ChatGPT解决这个技术问题 Extra ChatGPT

How do you implement a re-try-catch?

Try-catch is meant to help in the exception handling. This means somehow that it will help our system to be more robust: try to recover from an unexpected event.

We suspect something might happen when executing and instruction (sending a message), so it gets enclosed in the try. If that something nearly unexpected happens, we can do something: we write the catch. I don't think we called to just log the exception. I thing the catch block is meant to give us the opportunity of recovering from the error.

Now, let's say we recover from the error because we could fix what was wrong. It could be super nice to do a re-try:

try{ some_instruction(); }
catch (NearlyUnexpectedException e){
   fix_the_problem();
   retry;
}

This would quickly fall in the eternal loop, but let's say that the fix_the_problem returns true, then we retry. Given that there is no such thing in Java, how would YOU solve this problem? What would be your best design code for solving this?

This is like a philosophical question, given that I already know what I'm asking for is not directly supported by Java.

What kind of exception is that?
I like the name of your exception though. ;)
In deed, there are not many exception from which you can recover from. I admit my initial motivation was not a real exception, but way to avoid an if that will happen almost never: I try to remove() from a java.util.Queue, which thorws and InvalidElementException when the queue is empty. Instead of asking if it's empty, I sourround the actions in a try-catch (which under concurrency becomes compulsory even with the previous if). In such a case, in the catch block I would ask to refill the queue with more elements and then, retry. Voila.
I can see the usual way of doing this would be for DB access, if the connection has failed reconnect, if it fails then throw major exception otherwise retry the call again. As has been said we could do it in a loop with a check at the bottom if(error<>0) then go back otherwise break;

r
rogerdpack

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.


I thought in something like this at first, without the maxTries. Thanks for the answer!
@AndresFarias.. Yeah, the most important point in this answer is to include a maxTries. Else it will run into an infinite loop if user continously gives wrong input, and hence will not exit. You're welcome though. :)
Is it possible adding Thread.sleep() function inside the catch at here. Because in some cases like waiting for page response in Selenium library that became critical. Thanks.
Works great! For beginners: If you get positive infinite loop, check if You added "break;" at the end in "try" block.
change this. if(++count >= maxTries)
a
ach

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
    }
});

You should re-throw the exception if the last re-try fails, as done in the other answers given.
g
geisterfurz007

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;
        }
    }
}

Wait, why not have the condition inside the for loop declaration like: for(int retries = 0; retries < 6; retries++) ??
Because I only want to throw in the last attempt, and therefore the catch block needs that condition, making the condition in the for redundant.
I do not think that continue is needed there.. And you can simply flip the if condition.
J
Jonathan

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.


very nice library.
for those wondering, you will need this in your gradle dependencies - compile 'net.jodah:failsafe:1.1.0'
A
AlexR

Although try/catch into while is well-known and good strategy I want to suggest you recursive call:

void retry(int i, int limit) {
    try {

    } catch (SomeException e) {
        // handle exception
        if (i >= limit) {
            throw e;  // variant: wrap the exception, e.g. throw new RuntimeException(e);
        }
        retry(i++, limit);
    }
}

How is recursion better than a loop for this use case?
The stack trace may look a little odd on this one, because wouldn't it have limit count of the method being recursed? As opposed to the loop version, which will throw at the 'original' level...
Sure looks elegant on paper but I'm not sure recursion is the right approach somehow.
I don't understand why recursion here too. Anyway, I think it could be simplified to: void retry(int times) { (...) if (times==0) throw w; retry(times--);
It is poor practice to use recursion as a substitute for mere iteration. Recursion is for use when you want to push and pop some data.
M
Mohamed Taher Alrefaie

You can use AOP and Java annotations from jcabi-aspects (I'm a developer):

@RetryOnFailure(attempts = 3, delay = 5)
public String load(URL url) {
  return url.openConnection().getContent();
}

You could also use @Loggable and @LogException annotations.


