improve jwt parser memory allocation

re-use buffer instead of creating new ones
avoid creating unneeded buffers in the Strings util methods
Stop continuously copying array with StringBuilder#deleteCharAt
work directly on StringBuilder instead of creating a temporary String

test added to cover the modified methods

src/main/java/io/jsonwebtoken/impl/DefaultJwtParser.java

@@ -213,7 +213,8 @@ public class DefaultJwtParser implements JwtParser {
 
             if (c == SEPARATOR_CHAR) {
 
-                String token = Strings.clean(sb.toString());
+                CharSequence tokenSeq = Strings.clean(sb);
+                String token = tokenSeq!=null?tokenSeq.toString():null;
 
                 if (delimiterCount == 0) {
                     base64UrlEncodedHeader = token;
@@ -222,7 +223,7 @@ public class DefaultJwtParser implements JwtParser {
                 }
 
                 delimiterCount++;
-                sb = new StringBuilder(128);
+                sb.setLength(0);
             } else {
                 sb.append(c);
             }

src/main/java/io/jsonwebtoken/lang/Strings.java

@@ -159,22 +159,38 @@ public final class Strings {
      * @see java.lang.Character#isWhitespace
      */
     public static String trimWhitespace(String str) {
+        return (String) trimWhitespace((CharSequence)str);
+    }
+    
+    
+    private static CharSequence trimWhitespace(CharSequence str) {
         if (!hasLength(str)) {
             return str;
         }
-        StringBuilder sb = new StringBuilder(str);
-        while (sb.length() > 0 && Character.isWhitespace(sb.charAt(0))) {
-            sb.deleteCharAt(0);
+        final int length = str.length();
+
+        int start = 0;
+		while (start < length && Character.isWhitespace(str.charAt(start))) {
+            start++;
         }
-        while (sb.length() > 0 && Character.isWhitespace(sb.charAt(sb.length() - 1))) {
-            sb.deleteCharAt(sb.length() - 1);
+        
+		int end = length;
+        while (start < length && Character.isWhitespace(str.charAt(end - 1))) {
+            end--;
         }
-        return sb.toString();
+        
+        return ((start > 0) || (end < length)) ? str.subSequence(start, end) : str;
     }
 
     public static String clean(String str) {
+    	CharSequence result = clean((CharSequence) str);
+        
+        return result!=null?result.toString():null;
+    }
+    
+    public static CharSequence clean(CharSequence str) {
         str = trimWhitespace(str);
-        if ("".equals(str)) {
+        if (!hasLength(str)) {
             return null;
         }
         return str;

src/test/groovy/io/jsonwebtoken/lang/StringsTest.groovy

@@ -14,4 +14,46 @@ class StringsTest {
         assertTrue Strings.hasText("  foo   ");
         assertTrue Strings.hasText("foo")
     }
+    
+    @Test
+    void testClean() {
+        assertEquals "this is a test", Strings.clean("this is a test")
+        assertEquals "this is a test", Strings.clean("   this is a test")
+        assertEquals "this is a test", Strings.clean("   this is a test   ")
+        assertEquals "this is a test", Strings.clean("\nthis is a test \t  ")
+        assertNull Strings.clean(null)
+        assertNull Strings.clean("")
+        assertNull Strings.clean("\t")
+        assertNull Strings.clean("      ")
+    }
+    
+    @Test
+    void testCleanCharSequence() {
+    	def result = Strings.clean(new StringBuilder("this is a test"))
+    	assertNotNull result
+        assertEquals "this is a test", result.toString()
+        
+        result = Strings.clean(new StringBuilder("   this is a test"))
+    	assertNotNull result
+        assertEquals "this is a test", result.toString()
+        
+        result = Strings.clean(new StringBuilder("   this is a test   "))
+    	assertNotNull result
+        assertEquals "this is a test", result.toString()
+        
+        result = Strings.clean(new StringBuilder("\nthis is a test \t  "))
+    	assertNotNull result
+        assertEquals "this is a test", result.toString()
+        
+        assertNull Strings.clean((StringBuilder) null)
+        assertNull Strings.clean(new StringBuilder(""))
+        assertNull Strings.clean(new StringBuilder("\t"))
+        assertNull Strings.clean(new StringBuilder("      "))
+    }
+    
+    
+    @Test
+    void testTrimWhitespace() {
+    	assertEquals "", Strings.trimWhitespace("      ")
+    }
 }