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Java - Annotation for logging Object (CustomException) instantiations?

Small Java question regarding object instantiation and logging please.
In our (way too big) project we have one particular exception MyCustomException which is thrown.
The usual code will be something like:
if (conditionNotMet()) {
throw new MyCustomException();
try {
} catch (SomeException e) {
throw new MyCustomException();
There are a good thousands of throws of this kind.
And for all of them, we would like to add logging, something like:
if (conditionNotMet()) {
LOGGER.error(something bad happened, throwing a new MyCustomException());
throw new MyCustomException();
try {
} catch (SomeException e) {
LOGGER.error(something bad happened, throwing a new MyCustomException());
throw new MyCustomException();
As you can imagine, since we have thousands and thousands of those, we are wasting tremendous times adding the LOGGER in all the places.
I was wondering, is there some kind of annotation we can put on the MyCustomException, something like:
#LogMeWhenIamCreated
public MyCustomException(...) {
So we can put this annotation in only one place, and still be able to see the logs we want, without us having to go through the entire code base and the thousands of throws?
Thank you

I see three options here:
Use AOP to handle creation of MyCustomException. Follow this answer to see how you can write the aspect for class creation. It's also possible to write aspect for #LogMeWhenIamCreated annoptation.
Use regex to find all throw new MyCustomException(); constructions and add logging before throwing. The disadvantage is obvious - a lot of changes.
Add logging to the MyCustomException constructor as Rohan suggested.
The disadvantage for options 1 and 2: if you have places where you construct the exception and don't throw it, the log message will still be added.

How am I supposed to let an Unchecked Exception bubble up and log?

So quoting from this page, which is titled: Exception-Handling Antipatterns Blog and seems to be written (or at least to be approved) by Oracle..
An unchecked exception probably shouldn't be retried, and the correct response is usually to do nothing, and let it bubble up out of your method and through the execution stack. This is why it doesn't need to be declared in a throws clause. Eventually, at a high level of execution, the exception should probably be logged.
I am not sure if I understand this. How can I log an unchecked exception? If I have something like:
public static void main(String args) {
foo();
// How do I know what to log here? The method I am calling
// is not throwing an Exception.
// Do I just blindly catch(Exception ex)?
}
static void foo() {
bar();
}
static void bar() {
baz();
}
static void baz() {
// I will do nothing as Oracle suggests and let this exception bubble up.. I wonder who is going to catch it and how this is going to be logged though!
throw new NullPointerException();
}
Can you help me understand what Oracle is suggesting here? I do not see any direct (or clear) way to catch runtime exceptions (I do not understand why it is not just called unchecked exceptions..) in higher levels and I am not sure how this suggested practice is useful. To me it would make more sense if it were talking about checked exceptions. Something like..
If a checked exception is thrown in a method that is not reasonable to be re-tried, the correct response is to let it bubble up and log..

You can also register a global ExceptionHandler that will handle the Exceptions that were not caught by your code:
Thread.setDefaultUncaughtExceptionHandler
This exception handle could then log whatever occured.

First of all, this is a general advice and it depends on the context. The idea behind it is that when a runtime exception occurs (ex. NullPointerException), the system is usually in an indeterministic state, meaning the rest of the code is not be guaranteed to execute as expected, so it's better to stop everything.
In most cases, your code will run in a separate thread and the exception will only stop the current thread, while the rest of the program keeps running.
This is not the case in your example, because everything is executed in a single thread, so the uncaught exception will effectively stop the whole program. In this scenario you might want to catch the exception and handle it.
public static void main(String args) {
try {
foo();
catch(Throwable t) {
t.printStackTrace(); // log exception
// handle the failure
}
}
You can also catch the exception earlier on, log and rethrow it further.
static void bar() {
try {
baz();
catch (Throwable t) { // catch
t.printStackTrace(); // log
throw t; // rethrow further
}
}
Edit: catch Throwable instead of Exception, will also catch Error
Note: Catching throwable is usually a bad idea, and should only be done with a specific purpose, not in general case. See #RC.'s comment.

As I understand it the documentation is suggesting that you have a generic handler at a high level of your code that logs such 'unexpected' (unrecoverable?) exceptions just as the comments in your main method suggest. So it might look something like this
public static void main(String args) {
try {
foo();
}
catch (ArithmeticException aex) { //if it's arithmetic log differently
log("arith issue! "+aex.getMessage());
}
catch (Exception ex) { //Otherwise do the best we can
log("unknown issue! "+ex.getMessage())
}
}
So there is still no path to recovery but at least before the process ends you get a chance to log the issue. You can also use the methods of Exception (or throwable) to get the stack trace and first causal exceptions in many case - so there is is a lot of extra useful information that might be logged.