Wow ! Sounds Fancy ! :)
Should be top answer.
is there a way to "fix" the error when attempt fails (do some adoptions that may fix the next attempt)? see question: fix_the_problem(); in the catch block
Given the amount of open issues and the time passed for acknowledged bugs not being fixed, I would not rely on this library.
S
Stephen P

Most of these answers are essentially the same. Mine is also, but this is the form I like

boolean completed = false;
Throwable lastException = null;
for (int tryCount=0; tryCount < config.MAX_SOME_OPERATION_RETRIES; tryCount++)
{
    try {
        completed = some_operation();
        break;
    }
    catch (UnlikelyException e) {
        lastException = e;
        fix_the_problem();
    }
}
if (!completed) {
    reportError(lastException);
}

One drawback is that you also call fix_the_problem after the last attempt. That could be a costly operation and could waste some time.
@JoachimSauer True. You could if (tryCount < max) fix() -- but this is the format of a general approach; the details would depend on a specific case. There's also a guava based Retryer I've been looking at.
V
Vivek Sethi

Spring AOP and annotation based solution:

Usage (@RetryOperation is our custom annotation for the job):

@RetryOperation(retryCount = 1, waitSeconds = 10)
boolean someMethod() throws Exception {
}

We'll need two things to accomplish this: 1. an annotation interface, and 2. a spring aspect. Here's one way to implement these:

The Annotation Interface:

import java.lang.annotation.*;

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface RetryOperation {
    int retryCount();
    int waitSeconds();
}

The Spring Aspect:

import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.reflect.MethodSignature;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;
import java.lang.reflect.Method;

@Aspect @Component 
public class RetryAspect {

    private static final Logger LOGGER = LoggerFactory.getLogger(RetryAspect.class);

    @Around(value = "@annotation(RetryOperation)")
    public Object retryOperation(ProceedingJoinPoint joinPoint) throws Throwable {

        Object response = null;
        Method method = ((MethodSignature) joinPoint.getSignature()).getMethod();
        RetryOperation annotation = method.getAnnotation(RetryOperation.class);
        int retryCount = annotation.retryCount();
        int waitSeconds = annotation.waitSeconds();
        boolean successful = false;

        do {
            try {
                response = joinPoint.proceed();
                successful = true;
            } catch (Exception ex) {
                LOGGER.info("Operation failed, retries remaining: {}", retryCount);
                retryCount--;
                if (retryCount < 0) {
                    throw ex;
                }
                if (waitSeconds > 0) {
                    LOGGER.info("Waiting for {} second(s) before next retry", waitSeconds);
                    Thread.sleep(waitSeconds * 1000l);
                }
            }
        } while (!successful);

        return response;
    }
}

Y
Yogendra Singh

Use a while loop with local status flag. Initialize the flag as false and set it to true when operation is successful e.g. below:

  boolean success  = false;
  while(!success){
     try{ 
         some_instruction(); 
         success = true;
     } catch (NearlyUnexpectedException e){
       fix_the_problem();
     }
  }

This will keep retrying until its successful.

If you want to retry only certain number of times then use a counter as well:

  boolean success  = false;
  int count = 0, MAX_TRIES = 10;
  while(!success && count++ < MAX_TRIES){
     try{ 
         some_instruction(); 
         success = true;
     } catch (NearlyUnexpectedException e){
       fix_the_problem();
     }
  }
  if(!success){
    //It wasn't successful after 10 retries
  }

This will try max 10 times if not successful until then an will exit if its successful before hand.


