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
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");
}
其他回答
Try-Catch所做的就是允许程序优雅地失败。在catch语句中，通常尝试记录错误，如果需要，可能还会回滚更改。
bool finished = false;
while(finished == false)
{
try
{
//your code here
finished = true
}
catch(exception ex)
{
log.error("there was an error, ex");
}
}
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");
}
通常，最好的设计取决于特定的环境。通常我会这样写:
for (int retries = 0;; retries++) {
try {
return doSomething();
} catch (SomeException e) {
if (retries < 6) {
continue;
} else {
throw e;
}
}
}
如果不是所有异常都需要重试，那么只有一些例外。如果至少要尝试一次，这里有一个替代的实用方法:
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;
}
}
用法:
runWithRetry(() -> {
// do something
}, TimeoutException.class, 5)
强制性的“企业级”解决方案:
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);
}
}
}
}
并呼吁:
OperationHelper.doWithRetry(5, new Operation() {
@Override public void doIt() {
//do some stuff
}
@Override public void handleException(Exception cause) {
//recover from the Exception
}
});
