Provide a public API for resolving the type of a field

spring-restdocs-core/src/main/java/org/springframework/restdocs/payload/AbstractFieldsSnippet.java

@@ -38,6 +38,7 @@
  *
  * @author Andreas Evers
  * @author Andy Wilkinson
+ * @author Mathias Düsterhöft
  */
 public abstract class AbstractFieldsSnippet extends TemplatedSnippet {
 
@@ -160,15 +161,15 @@ protected Map<String, Object> createModel(Operation operation) {
 			content = verifyContent(
 					this.subsectionExtractor.extractSubsection(content, contentType));
 		}
-		ContentHandler contentHandler = getContentHandler(content, contentType);
+		ContentHandler contentHandler = ContentHandler.forContent(content, contentType);
 
 		validateFieldDocumentation(contentHandler);
 
 		List<FieldDescriptor> descriptorsToDocument = new ArrayList<>();
 		for (FieldDescriptor descriptor : this.fieldDescriptors) {
 			if (!descriptor.isIgnored()) {
 				try {
-					Object type = contentHandler.determineFieldType(descriptor);
+					Object type = contentHandler.resolveFieldType(descriptor);
 					descriptorsToDocument.add(copyWithType(descriptor, type));
 				}
 				catch (FieldDoesNotExistException ex) {
@@ -200,36 +201,6 @@ private byte[] verifyContent(byte[] content) {
 		return content;
 	}
 
-	private ContentHandler getContentHandler(byte[] content, MediaType contentType) {
-		ContentHandler contentHandler = createJsonContentHandler(content);
-		if (contentHandler == null) {
-			contentHandler = createXmlContentHandler(content);
-			if (contentHandler == null) {
-				throw new PayloadHandlingException("Cannot handle " + contentType
-						+ " content as it could not be parsed as JSON or XML");
-			}
-		}
-		return contentHandler;
-	}
-
-	private ContentHandler createJsonContentHandler(byte[] content) {
-		try {
-			return new JsonContentHandler(content);
-		}
-		catch (Exception ex) {
-			return null;
-		}
-	}
-
-	private ContentHandler createXmlContentHandler(byte[] content) {
-		try {
-			return new XmlContentHandler(content);
-		}
-		catch (Exception ex) {
-			return null;
-		}
-	}
-
 	private void validateFieldDocumentation(ContentHandler payloadHandler) {
 		List<FieldDescriptor> missingFields = payloadHandler
 				.findMissingFields(this.fieldDescriptors);

spring-restdocs-core/src/main/java/org/springframework/restdocs/payload/ContentHandler.java

@@ -18,12 +18,15 @@
 
 import java.util.List;
 
+import org.springframework.http.MediaType;
+
 /**
  * A handler for the content of a request or response.
  *
  * @author Andy Wilkinson
+ * @author Mathias Düsterhöft
  */
-interface ContentHandler {
+interface ContentHandler extends FieldTypeResolver {
 
 	/**
 	 * Finds the fields that are missing from the handler's payload. A field is missing if
@@ -48,11 +51,26 @@ interface ContentHandler {
 	String getUndocumentedContent(List<FieldDescriptor> fieldDescriptors);
 
 	/**
-	 * Returns the type of the field that is described by the given
-	 * {@code fieldDescriptor} based on the content of the payload.
-	 * @param fieldDescriptor the field descriptor
-	 * @return the type of the field
+	 * Create a {@link ContentHandler} for the given content type and payload.
+	 * @param content the payload
+	 * @param contentType the content type
+	 * @return the ContentHandler
+	 * @throws PayloadHandlingException if no known ContentHandler can handle the content
 	 */
-	Object determineFieldType(FieldDescriptor fieldDescriptor);
+	static ContentHandler forContent(byte[] content, MediaType contentType) {
+
+		try {
+			return new JsonContentHandler(content);
+		}
+		catch (Exception je) {
+			try {
+				return new XmlContentHandler(content);
+			}
+			catch (Exception xe) {
+				throw new PayloadHandlingException("Cannot handle " + contentType
+						+ " content as it could not be parsed as JSON or XML");
+			}
+		}
+	}
 