Rather than checking for !success in your while, you can just break out of while when success is true.
@RohitJain: It looks more clean to me.
@YogendraSingh.. Strange. as you are not modifying your success anywhere in your catch. So it seems redundant to check for it, on every run of catch.
@RohitJain: Catch is just correcting the data. It will go back and run the statement again. If successful, it will modify the success. Try it out.
G
GirishB

This is an old question but a solution is still relevant. Here is my generic solution in Java 8 without using any third party library:

public interface RetryConsumer<T> {
    T evaluate() throws Throwable;
}
public interface RetryPredicate<T> {
    boolean shouldRetry(T t);
}
public class RetryOperation<T> {
    private RetryConsumer<T> retryConsumer;
    private int noOfRetry;
    private int delayInterval;
    private TimeUnit timeUnit;
    private RetryPredicate<T> retryPredicate;
    private List<Class<? extends Throwable>> exceptionList;

    public static class OperationBuilder<T> {
        private RetryConsumer<T> iRetryConsumer;
        private int iNoOfRetry;
        private int iDelayInterval;
        private TimeUnit iTimeUnit;
        private RetryPredicate<T> iRetryPredicate;
        private Class<? extends Throwable>[] exceptionClasses;

        private OperationBuilder() {
        }

        public OperationBuilder<T> retryConsumer(final RetryConsumer<T> retryConsumer) {
            this.iRetryConsumer = retryConsumer;
            return this;
        }

        public OperationBuilder<T> noOfRetry(final int noOfRetry) {
            this.iNoOfRetry = noOfRetry;
            return this;
        }

        public OperationBuilder<T> delayInterval(final int delayInterval, final TimeUnit timeUnit) {
            this.iDelayInterval = delayInterval;
            this.iTimeUnit = timeUnit;
            return this;
        }

        public OperationBuilder<T> retryPredicate(final RetryPredicate<T> retryPredicate) {
            this.iRetryPredicate = retryPredicate;
            return this;
        }

        @SafeVarargs
        public final OperationBuilder<T> retryOn(final Class<? extends Throwable>... exceptionClasses) {
            this.exceptionClasses = exceptionClasses;
            return this;
        }

        public RetryOperation<T> build() {
            if (Objects.isNull(iRetryConsumer)) {
                throw new RuntimeException("'#retryConsumer:RetryConsumer<T>' not set");
            }

            List<Class<? extends Throwable>> exceptionList = new ArrayList<>();
            if (Objects.nonNull(exceptionClasses) && exceptionClasses.length > 0) {
                exceptionList = Arrays.asList(exceptionClasses);
            }
            iNoOfRetry = iNoOfRetry == 0 ? 1 : 0;
            iTimeUnit = Objects.isNull(iTimeUnit) ? TimeUnit.MILLISECONDS : iTimeUnit;
            return new RetryOperation<>(iRetryConsumer, iNoOfRetry, iDelayInterval, iTimeUnit, iRetryPredicate, exceptionList);
        }
    }

    public static <T> OperationBuilder<T> newBuilder() {
        return new OperationBuilder<>();
    }

    private RetryOperation(RetryConsumer<T> retryConsumer, int noOfRetry, int delayInterval, TimeUnit timeUnit,
                           RetryPredicate<T> retryPredicate, List<Class<? extends Throwable>> exceptionList) {
        this.retryConsumer = retryConsumer;
        this.noOfRetry = noOfRetry;
        this.delayInterval = delayInterval;
        this.timeUnit = timeUnit;
        this.retryPredicate = retryPredicate;
        this.exceptionList = exceptionList;
    }

    public T retry() throws Throwable {
        T result = null;
        int retries = 0;
        while (retries < noOfRetry) {
            try {
                result = retryConsumer.evaluate();
                if (Objects.nonNull(retryPredicate)) {
                    boolean shouldItRetry = retryPredicate.shouldRetry(result);
                    if (shouldItRetry) {
                        retries = increaseRetryCountAndSleep(retries);
                    } else {
                        return result;
                    }
                } else {
                    // no retry condition defined, no exception thrown. This is the desired result.
                    return result;
                }
            } catch (Throwable e) {
                retries = handleException(retries, e);
            }
        }
        return result;
    }

