Could anyone please help with understanding of the following. Here is the code:
public class GoLoose {
public static void main(String[] args) {
try{
new Lost();
}catch (Throwable e){
e.printStackTrace();
}
new Lost();
}
}
class Lost{
final static int i = 1 / 0;
}
the result will be like:
java.lang.ExceptionInInitializerError
at test_linkage.GoLoose.main(GoLoose.java:7)
Caused by: java.lang.ArithmeticException: / by zero
at test_linkage.Lost.<clinit>(GoLoose.java:17)
... 1 more
Exception in thread "main" java.lang.NoClassDefFoundError: Could not initialize class test_linkage.Lost
at test_linkage.GoLoose.main(GoLoose.java:11)
As far as I can understand, it loads Lost's class file, then compiles and then tries to initialize static variable 'i' of the the Lost class - it fails with ArithmeticException wrapped by ExceptionInInitializerError. We catch it and only print and go further. Next, while trying to create a new instance of Lost again, it throws NoClassDefFoundError like it doesn't try to initialize Lost class now. And that is what I don't understand-why it don't try again? Why there is no ArithmeticException again?
It's said in the spec under 5.5. Initialization part: "If the Class object for C is in an erroneous state, then initialization is not possible. Release LC and throw a NoClassDefFoundError."
May it be that this is exactly what happens in my code? Like, after first attempt of initialization, if it goes wrong, class gets some "erroneous state" and having this state the class will never be eligible for further attempts of initialization. But then, what exactly is this state and where is it stored?
Thanks!
Related
I'm using this library:
"io.github.microutils:kotlin-logging:2.0.4"
with this logging implementation:
"ch.qos.logback:logback-classic:1.2.3"
In my code I call:
private val logger = KotlinLogging.logger{}
and then use this logger as follows:
logger.debug("message")
this runs fine until I try to debug my code at which point the following to two NoSuchMethodErrors pop up in the library:
private static IMarkerFactory bwCompatibleGetMarkerFactoryFromBinder() throws
NoClassDefFoundError {
try {
return StaticMarkerBinder.getSingleton().getMarkerFactory();
} catch (NoSuchMethodError var1) {
return StaticMarkerBinder.SINGLETON.getMarkerFactory();
}
}
And:
private static MDCAdapter bwCompatibleGetMDCAdapterFromBinder() throws
NoClassDefFoundError {
try {
return StaticMDCBinder.getSingleton().getMDCA();
} catch (NoSuchMethodError var1) {
return StaticMDCBinder.SINGLETON.getMDCA();
}
}
(the first time I try to log something)
Others on my team do not experience this issue. they are on macs, in case that matters.
If, I just continue running the code everything is fine as the exception is caught, but I don't want to hit continue twice anytime I want to debug. I'm willing to ignore exceptions if that is possible, or better yet, fix the underlying issue.
Assume I have a class C that holds resources that need to be closed as member variables.
public class C {
private ClosableResource1 closableResource1;
private ClosableResource2 closableResource2;
.....
public C(){
closableResource1 = new ClosableResource1();
closableResource2 = new ClosableResource2();
.....
// some logic that can fail
}
close(){
closableResource1.close()
closableResource2.close()
.....
}
}
If the constructor succeeds I can be sure that close() will be called eventually by some entity manager and all the resources will be freed.
But how can I make sure I close the resources when the constructor fails? The failure can happen because I have additional logic in the constructor that can throw exception or I get some RuntimeException outside of my control?
Some things I though of:
Wrapping the constructor body with a try-catch block. Then, assuming I have a lot of closable members I'll have to have a big if statement in the catch block checking which resources were already initializing and only close them.
Offloading the ClosableResources creation to some init() function. Then I would have to make sure init() succeeded every time I try to use the object.
Is there some elegant solution? Or is this much more implementation specific then that?