There is a very straightforward way to catch unchecked exceptions, since they are all subclasses of RuntimeException or Error:
public static void main(String[] args) {
try {
// your code
} catch (RuntimeException | Error e) {
// handle uncaught exceptions, e.g.
e.printStackTrace();
}
}

How do I know what to log here? The method I am calling is not throwing an Exception.
As Joshua Bloch recommends in the Effective Java
Use the Javadoc #throws tag to document each unchecked exception that
a method can throw, but do not use the throws keyword to include
unchecked exceptions in the method declaration
And if you are using method wrapping in multilayered app i can recommend use exception translation:
Higher layers should catch lower-level exceptions and, in their place, throw exceptions that can be explained in terms of the higher-level abstraction
See Effective Java item 61
So i think for your example actually you should use something like:
try {
bar();
} catch(NullPointerException e) {
throw new HigherLevelException(...);
}

The most important guideline regarding exceptions is that a method that couldn't sucessfully complete its task should throw an exception.
Only if you can guarantee successful completion of your method's task, you should catch an exception inside your method (without re-throwing this or another exception). From my experience that's only true in very specific situations, e.g. if you have an alternative way to try if some first attempt fails, or if you really really understand all possible causes of this specific Exception class that you are about to catch.
Speaking about RuntimeExceptions, there are so many different types of RuntimeException that you can hardly justify an assertion like "When such an exception arises in my code or a method called from inside my code, that won't affect the outcome of my method - I can continue just as if nothing happened." So, you should signal to your caller that you failed to fulfill your task, and the clearest way to do that is to let the exception ripple through, without try/catch block or throws declaration, just relying on Java's default behaviour.
In my opinion, the same reasoning applies to nearly all kinds of exceptions, not only RuntimeExceptions.
The difference with checked exceptions is that you have to declare them in the throws clause of your method. Then you have two choices: list the exception in the throws clause of your method (and all parent methods as well!) or catch the exception, wrap it in a new RuntimeException(ex), and throw that from your method.
With e.g. a typical GUI application, your users will be grateful if a problem in one menu function won't crash the whole application - probably other menu items might still work as expected. So, top-level commands or menu items are typically the places where to catch exceptions, tell the user something like "Oops!", log the exception to some file for later inspection, and allow the user to continue with another action.
In your main/foo/bar/baz application, I don't see a place where continuing after an exception makes sense. So the whole program should be aborted (which happens automatically in your case). If you want some error logging to a file, then establish an uncaught exception handler or wrap the body of main() in a try / catch(Throwable t) block. You'll probably want every exception logged, whatever type it is, so catch them all, and that's why I'm suggesting Throwable.

public static void main(String[] args) {
try {
foo();
}
catch(NullPointerException e){
System.out.println("NullPointerException in main.");
}
}
static void foo() {
bar();
}
static void bar() {
baz();
}
static void baz() {
// I will do nothing as Oracle suggests and let this exception bubble up.. I wonder who is going to catch it and how this is going to be logged though!
throw new NullPointerException();
}
OUTPUT :
NullPointerException in main.
Basically the error is expected at a higher level, so there is no need to catch it on the baz() method level. If I understood correctly.

You can catch them just like any other exception with try-catch block. But the benefit is that you don't have to.
Use cases can vary. To my mind, the most popular is when it doesn't make sense to catch the exception right in that place or the appropriate handling should be implemented several levels (in terms of methods) higher than the method, calling the one throwing the exception (sorry, if that is not clear enough).
For example, the typical web application layout in java is as follows: you have a layer of controllers, a layer of services and a layer of dao. First one is responsible for dispatching requests, the second one is for managing business logic and the last one makes actual calls to db. So here for example it often doesn't make much sense to catch the exception in service layer if something goes wrong on the dao level. Here unchecked exceptions can be used. You log an exception and throw an unchecked exception so it could be handled some levels above for a user to get valuable feedback of work of the application.
If in this case you throw a checked exception you will have to rethrow it every level above just to bubble up it to the place of the actual handling. So here the unchecked exception is better to use in order not to copy and paste all that ugly try-catch block, rethrowing an exception and add the throws clause to the method.

