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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* CWE - https://cwe.mitre.org/data/definitions/459[CWE-459 - Incomplete Cleanup]
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* CWE - https://cwe.mitre.org/data/definitions/772[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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