You can do something like below:
public class C {
private List<AutoCloseable> closableResources = new ArrayList();
private ClosableResource1 closableResource1;
private ClosableResource2 closableResource2;
.....
public C() {
closableResource1 = new ClosableResource1();
closableResources.add(closableResource1)
closableResource2 = new ClosableResource2();
closableResources.add(closableResource2);
.....
try {
// some logic that can fail
} catch(Exception e) {
close();
}
}
close(){
for (AutoCloseable closableResource : closableResources) {
if (closableResource != null) {
closableResource.close();
}
}
}
}
Surrounding your code with try-catch and closing all your resources in catch is the correct solution here. Also read about method finalize() (Here is one tutorial). In general, I would recommend one method that cleans up all the resources (like you suggested method close(), I would call it though cleanup()) and call that method in your catch section and in your finalize() method
I asked and answered a very similar question here. It is very important that a constructor either succeeds or fails completely i.e. leaving no resources open. In order to achieve that I would follow each resource creation statement by a try-catch block. The catch block closes the resource and rethrows the exception so it is not lost:
public C() {
closableResource1 = new ClosableResource1();
closableResource2 = new ClosableResource2();
try {
// .....
// some logic that can fail and throw MyCheckedException or some RuntimeException
} catch (RuntimeException | MyCheckedException e) {
try {closableResource1.close();} catch (Exception ignore) {}
try {closableResource1.close();} catch (Exception ignore) {}
throw e;
}
}
If creating a resource can fail you need nested try-catch blocks as demonstrated here.
Here's a wild idea: create a class called something like DefusableCloser (that you can "defuse", like an explosive device being made safe):
class DefusableCloser implements AutoCloseable {
boolean active = true;
final AutoCloseable closeable;
DefusableCloser(AutoCloseable closeable) {
this.closeable = closeable;
}
#Override public void close() throws Exception {
if (active) closeable.close();
}
}
Now you can use this in a try-with-resources block:
c1 = new CloseableResource();
try (DefusableCloseable d1 = new DefusableCloseable(c1)) {
c2 = new CloseableResource();
try (DefusableCloseable d2 = new DefusableCloseable(c2)) {
// Do the other stuff which might fail...
// Finally, deactivate the closeables.
d1.active = d2.active = false;
}
}
If execution doesn't reach d1.active = d2.active = false;, the two closeables (or one, if the exception was in creating the second resource) will be closed. If execution does reach that line, they won't be closed and you can use them.
The advantage of doing it like this is that the exceptions will be correctly handled.
Note that the ordering is important: don't be tempted to create the two CloseableResources first, then the two DefusableCloseables: doing that won't handle an exception from creating the second CloseableResource. And don't put the creation of the CloseableResources into the TWR, as that would guarantee their closure.
For closing the resources in your class' close() method, you can also use try-with-resources to ensure that both resources are closed:
try (c1; c2) {}
You don't actually have to declare a new variable in the TWR syntax: you can just effectively say "close the resource for this existing variable afterwards", as shown here.
I am trying to learn unit testing with Akka.
I have a situation where one of my tests was throwing an exception on construction and was wondering what the best way to capture this and log or otherwise throw it would be. As it stands now I had to attach a debugger and see where it threw.
I thought that I could perhaps create another actor which does logging and, on error, have a message sent to it. Breakpoints I put in the ErrorActor were never hit though. It seems as though the RootActor failed and timed out before the message was sent / received.
Is there something I'm doing wrong here or am I fundamentally off base with this? What is the the recommended way to catch errors in unit tests?
Thanks very much
[Fact]
public void CreateRootActor()
{
// Arrange
var props = Props.Create(() => new RootActor());
Sys.ActorOf(Props.Create( () =>new TestErrorActor(TestLogger)), ActorPaths.ErrorActor.Name); // register my test actor
// Act
var actor = new TestActorRef<RootActor>(this.Sys, props);
// Assert
Assert.IsType<RootActor>(actor.UnderlyingActor);
}
public class RootActor : ReceiveActor
{
private ITenantRepository tenantRepository;
public RootActor(ILifetimeScope lifetimeScope)
{
try
{
this.tenantRepository = lifetimeScope.Resolve<ITenantRepository>(); // this throws
}
catch (Exception e)
{
Context.ActorSelection(ErrorActor.Name).Tell(new TestErrorActor.RaiseError(e));
throw;
}
....
