File not found exception ошибка

This is the third part in the series named Debugging common .NET exceptions. Today, I want to help you track down and fix a very common and very well-known exception, System.IO.FileNotFoundException. Admitted! In all instances this error is caused by trying to access a file that isn’t there. But, there are actually multiple scenarios that can trigger this exception. You may think you know everything there is to know about this exception, but I bet there is something left for you to learn. At least I did while digging down into the details for this post. Stay tuned to get the full story.

Types of file not found errors

Let’s dig into the different causes of this error. The Message property on FileNotFoundException gives a hint about what is going on.

Could not find file ‘filename’

As the message says, you are trying to load a file that couldn’t be found. This type of error can be re-created using a single line of code:

try
{
    File.ReadAllText("non-existing.file");
}
catch (FileNotFoundException e)
{
    Console.WriteLine(e.ToString());
}

line 3 is the important one here. I’m trying to load a file that doesn’t exist on the file system (non-existing.file). In the example above, the program will print output to the console looking similar to this:

System.IO.FileNotFoundException: Could not find file 'APP_PATHbinDebugnon-existing.file'.
File name: 'APP_PATHbinDebugnon-existing.file'
   at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
   at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)
   at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)
   at System.IO.StreamReader..ctor(String path, Encoding encoding, Boolean detectEncodingFromByteOrderMarks, Int32 bufferSize, Boolean checkHost)
   at System.IO.File.InternalReadAllText(String path, Encoding encoding, Boolean checkHost)
   at System.IO.File.ReadAllText(String path)
   at ConsoleApp.Program.Main(String[] args) in APP_PATHProgram.cs:line 19

APP_PATH will be the absolute path to the file that cannot be found. This type of FileNotFoundException actually contains all the information needed to debug the problem. The exception message contains a nice error description, as well as an absolute path to the missing file. If you want to present the user with the path or maybe create the file when not found, there is a nifty property available on FileNotFoundException:

catch (FileNotFoundException e)
{
    File.Create(e.FileName);
}

In the example I simply create the missing file by using the Filename property. I’ve seen code parsing the exception message to get the name of the missing file, which is kind of a downer when the absolute path is available right there on the exception 🙂

The system cannot find the file specified. (Exception from HRESULT: 0x80070002)

This error is typically thrown when trying to load an assembly that doesn’t exist. The error can be re-created like this:

try
{
    Assembly.LoadFile("c:\Nonexisting.dll");
}
catch (FileNotFoundException e)
{
    Console.WriteLine(e.ToString());
}

In this scenario, the program still throws a FileNotFoundException. But the exception message is different:

System.IO.FileNotFoundException: The system cannot find the file specified. (Exception from HRESULT: 0x80070002)
   at System.Reflection.RuntimeAssembly.nLoadFile(String path, Evidence evidence)
   at System.Reflection.Assembly.LoadFile(String path)
   at ConsoleApp.Program.Main(String[] args) in APP_PATHProgram.cs:line 20

Unlike the error thrown on reading the missing file, messages from the System.Reflection namespace are harder to understand. To find the cause of this error you will need to look through the stack trace, which hints that this is during Assembly.LoadFile. Notice that no filename is present in the exception message and in this case, the Filename property on FileNotFoundException is null.

Could not load file or assembly ‘assembly’ or one of its dependencies. The system cannot find the file specified.

An error similar to the one above is the Could not load file or assembly 'assembly' or one of its dependencies. The system cannot find the file specified. error. This also means that the program is trying to load an assembly that could not be found. The error can be re-created by creating a program that uses another assembly. Build the program, remove the references assembly (the .dll file) from the binDebug folder and run the program. In this case, the program fails during startup:

Unhandled Exception: System.IO.FileNotFoundException: Could not load file or assembly 'Lib, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. The system cannot find the file specified.
   at ConsoleApp.Program.Main(String[] args)

In this example, I’m referencing an assembly named Lib, which doesn’t exist on the disk or in the Global Assembly Cache (GAC).

The typical cause of this error is that the referenced assembly isn’t on the file system. There can be multiple causes of this. To help you debug this, here are some things to check:

1. If you are deploying using a system like Azure DevOps or Octopus Deploy, make sure all the files from the build output are copied to the destination.
2. Right-click the referenced assembly in Visual Studio, click Properties and make sure that Copy Local is set to true:

Access errors when running on IIS

Until now all instances of this error have been a missing file from the disk. I want to round off this post with a quick comment about security. In some cases, the FileNotFoundException can be caused by the user account trying to access the file, and simply don’t have the necessary access. Under optimal circumstances, the framework should throw a System.UnauthorizedAccessException when this happens. But I have seen the issue in the past when hosting websites on IIS. Make sure that the ASP.NET worker process account (or NETWORK SERVICE depending on which user you are using) has access to all files and folders needed to run the application.

To make sure that the app pool user has access:

1. Right-click the folder containing your web application
2. Click Properties
3. Select the Security tab
4. Click Edit…
5. Click Add…
6. Input IIS AppPoolDefaultAppPool in the text area
7. Click Check Names and verify that the user is resolved
8. Click OK
9. Assign Full control to the new user and save

Also make sure to read the other posts in this series: Debugging common .NET exception.