    private int handleException(int retries, Throwable e) throws Throwable {
        if (exceptionList.contains(e.getClass()) || (exceptionList.isEmpty())) {
            // exception is excepted, continue retry.
            retries = increaseRetryCountAndSleep(retries);
            if (retries == noOfRetry) {
                // evaluation is throwing exception, no more retry left. Throw it.
                throw e;
            }
        } else {
            // unexpected exception, no retry required. Throw it.
            throw e;
        }
        return retries;
    }

    private int increaseRetryCountAndSleep(int retries) {
        retries++;
        if (retries < noOfRetry && delayInterval > 0) {
            try {
                timeUnit.sleep(delayInterval);
            } catch (InterruptedException ignore) {
                Thread.currentThread().interrupt();
            }
        }
        return retries;
    }
}

Let's have a test case like:

@Test
public void withPredicateAndException() {
    AtomicInteger integer = new AtomicInteger();
    try {
        Integer result = RetryOperation.<Integer>newBuilder()
                .retryConsumer(() -> {
                    int i = integer.incrementAndGet();
                    if (i % 2 == 1) {
                        throw new NumberFormatException("Very odd exception");
                    } else {
                        return i;
                    }
                })
                .noOfRetry(10)
                .delayInterval(10, TimeUnit.MILLISECONDS)
                .retryPredicate(value -> value <= 6)
                .retryOn(NumberFormatException.class, EOFException.class)
                .build()
                .retry();
        Assert.assertEquals(8, result.intValue());
    } catch (Throwable throwable) {
        Assert.fail();
    }
}

nice idea, a builder fro that!
J
Jordan Kaye

A simple way to solve the issue would be to wrap the try/catch in a while loop and maintain a count. This way you could prevent an infinite loop by checking a count against some other variable while maintaining a log of your failures. It isn't the most exquisite solution, but it would work.


r
rogerdpack

In case it's useful, a couple more options to consider, all thrown together (stopfile instead of retries, sleep, continue larger loop) all possibly helpful.

 bigLoop:
 while(!stopFileExists()) {
    try {
      // do work
      break;
    }
    catch (ExpectedExceptionType e) {

       // could sleep in here, too.

       // another option would be to "restart" some bigger loop, like
       continue bigLoop;
    }
    // ... more work
}

Down voters please leave comments as to why, thanks!
This is a sheer ignorance to downvote and not cite a reason.
sleeping there is not obvious since the while loop wouldn't wait
S
S.D.

If not all exceptions warrant a retry, only some. And if at least one try has to be made, Here is an alternative utility method:

void runWithRetry(Runnable runnable, Class<Exception> exClass, int maxRetries) {
        Exception err = null;
        do {
            maxRetries--;
            try {
                runnable.run();
                err = null;
            } catch (Exception e) {
                if(exClass.isAssignableFrom(e.getClass())){
                    err = e;
                }else {
                    throw e;
                }
            }
        } while (err != null && maxRetries > 0);

        if (err != null) {
            throw err;
        }
    }

Usage:

    runWithRetry(() -> {
       // do something
    }, TimeoutException.class, 5)

S
Sam I am says Reinstate Monica

All a Try-Catch does is allow your program to fail gracefully. In a catch statement, you generally try to log the error, and maybe roll back changes if you need to.

bool finished = false;

while(finished == false)
{
    try
    {
        //your code here
        finished = true
    }
    catch(exception ex)
    {
        log.error("there was an error, ex");
    }
}

do you mean as opposed to (!finished)?
@RohitJain it looks too much like while(finished). I prefer to use the more verbose version.
How on earth does while(!finished) look like while (finished)??
@Rohit Because it's only one character different. They all get compiled down to the same thing. In C#, I use a String extension method IsPopulated() which just returns !IsNullOrEmpty() to ensure that my intent is understood by all developers.
R
Rahul Malhotra

Use a do-while to design re-try block.

