Exception thrown inside catch block - will it be recaught or not?

java

exception-handling

try-catch-blocks

best-practices

byAnton Shumikhin·Feb 6, 2025

Should an exception crop up within a catch block, it will not be recaught by the original catch. Instead, apply this nested try-catch structure:

try {
    // risky code
} catch (InitialException e) {
    try {
        // handle risky code appropriately
    } catch (SubsequentException e2) {
        // deal with any secondary issues or exceptions
    }
}

This blueprint ensures that any secondary issues are handled efficiently by the corresponding nested catch, rather than leaving the exceptions unattended or being thrown up the stack.

Know your structured exception handling

Java Language Specification (JLS) 14.19.1 crisply illustrates how try-catch blocks should behave. According to the specification, whenever an exception is thrown - either from a try block or a catch block - it travels upwards, looking for an appropriate catch. Once it exits a catch block, it never comes back. This is indicative of a one-way traffic.

Mastering exception handling: A guide to the tricky bits

Working with catch blocks demands care to ensure predictable handling of exceptions.

Specific Catch blocks: Order Matters

Catch block order is crucial. Java checks catch blocks sequentially, from top to bottom, catching the first applicable type it encounters. This implies that if an ApplicationException is thrown within a catch block, it will not be caught by a subsequent catch(Exception e) block, unless this second catch block is properly nested.

The Finally Block's Roadshow

Regardless of whether an exception is thrown, a finally block executes after every try-catch block. If a catch block throws an exception followed by another from the finally block, the second error could override the first, leading to potential data loss.

The Exception Handling Bible: Best Practices

To address exceptions elegantly, keep try-catch blocks granular wherever possible. This allows precise control and management of varying types of exceptions and situations.

Handling alternative scenarios: Be Prepared

Having covered the basics, we'll now delve into a few alternate scenarios that could make exception handling a bit twisted.

Elegant Rethrows: Carefully looping the boomerang

While rethrowing exceptions, a good understanding of the call stack is key. If you must rethrow, consider wrapping the exception in a new type or packing in additional contextual information.

Compiler-driven safety: Don't Skip the seatbelt

Java's trusty compiler ensures reliable behavior through structured exception handling. It won't compile code where an exception is thrown within a catch block that could potentially be re-caught by the same try's catch blocks.

The Asynchronous beast: Multithreading

In multithreaded or asynchronous scenarios, exceptions thrown in one thread won't be caught by try-catch blocks in another. Proper synchronization or concurrent utilities might be needed to ensure your boomerang doesn't end up elsewhere.

Implement measures to prevent exception masking. When exceptions are thrown successively, information about the root issue can be obscured, or even lost. Remember, you are the Sherlock Holmes in this crime scene.

explain-codes / Java / Exception thrown inside catch block - will it be recaught or not?

Linked

Java exception not caught?



Can I catch multiple Java exceptions in the same catch clause?



What is the difference between Errors and Exceptions?



Does a finally block run even if you throw a new Exception?



Does a finally block always get executed in Java?

