I'm trying to write an utility which automatically propagate checked exception in a reactiv way without writing boiler plate code with static block inside my operators:
public class ReactRethrow {
public static <T, R> Function<T, R> rethrow(Function<T, R> catchedFunc) {
return t -> {
try {
return catchedFunc.apply(t);
} catch (Exception e) {
throw Exceptions.propagate(e);
}
};
}
}
but it stil complaining about IOException here:
Flux.fromArray(resources).map(ReactRethrow.rethrow(resource -> Paths.get(resource.getURI())))
any idea?
Well for a reason I do not clearly understand You have to take as parameter a function which throw exceptions and so declare a specific functionalInterface:
public class ReactRethrow {
public static <T, R> Function<T, R> rethrow(FunctionWithCheckeException<T, R> catchedFunc) {
return t -> {
try {
return catchedFunc.call(t);
} catch (Exception e) {
throw Exceptions.propagate(e);
}
};
}
#FunctionalInterface
public interface FunctionWithCheckeException<T, R> {
R call(T t) throws Exception;
}
}
from here https://leoniedermeier.github.io/docs/java/java8/streams_with_checked_exceptions.html
Related
I have a class with many functions
public class Test {
public void a() {
try {
doSomething1();
} catch (AException e) {
throw new BException(e.getMessage(), e.getCause());
}
}
public void b() {
try {
doSomething2();
} catch (AException e) {
throw new BException(e.getMessage(), e.getCause());
}
}
}
In each method, an exception of certain type is caught and converted to another exception and thrown.
I want to remove duplication.
You may remove duplication using lambda:
The CallableEx takes any exception, in case you are working with checked exception. You would not need it if AException was an unchecked exception. Callable interface won't help you much because it throws an Exception and not your AException: you would have to check for instance and so on.
You could probably write the body instead of this::doSomething1, but I advise against it: this makes the code clearer and it separates concerns.
You could probably also use an annotation processor to do the same job and to rewrite the method in order to wrap your AException into a BException. You would not have duplication in your Java code, but your bytecode certainly will.
Here the example with lambda:
public class Test {
#FunctionalInterface
interface CallableEx<T, E extends Exception> {
T run() throws E;
}
private <T> void handleException(CallableEx<T, AException> forrestGump) {
try {
return forrestGump.run();
} catch (AException e) {
throw new BException(e.getMessage(), e.getCause());
}
}
public String a() {
return handleException(this::doSomething1);
}
public int b(int a, int b) {
return handleException(() -> this.doSomething2(a, b));
}
public <T extends Foobar> void c(T my) {
handleException(() -> this.doSomething3(my));
}
private String doSomething1() {return "A";}
private int doSomething2(int a, int b) {return a + b;}
private <T extends Foobar> void doSomething3(T my) {my.foo();}
}
I am new the java, needing some help.
I need to find which method throws an exception, if any. I can modify catch block ONLY. Can't use StackTrace - I've been suggested to use collections. Thanks for help.
public class Xc {
void canException() throws Exception {
if (new java.util.Random().nextInt(5) == 0)
throw new Exception();
}
public static void main(String[] args) {
Xc z = new Xc();
try {
z.canException();
z.canException();
z.canException();
z.canException();
z.canException();
}
catch (Exception e) {
//can modify this block only
}
}
}
I stumbled over this problem. Lets say i have an Func1 which parses some json string and returns the ServerState (Enum). For some reason the state cant be unknown by the Client or the JSON is bad for some reason.
How do i propagate the Exception from call Method ?
public static class ParseProgressFunction implements Func1<String, Observable<ServerState>> {
#Override
public Observable<ServerState> call(String progress) {
try {
final ServerState serverState = ServerParser.parseProgress(progress);
} catch (JSONException e) {
e.printStackTrace();
} catch (UnknownServerStateException e) {
e.printStackTrace();
}
}
}
This is the Idea i like to implement this:
#Override
public void onReceiveServerState(final Observable<String> state) {
state.flatMap(new ParseProgressFunction());
There must be some best practice, right ?
Happy Easter
As your function return an Observable, you can return a new error Observable with your exception.
return Observable.error(you exception);
I am looking for a way to catch all exceptions thrown by JUnit tests then re-throw them; to add more detail to the error message about the test state when the exception occurred.
JUnit catches errors thrown in org.junit.runners.ParentRunner
protected final void runLeaf(Statement statement, Description description,
RunNotifier notifier) {
EachTestNotifier eachNotifier = new EachTestNotifier(notifier, description);
eachNotifier.fireTestStarted();
try {
statement.evaluate();
} catch (AssumptionViolatedException e) {
eachNotifier.addFailedAssumption(e);
} catch (Throwable e) {
eachNotifier.addFailure(e);
} finally {
eachNotifier.fireTestFinished();
}
}
This method is unfortunately is final so it cannot be overridden. Also as exceptions are being caught something like Thread.UncaughtExceptionHandler will not help. The only other solution I can think of is try/catch block around each test but that solution is not very maintainable. Could anyone point me to a better solution?