boolean successful = false;
int maxTries = 3;
do{
  try {
    something();
    success = true;
  } catch(Me ifUCan) {
    maxTries--;
  }
} while (!successful || maxTries > 0)

The code should throw the original exception if unsuccessfull
J
Jonas_Hess

Here a reusable and more generic approach for Java 8+ that does not require external libraries:

public interface IUnreliable<T extends Exception>
{
    void tryRun ( ) throws T;
}

public static <T extends Exception> void retry (int retryCount, IUnreliable<T> runnable) throws T {
    for (int retries = 0;; retries++) {
        try {
            runnable.tryRun();
            return;
        } catch (Exception e) {
            if (retries < retryCount) {
                continue;
            } else {
                throw e;
            }
        }
    }
}

Usage:

@Test
public void demo() throws IOException {
    retry(3, () -> {
        new File("/tmp/test.txt").createNewFile();
    });
}

b
bnsd55

You can use https://github.com/bnsd55/RetryCatch

Example:

RetryCatch retryCatchSyncRunnable = new RetryCatch();
        retryCatchSyncRunnable
                // For infinite retry times, just remove this row
                .retryCount(3)
                // For retrying on all exceptions, just remove this row
                .retryOn(ArithmeticException.class, IndexOutOfBoundsException.class)
                .onSuccess(() -> System.out.println("Success, There is no result because this is a runnable."))
                .onRetry((retryCount, e) -> System.out.println("Retry count: " + retryCount + ", Exception message: " + e.getMessage()))
                .onFailure(e -> System.out.println("Failure: Exception message: " + e.getMessage()))
                .run(new ExampleRunnable());

Instead of new ExampleRunnable() you can pass your own anonymous function.


J
Jose Martinez

Simplifying @ach's previous solution into one file and using functional interfaces.

public class OperationHelper {

    public static void doWithRetry(int maxAttempts, Runnable operation, Consumer<Exception> handle) {
        for (int count = 0; count < maxAttempts; count++) {
            try {
                operation.run();
                count = maxAttempts; //don't retry
            } catch (Exception e) {
                handle.accept(e);
            }
        }
    }
}

A
Aashutosh Taikar

https://onlinegdb.com/a-7RsL1Gh

    public void doSomething() throws Exception{
      final int MAX_TRIES = 10;
      int count = 0;
      
      while(count++ < MAX_TRIES){
         try{ 
            System.out.println("trying");
            causeIssue(count); // throws error/exception till count 2
            System.out.println("trying successful");
            break; // break on success
         } catch (Exception e){
           System.out.println("caught, logging Exception:" + count);
         } catch (Error e){
           System.out.println("caught, logging Error:" + count);
         }
      }
    }

Output:

trying
caught, logging Error:1
trying
caught, logging Error:2
trying
trying successful

K
KnightHawk

I know there are already many similar answers here, and mine is not much different, but I will post it anyway because it deals with a specific case/issue.

When dealing with the facebook Graph API in PHP you sometimes get an error, but immediately re-trying the same thing will give a positive result (for various magical Internet reasons that are beyond the scope of this question). In this case there is no need to fix any error, but to simply try again because there was some kind of "facebook error".

This code is used immediately after creating a facebook session:

//try more than once because sometimes "facebook error"
$attempt = 3;
while($attempt-- > 0)
{
    // To validate the session:
    try 
    {
        $facebook_session->validate();
        $attempt = 0;
    } 
    catch (Facebook\FacebookRequestException $ex)
    {
        // Session not valid, Graph API returned an exception with the reason.
        if($attempt <= 0){ echo $ex->getMessage(); }
    } 
    catch (\Exception $ex) 
    {
        // Graph API returned info, but it may mismatch the current app or have expired.
        if($attempt <= 0){ echo $ex->getMessage(); }
    }
}

Also, by having the for loop count down to zero ($attempt--) it makes it pretty easy to change the number of attempts in the future.


