Try-catch是用来帮助异常处理的。这意味着它将在某种程度上帮助我们的系统变得更加健壮:尝试从意外事件中恢复。

我们怀疑在执行和指令(发送消息)时可能会发生一些事情,因此它被包含在try中。如果发生了几乎意想不到的事情,我们可以做些什么:我们编写捕获。我不认为我们调用只是为了记录异常。我认为catch块是为了给我们从错误中恢复的机会。

现在,假设我们从错误中恢复,因为我们可以修复错误。如果能再试一次,那就太好了:

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

这将很快陷入永恒循环,但让我们假设fix_the_problem返回true,然后重试。假设在Java中没有这样的东西,你将如何解决这个问题?你认为解决这个问题的最佳设计代码是什么?

这就像一个哲学问题,因为我已经知道Java不直接支持我所要求的内容。


当前回答

你可以使用https://github.com/bnsd55/RetryCatch

例子:

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());

你可以传递自己的匿名函数,而不是新的ExampleRunnable()。

其他回答

你可以从jcabi-aspect(我是一名开发人员)使用AOP和Java注释:

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

您还可以使用@Loggable和@LogException注释。

下面是Java 8+的可重用和更通用的方法,不需要外部库:

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;
            }
        }
    }
}

用法:

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

这里是我的解决方案类似于其他人可以包装一个函数,但允许您获得函数返回值,如果它成功。

    /**
     * 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");
    }

将@ach之前的解决方案简化为一个文件,并使用功能接口。

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);
            }
        }
    }
}

生产就绪代码:

@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);
                }
            }
        }
    }
}

在代码中使用默认实现:

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

当需要自定义异常句柄时使用:

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