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Never use return, break, continue, or throw statements within a finally block. When program execution enters a try block that has a finally block, the finally block always executes , regardless of whether the try block (or any associated catch blocks) execute executes to normal completion. Statements that cause the finally block to terminate complete abruptly also cause the try block to terminate complete abruptly , and consequently mask suppress any exception thrown from the try or catch blocks (JLS 2005).

Never use return, break, continue or throw statements within a finally block.

. According to The Java Language Specification, §14.20.2, "Execution of try-finally and try-catch-finally" [JLS 2015]:

If execution of the try block completes abruptly for any other reason R, then the finally block is executed. Then there is a choice:

• If the finally block completes normally, then the try statement completes abruptly for reason R.
• If the finally block completes abruptly for reason S, then the try statement completes abruptly for reason S (and reason R is discarded).

Noncompliant Code Example

In this noncompliant code example, the finally block completes abruptly due to because of a return statement . in the block:

class TryFinally {              
  private static boolean doLogic() {
    try {
      throw new IllegalStateException(); 
    } finally {
      System.out.println("Uncaughtlogic Exceptiondone");
      return true;
    }
  }

  public static void main(String[] args) {
    doLogic();	
  }
}

Consequently, when the IllegalStateException is thrown, it does not propagate all the way up through the call stack. Rather, the abrupt termination The IllegalStateException is suppressed by the abrupt completion of the finally block suppresses the IllegalStateException because it caused by the return statement becomes the final cause of abrupt termination of the try block.

Compliant Solution

This compliant solution removes the return statement from the finally block.:

class TryFinally {         
  private static boolean doLogic() {
    try {
      throw new IllegalStateException(); 
    } finally {
      System.out.println("Caughtlogic Exceptiondone");
    }
    // Any return statements must go here; 
    // applicable only when exception is thrown conditionally
  }
}

Exceptions

ERRO4-J-EX0: Control flow statements whose destination is within the finally block are perfectly acceptable. For example, the following code does not violate this rule because the break statement exits within the while loop but not within the finally block:

class TryFinally {
  public static void main(String[] args) {
    doLogic();	
  }
}

If this example had a return statement outside the finally block, the compiler would report an error because the return statement would be unreachable due to the unconditional throwing of IllegalStateException. If the exception were thrown conditionally, the return statement could be used without compilation error.

Risk Assessment

private static boolean doLogic() {
    try {
      throw new IllegalStateException();
    } finally {
      int c;
      try {
        while ((c = input.read()) != -1) {
          if (c > 128) {
            break;
          }
        }
      } catch (IOException x) {
        // Forward to handler
      }
      System.out.println("logic done");
    }
    // Any return statements must go here; applicable only when exception is thrown conditionally
  }
}

Risk Assessment

Abrupt completion of Exiting abruptly from a finally block masks any exceptions thrown inside the associated try and catch blocks.

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this guideline on the CERT website.

Bibliography

\[[Bloch 2005|AA. Bibliography#Bloch 05]\] Puzzle 36: Indecision
\[[Chess 2007|AA. Bibliography#Chess 07]\] 8.2 Managing Exceptions, "The Vanishing Exception"
\[[JLS 2005|AA. Bibliography#JLS 05]\] [Section 14.20.2, Execution of try-catch-finally|http://java.sun.com/docs/books/jls/third_edition/html/statements.html#14.20.2]\[[MITRE 2009|AA. Bibliography#MITRE 09]\] [CWE ID 705|http://cwe.mitre.org/data/definitions/705.html] "Incorrect Control Flow Scoping", [CWE ID 584|http://cwe.mitre.org/data/definitions/584.html] "Return Inside Finally Block"

Automated Detection

Related Guidelines

Bibliography

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Image Added Image Added Image AddedERR03-J. Use a logging API to log critical security exceptions      06. Exceptional Behavior (ERR)      ERR05-J. Handle checked exceptions that can be thrown within a finally block