Use try-with-resources or close this "BufferedWriter" in a "finally" clause. Open
BufferedWriter output = new BufferedWriter(new FileWriter(file));
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- Exclude checks
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.
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.
Noncompliant Code Example
private void readTheFile() throws IOException { Path path = Paths.get(this.fileName); BufferedReader reader = Files.newBufferedReader(path, this.charset); // ... reader.close(); // Noncompliant // ... Files.lines("input.txt").forEach(System.out::println); // Noncompliant: The stream needs to be closed } private void doSomething() { OutputStream stream = null; try { for (String property : propertyList) { stream = new FileOutputStream("myfile.txt"); // Noncompliant // ... } } catch (Exception e) { // ... } finally { stream.close(); // Multiple streams were opened. Only the last is closed. } }
Compliant Solution
private void readTheFile(String fileName) throws IOException { Path path = Paths.get(fileName); try (BufferedReader reader = Files.newBufferedReader(path, StandardCharsets.UTF_8)) { reader.readLine(); // ... } // .. try (Stream<String> input = Files.lines("input.txt")) { input.forEach(System.out::println); } } private void doSomething() { OutputStream stream = null; try { stream = new FileOutputStream("myfile.txt"); for (String property : propertyList) { // ... } } catch (Exception e) { // ... } finally { stream.close(); } }
Exceptions
Instances of the following classes are ignored by this rule because close
has no effect:
-
java.io.ByteArrayOutputStream
-
java.io.ByteArrayInputStream
-
java.io.CharArrayReader
-
java.io.CharArrayWriter
-
java.io.StringReader
-
java.io.StringWriter
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.
try (BufferedReader br = new BufferedReader(new FileReader(fileName))) { //... } catch ( ... ) { //... }
See
- MITRE, CWE-459 - Incomplete Cleanup
- MITRE, CWE-772 - Missing Release of Resource after Effective Lifetime
- CERT, FIO04-J. - Release resources when they are no longer needed
- CERT, FIO42-C. - Close files when they are no longer needed
- Try With Resources
Change this "try" to a try-with-resources. Open
try {
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Java 7 introduced the try-with-resources statement, which guarantees that the resource in question will be closed. Since the new syntax is closer
to bullet-proof, it should be preferred over the older try
/catch
/finally
version.
This rule checks that close
-able resources are opened in a try-with-resources statement.
Note that this rule is automatically disabled when the project's sonar.java.source
is lower than 7
.
Noncompliant Code Example
FileReader fr = null; BufferedReader br = null; try { fr = new FileReader(fileName); br = new BufferedReader(fr); return br.readLine(); } catch (...) { } finally { if (br != null) { try { br.close(); } catch(IOException e){...} } if (fr != null ) { try { br.close(); } catch(IOException e){...} } }
Compliant Solution
try ( FileReader fr = new FileReader(fileName); BufferedReader br = new BufferedReader(fr) ) { return br.readLine(); } catch (...) {}
or
try (BufferedReader br = new BufferedReader(new FileReader(fileName))) { // no need to name intermediate resources if you don't want to return br.readLine(); } catch (...) {}
See
- CERT, ERR54-J. - Use a try-with-resources statement to safely handle closeable resources