D
David Kayo

following is my solution with very simple approach!

               while (true) {
                    try {
                        /// Statement what may cause an error;
                        break;
                    } catch (Exception e) {

                    }
                }

please look at @Rohit Jain answer which is more specific and not an infinite loop in negative cases.
J
Josh

Im not sure if this is the "Professional" way to do it and i'm not entirely sure if it works for everything.

boolean gotError = false;

do {
    try {
        // Code You're Trying
    } catch ( FileNotFoundException ex ) {
        // Exception
        gotError = true;
    }
} while ( gotError = true );

I think the best approach is do-while, even it is the one of the rare convenient purpose of do-while loop. Only thing you may want to edit while parentheses as while ( gotError );
t
tushar Mandar

https://github.com/tusharmndr/retry-function-wrapper/tree/master/src/main/java/io

int MAX_RETRY = 3; 
RetryUtil.<Boolean>retry(MAX_RETRY,() -> {
    //Function to retry
    return true;
});

J
João Pimentel Ferreira

The issue with the remaining solutions is that, the correspondent function tries continuously without a time interval in-between, thus over flooding the stack.

Why not just trying only every second and ad eternum?

Here a solution using setTimeout and a recursive function:

(function(){ try{ Run(); //tries for the 1st time, but Run() as function is not yet defined } catch(e){ (function retry(){ setTimeout(function(){ try{ console.log("trying..."); Run(); console.log("success!"); } catch(e){ retry(); //calls recursively } }, 1000); //tries every second }()); } })(); //after 5 seconds, defines Run as a global function var Run; setTimeout(function(){ Run = function(){}; }, 5000);

Replace the function Run() by the function or code that you'd like to retry every second.


N
NKR

Give it a try using springs @Retryable annotation , the below method will retry for 3 attempts when RuntimeException occurs

@Retryable(maxAttempts=3,value= {RuntimeException.class},backoff = @Backoff(delay = 500))
public void checkSpringRetry(String str) {
    if(StringUtils.equalsIgnoreCase(str, "R")) {
        LOGGER.info("Inside retry.....!!");
        throw new RuntimeException();
    }
}

H
Hari Krishna

Below snippet execute some code snippet. If you got any error while executing the code snippet, sleep for M milliseconds and retry. Reference link.

public void retryAndExecuteErrorProneCode(int noOfTimesToRetry, CodeSnippet codeSnippet, int sleepTimeInMillis)
  throws InterruptedException {

 int currentExecutionCount = 0;
 boolean codeExecuted = false;

 while (currentExecutionCount < noOfTimesToRetry) {
  try {
   codeSnippet.errorProneCode();
   System.out.println("Code executed successfully!!!!");
   codeExecuted = true;
   break;
  } catch (Exception e) {
   // Retry after 100 milliseconds
   TimeUnit.MILLISECONDS.sleep(sleepTimeInMillis);
   System.out.println(e.getMessage());
  } finally {
   currentExecutionCount++;
  }
 }

 if (!codeExecuted)
  throw new RuntimeException("Can't execute the code within given retries : " + noOfTimesToRetry);
}

J
James Mudd

Here is my solution similar to some others can wrap a function, but allows you to get the functions return value, if it suceeds.