 }

spring-restdocs-core/src/main/java/org/springframework/restdocs/payload/FieldTypeResolver.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2014-2018 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.restdocs.payload;
+
+import org.springframework.http.MediaType;
+
+/**
+ * Public abstraction for external access to field type determination for xml and json
+ * payloads.
+ *
+ * @author Mathias Düsterhöft
+ * @since 2.0.3
+ */
+public interface FieldTypeResolver {
+
+	/**
+	 * Create a FieldTypeResolver for the given content and contentType.
+	 * @param content the payload that the {@link FieldTypeResolver} should handle
+	 * @param contentType the content type of the payload
+	 * @return the {@link FieldTypeResolver}
+	 */
+	static FieldTypeResolver forContent(byte[] content, MediaType contentType) {
+		return ContentHandler.forContent(content, contentType);
+	}
+
+	/**
+	 * Returns the type of the field that is described by the given
+	 * {@code fieldDescriptor} based on the content of the payload.
+	 * @param fieldDescriptor the field descriptor
+	 * @return the type of the field
+	 */
+	Object resolveFieldType(FieldDescriptor fieldDescriptor);
+
+}

spring-restdocs-core/src/main/java/org/springframework/restdocs/payload/JsonContentHandler.java

@@ -32,8 +32,9 @@
  * A {@link ContentHandler} for JSON content.
  *
  * @author Andy Wilkinson
+ * @author Mathias Düsterhöft
  */
-class JsonContentHandler implements ContentHandler {
+class JsonContentHandler implements ContentHandler, FieldTypeResolver {
 
 	private final JsonFieldProcessor fieldProcessor = new JsonFieldProcessor();
 
@@ -145,7 +146,7 @@ private boolean isEmpty(Object object) {
 	}
 
 	@Override
-	public Object determineFieldType(FieldDescriptor fieldDescriptor) {
+	public Object resolveFieldType(FieldDescriptor fieldDescriptor) {
 		if (fieldDescriptor.getType() == null) {
 			return this.fieldTypeResolver.resolveFieldType(fieldDescriptor,
 					readContent());

spring-restdocs-core/src/main/java/org/springframework/restdocs/payload/XmlContentHandler.java

@@ -190,7 +190,7 @@ private String prettyPrint(Document document) {
 	}
 
 	@Override
-	public Object determineFieldType(FieldDescriptor fieldDescriptor) {
+	public Object resolveFieldType(FieldDescriptor fieldDescriptor) {
 		if (fieldDescriptor.getType() != null) {
 			return fieldDescriptor.getType();
 		}

spring-restdocs-core/src/test/java/org/springframework/restdocs/payload/FieldTypeResolverTests.java

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2014-2018 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.restdocs.payload;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+
+import org.springframework.http.MediaType;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link FieldTypeResolver}.
+ *
+ * @author Mathias Düsterhöft
+ */
+public class FieldTypeResolverTests {
+
+	@Rule
+	public ExpectedException thrownException = ExpectedException.none();
+
+	@Test
+	public void returnJsonFieldTypeResolver() {
+		assertThat(FieldTypeResolver.forContent("{\"field\": \"value\"}".getBytes(),
+				MediaType.APPLICATION_JSON)).isInstanceOf(JsonContentHandler.class);
+	}
+
+	@Test
+	public void returnXmlContentHandler() {
+		assertThat(FieldTypeResolver.forContent("<a><b>5</b></a>".getBytes(),
+				MediaType.APPLICATION_XML)).isInstanceOf(XmlContentHandler.class);
+	}
+
+	@Test
+	public void throwOnInvalidContent() {
+		this.thrownException.expect(PayloadHandlingException.class);
+		FieldTypeResolver.forContent("some".getBytes(), MediaType.APPLICATION_XML);
+	}
+
+}

spring-restdocs-core/src/test/java/org/springframework/restdocs/payload/JsonContentHandlerTests.java

@@ -29,6 +29,7 @@
  * Tests for {@link JsonContentHandler}.
  *
  * @author Andy Wilkinson
+ * @author Mathias Düsterhöft
  */
 public class JsonContentHandlerTests {
 