You could create a TestRule for this.
public class BetterException implements TestRule {
public Statement apply(final Statement base, Description description) {
return new Statement() {
public void evaluate() {
try {
base.evaluate();
} catch(Throwable t) {
throw new YourException("more info", t);
}
}
};
}
}
public class YourTest {
#Rule
public final TestRule betterException = new BetterException();
#Test
public void test() {
throw new RuntimeException();
}
}
I have some methods which throws some exception, and I want to use AspectJ around advise to calculate the execution time and if some exception is thrown and to log into error log and continue the flow by re-throwing the exception.
I tried to achieve this by following but eclipse says "Unhandled Exception type".
Code-against whom AspectJ is to used :-
public interface Iface {
public void reload() throws TException;
public TUser getUserFromUserId(int userId, String serverId) throws ResumeNotFoundException, TException;
public TUser getUserFromUsername(String username, String serverId) throws ResumeNotFoundException, TException;
public TResume getPartialActiveProfileFromUserId(int userId, int sectionsBitField, String serverId) throws ResumeNotFoundException, UserNotFoundException;
public TResume getPartialActiveProfileFromUsername(String username, int sectionsBitField, String serverId) throws ResumeNotFoundException, UserNotFoundException, TException;
}
Code AspectJ :-
public aspect AspectServerLog {
public static final Logger ERR_LOG = LoggerFactory.getLogger("error");
Object around() : call (* com.abc.Iface.* (..)) {
Object ret;
Throwable ex = null;
StopWatch watch = new Slf4JStopWatch();
try {
ret = proceed();
} catch (UserNotFoundException e) {
ex = e;
throw e;
} catch (ResumeNotFoundException e) {
ex = e;
throw e;
} catch (Throwable e) {
ex = e;
throw new RuntimeException(e);
} finally {
watch.stop(thisJoinPoint.toShortString());
if (ex != null) {
StringBuilder mesg = new StringBuilder("Exception in ");
mesg.append(thisJoinPoint.toShortString()).append('(');
for (Object o : thisJoinPoint.getArgs()) {
mesg.append(o).append(',');
}
mesg.append(')');
ERR_LOG.error(mesg.toString(), ex);
numEx++;
}
}
return ret;
}
}
Please help why this AspectJ is not working.
you can avoid catching the exceptions and just use a try/finally block without the catch.
And if you really need to log the exception you can use an after throwing advice, like this:
public aspect AspectServerLog {
public static final Logger ERR_LOG = LoggerFactory.getLogger("error");
Object around() : call (* com.abc.Iface.* (..)) {
StopWatch watch = new Slf4JStopWatch();
try {
return proceed();
} finally {
watch.stop(thisJoinPoint.toShortString());
}
}
after() throwing (Exception ex) : call (* com.abc.Iface.* (..)) {
StringBuilder mesg = new StringBuilder("Exception in ");
mesg.append(thisJoinPoint.toShortString()).append('(');
for (Object o : thisJoinPoint.getArgs()) {
mesg.append(o).append(',');
}
mesg.append(')');
ERR_LOG.error(mesg.toString(), ex);
}
}
I'm afraid you cannot write advice to throw exceptions that aren't declared to be thrown at the matched join point. Per: http://www.eclipse.org/aspectj/doc/released/progguide/semantics-advice.html :
"An advice declaration must include a throws clause listing the checked exceptions the body may throw. This list of checked exceptions must be compatible with each target join point of the advice, or an error is signalled by the compiler."
There has been discussion on the aspectj mailing list about improving this situation - see threads like this: http://dev.eclipse.org/mhonarc/lists/aspectj-dev/msg01412.html
but basically what you will need to do is different advice for each variant of exception declaration. For example:
Object around() throws ResumeServiceException, ResumeNotFoundException, TException:
call (* Iface.* (..) throws ResumeServiceException, ResumeNotFoundException, TException) {
that will advise everywhere that has those 3 exceptions.
There is an "ugly" workaround - I found them in Spring4 AbstractTransactionAspect
Object around(...): ... {
try {
return proceed(...);
}
catch (RuntimeException ex) {
throw ex;
}
catch (Error err) {
throw err;
}
catch (Throwable thr) {
Rethrower.rethrow(thr);
throw new IllegalStateException("Should never get here", thr);
}
}
/**
* Ugly but safe workaround: We need to be able to propagate checked exceptions,
* despite AspectJ around advice supporting specifically declared exceptions only.
*/
private static class Rethrower {
public static void rethrow(final Throwable exception) {
class CheckedExceptionRethrower<T extends Throwable> {
#SuppressWarnings("unchecked")
private void rethrow(Throwable exception) throws T {
throw (T) exception;
}
}
new CheckedExceptionRethrower<RuntimeException>().rethrow(exception);
}
}