Make it compilable

src/main/java/com/apicatalog/rdf/Rdf.java

@@ -28,6 +28,7 @@
 import com.apicatalog.rdf.io.error.UnsupportedContentException;
 import com.apicatalog.rdf.lang.XsdConstants;
 import com.apicatalog.rdf.spi.RdfProvider;
+import com.apicatalog.rdf.uri.UriUtils;
 
 public final class Rdf {
 
@@ -125,11 +126,11 @@ public static RdfValue createValue(String value) {
             throw new IllegalArgumentException();
         }
 
-        if (BlankNode.isWellFormed(value)) {
+        if (UriUtils.isBlanNode(value)) {
             return RdfProvider.provider().createBlankNode(value);
         }
 
-        if (UriUtils.isAbsoluteUri(value, true)) {
+        if (UriUtils.isAbsoluteUri(value)) {
             return RdfProvider.provider().createIRI(value);
         }
 
@@ -176,11 +177,11 @@ public static RdfResource createResource(String resource) {
             throw new IllegalArgumentException("The resource value cannot be null.");
         }
 
-        if (BlankNode.isWellFormed(resource)) {
+        if (UriUtils.isBlanNode(resource)) {
             return RdfProvider.provider().createBlankNode(resource);
         }
 
-        if (UriUtils.isAbsoluteUri(resource, true)) {
+        if (UriUtils.isAbsoluteUri(resource)) {
             return RdfProvider.provider().createIRI(resource);
         }
 

src/main/java/com/apicatalog/rdf/io/nquad/NQuadsReader.java

@@ -28,6 +28,7 @@
 import com.apicatalog.rdf.io.error.RdfReaderException;
 import com.apicatalog.rdf.io.nquad.Tokenizer.Token;
 import com.apicatalog.rdf.io.nquad.Tokenizer.TokenType;
+import com.apicatalog.rdf.uri.UriUtils;
 
 /**
  *
@@ -241,7 +242,7 @@ private void skipWhitespace(int min) throws RdfReaderException {
     }
 
     private static final void assertAbsoluteIri(final String iri, final String what) throws RdfReaderException {
-        if (UriUtils.isNotAbsoluteUri(iri)) {
+        if (!UriUtils.isAbsoluteUri(iri)) {
             throw new RdfReaderException(what + " must be an absolute IRI [" + iri  +  "]. ");
         }
     }    

src/main/java/com/apicatalog/rdf/uri/UriUtils.java

@@ -0,0 +1,93 @@
+/*
+ * Copyright 2020 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.apicatalog.rdf.uri;
+
+import java.util.Arrays;
+
+import com.apicatalog.rdf.lang.RdfAlphabet;
+
+public final class UriUtils {
+
+    private UriUtils() {
+    }
+
+    public static final boolean isAbsoluteUri(final String uri) {
+        // then validate just a scheme
+        return startsWithScheme(uri);
+    }
+
+    private static final boolean startsWithScheme(final String uri) {
+
+        if (uri == null
+                || uri.length() < 2 // a scheme must have at least one letter followed by ':'
+                || !Character.isLetter(uri.codePointAt(0)) // a scheme name must start with a letter
+                ) {
+            return false;
+        }
+
+        for (int i = 1; i < uri.length(); i++) {
+
+            if (
+                //  a scheme name must start with a letter followed by a letter/digit/+/-/.
+                Character.isLetterOrDigit(uri.codePointAt(i))
+                        || uri.charAt(i) == '-' || uri.charAt(i) == '+' || uri.charAt(i) == '.'
+                ) {
+                continue;
+            }
+
+            // a scheme name must be terminated by ':'
+            return uri.charAt(i) == ':';
+        }
+        return false;
+    }
+
+    /**
+     * BLANK_NODE_LABEL ::= '_:' (PN_CHARS_U | [0-9]) ((PN_CHARS | '.')* PN_CHARS)?
+     *
+     * @see <a href="https://www.w3.org/TR/n-quads/#sec-grammar">N-Quads Grammar</a>
+     *
+     * @param blankNodeId to check
+     * @return <code>true</code> if the provided string is well formed blank node identifier
+     */
+    public static boolean isBlanNode(final String blankNodeId) {
+
+        if (blankNodeId == null) {
+            throw new IllegalArgumentException();
+        }
+
+        if (blankNodeId.length() < 3) {
+            return false;
+        }
+
+        int[] chars = blankNodeId.codePoints().toArray();
+
+        if (chars[0] != '_'
+                || chars[1] != ':'
+                || (RdfAlphabet.PN_CHARS_U.negate().test(chars[2])
+                        && RdfAlphabet.ASCII_DIGIT.negate().test(chars[2]))
+                || chars[chars.length - 1] == '.'
+                        )  {
+            return false;
+        }
+
+        if (chars.length == 3) {
+            return true;
+        }
+
+        return Arrays.stream(chars, 3, chars.length - 1).allMatch(RdfAlphabet.PN_CHARS.or(ch -> ch == '.'));
+    }
+
+}