Java: Exception Handler

Question

I have a project having Exception handling written in the following way:

Parent class has all the exception handling logic. And the invoked class just throws exception and the invoker class handles with appropriate logic.

Now the problem that I am facing invoked class opens different stuffs for example, a file. These files are not getting closed at the time of exception.

so what should be the appropriate way of exception handling in this case.

    class A
    {
    private void createAdminClient()
    {

        try
        {
            B b = new B();          
                b.getClinetHandler();
        }
        catch(CustomException1 e1)
        {
        }   
        catch(CustomException2 e1)
        {
        }   
        catch(CustomException3 e1)
        {
        }
        catch(CustomException4 e1)
        {
        }
    }
}

class B
{
    ................
    ................

    getClinetHandler() throws Exception
    {
        --------------------------      
        ---- open a file----------
        --------------------------
        ----lines of code---------
        --------------------------      

        Exceptions can happen in these lines of code.
        And closing file may not be called      

        --------------------------      
        ---- close those files----
        --------------------------

    }

}

Sean · Accepted Answer · 2013-12-10 16:59:15Z

2

You can wrap the code which may throw an exception in a try...finally block:

getClientHandler() throws Exception {
    // Declare things which need to be closed here, setting them to null
    try {
        // Open things and do stuff which may throw exception
    } finally {
        // If the closable things aren't null close them
    }
}

This way the exception still bubbles up to the exception handler but the finally block ensures that the closing code still gets called in the event of an exception.

answered Dec 10, 2013 at 16:59

Sean

4,48028 silver badges22 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

stinepike · Accepted Answer · 2013-12-10 16:55:25Z

0

use a finally block to complete the final tasks. for example

    try
    {
        B b = new B();          
            b.getClinetHandler();
    }
    catch(CustomException1 e1)
    {
    }  
    finally{
       // close files
    }

From the doc

The finally block always executes when the try block exits. This ensures that the finally block is executed even if an unexpected exception occurs. But finally is useful for more than just exception handling — it allows the programmer to avoid having cleanup code accidentally bypassed by a return, continue, or break. Putting cleanup code in a finally block is always a good practice, even when no exceptions are anticipated.

answered Dec 10, 2013 at 16:55

stinepike

54.9k14 gold badges95 silver badges116 bronze badges

Comments

0circle0 · Accepted Answer · 2013-12-10 16:56:25Z

0

This is how I do it

try {
    //What to try
} catch (Exception e){
        //Catch it
    } finally {
                    //Do finally after you catch exception
        try {
            writer.close(); //<--Close file
        } catch (Exception EX3) {}
    }

answered Dec 10, 2013 at 16:56

0circle0

514 bronze badges

Comments

Community · Accepted Answer · 2017-05-23 11:57:34Z

0

Use a finally block to handle post-processing execution (regardless whether it succeeded or failed). Like so:

// Note: as Sean pointed out, the b variable is not visible to the finally if it 
// is declared within the try block, therefore it will be set up before we enter
// the block.
    B b = null; 

    try {
        b = new B();          
        b.getClinetHandler();
    }
    catch(CustomException1 e1) {
    } // and other catch blocks as necessary...
    finally{
        if(b != null)
            b.closeFiles() // close files here
    }

The finally block is always executed, regardless, even if you throw or return from the try or catch blocks.

This answer provides a very good explanation of how the finally block works in this situation, and when/how it is executed, and basically further illustrates what I just wrote.

edited May 23, 2017 at 11:57

CommunityBot

11 silver badge

answered Dec 10, 2013 at 16:56

Paul Richter

11.1k10 gold badges56 silver badges89 bronze badges

4 Comments

Sean Over a year ago

This isn't what they want. The closable objects aren't visible in this code block.

Paul Richter Over a year ago

@Sean I think it is what they want, as they are ultimately asking how to close the files after execution (in the getClientHandler method). However you have indeed pointed out a flaw, in that the b variable is not visible, which I will correct.

Exploring Over a year ago

Hi Teeg, the code snippet that I have pasted, basically the parent class has all the exception handling logic. If I choose this way in that case closeFiles and other handling closable objects handling logic has to go to the parent- which I do not want.

Paul Richter Over a year ago

@Baishakh Ah ok, fair enough that makes sense. Sean's answer is a better design approach in that regard.

Collectives™ on Stack Overflow

Java: Exception Handler

4 Answers 4

Comments

Comments

Comments

4 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

Comments

Comments

4 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related