I'm wondering how should one handle "contained" exceptions. Because the term isn't concrete enough, let me take an example of PrivilegedActionException.
In short, this exception will in its cause contain any checked exception thrown during the computation within PrivilegedAction.
Now if I have and method computate() throws IOException I'll - if executed on its own - handle it as:
try {
computate();
} catch (FileNotFoundException ex) {
// Handle file not found
} catch (SomeOtherSubtypeOfIOException ex) {
// handle that again
}
Now as this has been executed in PriviledgedAction the only exception I get is PrivilegedActionException:
try {
Subject.doAs(() -> computate());
} catch (PrivilegedActionException ex) {
// Now what?
}
I can get the IOException from previous example by calling ex.getCause() but how would that look like? The obvious way looks odd ...
catch (PrivilegedActionException ex) {
if (ex.getCause() instanceof FileNotFoundException.class) {
// handle FileNotFound
} else if (ex.getCause() instanceof xxx) {
// something else
}
}
You could get the cause and re-throw it. Then handle exception with an outer try-catch.
catch (PrivilegedActionException ex) {
Throwable cause = ex.getCause();
if(cause !=null) throw ex.getCause();
else ex.printStackTrace();
}
Related
private WebElement findElementByXpath(WebDriver driver, String xpath) throws WebElementNotFoundException, HopelessAccountException {
WebElement element = null;
try {
element = new WebDriverWait(driver, Duration.ofSeconds(dirationInSeconds))
.until(ExpectedConditions.elementToBeClickable(By.xpath(xpath)));
} catch (TimeoutException timeoutException) {
loggingService.timeMark("findElementByXpath", "TimeoutException");
throw new WebElementNotFoundException();
} catch (UnhandledAlertException alertException) {
loggingService.timeMark("findElementByXpath", "alertException");
final String LIMITS_EXHAUSTED_MESSAGE = "Not enough limits!";
String message = alertException.getMessage();
if (message.contains(LIMITS_EXHAUSTED_MESSAGE)){
throw new HopelessAccountException(); // Attention.
}
} catch (Exception e) {
// Mustn't be here.
loggingService.timeMark("findElementByXpath", e.getMessage());
driver.quit();
System.out.println("QUIT!");
System.exit(0);
}
loggingService.timeMark("findElementByXpath", "end. Xpath: " + xpath);
return element;
}
Please, have a look at the line that I commented as "Attention".
I have caught the exception where there is not enough limits any more. And I throw the exception that the account is hopeless.
But it is immediately caught by just after the next few lines. Namely where I commented "Mustn't be here".
I would like to preserve this catching any exception. At least for debugging purpose.
Could you help me understand whether I can both throw HopelessAccountException and preserve the "catch Exception" block?
You can always modify your Exception block to rethrow e if it is an instance of HopelessAccountException:
} catch (Exception e) {
if (e instanceof HopelessAccountException) throw e; // preserves original stack trace
// Mustn't be here.
loggingService.timeMark("findElementByXpath", e.getMessage());
driver.quit();
System.out.println("QUIT!");
System.exit(0);
}
However as #fishinear indicates, in your posted code the Exception block would not be reached as a result of the throw of throw new HopelessAccountException() - if your actual code looked more like:
try {
try {
System.out.println("In A()");
// do something to cause an exception E3 (e.g. UnhandledAlertException)
throw new E3();
} catch (E3 e3) { // UnhandledAlertException
System.out.println("In E3 catch");
throw new E1(); // HopelessAccountException
}
} catch (Exception e) {
System.out.println("In Exception catch");
if (e instanceof E1) throw e; // rethrow HopelessAccountException
System.out.println("e: "+e);
}
Then the test-and-rethrow is possible.
Then when you rip out your debugging "try block" your code would behave the same (for the HopelessAcountException).
in your code that calls findElementByXpath(…) you could catch the broad Exception type there. This means in your findElementByXpath(…) method you could just handle the known exceptions and anything else could be captured in calling code
In Java, if I declare and caught an exception, can I handle the exception in a caller anyway? Or it needs not to be caught to handle it by caller?
class A {
void first() throws Exception {
try {
throw new Exception("my exception")
} catch (Exception e) {
log.message("Error in first()", e.getCouse)
throw e
}
}
}
class B {
Result second(A a) {
try {
a.first()
} catch (Exception e) {
log.message("Caught in B class", e.message)
return new Result(result: null, error: e.message)
}
}
second(A a)
}
You can simply rethrow the exception you've caught (obviously the surrounding method has to permit this via its signature etc.). The exception will maintain the original stack trace.
catch (WhateverException e) {
throw e;
}
You can also wrap the exception in another one AND keep the original stack trace by passing in the Exception as a Throwable as the cause parameter:
try
{
...
}
catch (Exception e)
{
throw new YourOwnException(e);
}
How to catch the exceptions thrown from CompletableFuture.completeExceptionally() while using CompletableFuture.get()?
