Overview
Exception management is one of the key areas for all kinds of application development. You should adopt an appropriate strategy for exception management to build high quality and robust applications. It is a very powerful concept and makes the development work very easy if it's used efficiently. Inappropriate way of handling exceptions can degrade the performance of your applications.
Introduction
Before dig into the details of exception management, it's very important to know what is an exception? The general meaning of "an exception is the breaching of a predefined assumption of the application". Remember, exception and error are not the same. To explain this, let me explain a couple of examples.
Example1
Let's say you are trying to log data to a file and your application assumes the file is present in the target path, but if it is not, then an exception would be raised. On the other hand, if your job is to trace the file and if it is present then log the data, in this scenario, raising an exception is a bad coding practice. It should be handled through validation code.
Example 2
Let's say in a normal ASP.NET application, you are trying to update all necessary fields to the database, and your application assumes the database connection is available; suppose the connection is not available, then raising an exception is an ideal solution. On the other hand, while updating the mandatory fields in database and if a few of them are having null values, then raising an exception is not necessary, it should be handled through validation code.
How to Handle
As a developer, you must take advantage of the structured exception handling mechanism through try
, catch
and finally
blocks. The .NET framework provides a broad hierarchy of exception classes to handle the different types of exceptions and all these classes are derived from Exception
class (base class). The developer can extend the exception mechanism through inheritance, it helps to implement custom error handling or provides a proper gateway for complex error handling for the application. Unfortunately, many developers misuse this architecture capability. One very important thing you should keep in mind is how to react when an exception occurs at runtime. The good approach to react to an exception is:
- Just ignore the exception or implement different possible
catch
blocks to catch the exception.
- Catch the exception and perform the required action for your application, and if you can not recover from the exception, rethrow the exception.
- Catch the exception and wrap with another exception which is more relevant for your application. Exception wrapping is used to avoid breaking the layer abstraction due to exception. For preserving the original exception, you can use the
InnerException
property of the Exception
class. This allows the original exception to be wrapped inside a new exception (which is more relevant for your application). To understand the wrapping of exceptions, let's look at this example inside a method of your application which caught a lower level exception called IOException
. You can wrap this original exception with an application level exception called LoadingException
or FailtoLoadInfo
or something else which is more relevant for your application, rather then alerting the lower level exception to the user.
The exception management architecture of an application should have the capability to:
- Detect exception
- Perform code clean up
- Wrap one exception inside another
- Replace one exception with another
- Log and report error information
- Generate events that can be monitored externally to assist system operation
At the beginning of the design, you must plan for a consistent and robust exception management architecture and it should be well encapsulated and abstract the details of logging and reporting throughout all architecture layers of your application. Let's discuss some of the best practices of exception management.
Best Practices
The following list contains tips/suggestions to be considered while handling exceptions:
- Exception is an expensive process, for this reason, you should use exceptions only in exceptional situations and not to control regular logic flow. For example:
void EmpExits ( string EmpId)
{
if ( dr.Read(EmpId) ==0 )
{
throw( new Exception("Emp Not found"));
}
}
The best practice is:
bool EmpExits ( string EmpId)
{
if ( dr.Read(EmpId) ==0 )
{
return false}
}
}
- Avoid exception handling inside loops. If it's really necessary, implement
try
/catch
block surrounding the loop.
- Adopt the standard way of handling exceptions, through
try
, catch
and finally
blocks. This is the recommended approach to handle exceptional error conditions in managed code, finally
blocks ensure that resources are closed even in the event of exceptions. For example:
SqlConnection conn = new SqlConnection("...");
try
{
conn.Open();
}
catch(…)
{
}
finally
{
if (conn.State==ConnectionState.Open)
conn.Close();
}
- Wherever possible, use validation code to avoid unnecessary exceptions. If you know that a specific avoidable condition can happen, precisely write code to avoid it. For example, checking for null before performing any operations on an object/variable can significantly increase performance by avoiding exceptions. For example:
double result = 0;
try{
result = firstVal/secondVal;
}
catch( System.Exception e){
}
This is better then the above code:
double result = 0;
if(secondVal >0)
result = firstVal/secondVal;
else
result = System.Double.NaN;
- Do not rethrow exceptions for unnecessary reasons because the cost of using
throw
to rethrow an existing exception is approximately the same as creating a new exception, and rethrowing an exception also makes it very difficult to debug the code. For example:
try {
} catch (Exception e) {
throw;
}
- The recommended way to handle different errors in different ways is by implement a series of
catch
statements. This is nothing but ordering your exception from more specific to more generic. For example, to handle file related exceptions, it's better to catch
FileNotFoundException
, DirectoryNotFoundException
, SecurityException
, IOException
, UnauthorizedAccessException
, and at last Exception
.
- ADO.NET errors should be captured through
SqlException
or OleDbException
.
- Your exception management system should be capable to detect an exception, wrap one exception inside another, replace one exception with another, and log and report the exception information for monitoring the application.
- It's recommended to use “Exception Management Application Block” provided by Microsoft. It is a simple and extensible framework for logging exception information to the event log, or you can customize it to write the exception information to other data sources without affecting your application code and implement all best practices tested in the Microsoft Lab.
For more information:
I am Anand Kumar from India my core expertise is developing robust service components using ATL COM ,Remoting and Web Service. I am passionate about performance optimization and best practices of .NET ,Microsoft Patterns and Practices & VSTS . I believe knowledge sharing is the greatest joy ,the philosophy behind knowledge sharing is gain more by sharing more , apart from my regular office work I do involve in various Microsoft User Group forums such as UG-Hyderabad ,Bangalore, Chennai etc. I am one of the core members of Microsoft User Group Hyderabad (MUGH ) and a volunteer member of INETA.