Throwing Exceptions5:32 with Alena Holligan
There are times when we would like our application to throw its own exceptions. Such as when a resource, like a file or a database, that SHOULD be available isn't.
We've looked at the simple example of how to catch exceptions 0:00 that php itself throws. 0:03 There are other times when we would like our application to throw its 0:05 own exceptions as well. 0:09 Such as when a resource, like a file or a database that should be available, isn't. 0:11 Remember, this should not be used in the normal flow of an application, but 0:17 only when something exceptional happens. 0:22 Let's go into work spaces and throw our own exceptions. 0:24 Let's try reading a file that doesn't exist. 0:28 Start with a new file named data.php. 0:31 Open your php tag and echo a line for the end of the file so 0:37 we can see what gets processed. 0:42 Now we can add a line to read the file. 0:48 file = F open, 0:54 data.txt. 0:57 We'll open this for reading and close the line. 1:02 Let's view this in the browser. 1:06 If error reporting is turned on for 1:12 warnings, we will get a warning, no such file or directory. 1:14 Because it's simply a warning and not a fatal error, 1:18 the script will continue to process, which is why we see End of File. 1:21 On a production server we don't want to show errors at all. 1:25 So let's stop displaying errors. 1:29 Ini_set display errors off. 1:36 Now when we refresh the page, we don't see any errors at all. 1:44 It looks like everything ran properly, but that's not actually what happened. 1:49 Exceptions allow us to catch issues and control what happens. 1:53 Let's throw an exception instead. 1:57 If we can't open our file for reading, Then we're going to throw a new exception. 2:03 Just like instantiating a new class object, 2:11 we'll use the keyword new and the class exception. 2:14 We can also pass an argument. 2:18 The message, unable to access file. 2:20 Instead of assigning this to an object variable 2:27 we're going to use the keyword throw. 2:30 Let's go back to the browser. 2:33 PHP will halt the flow of the script and 2:37 attempt to find the first matching catch block. 2:40 Just like with exceptions thrown by PHP, if the exception is not caught, 2:42 a PHP fatal error will be issued with an uncut exception message. 2:47 Since we have display errors turned off, we won't see the error. 2:52 But we get either this ugly error page or a blank screen, 2:55 because our scripts stops processing and we can't get to the end of the file. 2:59 Let's go back to work spaces. 3:03 Let's comment out this line so our display errors is back on. 3:08 Then we only want to display, fatal errors. 3:13 So we can set error_reporting(1). 3:15 Now when we refresh the browser we see the uncaught exception. 3:26 If we're going to throw errors, we need to catch them. 3:30 So let's surround this in a try catch block. 3:33 Try. 3:41 Catch. We'll catch the exception. 3:46 And assign it to e. 3:52 And then we can do our exception handling. 3:56 For now we'll echo. 3:59 E. 4:02 Get message. 4:03 Let's view this in the browser again. 4:06 Now the code performs are exception handling by showing the error and 4:11 allowing the script to continue. 4:14 This works, but it's not really how we would use exceptions. 4:16 Since we'll be using exceptions with object oriented code, 4:20 let's create a simple class and read the file in a method called Get Data. 4:23 Class, my data. 4:33 And then our method, using function, getData. 4:38 Now we can instantiate a new object and 4:51 place the call to the Get Data method within the try catch block. 4:53 Data = new myData. 4:57 And then try Data, getData. 5:05 Let's go back to the browser and refresh the page. 5:16 We see the exact same thing we did last time which is great. 5:21 We're still handling the exception but this time using a class and 5:24 object which is how will be handling exceptions in our application. 5:28
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