SEI CERT Oracle Coding Standard for Java

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Old Version 10

changes.mady.by.user Fred Long

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New Version 11

changes.mady.by.user Pranjal Jumde

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Comment: changed naming of wrapped functions and indentation

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Code Block
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langjava
public void fio54openFile_nce1nce(String filename) throws FileNotFoundException{
    OutputStream out = new FileOutputStream(filename);
    // Work with FILE
}

If the file existed before being opened, its former contents will be overwritten with the contents provided by the program.

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Code Block
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langjava
public void fio54noOverwrite_nce2nce(String filename) throws FileNotFoundException{
	  OutputStream out = new FileOutputStream(filename, true);
	  // Work with FILE
}

If the file existed before being opened, its new contents will be appended to the former contents. This code is compliant only if this was the intention of the programmer.

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Code Block
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langjava
public void fio54noAlter_nce3nce(String filename) throws FileNotFoundException{
    OutputStream out = new FileOutputStream(filename, true);
    if (!new File(filename).createNewFile()) {
        // File cannot be created...handle error
    } else {
        OutputStream out = new FileOutputStream(filename);
        // Work with FILE
    }
}

Unfortunately, this solution is subject to a TOCTOU (time-of-check-time-of-use) race condition. It is possible for an attacker to modify the file system such that the file that is created is not the file that is opened.

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Code Block
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langjava
public void fio54createFile_cs(String filename) throws FileNotFoundException{
    try (OutputStream out = new BufferedOutputStream(
         Files.newOutputStream( Paths.get(filename),
                                StandardOpenOption.CREATE_NEW))) {
            // Work with out
    } catch (IOException x) {
        // File not writable...handle error
    }
}

Applicability

The ability to determine if an existing file has been opened or a new file has been created provides greater assurance that a file other than the intended file is not opened or overwritten.

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