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

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;
        }
    }
}

其他回答

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();
    });
}

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);
         }
      }
    }

输出:

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

简单的

int MAX = 3;

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

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

        ...
        
        break;
    }
}

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
    }
});

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;
});