fixes #54 implement Const validator

Author: stevehu

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

@@ -0,0 +1,34 @@
+package com.networknt.schema;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.math.BigDecimal;
+import java.util.Collections;
+import java.util.LinkedHashSet;
+import java.util.Set;
+
+public class ConstValidator extends BaseJsonValidator implements JsonValidator {
+    private static final Logger logger = LoggerFactory.getLogger(ConstValidator.class);
+    JsonNode schemaNode;
+
+    public ConstValidator(String schemaPath, JsonNode schemaNode, JsonSchema parentSchema, ValidationContext validationContext) {
+        super(schemaPath, schemaNode, parentSchema, ValidatorTypeCode.CONST, validationContext);
+        this.schemaNode = schemaNode;
+    }
+
+    public Set<ValidationMessage> validate(JsonNode node, JsonNode rootNode, String at) {
+        debug(logger, node, rootNode, at);
+
+        Set<ValidationMessage> errors = new LinkedHashSet<ValidationMessage>();
+        if(schemaNode.isNumber() && node.isNumber()) {
+            if(schemaNode.decimalValue().compareTo(node.decimalValue()) != 0) {
+                errors.add(buildValidationMessage(at, schemaNode.asText()));
+            }
+        } else if (!schemaNode.equals(node)) {
+            errors.add(buildValidationMessage(at, schemaNode.asText()));
+        }
+        return Collections.unmodifiableSet(errors);
+    }
+}

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

@@ -70,7 +70,8 @@ public JsonValidator newValidator(String schemaPath, JsonNode schemaNode, JsonSc
     EXCLUSIVE_MAXIMUM("exclusiveMaximum", "1038", new MessageFormat("{0}: must have a exclusive maximum value of {1}"), ExclusiveMaximumValidator.class, 14),  // V6|V7|V201909
     EXCLUSIVE_MINIMUM("exclusiveMinimum", "1039", new MessageFormat("{0}: must have a exclusive minimum value of {1}"), ExclusiveMinimumValidator.class, 14),
     TRUE("true", "1040", null, TrueValidator.class, 14),
-    FALSE("false", "1041", new MessageFormat("Boolean schema false is not valid"), FalseValidator.class, 14);
+    FALSE("false", "1041", new MessageFormat("Boolean schema false is not valid"), FalseValidator.class, 14),
+    CONST("const", "1042", new MessageFormat("{0}: must be a constant value {1}"), ConstValidator.class, 14);
 
     private static Map<String, ValidatorTypeCode> constants = new HashMap<String, ValidatorTypeCode>();
     private static SpecVersion specVersion = new SpecVersion();

src/test/java/com/networknt/schema/V201909JsonSchemaTest.java

@@ -261,7 +261,6 @@ public void testBooleanSchemaValidator() throws Exception {
     }
 
     @Test
-    @Ignore
     public void testConstValidator() throws Exception {
         runTestFile("draft2019-09/const.json");
     }

src/test/java/com/networknt/schema/V7JsonSchemaTest.java

@@ -257,7 +257,6 @@ public void testBooleanSchemaValidator() throws Exception {
     }
 
     @Test
-    @Ignore
     public void testConstValidator() throws Exception {
         runTestFile("draft7/const.json");
     }