I have a void method that does some tasks trying to test exception scenarios but the test case is getting failed.
public void completetask(){
try{
RemoteUser rm = usrRepo.findById(12);
assistenRepo.save(rm);
}catch(Exception e){
log.error("Exception occurred while making changes {}", e,getMessage());
}
}
How can we test the exception scenario here on JUnit 5?
I have tried this but it's not working
#Test
public void completetaskTest(){
RemoteUser rm = getDummyRemoteUsr();
Mockito.when(usrRepo.findById(12)).thenReturn(rm);
Mockito.when(assistenRepo.save(rm)).thenThrow(new Exception("Error Abnormal"));
Exception exception = Assestions.assertThrow(Exception.class, () -> usrService.completetask());
String expectedMessage = "Exception occurred while making changes";
String actualMessage = exception.getMessage();
Assertions.assetTrue(actualMessage.contains(expectedMessage));
}
I am getting an error for this test case - the check exception is invalid for this method
Invalid java.lang.Exception : Error
Can I know what wrong I am doing here ?
You are not throwing your error, you are just writing a log with one log line.
catch(Exception e){
log.error("Exception occurred while making changes {}", e,getMessage());
}
Here is the javadoc on Assertions.assertThrows:
Assert that execution of the supplied executable throws an exception of the expectedType and return the exception.
If no exception is thrown, or if an exception of a different type is thrown, this method will fail.
If you do not want to perform additional checks on the exception instance, ignore the return value.
That's why your assertThrows method will fail under all circumstances.
So either throw an error in your method you want to test, or check the log print in exceptions for testing.
You are expecting your method to thrown an exception but in your code, you're handling and logging the exception and no exception is thrown:
public void completetask(){
try {
RemoteUser rm = usrRepo.findById(12);
assistenRepo.save(rm); // <-- Exception is thrown...
} catch(Exception e){ // <-- Catched here
log.error("Exception occurred while making changes {}", e,getMessage());
}
// <-- Method finishes normally.
}
You should be seeing the following in the output:
Exception occurred while making changes Error Abnormal
But your test will be failing here:
Exception exception = Assestions.assertThrow(Exception.class, () -> usrService.completetask());
Because the exception was never thrown. If you comment out the exception handling try / catch it will pass that point but now it will fail comparing the error messages.
EDIT:
I know this scenario but the problem here is how to solve this issue? How can we write test scenario for this condition –
If you want to verify your exception was handled just remove verification:
#Test
public void completetaskTest(){
RemoteUser rm = getDummyRemoteUsr();
when(usrRepo.findById(12)).thenReturn(rm);
when(assistenRepo.save(rm)).thenThrow(new Exception("Error Abnormal"));
assertTrue(true); // if we reached this line, in means the error has handled.
}
If you really want to go further and check if the message matches (which it might be overkill) you can check the logger, but again, I would't recommend it.
Something like this:
#Auto
Logger log;
...
#Test
public void completetaskTest(){
RemoteUser rm = getDummyRemoteUsr();
when(usrRepo.findById(12)).thenReturn(rm);
when(assistenRepo.save(rm)).thenThrow(new Exception("Error Abnormal"));
// Verify the `log.error` was invoked with exactly those parameters
verify(log, times(1)).error("Exception occurred while making changes {}", "Error Abnormal");
}
That means the exception was thrown, cached and the logger was invoked.
Let's say I have a code that does some DB work and has a happy path and the only unhappy flow, that only occurs when DB connection is down, like this:
public Report createReport(
String reportType, Report reportData, ReportUser reportUser, Timestamp createTs) {
KeyHolder reportIdHolder = new GeneratedKeyHolder();
try {
saveReportDetails(reportType, reportData, reportUser, createTs);
} catch (DataAccessException e) { <-------------- This extends RuntimeException
log.error(
"DataAccessException while trying to insert report with name {}",
reportData.getReportName(),
e);
throw e;
}
...
