Dropped Exception

ID

java.dropped_exception

Severity

low

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

Java

Tags

CWE:391, reliability

Description

Reports catch blocks where the caught exception variable is never referenced inside the block body. A silently swallowed exception hides failures and makes debugging extremely difficult.

Rationale

When an exception is caught but its variable is never used, the exception information (message, stack trace, cause chain) is lost. This pattern often indicates that the developer intended to handle the error but forgot, or copied the catch block from elsewhere without adapting it.

// Bad -- exception is silently swallowed
try {
    connection.close();
} catch (IOException e) {
    // e is never referenced
    retryLater();
}

Remediation

At a minimum, log the exception. If the exception is intentionally ignored, name the variable ignored (or any name starting with ignore) so the intent is explicit, or add a logger call in the catch body.

// Good -- exception is logged
try {
    connection.close();
} catch (IOException e) {
    log.warn("Failed to close connection", e);
    retryLater();
}

// Also accepted -- intent to ignore is explicit
try {
    connection.close();
} catch (IOException ignored) {
    retryLater();
}

Configuration

Property Default Description

omitIgnored

true

When true (default), the rule skips catches that signal intent to ignore the exception: variable name is _, ignored, or starts with ignore; or the catch body contains a logger-like call (trace, debug, info, warn, warning, error, fatal, severe, fine, config, log) or a console call (print, println, printf). Set to false to flag every silently-swallowed exception.

References