EXC33-J. Throw specific exceptions as opposed to the more general RuntimeException or Exception

A method should rarely throw RuntimeException or Exception. This is because handling these exceptions requires catching RuntimeException, which is forbidden in [EXC32-J. Catch specific exceptions as opposed to the more general RuntimeException]. Moreover, throwing a RuntimeException can lead to subtle errors such as a caller who fails to retrieve a return value from an offending method, is unable to check for appropriate feedback. The Java Language Specification (Section 8.4.7 Method Body) allows the declaration of a method with a return type without making it necessary to return a value if a runtime exception is thrown from within the method [[JLS 05]].

Instead, prefer throwing a more specific exception, subclassed from Exception. It is permissible to construct an exception class specifically for a single throw statement.

Noncompliant Code Example

This noncompliant code example takes a string and returns true if it consists of a capital letter followed by lowercase letters. To handle corner cases, it checks for the exceptional conditions and throws exceptions if they are likely to disrupt the normal operation.

boolean isCapitalized(String s) {
  if (s == null) {
    throw new RuntimeException("Null String");
  }
  if (s.equals("")) {
    return true;
  }
  String first = s.substring(0, 1);
  String rest = s.substring(1);
  return (first.equals(first.toUpperCase()) &&
          rest.equals(rest.toLowerCase()));
}

To handle the case of passing in a null string parameter, code calling this method may require catching RuntimeException, which is a violation of EXC32-J. Catch specific exceptions as opposed to the more general RuntimeException.

Compliant Solution

This compliant solution devotes a specific exception (NullPointerException) to denote the particular exceptional condition.

boolean isCapitalized(String s) {
  if (s == null) {
    throw new NullPointerException();
  }
  if (s.equals("")) {
    return true;
  }
  String first = s.substring(0, 1);
  String rest = s.substring(1);
  return (first.equals(first.toUpperCase()) &&
          rest.equals(rest.toLowerCase()));
}

Noncompliant Code Example

This noncompliant code example uses a broad Exception class in the throws declaration of the method.

private void doSomething() throws Exception {
//...
}

Compliant Solution

To be compliant, be as specific as possible when declaring exceptions and respect the required abstraction level.

private void doSomething() throws IOException {
//...
}

Using instanceof to check for narrower exceptions in a general catch block is not always helpful because it is usually impossible to enumerate all the exceptions that the code is capable of throwing.

Risk Assessment

Throwing RuntimeException and Exception prevents classes from catching the intended exceptions without catching other unintended exceptions as well.

Automated Detection

TODO

Related Vulnerabilities

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

References

[[MITRE 09]] CWE ID 397 "Declaration of Throws for Generic Exception", CWE ID 537 "Information Leak Through Java Runtime Error Message"
[[Goetz 04b]]
[[Tutorials 08]] Unchecked Exceptions — The Controversy

EXC32-J. Catch specific exceptions as opposed to the more general RuntimeException      13. Exceptional Behavior (EXC)      EXC34-J. Do not allow unsanitized user input to be logged