The correct answer is to use File.getCanonicalPath() to resolve the path and verify it starts with the intended directory. This method normalizes the path by resolving all symbolic links, relative segments like “..”, and platform-specific conventions into a single, absolute canonical form, which makes it impossible for an attacker to disguise traversal sequences such as “../../etc/passwd” as a legitimate filename. On the Oracle Certified Professional Java SE 17 Developer 1Z0-829 exam, this question tests your understanding of secure file I/O under the “Secure Coding” objectives, where the common trap is relying on methods like getAbsolutePath() that do not eliminate symbolic links or “..” components. Remember the memory tip: “Canonical cuts the climb”—canonical path cuts off any attempt to climb up the directory tree, ensuring the final path stays within the intended sandbox.
1Z0-829 Java I/O API and Securing Applications Practice Question
This 1Z0-829 practice question tests your understanding of java i/o api and securing applications. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A web application allows users to specify filenames for uploaded documents. The application saves files to a directory using the provided name. Which secure programming practice should be applied to prevent path traversal attacks?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use File.getCanonicalPath() to resolve the path and check it starts with the intended directory.
Option D is correct because `File.getCanonicalPath()` resolves all symbolic links, `.` and `..` sequences, and platform-specific path conventions to produce an absolute, unique path. By then verifying that this canonical path starts with the intended base directory (e.g., `/var/uploads/`), the application can definitively reject any path that escapes outside the allowed directory, even if the user-supplied filename contains encoded or obfuscated traversal sequences.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Validate that the filename contains only alphanumeric characters.
Why it's wrong here
Too restrictive; legitimate filenames may contain other characters.
✗
Generate a random UUID for each file, ignoring the user-provided filename.
Why it's wrong here
While generating a random UUID is safe, it does not validate the user's input path; the question asks about validating the provided name.
✗
Replace all occurrences of ".." and "/" with an empty string.
Why it's wrong here
Blacklisting is easily bypassed (e.g., using "....//").
✓
Use File.getCanonicalPath() to resolve the path and check it starts with the intended directory.
Why this is correct
By resolving the canonical path, the application can verify that the file lies within the allowed directory.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose Option C (string replacement) because it seems straightforward, but they overlook that simple blacklisting of `..` and `/` is trivially bypassed by double-encoding, nested patterns, or Unicode normalization, whereas canonical path resolution is the only robust defense against path traversal.
Detailed technical explanation
How to think about this question
Under the hood, `File.getCanonicalPath()` calls the native `realpath()` function on Unix-like systems or `GetFullPathNameW` on Windows, which resolves all path components including symbolic links and junction points. A subtle behavior is that on Windows, the canonical path may include a drive letter and use backslashes, so the check must be case-insensitive and normalize separators. In a real-world scenario, an attacker might use a deeply nested symlink inside the uploads directory that points to `/etc/passwd`; `getCanonicalPath()` will resolve that symlink and the prefix check will correctly reject the path.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Java I/O API and Securing Applications — This question tests Java I/O API and Securing Applications — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use File.getCanonicalPath() to resolve the path and check it starts with the intended directory. — Option D is correct because `File.getCanonicalPath()` resolves all symbolic links, `.` and `..` sequences, and platform-specific path conventions to produce an absolute, unique path. By then verifying that this canonical path starts with the intended base directory (e.g., `/var/uploads/`), the application can definitively reject any path that escapes outside the allowed directory, even if the user-supplied filename contains encoded or obfuscated traversal sequences.
What should I do if I get this 1Z0-829 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A web application allows users to upload profile pictures. The application saves the files to a directory using the original filename provided by the user. After a security review, the team discovered a critical path traversal vulnerability. Which remediation is most effective in preventing exploitation while maintaining usability?
easy
A.Store the files in a database BLOB instead of the filesystem.
B.Sanitize the filename by removing all occurrences of "../" and "/".
C.Check that the file extension is allowed (e.g., .jpg, .png) and no special characters.
✓ D.Generate a random UUID as the filename and store the original filename in a database.
Why D: Option D is correct because generating a random UUID as the filename eliminates the user's control over the file path, making path traversal attacks impossible. The original filename can be stored in a database for display purposes, preserving usability while ensuring the file is saved with a safe, unpredictable name.
Last reviewed: Jun 25, 2026
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