fixes #84 remove Java 8 optional to ensure that this library can be used in Android

Author: stevehu

src/main/java/com/networknt/schema/JsonMetaSchema.java

@@ -24,7 +24,6 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
-import java.util.Optional;
 import java.util.concurrent.ConcurrentHashMap;
 
 import org.apache.commons.lang3.StringUtils;
@@ -226,7 +225,7 @@ public String getUri() {
         return uri;
     }
 
-    public Optional<JsonValidator> newValidator(ValidationContext validationContext, String schemaPath, String keyword /* keyword */, JsonNode schemaNode,
+    public JsonValidator newValidator(ValidationContext validationContext, String schemaPath, String keyword /* keyword */, JsonNode schemaNode,
             JsonSchema parentSchema) {
 
         try {
@@ -236,9 +235,9 @@ public Optional<JsonValidator> newValidator(ValidationContext validationContext,
                     UNKNOWN_KEYWORDS.put(keyword, keyword);
                     logger.warn("Unknown keyword " + keyword + " - you should define your own Meta Schema. If the keyword is irrelevant for validation, just use a NonValidationKeyword");
                 }
-                return Optional.empty();
+                return null;
             }
-            return Optional.of(kw.newValidator(schemaPath, schemaNode, parentSchema, validationContext));
+            return kw.newValidator(schemaPath, schemaNode, parentSchema, validationContext);
         } catch (InvocationTargetException e) {
             if (e.getTargetException() instanceof JsonSchemaException) {
                 throw (JsonSchemaException) e.getTargetException();

src/main/java/com/networknt/schema/JsonSchema.java

@@ -23,7 +23,6 @@
 import java.util.Iterator;
 import java.util.LinkedHashSet;
 import java.util.Map;
-import java.util.Optional;
 import java.util.Set;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
@@ -113,9 +112,9 @@ private Map<String, JsonValidator> read(JsonNode schemaNode) {
             String pname = pnames.next();
             JsonNode n = schemaNode.get(pname);
 
-            Optional<JsonValidator> validator = validationContext.newValidator(getSchemaPath(), pname, n, this);
-            if (validator.isPresent()) {
-                validators.put(getSchemaPath() + "/" + pname, validator.get());
+            JsonValidator validator = validationContext.newValidator(getSchemaPath(), pname, n, this);
+            if (validator != null) {
+                validators.put(getSchemaPath() + "/" + pname, validator);
             }
 
         }

src/main/java/com/networknt/schema/ValidationContext.java

@@ -1,7 +1,5 @@
 package com.networknt.schema;
 
-import java.util.Optional;
-
 import com.fasterxml.jackson.databind.JsonNode;
 
 public class ValidationContext {
@@ -19,7 +17,7 @@ public ValidationContext(JsonMetaSchema metaSchema, JsonSchemaFactory jsonSchema
         this.jsonSchemaFactory = jsonSchemaFactory;
     }
 
-    public Optional<JsonValidator> newValidator(String schemaPath, String keyword /* keyword */, JsonNode schemaNode,
+    public JsonValidator newValidator(String schemaPath, String keyword /* keyword */, JsonNode schemaNode,
             JsonSchema parentSchema) {
         return metaSchema.newValidator(this, schemaPath, keyword, schemaNode, parentSchema);
     }