// More of the happy path code here
}
I've got a test for the happy path, but is it a good practice to test for the Runtime exception flow as well?
The app is a SpringBoot Rest app, so it doesn't die when the exception is rethrown after logging.
I am coding a Spring MVC, hibernate app. I can't decide where should I throw custom exceptions, what custom exceptions to throw and where to catch "Exception", in controller or service or DAO?
I tried to throw a custom exception in controller and service and catch "Exception" in the controller as the last catch block. But every time a custom exception is thrown, the last catch block( of Exception) catches it and throws CustomGenericException overriding the previous one.
//Controller
#PostMapping("/add/{user_id}/{book_id}")
public #ResponseBody
String addToCart(#PathVariable("user_id") Integer user_id,
#PathVariable("book_id") Integer book_id){
try {
return cartService.addBook(user_id, book_id);
}
catch (HibernateException | CannotCreateTransactionException dbException) {
throw new DatabaseDownException("Database error. Could not connect at this time.");
}
catch (Exception ex){
throw new CustomGenericException("Could not add book to cart at this time. Please try again later.");
}
}
//Service
#Override
public String addBook(int user_id, int book_id) {
if(bookDAO.getCount(book_id)>0) {
Cart cart = new Cart(user_id, book_id);
List<Cart> userCarts = cartDAO.getCart(user_id, 0);
for (Cart c : userCarts) {
if (c.getBook_id() == book_id) {
return "Book already in cart!";
}
}
List<Cart> issuedBooks =cartDAO.getCart(user_id, 1);
for(Cart c:issuedBooks){
if(c.getBook_id()==book_id){
return "Book already issued. Can't add another to cart.";
}
}
return cartDAO.addBookToCart(cart);
}
return "No more copies left. Please try again later.";
}
I want to know where should I throw exceptions, where to catch them and how to avoid custom thrown exceptions getting caught by last catch block.
#aks If you want to throw checked exceptions than you should pass "cause" exception to constructor of exception on higher level (in this case the last one catch) because otherwide the cause information is lost. Core Exception class has constructor with cause parameter to pass.
You can also try to use Controller Advice https://spring.io/blog/2013/11/01/exception-handling-in-spring-mvc
I hope I helped a little bit :)
read about chained exception in Java here
you are not wrapping exception object in your custom exception , that is why you feel like previous exception is getting overridden .
I have a Guava retryer around some code:
Retryer<Boolean> retryer = RetryerBuilder.<Boolean>newBuilder()
.retryIfExceptionOfType(Exception.class)
.withStopStrategy(MoreStopStrategies.liveStopAfterAttempt(retries))
.withWaitStrategy(MoreWaitStrategies.liveExponentialWait(TimeUnit.MILLISECONDS, retrySleep, TimeUnit.MILLISECONDS))
.build();
try {
retryer.call(() -> {
return doStuff();
});
} catch (ExecutionException | RetryException e) {
throw Throwables.propagate(e);
}
Let's say doStuff() throws an ArithmeticException. How do I catch that outside the retryer.call()?
So the retryer will try a couple times, fail, and enter into the catch (ExecutionException | RetryException e) block. How would I retrieve the ArithmeticException inside there?
Thanks!
This is a bit of a faulty pattern. You say that any exception is ok to retry. An ArithmeticException will then be ok to retry. This is not what you want.
This is how retries should be implemented. Note the comment on the second line.
Retryer<Boolean> retryer = RetryerBuilder.<Boolean>newBuilder()
// .retryIfExceptionOfType(Exception.class)
.withStopStrategy(MoreStopStrategies.liveStopAfterAttempt(retries))
.withWaitStrategy(MoreWaitStrategies.liveExponentialWait(TimeUnit.MILLISECONDS, retrySleep, TimeUnit.MILLISECONDS))
.build();
void doStuff() {
try {
retryer.call(() -> {
doRealStuff();
});
} catch (RetryException e) {
throw new RuntimeException("Call never succeeded", e);
} catch (ExecutionException e) {
Throwables.propagateIfPossible(e.getCause(), ArithmeticException.class);
throw new RuntimeException("Unexpected", e);
}
}
Then when you actually call doStuff:
try {
doStuff();
} catch(ArithmeticException e) {
System.err.println("Arithmetic exception caught:");
e.printStackTrace(System.err);
}
Without seeing your doStuff() or at least knowing what kinds of Exceptions it throws it's hard to answer.
