Exception chaining

Definition

Exception chaining means wrapping a low-level exception inside a higher-level one and keeping the original as its cause. The caller gets a meaningful message, and the full story is still available through getCause().

Example code

Wrapping a parse error in a service error

class ConfigException extends RuntimeException {
    ConfigException(String message, Throwable cause) {
        super(message, cause);                         // keep the original as the cause
    }
}

class Demo {
    static int readPort(String text) {
        try {
            return Integer.parseInt(text);
        } catch (NumberFormatException e) {
            throw new ConfigException("Invalid server port in config", e);
        }
    }

    public static void main(String[] args) {
        try {
            readPort("80x");
        } catch (ConfigException e) {
            System.out.println(e.getMessage());
            System.out.println("Caused by: " + e.getCause());
        }
    }
}

// Output:
// Invalid server port in config
// Caused by: java.lang.NumberFormatException: For input string: "80x"