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I’m trying to connect to Google Calendar’s API, but I am getting a FileNotFound exception. When it executes the line «new FileStream(‘client_secret.json’)…» this error below pops up. However I have looked manually in my directory, and I saw the exact file, clear as day. What am I doing wrong here?

An unhandled exception of type ‘System.IO.FileNotFoundException’ occurred in mscorlib.dll
Additional information: Could not find file ‘C:UsersZach StraleyDocumentsVisual Studio 2015Projects255Cal255CalbinDebugclient_secret.json’.

using Google.Apis.Auth.OAuth2;
using Google.Apis.Calendar.v3;
using Google.Apis.Calendar.v3.Data;
using Google.Apis.Services;
using Google.Apis.Util.Store;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace CalendarQuickstart
{
    class Program
    {
        // If modifying these scopes, delete your previously saved credentials
        // at ~/.credentials/calendar-dotnet-quickstart.json
        static string[] Scopes = { CalendarService.Scope.CalendarReadonly };
        static string ApplicationName = "Google Calendar API .NET Quickstart";

        static void Main(string[] args)
        {
            UserCredential credential;

            using (var stream =
                new FileStream("client_secret.json", FileMode.Open, FileAccess.Read))
            {
                string credPath = System.Environment.GetFolderPath(
                    System.Environment.SpecialFolder.Personal);
                credPath = Path.Combine(credPath, ".credentials/calendar-dotnet-quickstart.json");

                credential = GoogleWebAuthorizationBroker.AuthorizeAsync(
                    GoogleClientSecrets.Load(stream).Secrets,
                    Scopes,
                    "user",
                    CancellationToken.None,
                    new FileDataStore(credPath, true)).Result;
                Console.WriteLine("Credential file saved to: " + credPath);
            }

            // Create Google Calendar API service.
            var service = new CalendarService(new BaseClientService.Initializer()
            {
                HttpClientInitializer = credential,
                ApplicationName = ApplicationName,
            });

            // Define parameters of request.
            EventsResource.ListRequest request = service.Events.List("primary");
            request.TimeMin = DateTime.Now;
            request.ShowDeleted = false;
            request.SingleEvents = true;
            request.MaxResults = 10;
            request.OrderBy = EventsResource.ListRequest.OrderByEnum.StartTime;

            // List events.
            Events events = request.Execute();
            Console.WriteLine("Upcoming events:");
            if (events.Items != null && events.Items.Count > 0)
            {
                foreach (var eventItem in events.Items)
                {
                    string when = eventItem.Start.DateTime.ToString();
                    if (String.IsNullOrEmpty(when))
                    {
                        when = eventItem.Start.Date;
                    }
                    Console.WriteLine("{0} ({1})", eventItem.Summary, when);
                }
            }
            else
            {
                Console.WriteLine("No upcoming events found.");
            }
            Console.Read();

        }
    }
}

java.io.FileNotFoundException which is a common exception which occurs while we try to access a file. FileNotFoundExcetion is thrown by constructors RandomAccessFile, FileInputStream, and FileOutputStream. FileNotFoundException occurs at runtime so it is a checked exception, we can handle this exception by java code, and we have to take care of the code so that this exception doesn’t occur. 

Declaration : 

public class FileNotFoundException
  extends IOException
    implements ObjectInput, ObjectStreamConstants

Constructors : 

• FileNotFoundException() : It gives FileNotFoundException with null message.
• FileNotFoundException(String s) : It gives FileNotFoundException with detail message.

It doesn’t have any methods. Now let’s understand the hierarchy of this class i.e FileNotFoundException extends IOException which further extends the Exception class which extends the Throwable class and further the Object class. 

Hierarchy Diagram:

Why this Exception occurs? 

There are mainly 2 scenarios when FileNotFoundException occurs. Now let’s see them with examples provided:

1. If the given file is not available in the given location then this error will occur.
2. If the given file is inaccessible, for example, if it is read-only then you can read the file but not modify the file, if we try to modify it, an error will occur or if the file that you are trying to access for the read/write operation is opened by another program then this error will occur.

Scenario 1:

If the given file is not available in the given location then this error will occur.

Example: 

Output

prog.java:14: error: unreported exception FileNotFoundException; must be caught or declared to be thrown
    FileReader reader = new FileReader("file.txt");
                        ^
prog.java:25: error: unreported exception IOException; must be caught or declared to be thrown
    while ((data = br.readLine()) != null) 
                              ^
prog.java:31: error: unreported exception IOException; must be caught or declared to be thrown
    br.close();
            ^
3 errors

Scenario 2:

If the given file is inaccessible, for example, if it is read-only then you can read the file but not modify the file if we try to modify it, an error will occur or if the file that you are trying to access for the read/write operation is opened by another program then this error will occur.