    /**
     * Wraps a function with retry logic allowing exceptions to be caught and retires made.
     *
     * @param function the function to retry
     * @param maxRetries maximum number of retires before failing
     * @param delay time to wait between each retry
     * @param allowedExceptionTypes exception types where if caught a retry will be performed
     * @param <V> return type of the function
     * @return the value returned by the function if successful
     * @throws Exception Either an unexpected exception from the function or a {@link RuntimeException} if maxRetries is exceeded
     */
    @SafeVarargs
    public static <V> V runWithRetriesAndDelay(Callable<V> function, int maxRetries, Duration delay, Class<? extends Exception>... allowedExceptionTypes) throws Exception {
        final Set<Class<? extends Exception>> exceptions = new HashSet<>(Arrays.asList(allowedExceptionTypes));
        for(int i = 1; i <= maxRetries; i++) {
            try {
                return function.call();
            } catch (Exception e) {
                if(exceptions.contains(e.getClass())){
                    // An exception of an expected type
                    System.out.println("Attempt [" + i + "/" + maxRetries + "] Caught exception [" + e.getClass() + "]");
                    // Pause for the delay time
                    Thread.sleep(delay.toMillis());
                }else {
                    // An unexpected exception type
                    throw e;
                }
            }
        }
        throw new RuntimeException(maxRetries + " retries exceeded");
    }

s
seunggabi

simple

int MAX = 3;

int count = 0;
while (true) {
    try {
        ...

        break;
    } catch (Exception e) {
        if (count++ < MAX) {
            continue;
        }

        ...
        
        break;
    }
}

P
Pradeep Palaniswamy

This Solution allows you to configure a reusable functionality for retrying based on certain exception without using any external libraries

// Create a Function that suits your need .

@FunctionalInterface
public interface ThrowableBiFunction<U,T,R> {
    R apply(U u ,T t) throws Exception;
}

//Here's the crux of the solution

public interface ExceptionRetryable<T, U, R> {
    
 int getRetries();
   
 List<Class<? extends Exception>> getRetryableExceptions();

    default R execute(ThrowableBiFunction<T, U, R> function, T t, U u) throws Exception {
        int numberOfRetries = getRetries();
        return execute(function, t, u, numberOfRetries);
    }

    default R execute(ThrowableBiFunction<T, U, R> function, T t, U u, int retryCount) throws Exception {
        try {
            log.info(" Attempting to execute ExceptionRetryable#execute ,Number of remaining retries {} ",retryCount);
            return function.apply(t, u);
        } catch (Exception e) {

           log.info(" error occurred in ExceptionRetryable#execute",e);
            if (retryCount == 0)
                throw e;
            for (Class exp : getRetryableExceptions()) {
                if (e.getClass() == exp) {
                   return execute(function, t, u, retryCount - 1);
                }
            }
            throw e;
        }

    }
}

// create an implementation for exception retryable

public class TestRetryable implements ExceptionRetryable<String, String, List<String>> {
    @Override
    public int getRetries() {
        return 10;
    }

    @Override
    public List<Class<? extends Exception>> getRetryableExceptions() {
        return Arrays.asList(new Exception1().getClass(), new Exception2().getClass());
        ;
    }
}

// Finally create a ThrowableBiFunction that encapsulates that piece of code that needs to be retried on exception and an instance of ExceptionRetryable

 TestRetryable retryable = new TestRetryable();
    ThrowableBiFunction<Integer,Long, String> testRetrablefcn = { i, l ->
           // your code goes here
};
    Integer i = 0;
    Long l = 1l;
      String output = testRetrablefcn.execute(testRetrablefcn,i,l); 

D
Denis Bahlei

Production ready code:

@FunctionalInterface
public interface Operation {

    void doCall() throws IOException;

    default void handleException(Exception e) {
      //Your custom default implementation     
    }


public class OperationHelper {
    public static void doWithRetry(int maxAttempts, Operation operation) {

        for (int count = 0; count <= maxAttempts; count++) {
            try {
                operation.doCall();
                return;
            } catch (Exception e) {
                if (count == maxAttempts) {
                    e.printStackTrace();
                    return;
                } else {
                    operation.handleException(e);
                }
            }
        }
    }
}

Usage with default implementation in code:

OperationHelper.doWithRetry(10,
() -> //do your job );

Usage when custom exception handle is needed:

OperationHelper.doWithRetry(10, new Operation() {
    @Override public void doIt() {
        //do some stuff
    }
    @Override public void handleException(Exception cause) {
        //recover from the Exception
    }
});