UnexpectedInputException in Spring: Handling Unexpected Input Like a Pro

Have you ever encountered unexpected input while working with Spring applications? If so, you might have come across the UnexpectedInputException. Don’t fret! This handy exception handling mechanism in Spring can save the day by gracefully handling such scenarios. In this article, we will dive deep into the UnexpectedInputException, explore its purpose, understand its usage, and learn how to effectively handle unexpected input in your Spring applications.

Understanding the UnexpectedInputException

In the context of Spring Batch, the UnexpectedInputException is thrown when an item reader encounters unexpected input. This exception typically occurs when the application is unable to parse or process the input data correctly. It serves as a useful signal to notify the system about invalid or unexpected data.

The UnexpectedInputException is an instance of the ItemReaderException class and inherits its behavior. It encapsulates information about the exact cause of the problem, allowing you to take appropriate action.

Handling Unexpected Input with Grace

When faced with an UnexpectedInputException, you can handle it gracefully and provide feedback to the user, log the error for further analysis, or take any other recovery action specific to your application.

Let’s see an example where we have a simple item reader that reads a list of integers from a file:

public class IntegerItemReader implements ItemReader<Integer> {

    private BufferedReader reader;

    public IntegerItemReader(String filePath) {
        try {
            reader = new BufferedReader(new FileReader(filePath));
        } catch (FileNotFoundException e) {
            throw new IllegalArgumentException("File not found: " + filePath, e);
        }
    }

    @Override
    public Integer read() throws Exception {
        String line = reader.readLine();
        if (line != null) {
            try {
                return Integer.parseInt(line);
            } catch (NumberFormatException e) {
                throw new UnexpectedInputException("Invalid input: " + line, e);
            }
        }
        return null;
    }
}

In the read() method, we read a line from the file and try to parse it as an Integer. If the line contains invalid input, such as a non-numeric value, we throw an UnexpectedInputException with a meaningful error message.

Configuring Error Handling in Spring Batch

To handle the encountered UnexpectedInputException, we need to configure our Spring Batch job to specify the desired action. Spring Batch provides multiple error handling mechanisms, allowing you to choose the one that best suits your requirements.

One of the popular ways to handle exceptions in Spring Batch is by using the SkipPolicy interface. This allows you to skip and log the invalid input while continuing with the rest of the processing. Here’s an example of how to configure a SkipPolicy for our job:

@Configuration
@EnableBatchProcessing
public class BatchConfiguration {

    // ...

    @Bean
    public Step myStep(ItemReader<Integer> itemReader,
                       ItemProcessor<Integer, String> itemProcessor,
                       ItemWriter<String> itemWriter,
                       SkipPolicy skipPolicy) {
        return stepBuilderFactory.get("myStep")
                .<Integer, String>chunk(10)
                .reader(itemReader)
                .processor(itemProcessor)
                .writer(itemWriter)
                .faultTolerant()
                .skipPolicy(skipPolicy)
                .build();
    }

    @Bean
    public SkipPolicy skipPolicy() {
        return new MySkipPolicy();
    }

    // ...
}

In this example, we configure a custom SkipPolicy, named MySkipPolicy, that extends the SkipPolicy interface. The SkipPolicy determines whether a specific exception should be skipped or not.

Implementing a Custom SkipPolicy

Let’s implement our MySkipPolicy:

public class MySkipPolicy implements SkipPolicy {

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

    @Override
    public boolean shouldSkip(Throwable throwable, int skipCount) {
        if (throwable instanceof UnexpectedInputException) {
            LOGGER.warn("Skipping invalid input: {}", throwable.getMessage());
            return true;
        }
        return false;
    }
}

Our MySkipPolicy checks if the thrown exception is an UnexpectedInputException and logs a warning message with the details of the invalid input. If the exception is of a different type, we let the default behavior handle it.

Employing Additional Exception Handlers

Besides using SkipPolicy, Spring Batch also offers other exception handling mechanisms such as retrying the failed item, writing it to a separate file for manual review, retrying a specified number of times before considering it a failure, or even aborting the entire job. Choose the approach that aligns with your application’s requirements and best practices.

Conclusion

Handling unexpected input is crucial for maintaining robust and fault-tolerant Spring applications. Spring Batch provides powerful exception handling mechanisms, including the UnexpectedInputException, to help you gracefully handle such scenarios. By understanding the purpose and usage of this exception, and through appropriate configuration and implementation of exception handlers, you can ensure your application remains stable and provides meaningful error feedback to the user.