In general, if you have the Retryer consider every Exception unsuccessful, it will retry and eventuelly stop - but it catches any Throwable thrown inside the executed code (see Retryer code, line 162)
The solution is either:
If your doStuff() only throws an ArithmeticException in those cases that result in stopping the Retryer, and that a different kind of Exception marks that a retry is necessary, you can do retryIfExceptoinOfType(OtherException.class). Then, according to the docs the docs
Throws:
java.util.concurrent.ExecutionException - if the given callable throws an exception, and the rejection predicate considers the attempt as successful. The original exception is wrapped into an ExecutionException.
call() will throw an ExecutionException that you can catch outside of the Retryer and inspect the wrapped Exception.
If ArithmeticExcpetion is all doStuff() will throw, and that also indicates that the Retryer should retry, then you can write a custom StopStrategy that throw an ArithmeticExpcetion, it is catched nowhere in the Retryer.
However I advise you to completele rewrite your code, your data flow seems a bit broken. If an ArithmeticExpcetion (or actually even any Exception, as you specify Exception.class in the retryIf ) is to be expected, it should not also be unexpected and need special handling.
Can someone explain the difference between catching an Exception and catching an SQLException? I know that SQLException will print out more information if you choose to print out the exception errors, but is there anything else?
try {
//code
} catch(Exception ex) {
//code
}
And
try {
//code
} catch(SQLException ex) {
//code
}
What are the benefits and differences of using Exception and SQLException in the catch block?
This is not the only difference.
Catching Exception is dangerous because it also catches all RuntimeExceptions (therefore unchecked exceptions), and that include niceties such as NullPointerException etc which are clear programmer errors. Don't do that!
Also, Exception is a class like any other, so you can subclass it and add constructors/methods of yours. For instance, SQLException has a .getErrorCode() method which Exception does not have. If you only catch Exception, you cannot access this method.
In general, catching the "more precise" exception first is the best. For instance, with the new (in Java 7...) file API, you can easily distinguish between filesystem level errors and other I/O errors, since FileSystemException extends IOException:
try {
something();
} catch (FileSystemException e) {
// fs level error
} catch (IOException e) {
// I/O error
}
It's all about the hierarchy,when you are talking about the catching the exception.
Technically speaking, Exception - is the super class which catches each and every exception.
If you are writing something related to SQL in the try block and you know it may even throw SQL Exception.
Then you may declare it this way as well.
try
{
}catch(SQLException ex)
{
Do this,when SQL Exception is caught.
}
catch(Exception ex)
{
Generic Exception - works for all
}
SQLException inherits from Exception, so SQLException will contain more (and more specific) information than Exception (which is intended to apply generally to all exceptions).
You can also have multiple catch clauses; so you can first try to catch the SQLException, but if it's not a SQLException, then you can just catch the general Exception.
In general, you shouldn't catch exceptions unless you intend to handle them in some way. You can have a top-level exception handler that catches any exceptions that bubble up to the top of the call stack, so that your program doesn't crash on unhandled exceptions.
A - Explanation
SQLException is a subtype of java.lang.Exception and also it is implementing the Iterable<Throwable> class. Programmers prefer throwing different subtypes of Exception class because on some higher level, they want to catch the exact sub-Exception class so that they can be sure that that specific Exception is thrown on some exact scenario. Thus, they can know the exact source of Exception.