Here is some code
public CompletableFuture<Hello> sayHelloAsync() {
CompletableFuture<Hello> future = new CompletableFuture<>();
try{
sayHello(); //throws HelloException
} catch (HelloException ex) {
future.completeExceptionally(new MyException("hello exception"));
return future;
}
return future;
}
Now I want to do .get() or .join on this as follows
CompletableFuture<Hello> resultFuture = sayHelloAsync();
try{
result.get(); // throws ExecutionException but I want to catch My Exception in the simplest way possible but not by throwing another exception while catching the Execution exception and so on.
} catch(ExecutionException ex) {
throw ex.getCause();
} catch (MyException e) {
e.printStackTrace()
}
This is very ugly. Again I just want to catch MyException in few lines of code as possible and in the cleanest way possible. Not sure if isCompletedExceptionally(), exceptionally, join() can help somehow to catch MyException in the easiest way possible. If so how?
I have read the bug detectors in findbugs website, http://findbugs.sourceforge.net/bugDescriptions.html
I want to write a test code and use Findbugs to detect the REC error.
But the findbugs cannot. Why? Could you help me to solve this?
Thanks,
Below is the description in Findbugs.
REC: Exception is caught when Exception is not thrown (REC_CATCH_EXCEPTION)
This method uses a try-catch block that catches Exception objects, but Exception is not thrown within the try block, and RuntimeException is not explicitly caught. It is a common bug pattern to say try { ... } catch (Exception e) { something } as a shorthand for catching a number of types of exception each of whose catch blocks is identical, but this construct also accidentally catches RuntimeException as well, masking potential bugs.
A better approach is to either explicitly catch the specific exceptions that are thrown, or to explicitly catch RuntimeException exception, rethrow it, and then catch all non-Runtime Exceptions, as shown below:
try {
...
} catch (RuntimeException e) {
throw e;
} catch (Exception e) {
... deal with all non-runtime exceptions ...
}
My code is:
public static void test1(){
int A[] = {1,2,3};
int result = 5/0;//divided by 0
int arrOut = A[0]+A[4];//index out of bound
System.out.println(arrOut);
System.out.println(result);
try {
} catch (RuntimeException e) {
// TODO: handle exception
System.out.println("Runtimeex throw");
throw e;
} catch (Exception e) {
// TODO: handle exception
System.out.println("An try error occurred: 0 cannot be divided");
}
}
The try is where the exception occur that you want to catch. However, since it is occurring out of the try block, the exception is not caught by the catch part, which is why FindBugs reporting it as a useless try {...} catch {...} code. The proper code should be as follows.
int A[] = {1,2,3};
try {
int result = 5/0;//divided by 0
int arrOut = A[0]+A[4];//index out of bound
System.out.println(arrOut);
System.out.println(result);
} catch (RuntimeException e) {
// TODO: handle exception
System.out.println("Runtimeex throw");
throw e;
} catch (Exception e) {
// TODO: handle exception
System.out.println("An try error occurred: 0 cannot be divided");
}
}
java.net.ConnectException extends java.net.SocketException
If I do the following, will it cater for both exceptions? ie if I catch a "parent" exception using instanceof, does that include any subclassed exceptions?
catch (Exception e)
{
if (e instanceof java.net.SocketException)
{
System.out.println("You've caught a SocketException, OR a ConnectException");
}
}
(and for the record, yes I know catching plain Exceptions is bad, just using it for this example ;) )
Exceptions are regular classes, so instanceof works fine for them.
But you don't need such a thing. The following achieves the same result:
try {
throw new ConnectException();
} catch (SocketException e) {
System.out.println("You've caught a SocketException, OR a ConnectException");
}
Yes, it will cater for both. Because ConnectionException IS A SocketException, it also is an instance of it.
Bozho already has given the right answer. I don't know your particular usecase, but you'd rather catch different exceptions:
try {
...
}
catch (SocketException ex) {
System.out.println("You've caught a SocketException, OR a ConnectException");
}
catch (Exception ex) {
...
}
I know that it's now a good way but if you want to do custom action in a many places in code you can do something like this:
public class ImageIOExecption extends Exception {
Exception ex;
public ImageIOExecption(Exception ex) {
this.ex = ex;
doCatch();
}
private void doCatch() {
System.err.println(ex.getClass());
if (ex instanceof java.net.SocketTimeoutException) {
System.out.println("You've caught a SocketTimeoutException, OR a ConnectException");
}
if (ex instanceof java.net.SocketException) {
System.out.println("You've caught a SocketException, OR a ConnectException");
}
}
}
public BufferedImage getBufferedImage() {
try {
BufferedImage srcImage = ImageIO.read(is);
is.close();
return srcImage;
} catch (Exception ex) {
new ImageIOExecption(ex);
}
return null;
}
Yes, that is how instanceof works. For exceptions it is more common to use something like this if you care about different exceptions. It works because the JVM will work down the list of catch statements in order and execute the first one that matches.
catch(ConnectException e)
{
//got ConnectException
}
catch(SocketException e)
{
/got a SocketException
}
catch(Exception e)
{
//got some other exception
}
Or below if you dont care about the difference between Connection and Socket Exception
catch(SocketException e)
{
//got a SocketException or a subclass e.g. ConnectionException
}
catch(Exception e)
{
//got another type of exception
}