@@ -39,61 +40,61 @@ public class JsonContentHandlerTests {
 	public void typeForFieldWithNullValueMustMatch() {
 		this.thrown.expect(FieldTypesDoNotMatchException.class);
 		new JsonContentHandler("{\"a\": null}".getBytes())
-				.determineFieldType(new FieldDescriptor("a").type(JsonFieldType.STRING));
+				.resolveFieldType(new FieldDescriptor("a").type(JsonFieldType.STRING));
 	}
 
 	@Test
 	public void typeForFieldWithNotNullAndThenNullValueMustMatch() {
 		this.thrown.expect(FieldTypesDoNotMatchException.class);
 		new JsonContentHandler("{\"a\":[{\"id\":1},{\"id\":null}]}".getBytes())
-				.determineFieldType(
+				.resolveFieldType(
 						new FieldDescriptor("a[].id").type(JsonFieldType.STRING));
 	}
 
 	@Test
 	public void typeForFieldWithNullAndThenNotNullValueMustMatch() {
 		this.thrown.expect(FieldTypesDoNotMatchException.class);
 		new JsonContentHandler("{\"a\":[{\"id\":null},{\"id\":1}]}".getBytes())
-				.determineFieldType(
+				.resolveFieldType(
 						new FieldDescriptor("a.[].id").type(JsonFieldType.STRING));
 	}
 
 	@Test
 	public void typeForOptionalFieldWithNumberAndThenNullValueIsNumber() {
 		Object fieldType = new JsonContentHandler(
 				"{\"a\":[{\"id\":1},{\"id\":null}]}\"".getBytes())
-						.determineFieldType(new FieldDescriptor("a[].id").optional());
+						.resolveFieldType(new FieldDescriptor("a[].id").optional());
 		assertThat((JsonFieldType) fieldType).isEqualTo(JsonFieldType.NUMBER);
 	}
 
 	@Test
 	public void typeForOptionalFieldWithNullAndThenNumberIsNumber() {
 		Object fieldType = new JsonContentHandler(
 				"{\"a\":[{\"id\":null},{\"id\":1}]}".getBytes())
-						.determineFieldType(new FieldDescriptor("a[].id").optional());
+						.resolveFieldType(new FieldDescriptor("a[].id").optional());
 		assertThat((JsonFieldType) fieldType).isEqualTo(JsonFieldType.NUMBER);
 	}
 
 	@Test
 	public void typeForFieldWithNumberAndThenNullValueIsVaries() {
 		Object fieldType = new JsonContentHandler(
 				"{\"a\":[{\"id\":1},{\"id\":null}]}\"".getBytes())
-						.determineFieldType(new FieldDescriptor("a[].id"));
+						.resolveFieldType(new FieldDescriptor("a[].id"));
 		assertThat((JsonFieldType) fieldType).isEqualTo(JsonFieldType.VARIES);
 	}
 
 	@Test
 	public void typeForFieldWithNullAndThenNumberIsVaries() {
 		Object fieldType = new JsonContentHandler(
 				"{\"a\":[{\"id\":null},{\"id\":1}]}".getBytes())
-						.determineFieldType(new FieldDescriptor("a[].id"));
+						.resolveFieldType(new FieldDescriptor("a[].id"));
 		assertThat((JsonFieldType) fieldType).isEqualTo(JsonFieldType.VARIES);
 	}
 
 	@Test
 	public void typeForOptionalFieldWithNullValueCanBeProvidedExplicitly() {
 		Object fieldType = new JsonContentHandler("{\"a\": null}".getBytes())
-				.determineFieldType(
+				.resolveFieldType(
 						new FieldDescriptor("a").type(JsonFieldType.STRING).optional());
 		assertThat((JsonFieldType) fieldType).isEqualTo(JsonFieldType.STRING);
 	}

spring-restdocs-core/src/test/java/org/springframework/restdocs/payload/XmlContentHandlerTests.java

@@ -30,6 +30,7 @@
  * Tests for {@link XmlContentHandler}.
  *
  * @author Andy Wilkinson
+ * @author Mathias Düsterhöft
  */
 public class XmlContentHandlerTests {