Is "throws Throwable" good practice

In the past I'd read tons of code with methods like:
public Object doSomething() throws Throwable {
...
}
Is it common practice to do that?
What are pros & cons?
throws Trowable seemed to me like the "Agent Orange" way of getting the Exception- matter done
EDIT
Handle expected Exceptions in the Method
Throw unexpected Exceptions (one by one)
Don't care of Errors
Is that the way to go?

You should not throw Throwable. Here's why.
Throwable is the top of the hierarchy of things that can be thrown and is made up of Exceptions and Errors. Since Errors by definition arise from unsalvagable conditions, it is pointless to include them in your method declaration. That leaves just Exception.
You should declare your method with throws Exception instead.
Note that the narrower the range of throws the better.
Declaring your method to be throws Exception is ok if your method doesn't generate the exceptions, but instead calls other code that is declared as throws Exception and you want exceptions to percolate up the call stack.
If your method is the generating the exception, then declare a narrower range, eg throws IOException, MyProcessingException, etc

That's a loaded question. This isn't so much about exception handling as it is about code readability.
It depends where you get your code samples from. Professionals prefer to be more specific when throwing out of a method. The main reason is that it keeps your APIs more readable. For example, if your method throws Throwable, that basically means anything could happen and your method doesn't want to deal with it, no matter what. But really, only a limited number of things could happen:
Whatever checked exceptions resulting from other calls you are making in your method
Whatever checked exceptions you are throwing on purpose based on your own assertions
Whatever unchecked exception you didn't plan for
Errors (java.lang.Error) that are more global to the JVM and the environment
By specifically stating the exceptions you want to throw, you are telling the users of your API about what they should beware of. For example, when you use InputStream, you'll notice most methods throw at least java.io.IOException, which gives you some useful information about what you should watch for.
When coding, as a general rule, you want to try to keep your APIs as expressive as possible. You've got essentially one line of code to show the public API of a method (i.e. its signature, annotations too I guess), so you want it completely expressive (return type, name, parameters, but also the thrown exceptions).
As far as catching the throwables and printing the stack trace, I'd say that you should not catch the exception unless you can do something about it. Instead, let it roll up the call stack until some class catches it to do something about it. Sometimes, it may roll all the way up to your main class, which I guess would have to catch it and print the stack trace as last resort. Basically, if you can't act upon the exception, then let it go up the call stack. Also it is extremely rare that you find yourself in a situation where you should silence an exception (i.e. catch it but do nothing about it). That's usually inviting problems when comes time to troubleshoot issues.
Here is a fun but interesting article around misuse of exception handling in general.

In some rare cases it is acceptable to throw Throwables. For example, #Around advices in Spring AOP are usually declared to throw a Throwable.
The following example is copied verbatim from Spring AOP docs:
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.ProceedingJoinPoint;
#Aspect
public class AroundExample {
#Around("com.xyz.myapp.SystemArchitecture.businessService()")
public Object doBasicProfiling(ProceedingJoinPoint pjp) throws Throwable {
// start stopwatch
Object retVal = pjp.proceed();
// stop stopwatch
return retVal;
}
}
Why is doBasicProfiling declared to throw a Throwable? Because the original method (i.e. the execution join point), might throw an Error, RuntimeException, or a checked exception. So it only makes sense to declare doBasicProfiling to throw a Throwable.

Functionally, it is equivalent with throws Exception, since errors are unchecked.
I see no reason to declare a method to throw Throwable. However, this doesn't mean that catch and printStackTrace is a good alternative.
Usually, you want to catch throwables where you can do something sensible with them.
Code that throws a throwable you don't expect should explode gloriously, so you can see the error and fix the bug.

Is it common practice to do that?
In the JDK it is rare. This is mostly used when it is not clear how to handle checked exceptions.
What are pros & cons?
The pros is that you get your code to compile without worrying about checked exception.s
The cons is that exception you should be handling are being ignored.
Isn't it better to catch and printStackTrace()?
Unhandled exception are usually printed anyway so catching them doesn't help much.
You should catch an exception when you can add some value by doing so and add the exception to the throws clause when you can't.

It is really debatable matter.
Having method throwing too many exceptions will result in lot of error handling code. Some times it is not intended.
But because I don't like too many exception in signature does not mean that Lets use Parent of all exceptions and we are done!! It will not work.
What one can do is categorise exceptions such as BusinessException,ServiceException so that if you have a business rule which says that minimum balance in account can not be less than say 100$ then InsufficientBalance exception will be generated which will be child of BusinessException
so you method will be like
public Object doSomething() throws BusinessException {
if(!hasMinimumbalance())
{
throw new InsufficientBalance(ErrorCode);
}
}
What this will do is club related exceptions together and whenever API user wants to detect exception specific error then he can do it, else generic error handling is possible.
The core point here is on the UI you should display to the user that You have run out of balance and you can not withdraw money
You can say on the larger aspect to display human readable form of error it is really necessary to have separation of exceptions.

