DATAREST-354 - General rewrite of the JSONSchema support.

Significant overhaul of the JSONSchema support. This currently adds the following features:

- Complex nested types are exposed as descriptors with the properties pointing to them whenever necessary.
- Sets are treated as unique collections.
- Enums are handled as expected (enum values are listed).
- Renamings via @JsonProperty are considered.
- @JsonProperty(required = true) is considered and added to required properties.
- Date/time types (legacy Date, JSR-310, ThreeTenBP and Joda Time) are exposed with format "date-time".
- Objects with @JsonValue methods are considered to be rendered as String value.
- Formats and patterns can be manually configured on MetadataConfiguration.

TODOs:

- Implementation polish, JavaDoc
- Automatically inspect ObjectMapper to detect customizations made through Mixins and custom Serializers.

spring-data-rest-core/src/main/java/org/springframework/data/rest/core/config/JsonSchemaFormat.java

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2015 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 org.springframework.data.rest.core.config;
+
+import java.util.Locale;
+
+import com.fasterxml.jackson.annotation.JsonValue;
+
+/**
+ * An enum to represent JSON Schema pre-defined formats.
+ *
+ * @author Oliver Gierke
+ * @since 2.3
+ */
+public enum JsonSchemaFormat {
+
+	EMAIL, DATE_TIME, HOSTNAME, IPV4, IPV6, URI;
+
+	/*
+	 * (non-Javadoc)
+	 * @see java.lang.Enum#toString()
+	 */
+	@JsonValue
+	public String toString() {
+		return name().toLowerCase(Locale.US).replaceAll("_", "-");
+	}
+}

spring-data-rest-core/src/main/java/org/springframework/data/rest/core/config/MetadataConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014 the original author or authors.
+ * Copyright 2014-2015 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.
@@ -15,6 +15,13 @@
  */
 package org.springframework.data.rest.core.config;
 
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.regex.Pattern;
+
+import org.springframework.util.Assert;
+
 /**
  * Configuration for metadata exposure.
  * 
@@ -22,6 +29,8 @@ package org.springframework.data.rest.core.config;
  */
 public class MetadataConfiguration {
 
+	private final Map<Class<?>, JsonSchemaFormat> schemaFormats = new HashMap<Class<?>, JsonSchemaFormat>();
+	private final Map<Class<?>, Pattern> patterns = new HashMap<Class<?>, Pattern>();
 	private boolean omitUnresolvableDescriptionKeys = true;
 	private boolean alpsEnabled = true;
 
@@ -63,4 +72,56 @@ public class MetadataConfiguration {
 	public boolean alpsEnabled() {
 		return alpsEnabled;
 	}
+
+	public void registerJsonSchemaFormat(JsonSchemaFormat format, Class<?>... types) {
+
+		Assert.notNull(format, "JsonSchemaFormat must not be null!");
+
+		for (Class<?> type : types) {
+			schemaFormats.put(type, format);
+		}
+	}
+
+	/**
+	 * Returns the {@link JsonSchemaFormat} to be used for the given type.
+	 * 
+	 * @param type must not be {@literal null}.
+	 * @return
+	 */
+	public JsonSchemaFormat getSchemaFormatFor(Class<?> type) {
+		return schemaFormats.get(type);
+	}
+
+	/**
+	 * Registers the given formatting patter for the given value type.
+	 * 
+	 * @param pattern must not be {@literal null} or empty.
+	 * @param type must not be {@literal null}.
+	 */
+	public void registerFormattingPatternFor(String pattern, Class<?> type) {
+
+		Assert.hasText(pattern, "Pattern must not be null or empty!");
+		Assert.notNull(type, "Type must not be null!");
+
+		this.patterns.put(type, Pattern.compile(pattern));
+	}
+
+	/**
+	 * Returns the {@link Pattern} registered for the given value type.
+	 * 
+	 * @param type must not be {@literal null}.
+	 * @return
+	 */
+	public Pattern getPatternFor(Class<?> type) {
+
+		Assert.notNull(type, "Type must not be null!");
+
+		for (Entry<Class<?>, Pattern> entry : this.patterns.entrySet()) {
+			if (entry.getKey().isAssignableFrom(type)) {
+				return entry.getValue();
+			}
+		}
+
+		return this.patterns.get(type);
+	}
 }

spring-data-rest-core/src/test/java/org/springframework/data/rest/core/domain/jpa/Person.java

@@ -1,3 +1,18 @@
+/*
+ * Copyright 2013-2015 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 org.springframework.data.rest.core.domain.jpa;
 
 import java.util.ArrayList;
@@ -5,6 +20,7 @@ import java.util.Calendar;
 import java.util.Collections;
 import java.util.Date;
 import java.util.List;
+
 import javax.persistence.Entity;
 import javax.persistence.GeneratedValue;
 import javax.persistence.Id;
@@ -15,6 +31,7 @@ import javax.persistence.PrePersist;
  * An entity that represents a person.
  * 
  * @author Jon Brisbin
+ * @author Oliver Gierke
  */
 @Entity
 public class Person {