are assuming that a thrown exception indicates a "problem" that your "need" to know about. But this is wrong. If an exception is thrown, caught and handled, all is well. The only thing you need to be worried about is an exception that is thrown but not handled (not caught). But you can do that in a try...catch clause yourself.