Example:

Output

java.security.AccessControlException: access denied ("java.io.FilePermission" "file.txt" "write")
    at java.base/java.security.AccessControlContext.checkPermission(AccessControlContext.java:472)
    at java.base/java.security.AccessController.checkPermission(AccessController.java:897)
    at java.base/java.lang.SecurityManager.checkPermission(SecurityManager.java:322)
    at java.base/java.lang.SecurityManager.checkWrite(SecurityManager.java:752)
    at java.base/java.io.FileOutputStream.<init>(FileOutputStream.java:225)
    at java.base/java.io.FileOutputStream.<init>(FileOutputStream.java:187)
    at java.base/java.io.FileWriter.<init>(FileWriter.java:96)
    at Example2.main(File.java:19)

Handling Exception:

Firstly we have to use the try-catch block if we know whether the error will occur. Inside try block all the lines should be there if there are chances of errors. There are other remedies to handle the exception:

1. If the message of the exception tells that there is no such file or directory, then you re-verify whether you mentioned the wrong file name in the program or file exists in that directory or not.
2. If the message of the exception tells us that access is denied then we have to check the permissions of the file (read, write, both read and write) and also check whether that file is in use by another program.
3. If the message of the exception tells us that the specified file is a directory then you must either delete the existing directory(if the directory not in use) or change the name of the file.

Автор оригинала: baeldung.

1. введение

В этой статье мы поговорим об очень распространенном исключении в Java – исключении FileNotFoundException .

Мы рассмотрим случаи, когда это может произойти, возможные способы лечения и некоторые примеры.

2. Когда Возникает исключение?

Как указано в документации API Java, это исключение может быть вызвано, когда:

• Файл с указанным именем пути не существует не существует
• Файл с указанным именем пути существует , но недоступен по какой-либо причине (запрошена запись для файла только для чтения или разрешения не позволяют получить доступ к файлу)

3. Как с Этим справиться?

Прежде всего, принимая во внимание, что он расширяет java.io.IOException , который расширяет java.lang.Исключение , вам нужно будет справиться с ним с помощью блока try-catch , как и с любым другим проверенным E xception .

Затем, что делать (связано с бизнесом/логикой) внутри блока try-catch на самом деле зависит от того, что вам нужно сделать.

Возможно, вам это понадобится:

• Создание исключения для конкретного бизнеса: это может быть ошибка stopexecutionerror, но вы оставите решение в верхних слоях приложения (не забудьте включить исходное исключение)
• Предупредите пользователя диалогом или сообщением об ошибке: это не ошибка stopexecutionerror, поэтому достаточно просто уведомить
• Создание файла: чтение необязательного файла конфигурации, его поиск и создание нового файла со значениями по умолчанию
• Создайте файл по другому пути: вам нужно что-то написать, и если первый путь недоступен, попробуйте использовать отказоустойчивый
• Просто зарегистрируйте ошибку: эта ошибка не должна останавливать выполнение, но вы регистрируете ее для дальнейшего анализа

4. Примеры

Теперь мы рассмотрим несколько примеров, все из которых будут основаны на следующем тестовом классе:

public class FileNotFoundExceptionTest {

    private static final Logger LOG
      = Logger.getLogger(FileNotFoundExceptionTest.class);
    private String fileName = Double.toString(Math.random());
    
    protected void readFailingFile() throws IOException {
        BufferedReader rd = new BufferedReader(new FileReader(new File(fileName)));
        rd.readLine();
        // no need to close file
    }

    class BusinessException extends RuntimeException {
        public BusinessException(String string, FileNotFoundException ex) {
            super(string, ex);
        }
    }
}

4.1. Регистрация исключения

Если вы запустите следующий код, он “зарегистрирует” ошибку в консоли:

@Test
public void logError() throws IOException {
    try {
        readFailingFile();
    } catch (FileNotFoundException ex) {
        LOG.error("Optional file " + fileName + " was not found.", ex);
    }
}

4.2. Создание исключения для конкретного бизнеса

Далее приведен пример создания исключения для конкретного бизнеса, чтобы ошибка могла быть обработана на верхних уровнях:

@Test(expected = BusinessException.class)
public void raiseBusinessSpecificException() throws IOException {
    try {
        readFailingFile();
    } catch (FileNotFoundException ex) {
        throw new BusinessException(
          "BusinessException: necessary file was not present.", ex);
    }
}

4.3. Создание файла

Наконец, мы попытаемся создать файл, чтобы его можно было прочитать (возможно, для потока, который непрерывно читает файл), но снова поймаем исключение и обработаем возможную вторую ошибку:

@Test
public void createFile() throws IOException {
    try {
        readFailingFile();
    } catch (FileNotFoundException ex) {
        try {
            new File(fileName).createNewFile();
            readFailingFile();            
        } catch (IOException ioe) {
            throw new RuntimeException(
              "BusinessException: even creation is not possible.", ioe);
        }
    }
}

5. Заключение

В этой быстрой записи мы видели, когда может возникнуть исключение FileNotFoundException и несколько вариантов его обработки.

Как всегда, полные примеры находятся на Github .