B - Example
Consider you have written a method that throws multiple exceptions. Let's say, you take a json String and parse it, then persist it on the database. Consider the following method;
public boolean persistCustomer(String jsonString) throws SQLException, IOException {
Connection conn = getConnection();
PreparedStatement preparedStatement = null;
ObjectMapper objectMapper = new ObjectMapper();
try {
Customer customer = objectMapper.readValue(jsonString, Customer.class);
preparedStatement = conn.prepareStatement(PERSIST_CUSTOMER);
preparedStatement.setString (1, customer.getName());
preparedStatement.setInt (2, customer.getAge());
preparedStatement.setBoolean (3, customer.getIsRegular());
preparedStatement.executeUpdate();
return true;
} catch (IOException e) {
throw e;
} finally {
try {
if (preparedStatement != null)
preparedStatement.close();
if (conn != null)
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
In this method, we are converting JSON into a Customer class and also we persist customer class to the database.
The following lines throw SQLException;
preparedStatement = conn.prepareStatement(PERSIST_CUSTOMER);
preparedStatement.setString (1, customer.getName());
preparedStatement.setInt (2, customer.getAge());
preparedStatement.setBoolean (3, customer.getIsRegular());
preparedStatement.executeUpdate();
prepareStatement(), setters and executeUpdate() methods, all of them throwing SQLException's. But also, the line that which we convert JSON in a String into a Customer object, also throws several Exceptions other than SQLException.
Customer customer = objectMapper.readValue(jsonString, Customer.class);
readValue() method throws JsonParseException, JsonMappingException and also IOException. All of them can be catched using an IOException because the JSON related exceptions extend IOException.
I'm going to provide two different examples so that it will be obvious to understand why we need different types of Exceptions.
C - Bad Practice: Using Exception To Catch All Exceptions
public class BadPracticeExample {
public static void main(String[] args) {
MySQLUtil dbUtil = new MySQLUtil();
String jsonString = "{\"name\":\"Levent\",\"age\":31,\"isRegular\":true}";
try {
dbUtil.persistCustomer(jsonString);
} catch (Exception e) {
System.out.println("A problem occured");
}
}
}
As you can see, it catches the Exception but what are we going to do if we need special exception handling for two different sources of problems? persistCustomer can throw either IOException or an SQLException and what if we need to do different set of tasks to handle those problems? I want to send an email to the database admin when an SQLException occurs and I want to continue when a JSON parsing problem occurs, on the case that an IOException is catched?
In this scenario you can't do that. Here is the output of the code snippet above and we are only sure that an Exception occured but we don't have any idea about what is the source of it;
A problem occured
D - Good Practice Example I: SQL Exception catched
public class GoodPracticeExample {
public static void main(String[] args) {
MySQLUtil dbUtil = new MySQLUtil();
String jsonString = "{\"name\":\"Levent\",\"age\":31,\"isRegular\":true}";
try {
dbUtil.persistCustomer(jsonString);
} catch (SQLException e) {
System.out.println("SQL Exception catched, SQL State : " + e.getSQLState());
System.out.println("Error Code : " + e.getErrorCode());
System.out.println("Error Message : " + e.getMessage());
} catch (IOException e) {
System.out.println("Cannot parse JSON : " + jsonString);
System.out.println("Error Message : " + e.getMessage());
}
}
}
As you can see, we catch for both, JSON and SQL problem and in this example, submethod is trying to persist DB where there is no table. The output is as below;
SQL Exception catched, SQL State : 42000
Error Code : 1142
Error Message : INSERT command denied to user 'levent'#'example.com' for table 'CUSTOMER'
So we have catched SQL Exception and we have all parameters we need to send an alarm email. We can add additional handler or utility methods on the SQLException catch block.