Are you asking about Throwable specifically? If so, then it's not good practice. It doesn't provide any useful information to class (method) user.

Throwing (and catching) Throwable (or Exception) is generally bad practice because it 'blankets' any specific exceptions you might want to catch. Then you would have to resort to ugliness like below:
public void myMethod() throws Throwable {
if (x) {
throw new MyException1();
}
if (y) {
throw new MyException2();
}
}
public void callingMethod() {
try {
myMethod();
}
catch(Throwable t) {
if (t instanceof MyException1) {
// handle exception 1
}
else if (t instanceof MyException2) {
// handle exception 2
}
else {
// handle other exceptions
}
}
}
Which is error prone (and flagged by CheckStyle as a code violation). It is much preferrable to have code like this:
public void myMethod() throws MyException1, MyException2 {
if (x) {
throw new MyException1();
}
if (y) {
throw new MyException2();
}
}
public void callingMethod() {
try {
myMethod();
}
catch(MyException1 e) {
// handle exception 1
}
catch(MyException2 e) {
// handle exception 2
}
}
Handling an exception just by calling printStackTrace() is usually not a good idea. printStackTrace() sends the stacktrace to standard error, which may not be read at all. A better option is to use the application's logging facility (like log4j) to report the exception. Even then, just logging it might no be enough.
My rule of thumb is:
If you can handle an exception locally, do so. For example when parsing a String as an Integer you could catch the NumberFormatException and return a default value:
prvate int parseAmount(String amountValue) {
int amount;
try {
amount = Integer.parseInt(amountValue);
}
catch(NumberFormatException e) {
// default amount
amount = 0;
}
return amount;
}
If you cannot handle an exception locally, consider if you should expose the exception type that is being thrown. If this type is some obscure (implementation-dependent) type, then wrapping it in your own generic exception type is probably a good idea:
private Customer getCustomer(int customerId) throws ServiceException {
try {
return customerService.getCustomer(customerId);
}
catch(CustomerServiceSpaghettiTangledException e) {
throw new ServiceException("Error calling the customer service", e);
}
}
Here 'ServiceException' is a subclass of Exception created by you. Spring also offers an exception hierarchy specifically for this purpose.
By wrapping the exception you hide the implementation details, making your service layer much simpler to use.
If you decide to throw an exception from your method, you will need to handle it 'higher up' in the callstack. This can be a generic error page in your web application stating that something went wrong and possibly providing an error message or code. In some cases the higher level code can attempt a retry or possibly an alternative way to obtain the required result.

The only use case I can think of would be for test code like unit tests. But Adam's counterpoint still stands "If so, then it's not good practice. It doesn't provide any useful information to class (method) user."

Should I create a custom exception type so my code is easier to unit test

In my unit test, I test a method for an expected RuntimeException and I want to distinct those thrown by my component from ones thrown by the code called in the method.
Creating a custom exception type is unnecessary and does not solve the problem if the method throws the same exception type but for different reasons, e.g. InvalidArgumentException.
Looks like the only way to tell them is the message or the error code. Because the message can be changed during development, the error code seems the only reliable option.
What is the best practice for creating of system of error codes so they don't conflict with ones of external packages, eg. third party libraries?

Creating a custom exception type is unnecessary and does not solve the
problem if the method throws the same exception type but for different
reasons, e.g. InvalidArgumentException.
Why do you think it's unnecessary? This is what you should do. Derive your own custom exception classes, throw their instances from your code and catch them outside (in your unit tests). The catch statement can be repeated in anticipation of multiple different exception classes:
try {
// something
} catch (MySpecificException e) {
// you know that your code threw this
} catch (Exception e) {
// this is coming from somewhere else
}

