Java's file-manipulation methods often indicate failure with a return value instead of throwing an exception. Consequently, programs that ignore the return values from file operations often fail to detect that those operations have failed. Java programs must check the return values of methods that perform file I/O. This is a specific instance of EXP00-J. Do not ignore values returned by methods.

Noncompliant Code Example (delete())

This noncompliant code example attempts to delete a specified file but gives no indication of its success. The Java platform requires File.delete() to throw a SecurityException only when the program lacks authorization to delete the file [API 2014]. No other exceptions are thrown, so the deletion can silently fail.

File file = new File(args[0]);
file.delete();

Compliant Solution

This compliant solution checks the return value of delete():

File file = new File("file");
if (!file.delete()) {
  // Deletion failed, handle error
}

Compliant Solution

This compliant solution uses the java.nio.file.Files.delete() method from Java SE 7 to delete the file:

Path file = new File(args[0]).toPath();
try {
  Files.delete(file);
} catch (IOException x) {
  // Deletion failed, handle error
}

The Java SE 7 Documentation [J2SE 2011] defines Files.delete() to throw the following exceptions:

Because SecurityException is a runtime exception, it need not be declared. Because NoSuchFileException and DirectoryNotExmptyException both inherit from IOException, they will be caught by the compliant solution's catch clause.

Risk Assessment

Failure to check the return values of methods that perform file I/O can result in unexpected behavior.

Automated Detection

Tool	Version	Checker	Description
CodeSonar		JAVA.FUNCS.IRV	Ignored Return Value (Java)
SonarQube		S899

Related Guidelines

Bibliography