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Place any code statements that might raise or throw an exception in a try block, and place statements used to handle the exception or exceptions in one or more catch blocks below the try block. Each catch block includes the exception type and can contain additional statements needed to handle that exception type.
Throw, and Try...Catch... The try statement defines a code block to run (to try). The catch statement defines a code block to handle any error. The finally statement defines a code block to run regardless of the result. The throw statement defines a custom error.
In Java, a try block installs itself into a special table (in the class file). When the JVM throws an exception, it looks at that table to see where the next catch or finally block to go to is. Show activity on this post. When an exception occurs a special instruction is executed (usually called interrupt).
try – You must use this keyword in front of the method that throws. Think of it like this: “You're trying to execute the method. catch – If the throwing method fails and raises an error, the execution will fall into this catch block. This is where you'll write code display a graceful error message to the user.
You need to enclose your try-catch inside a while loop like this: -
int count = 0;
int maxTries = 3;
while(true) {
try {
// Some Code
// break out of loop, or return, on success
} catch (SomeException e) {
// handle exception
if (++count == maxTries) throw e;
}
}
I have taken count and maxTries to avoid running into an infinite loop, in case the exception keeps on occurring in your try block.
Obligatory "enterprisy" solution:
public abstract class Operation {
abstract public void doIt();
public void handleException(Exception cause) {
//default impl: do nothing, log the exception, etc.
}
}
public class OperationHelper {
public static void doWithRetry(int maxAttempts, Operation operation) {
for (int count = 0; count < maxAttempts; count++) {
try {
operation.doIt();
count = maxAttempts; //don't retry
} catch (Exception e) {
operation.handleException(e);
}
}
}
}
And to call:
OperationHelper.doWithRetry(5, new Operation() {
@Override public void doIt() {
//do some stuff
}
@Override public void handleException(Exception cause) {
//recover from the Exception
}
});
As usual, the best design depends on the particular circumstances. Usually though, I write something like:
for (int retries = 0;; retries++) {
try {
return doSomething();
} catch (SomeException e) {
if (retries < 6) {
continue;
} else {
throw e;
}
}
}
Your exact scenario handled via Failsafe:
RetryPolicy retryPolicy = new RetryPolicy()
.retryOn(NearlyUnexpectedException.class);
Failsafe.with(retryPolicy)
.onRetry((r, f) -> fix_the_problem())
.run(() -> some_instruction());
Pretty simple.
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