Add ValidationException#getAllMessages()

Walk through all nested violations and return the list of error messages.
This is particularly useful for use by a REST API when validating the
schema of an incoming JSON payload. The flat list of messages provides
a convenient format for clients to log, and even parse, the errors.

Author: srfarley

core/src/main/java/org/everit/json/schema/ValidationException.java

@@ -21,7 +21,6 @@
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
-import java.util.Objects;
 import java.util.stream.Collectors;
 
 import static java.util.Objects.requireNonNull;
@@ -37,6 +36,18 @@ private static int getViolationCount(final List<ValidationException> causes) {
         return Math.max(1, causeCount);
     }
 
+    private static List<String> getAllMessages(final List<ValidationException> causes) {
+        List<String> messages = causes.stream()
+                .filter(cause -> cause.causingExceptions.isEmpty())
+                .map(ValidationException::getMessage)
+                .collect(Collectors.toList());
+        messages.addAll(causes.stream()
+                .filter(cause -> !cause.causingExceptions.isEmpty())
+                .flatMap(cause -> getAllMessages(cause.getCausingExceptions()).stream())
+                .collect(Collectors.toList()));
+        return messages;
+    }
+
     /**
      * Sort of static factory method. It is used by {@link ObjectSchema} and {@link ArraySchema} to
      * create {@code ValidationException}s, handling the case of multiple violations occuring during
@@ -241,6 +252,18 @@ public List<ValidationException> getCausingExceptions() {
         return causingExceptions;
     }
 
+    /**
+     * Returns all messages collected from all violations, including nested causing exceptions.
+     * @return all messages
+     */
+    public List<String> getAllMessages() {
+        if (causingExceptions.isEmpty()) {
+            return Collections.singletonList(getMessage());
+        } else {
+            return getAllMessages(causingExceptions).stream().collect(Collectors.toList());
+        }
+    }
+
     /**
      * Returns a programmer-readable error description prepended by {@link #getPointerToViolation()
      * the pointer to the violating fragment} of the JSON document.

core/src/test/java/org/everit/json/schema/ObjectSchemaTest.java

@@ -22,6 +22,7 @@
 import org.junit.Assert;
 import org.junit.Test;
 
+import java.util.List;
 import java.util.concurrent.Callable;
 
 import static org.junit.Assert.assertTrue;
@@ -136,9 +137,15 @@ public void multipleViolations() {
             Assert.fail("did not throw exception for 3 schema violations");
         } catch (ValidationException e) {
             Assert.assertEquals(3, e.getCausingExceptions().size());
-            Assert.assertEquals(1, TestSupport.countCauseByJsonPointer(e, "#/numberProp"));
             Assert.assertEquals(1, TestSupport.countCauseByJsonPointer(e, "#"));
+            Assert.assertEquals(1, TestSupport.countCauseByJsonPointer(e, "#/numberProp"));
             Assert.assertEquals(1, TestSupport.countCauseByJsonPointer(e, "#/stringPatternMatch"));
+
+            List<String> messages = e.getAllMessages();
+            Assert.assertEquals(3, messages.size());
+            Assert.assertEquals(1, TestSupport.countMatchingMessage(messages, "#:"));
+            Assert.assertEquals(1, TestSupport.countMatchingMessage(messages, "#/numberProp:"));
+            Assert.assertEquals(1, TestSupport.countMatchingMessage(messages, "#/stringPatternMatch:"));
         }
     }
 
@@ -186,6 +193,18 @@ public void multipleViolationsNested() throws Exception {
             Assert.assertEquals(1, TestSupport.countCauseByJsonPointer(nested2Exception, "#/nested/nested"));
             Assert.assertEquals(1, TestSupport.countCauseByJsonPointer(nested2Exception, "#/nested/nested/numberProp"));
             Assert.assertEquals(1, TestSupport.countCauseByJsonPointer(nested2Exception, "#/nested/nested/stringPatternMatch"));
+
+            List<String> messages = subjectException.getAllMessages();
+            Assert.assertEquals(9, messages.size());
+            Assert.assertEquals(1, TestSupport.countMatchingMessage(messages, "#:"));
+            Assert.assertEquals(1, TestSupport.countMatchingMessage(messages, "#/numberProp:"));
+            Assert.assertEquals(1, TestSupport.countMatchingMessage(messages, "#/stringPatternMatch:"));
+            Assert.assertEquals(1, TestSupport.countMatchingMessage(messages, "#/nested:"));
+            Assert.assertEquals(1, TestSupport.countMatchingMessage(messages, "#/nested/numberProp:"));
+            Assert.assertEquals(1, TestSupport.countMatchingMessage(messages, "#/nested/stringPatternMatch:"));
+            Assert.assertEquals(1, TestSupport.countMatchingMessage(messages, "#/nested/nested:"));
+            Assert.assertEquals(1, TestSupport.countMatchingMessage(messages, "#/nested/nested/numberProp:"));
+            Assert.assertEquals(1, TestSupport.countMatchingMessage(messages, "#/nested/nested/stringPatternMatch:"));
         }
     }
 

core/src/test/java/org/everit/json/schema/TestSupport.java

@@ -17,6 +17,8 @@
 
 import org.junit.Assert;
 
+import java.util.List;
+
 public class TestSupport {
 
     public static class Failure {
@@ -95,6 +97,12 @@ public static long countCauseByJsonPointer(final ValidationException root, final
                 .count();
     }
 
+    public static long countMatchingMessage(final List<String> messages, final String expectedSubstring) {
+        return messages.stream()
+                .filter(message -> message.contains(expectedSubstring))
+                .count();
+    }
+
     public static void expectFailure(final Schema failingSchema,
             final Class<? extends Schema> expectedViolatedSchemaClass,
             final String expectedPointer, final Object input) {