CODEWITHSUNDEEP
javarethrowmulti-catch
LaBlum
LaBlum

Reputation: 61

When to use multi-catch and when to use rethrow?

I'm very uncertain about this two topics. I know that i should use multi-catch for exceptions which need to handle the same way. But for what purpose do i really need something like that.

private void something(String name) throws IOException, RemoteException {
    try {
        ...
    } catch (Exception ex) {

        ... // do something

        throw ex;
    }
}

Upvotes: 5

Views: 853

Answers (3)

adi
adi

Reputation: 304

ReThrow

Whenever you want to notify caller method about exception, you catch and rethrow exception.

Say some method callSomething() is calling your method something(). If any exception occurs inside something (), it will just catch exception, so application doesn't fail, and rethrow it to the callSomething() method. Then callSomething() will notify client about internal error.

Other example is, in MVC pattern, request submitted by client is served by some method from controller based on request mapping. Controller will call service, and service will interact with some method of dao. If some exception occurs in DAO, then DAO will rethrow exception to service, service will rethrow to controller, and it is controller which will notify client about error message. This is known as Exception propagation in java. An exception propagates from method to method, up the call stack, until it's caught.

Multi catch

If you want to perform same action for multiple types of exception, then you use multi catch.

Upvotes: 2

11thdimension
11thdimension

Reputation: 10653

You'll need rethrow in following situations

  1. You want to preprocess something before letting the exception leave the method. However, if you don't care about the type of the exception then preprocessing can be done in the finally block as well.
  2. You're trying to convert the checked exceptions into unchecked exception. In that case you'll be catching all the exceptions as catch(Exception ex) and rethrowing them as throw new RuntimeException(ex).
  3. You want your custom exception to be thrown instead of in built ones. So you'll catch all the exceptions and then create your own exception object preferably unchecked one and throw that. Many APIs do this, for example Spring converts untuitive JDBC exceptions to Spring custom exceptions.
  4. This one is kind of like preprocessing. You want to keep track of all the exceptions thrown by creating an ArrayList or something, so that at the end of a program with multiple steps you know which steps throw exceptions. I have seen this one being used in Talend generated Java code.

Upvotes: 2

davidxxx
davidxxx

Reputation: 131496

You can do it if you consider for this method that any exception thrown during its execution should be handled in the same way and you want perform a task before letting propagate the exception to the client

For example, suppose you want to do a particular processing when the exception happens such as logging the information. So you catch it to do this task.
Nevertheless you consider that the caught exception is a problem and that logging it was not a "real" handling of the exception. So, you let it propagate by rethrowing it.

Upvotes: 3

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