6f24cc0632
In some cases, the `rule.adoc` at root of a rule is never included anywhere and thus is dead code. It's a maintenance cost by itself, but also it misses opportunities to inline code that seems used by two documents when in fact only one document is actually rendered. And this missed opportunity, in turn, stops us from applying the correct language tag on the code samples.
128 lines
3.6 KiB
Plaintext
128 lines
3.6 KiB
Plaintext
== Why is this an issue?
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Connections, streams, files, and other classes that implement the ``++Closeable++`` interface or its super-interface, ``++AutoCloseable++``, needs to be closed after use. Further, that ``++close++`` call must be made in a ``++finally++`` block otherwise an exception could keep the call from being made. Preferably, when class implements ``++AutoCloseable++``, resource should be created using "try-with-resources" pattern and will be closed automatically.
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Failure to properly close resources will result in a resource leak which could bring first the application and then perhaps the box the application is on to their knees.
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=== Noncompliant code example
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[source,java]
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----
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private void readTheFile() throws IOException {
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Path path = Paths.get(this.fileName);
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BufferedReader reader = Files.newBufferedReader(path, this.charset);
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// ...
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reader.close(); // Noncompliant
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// ...
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Files.lines("input.txt").forEach(System.out::println); // Noncompliant: The stream needs to be closed
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}
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private void doSomething() {
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OutputStream stream = null;
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try {
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for (String property : propertyList) {
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stream = new FileOutputStream("myfile.txt"); // Noncompliant
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// ...
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}
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} catch (Exception e) {
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// ...
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} finally {
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stream.close(); // Multiple streams were opened. Only the last is closed.
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}
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}
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----
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=== Compliant solution
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[source,java]
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----
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private void readTheFile(String fileName) throws IOException {
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Path path = Paths.get(fileName);
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try (BufferedReader reader = Files.newBufferedReader(path, StandardCharsets.UTF_8)) {
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reader.readLine();
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// ...
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}
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// ..
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try (Stream<String> input = Files.lines("input.txt")) {
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input.forEach(System.out::println);
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}
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}
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private void doSomething() {
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OutputStream stream = null;
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try {
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stream = new FileOutputStream("myfile.txt");
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for (String property : propertyList) {
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// ...
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}
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} catch (Exception e) {
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// ...
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} finally {
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stream.close();
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}
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}
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----
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=== Exceptions
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Instances of the following classes are ignored by this rule because ``++close++`` has no effect:
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* ``++java.io.ByteArrayOutputStream++``
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* ``++java.io.ByteArrayInputStream++``
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* ``++java.io.CharArrayReader++``
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* ``++java.io.CharArrayWriter++``
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* ``++java.io.StringReader++``
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* ``++java.io.StringWriter++``
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Java 7 introduced the try-with-resources statement, which implicitly closes ``++Closeables++``. All resources opened in a try-with-resources statement are ignored by this rule.
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[source,java]
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----
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try (BufferedReader br = new BufferedReader(new FileReader(fileName))) {
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//...
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}
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catch ( ... ) {
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//...
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}
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----
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== Resources
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* https://cwe.mitre.org/data/definitions/459[MITRE, CWE-459] - Incomplete Cleanup
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* https://cwe.mitre.org/data/definitions/772[MITRE, CWE-772] - Missing Release of Resource after Effective Lifetime
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* https://wiki.sei.cmu.edu/confluence/x/vjdGBQ[CERT, FIO04-J.] - Release resources when they are no longer needed
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* https://wiki.sei.cmu.edu/confluence/x/QtUxBQ[CERT, FIO42-C.] - Close files when they are no longer needed
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* https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html[Try With Resources]
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ifdef::env-github,rspecator-view[]
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'''
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== Implementation Specification
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(visible only on this page)
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=== Message
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Use try-with-resources or close this "xxx" in a "finally" clause.
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=== Parameters
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.excludedResourceTypes
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****
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Comma separated list of the excluded resource types, using fully qualified names (example: "org.apache.hadoop.fs.FileSystem")
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****
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'''
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== Comments And Links
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(visible only on this page)
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include::../comments-and-links.adoc[]
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endif::env-github,rspecator-view[]
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