--Edit--
Sorry, I didn't see the java tag. Even though the following example uses PHP constructs, the principles should still apply.
--Original--
I use custom exception codes in only a few, very specific cases, and I store these codes in a custom exception class which extends the default exception class. They are stored in the class as constants, as the value doesn't really matter, but the context does.
Consider:
class CoreLib_Api_Exception extends Exception
{
const EXCEPTION_FORMAT = '%s (%s): %s';
const CODE_FILE_DNE = 100;
const CODE_DIR_BASE_EQUALS_REMOVE = 101;
const CODE_XML_READER_UNABLE_TO_OPEN = 200;
const CODE_XML_READER_UNABLE_TO_READ = 201;
}
// Example usage
class CoreLib_Api_Reader
{
protected function getReader()
{
$reader = new CoreLib_Api_Xml_Reader();
if (!#$reader->open($this->getFileUri())) {
$e = new CoreLib_Api_Exception(sprintf('Could not open %s for parsing', $this->getFileUri()), CoreLib_Api_Exception::CODE_XML_READER_UNABLE_TO_OPEN);
throw $e;
}
}
}
// Calling code
try {
$reader = CoreLib_Api_Reader();
$reader->setFileUri($fileUri);
$reader->getReader();
} catch (Exception $e) {
// If code is anything other than open, throw it
if ($e->getCode() !== CoreLib_Api_Exception::CODE_XML_READER_UNABLE_TO_OPEN) {
throw $e;
}
$e = null;
$reader = null;
}
By using the exception code, I can check to determine if the reader is unable to open the file, if so ignore the exception and move on, otherwise throw the exception and break the flow.
And if one of my exception codes collides with a third party exception code, it doesn't matter, as I mentioned before, using constants, the context will dictate which code I want to match on.

I test a method for an expected RuntimeException
I think this is a mistake. A RuntimeException should be used only for indicating bugs in the code that the code itself can detect. Testing should test only for specified (defined) behaviour. But when there is a bug in some code, its behaviour is undefined (who knows where the bug could be or what it might do). So there is no point in trying to specify what RuntimeExceptions some code should throw; that is like specifying how the code should behave "in the presence of a bug". Throwing particular RuntimeExceptions with particular messages should be seen as a courtesy to the maintenance programmer (who is likely to be you).

Huge exception handling blocks in Java

At the moment i working with library which can throw hell alot of different exceptions(8-10 per method call) and most of them must be handled, worse of all every method (at any time) can throw AuthenticationExpiredException, and i must re-attempt to authenticate. For example:
try {
xStream = xSet.createXStream(id, binding, mimeType); //Method call
} catch (AuthenticationExpiredException authenticationExpiredException) {
try {
this.authenticate(); // re-authenticate
xStream = xSet.createXStream(id, binding, mimeType); //Method call again
} catch (XAMException xamException) {
throw new ConnectorException(
"Error occurred during creating new Blob after attempting to re-authenticate",
xamException);
}
} catch (XSystemCorruptException xSystemCorruptException) {
this.entities.clear();
this.closeConnection();
throw new ConnectorException("XSystem was corrupt and connection was closed",
xSystemCorruptException);
} catch (XSetCorruptException xSetCorruptException) {
this.closeEntity(entity);
throw new ConnectorException("XSet for entity: " + entity.getXuid()
+ " was currupt and removed", xSetCorruptException);
} catch (XAMException xamException) {
throw new ConnectorException(
"Error occurred during creating new Blob.", xamException);
}
And this is one of the smallest examples of exception handling. The main question here, is there any way to reduce amount of code which handle exceptions, and make logic cleaner?
UPDATE
Thanks for your feedback. I decided to create separate wrapper for this library by wrapping every method and handling them respectively. To support different handling methods i created interface for wrapper and then implemented it with my custom wrapper like this:
public interface XAMLibraryWrapper{
// Methods
}
/**
* Will attempt to recover before throwing RuntimeException
*/
public class RecoveringXAMLibraryWrapper implements XAMLibraryWrapper{
// Implementation
}

If there is a consistent way to handle those method (i.e. you always wrap them in the same way and re-throw a RuntimeException, then a custom wrapper library might be the appropriate approach. This can still work when there are 2-3 different ways to handle them (by providing 2-3 wrapper methods (or even classes) for a single wrapped method/class).
Alternatively, if two or more exception types have the exact same handling code, then you can try to look for Java 7 to get multi-catch.

You can use Template method pattern. JdbcTemplate is a wonderful example how this design pattern can simplify exception-heavy code (SQLExceptions in this case).

If the API is indeed designed to throw that many exceptions, and each of them requires different handling, then there isn't much you can do.
One thing you can do is move repeated code in a separate method, or use Java 7 multi-catch.

If you have different things to do for each exception I'm afraid all those catch statements might be necessary. However, if you have lot's of catch statements with the same content or lot's of resources to close, you might have a look into the new Java 7 features like multiple exceptions in one catch and automatic resource handling. I'm not sure Java 7 is an option for you though.