I got around this by using Akka.Logger.Serilog and a try / catch in the RootActor. I deleted the ErrorActor.
I would like to catch any throwable during a Selenium test e.g. in order to make a screenshot. The only solution I could come up with for now is to separately surround the test steps with a try and catch block in every test method as following:
#Test
public void testYouTubeVideo() throws Throwable {
try {
// My test steps go here
} catch (Throwable t) {
captureScreenshots();
throw t;
}
}
I'm sure there is a better solution for this. I would like a higher, more centralized location for this try-catch-makeScreenshot routine, so that my test would be able to include just the test steps again. Any ideas would be greatly appreciated.
You need to declare a TestRule, probably a TestWatcher or if you want to define the rules more explicitly, ExternalResource. This would look something like:
public class WatchmanTest {
#Rule
public TestRule watchman= new TestWatcher() {
#Override
protected void failed(Description d) {
// take screenshot here
}
};
#Test
public void fails() {
fail();
}
#Test
public void succeeds() {
}
}
The TestWatcher anonymous class can of course be factored out, and just referenced from the test classes.
I solved a similar problem using Spring's AOP. In summary:
Declare the selenium object as a bean
Add an aspect using
#AfterThrowing
The aspect can take the screenshot and save it to a
file with a semirandom generated name.
The aspect also rethrows the exception, with the exception message including the filename so you can look at it afterwards.
I found it more helpful to save the HTML of the page due to flakiness of grabbing screenshots.
I've got a rule like this:
declaration returns [RuntimeObject obj]:
DECLARE label value { $obj = new RuntimeObject($label.text, $value.text); };
Unfortunately, it throws an exception in the RuntimeObject constructor because $label.text is null. Examining the debug output and some other things reveals that the match against "label" actually failed, but the Antlr runtime "helpfully" continues with the match for the purpose of giving a more helpful error message (http://www.antlr.org/blog/antlr3/error.handling.tml).
Okay, I can see how this would be useful for some situations, but how can I tell Antlr to stop doing that? The defaultErrorHandler=false option from v2 seems to be gone.
I don't know much about Antlr, so this may be way off base, but the section entitled "Error Handling" on this migration page looks helpful.
It suggests you can either use #rulecatch { } to disable error handling entirely, or override the mismatch() method of the BaseRecogniser with your own implementation that doesn't attempt to recover. From your problem description, the example on that page seems like it does exactly what you want.
You could also override the reportError(RecognitionException) method, to make it rethrow the exception instead of print it, like so:
#parser::members {
#Override
public void reportError(RecognitionException e) {
throw new RuntimeException(e);
}
}
However, I'm not sure you want this (or the solution by ire_and_curses), because you will only get one error per parse attempt, which you can then fix, just to find the next error. If you try to recover (ANTLR does it okay) you can get multiple errors in one try, and fix all of them.
You need to override the mismatch and recoverFromMismatchedSet methods to ensure an exception is thrown immediately (examples are for Java):
#members {
protected void mismatch(IntStream input, int ttype, BitSet follow) throws RecognitionException {
throw new MismatchedTokenException(ttype, input);
}
public Object recoverFromMismatchedSet(IntStream input, RecognitionException e, BitSet follow) throws RecognitionException {
throw e;
}
}
then you need to change how the parser deals with those exceptions so they're not swallowed:
#rulecatch {
catch (RecognitionException e) {
throw e;
}
}
(The bodies of all the rule-matching methods in your parser will be enclosed in try blocks, with this as the catch block.)
For comparison, the default implementation of recoverFromMismatchedSet inherited from BaseRecognizer:
public Object recoverFromMismatchedSet(IntStream input, RecognitionException e, BitSet follow) throws RecognitionException {
if (mismatchIsMissingToken(input, follow)) {
reportError(e);
return getMissingSymbol(input, e, Token.INVALID_TOKEN_TYPE, follow);
}
throw e;
}
and the default rulecatch:
catch (RecognitionException re) {
reportError(re);
recover(input,re);
}