root cause finder

core-java-modules/core-java-lang-2/src/test/java/com/baeldung/exceptions/RootCauseFinder.java

@@ -0,0 +1,61 @@
+package com.baeldung.exceptions;
+
+import java.util.Objects;
+
+/**
+ * Utility class to find root cause exceptions.
+ */
+public class RootCauseFinder {
+
+    public static Throwable findCauseUsingPlainJava(Throwable throwable) {
+        Objects.requireNonNull(throwable);
+        Throwable rootCause = throwable;
+        while (rootCause.getCause() != null) {
+            rootCause = rootCause.getCause();
+        }
+        return rootCause;
+    }
+
+    static class IntParser {
+
+        private IntParser() {
+        }
+
+        public static int parse(String input) throws InvalidNumber {
+            if (input == null || input.isEmpty()) {
+                throw new IllegalArgumentException();
+            }
+
+            try {
+                return new IntParser().stringToInt(input.trim());
+            } catch (NaNException ex) {
+                throw new InvalidNumber(input, ex);
+            }
+        }
+
+        private int stringToInt(String numberAsString) throws NaNException {
+            try {
+                return Integer.valueOf(numberAsString);
+            } catch (NumberFormatException ex) {
+                throw new NaNException(numberAsString, ex);
+            }
+        }
+
+    }
+
+    static class InvalidNumber extends Exception {
+
+        InvalidNumber(String input, Throwable thr) {
+            super("Invalid input for a number: " + input, thr);
+        }
+    }
+
+    static class NaNException extends Exception {
+
+        NaNException(String number, Throwable thr) {
+            super(number + "is not a number", thr);
+        }
+
+    }
+
+}