D - Good Practice Example II: IOExceptoin catched on Parsing Error
public class GoodPracticeExample {
public static void main(String[] args) {
MySQLUtil dbUtil = new MySQLUtil();
String jsonString = "{\"Zname\":\"Levent\",\"age\":31,\"isRegular\":true}";
try {
dbUtil.persistCustomer(jsonString);
} catch (SQLException e) {
System.out.println("SQL Exception catched, SQL State : " + e.getSQLState());
System.out.println("Error Code : " + e.getErrorCode());
System.out.println("Error Message : " + e.getMessage());
} catch (IOException e) {
System.out.println("Cannot parse JSON : " + jsonString);
System.out.println("Error Message : " + e.getMessage());
}
}
}
If you've noticed, I"ve corrupted the JSON to cause an IOException. Now in the json string, instead of "name", "Zname" is written which will cause Jackson Parser to fail. Let's checkout the output of this code.
Cannot parse JSON : {"Zname":"Levent","age":31,"isRegular":true}
Error Message : Unrecognized field "Zname" (class com.divilioglu.db.utils$Customer), not marked as ignorable (3 known properties: "isRegular", "name", "age"])
at [Source: (String)"{"Zname":"Levent","age":31,"isRegular":true}"; line: 1, column: 11] (through reference chain: com.divilioglu.db.utils.MySQLUtil$Customer["Zname"])
As you can see, we catched the specific scenario and we are sure, this comes from the line in dbUtil.persistCustomer() method which can be seen below;
Customer customer = objectMapper.readValue(jsonString, Customer.class);
E - Conclusion
So as it is a best practice to create new Exceptions by extending existing Exception classes. While writing your code at first, you may think that it is an overkill and you won't need additional Exception classes, but you will need them when you need distinguish the source of the problem and handle them independently.
In this example demonstrated above, I can independently catch IOException and SQLException and the sources of both Exceptions are coming from the same method. I want to distinguish both so that I can handle them independently. You cannot have that flexibility if you just wrap all the Exceptions with the base Exception class.
Exception is a standard class from which every exceptions inherit.
SQLException is a class that inherits from Exception and that is designed specifically for database(SQL) exceptions.
By doing
try {
// Your code here
} catch (Exception e) {
// Catching here
}
You are catching every type of exception possible... But then, you might not be able to know how to react to a specific exception.
but by doing
try {
// Your code here
} catch (SQLException e) {
// Catching here
}
You know that the exception happened while working on a database and it helps you know how to react to the exception.
As you see SQLException extends exception. So that's the only difference really. When you are catching exception then you will catch ALL exceptions (which is bad). But when you are catching SQLException then you catch only that(which is good because that is what you are seeking).
If an exception in between the try and catch blocks is thrown that is not a SQL Exception (these will typically only come from database-related code), for example a Null Pointer Exception, the Exception catch will catch it but the SQLException will not.
SQLException is an Exception so you are just getting a more specific exception.
According to Oracle's javadocs, this specific information you get is:
a string describing the error. This is used as the Java Exception
message, available via the method getMessage.
a "SQLstate" string, which follows either the XOPEN SQLstate
conventions or the SQL:2003 conventions. The values of the SQLState
string are described in the appropriate spec. The DatabaseMetaData
method getSQLStateType can be used to discover whether the driver
returns the XOPEN type or the SQL:2003 type.
an integer error code that is specific to each vendor. Normally this
will be the actual error code returned by the underlying database.
a chain to a next Exception. This can be used to provide additional
error information.
the causal relationship, if any for this SQLException.
SQLException is a specialized exception derived from Exception.
If you catch Exception, all exception shall get caught. Even undesirable exceptions.
If you catch only its specialiazation, the SQLException, only the SQLException itself or its derived shall get caught.
One shall catch only exceptions one can handle or wishes to handle, and let the others bubble up.
For further reference, please take a look at the following:
Exception
SQLException
SQL exception is a frequent error while working in Java Database Connectivity (JDBC).Its related to accessing or setting column in your SQL Query using prepared statement.
SQLException is a derived from Exception and contains more specific information related to accessing or setting column in your SQL query, while exception is usually more general.