fix: issue#62 strip auth key

Fixing the issue raised in #62

Problem: auth key with leading / trailing whitespaces is throwing exceptions. For example, assigning the secret via `echo` leaves a trailing `\n`.

Solution: strip input auth key as an input sanitization procedure

Notice: Java 8 does not support `String.strip()`, while `String.trim()` does not support Unicode whitespaces. Therefore, using regex expressions for stripping.

Author: timazhum

deepl-java/src/main/java/com/deepl/api/Translator.java

@@ -44,6 +44,8 @@ public Translator(String authKey, TranslatorOptions options) throws IllegalArgum
     if (authKey == null || authKey.length() == 0) {
       throw new IllegalArgumentException("authKey must be a non-empty string");
     }
+    authKey = StringUtil.strip(authKey);
+
     String serverUrl =
         (options.getServerUrl() != null)
             ? options.getServerUrl()

deepl-java/src/main/java/com/deepl/api/utils/StringUtil.java

@@ -0,0 +1,23 @@
+package com.deepl.api.utils;
+
+public class StringUtil {
+  /**
+   * Java 11's String.strip() equivalent for returning a value with all leading and trailing {@link
+   * Character#isWhitespace(int) white space} removed.
+   *
+   * <p>Java 8 does not support the String.strip() operation, and String.trim() only works for ASCII
+   * whitespaces, failing to handle Unicode whitespaces, Therefore, this method sanitizes a string
+   * value using regex expressions.
+   *
+   * <p>
+   *
+   * @param value - string value to strip
+   * @return a string whose value is this string, with all leading and trailing white space removed
+   */
+  public static String strip(String value) {
+    if (value == null) {
+      return null;
+    }
+    return value.replaceAll("^[\\p{javaWhitespace}\u00A0]+|[\\p{javaWhitespace}\u00A0]+$", "");
+  }
+}

deepl-java/src/test/java/com/deepl/api/utils/StringUtilTest.java

@@ -0,0 +1,45 @@
+package com.deepl.api.utils;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+class StringUtilTest {
+
+  @Test
+  void testStripNullString() {
+    assertNull(StringUtil.strip(null));
+  }
+
+  @Test
+  void testStripEmptyString() {
+    assertEquals("", StringUtil.strip(""));
+  }
+
+  @Test
+  void testStripAllWhitespace() {
+    // ASCII whitespace
+    assertEquals("", StringUtil.strip("   "));
+    assertEquals("", StringUtil.strip("\t\n\r\f"));
+    // Unicode whitespace
+    assertEquals("", StringUtil.strip("\u00A0\u2002\u2003"));
+  }
+
+  @Test
+  void testStripLeadingTrailingWhitespace() {
+    // ASCII
+    assertEquals("Lorem", StringUtil.strip("  Lorem  "));
+    assertEquals("Lorem Ipsum", StringUtil.strip("\tLorem Ipsum\n"));
+    // Unicode
+    String input = "\u00A0\u2002Lorem Ipsum\u205F";
+    assertEquals("Lorem Ipsum", StringUtil.strip(input));
+  }
+
+  @Test
+  void testStripNoChanges() {
+    assertEquals("LoremIpsum", StringUtil.strip("LoremIpsum"));
+    assertEquals("Lorem   Ipsum", StringUtil.strip("Lorem   Ipsum"));
+    String input = "Lorem\u2003Ipsum"; // Unicode em space in the middle
+    assertEquals(input, StringUtil.strip(input));
+  }
+}