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In contrast with C and C++, Java does not flush unwritten buffered data or close open files when it exits, so programs must do this manually.
Noncompliant Code Example
This example creates a new file, outputs some text to it, and abruptly exits using Runtime.exit(). Consequently, the file is closed without the text actually being written to it.
| Code Block | ||
|---|---|---|
| ||
public class CreateFile {
public static void main(String[] args) throws FileNotFoundException {
final PrintStream out = new PrintStream( new BufferedOutputStream(
new FileOutputStream("foo.txt")));
out.println("hello");
Runtime.getRuntime().exit(1);
}
}
|
Compliant Solution (OutputStream.close())
This solution explicitly closes the file before exiting
| Code Block | ||
|---|---|---|
| ||
public class CreateFile {
public static void main(String[] args) throws FileNotFoundException {
final PrintStream out = new PrintStream( new BufferedOutputStream(
new FileOutputStream("foo.txt")));
out.println("hello");
out.close();
Runtime.getRuntime().exit(1);
}
}
|
Compliant Solution (Shutdown Hook)
This compliant solution adds a shutdown hook to close the file. This hook is invoked by Runtime.exit() is called before the JVM is halted.
| Code Block | ||
|---|---|---|
| ||
public class CreateFile {
public static void main(String[] args) throws FileNotFoundException {
final PrintStream out = new PrintStream( new BufferedOutputStream(
new FileOutputStream("foo.txt")));
Runtime.getRuntime().addShutdownHook(new Thread(new Runnable() {
public void run() {
out.close();
}
}));
out.println("hello");
Runtime.getRuntime().exit(1);
}
}
|
Noncompliant Code Example (Runtime.halt())
This noncompliant code example calls Runtime.halt() instead of Runtime.exit(). Runtime.halt() stops the JVM without invoking any shutdown hooks; consequently the file is not properly written to or closed.
| Code Block | ||
|---|---|---|
| ||
public class CreateFile {
public static void main(String[] args) throws FileNotFoundException {
final PrintStream out = new PrintStream( new BufferedOutputStream(
new FileOutputStream("foo.txt")));
Runtime.getRuntime().addShutdownHook(new Thread(new Runnable() {
public void run() {
out.close();
}
}));
out.println("hello");
Runtime.getRuntime().halt(1);
}
}
|
Risk Assessment
Using Runtime.halt() in place of Runtime.exit() may not perform necessary cleanup, potentially leaving sensitive data exposed or leaving data in an inconsistent state.
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