Скачать или смотреть How to Load Files from Web Context in Java Servlets: Fixing File Not Found Errors

Discover the solution to loading files from the web context in Java servlets, avoiding File Not Found exceptions with simple code corrections.
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This video is based on the question https://stackoverflow.com/q/67605711/ asked by the user 'mrcrag' ( https://stackoverflow.com/u/3084236/ ) and on the answer https://stackoverflow.com/a/67606909/ provided by the user 'mrcrag' ( https://stackoverflow.com/u/3084236/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Fixing File Not Found Errors When Accessing Files in Java Servlets

When working on Java servlets, you may encounter an issue where it appears that a file exists in the browser, yet your application throws a FileNotFoundException. One common scenario is attempting to load a file using the context path, as seen below:

[[See Video to Reveal this Text or Code Snippet]]

In this example, you might check the existence of default.png only to find that fi.exists() returns false. Despite being accessible via browser at contextPath + "/images/default.png", the application cannot locate the file. This guide aims to clarify why this occurs and offer a concrete solution.

Understanding the Problem

The main issue stems from the way the file path is constructed when using getContextPath(). The method returns the relative URL of the application, which does not correspond to the server's filesystem path where the files are stored. Therefore, when you create a File object using this path, it does not lead to the actual file on the server, resulting in a false response from exists().

Example Scenario

Access via Browser: http://yourserver.com/yourapp/images/...

Your Code Path: contextPath + "/images/default.png" (this will not work)

The Solution

To fix this issue, instead of using getContextPath(), you should use getRealPath(). This method returns the actual filesystem path on the server where the specified resource can be found. Here’s how to correctly implement this change:

Step-by-Step Solution

Retrieve the Real Path: Use req.getServletContext().getRealPath("/images/default.png") to get the correct path.

Create the File Object: Construct the File object using this real path.

Check Existence: Now, you can safely check if the file exists.

Updated Code Example

Here's the corrected version of the previous code:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By changing the method used to obtain the file path from getContextPath() to getRealPath(), you can directly access the correct location of your files in the server's filesystem. This solution ensures that the FileNotFoundException no longer disrupts your application's functionality.

Should any further questions arise or if you require additional clarification, feel free to reach out in the comments below!