Make it easier to document common portions of req and resp payloads

This commit adds a new andWithPrefix(String, FieldDescriptor[]) method
to both RequestFieldsSnippet and ResponseFieldsSnippet. It can be
used to add descriptors to an existing snippet, applying the given
prefix to the additional descriptors as it does so. This allows the
descriptors for a portion of a payload to be created once and then
reused, irrespective of where in the payload the portion appears.

Closes gh-221

docs/src/test/java/com/example/Payload.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2014-2016 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 com.example;
+
+import org.springframework.restdocs.payload.FieldDescriptor;
+
+import static org.springframework.restdocs.payload.PayloadDocumentation.fieldWithPath;
+
+public class Payload {
+
+	@SuppressWarnings("unused")
+	public void bookFieldDescriptors() {
+		// tag::book-descriptors[]
+		FieldDescriptor[] book = new FieldDescriptor[] {
+				fieldWithPath("title").description("Title of the book"),
+				fieldWithPath("author").description("Author of the book") };
+		// end::book-descriptors[]
+	}
+
+}

docs/src/test/java/com/example/mockmvc/Payload.java

@@ -27,6 +27,7 @@ import static org.springframework.restdocs.snippet.Attributes.key;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
 
 import org.springframework.http.MediaType;
+import org.springframework.restdocs.payload.FieldDescriptor;
 import org.springframework.restdocs.payload.JsonFieldType;
 import org.springframework.test.web.servlet.MockMvc;
 
@@ -70,4 +71,24 @@ public class Payload {
 			// end::constraints[]
 	}
 
+	public void descriptorReuse() throws Exception {
+		FieldDescriptor[] book = new FieldDescriptor[] {
+				fieldWithPath("title").description("Title of the book"),
+				fieldWithPath("author").description("Author of the book") };
+
+		// tag::single-book[]
+		this.mockMvc.perform(get("/books/1").accept(MediaType.APPLICATION_JSON))
+				.andExpect(status().isOk())
+				.andDo(document("book", responseFields(book))); // <1>
+				// end::single-book[]
+
+		// tag::book-array[]
+		this.mockMvc.perform(get("/books").accept(MediaType.APPLICATION_JSON))
+				.andExpect(status().isOk())
+				.andDo(document("book", responseFields(
+						fieldWithPath("[]").description("An array of books")) // <1>
+						.andWithPrefix("[].", book))); // <2>
+		// end::book-array[]
+	}
+
 }

docs/src/test/java/com/example/restassured/Payload.java

@@ -16,6 +16,7 @@
 
 package com.example.restassured;
 
+import org.springframework.restdocs.payload.FieldDescriptor;
 import org.springframework.restdocs.payload.JsonFieldType;
 
 import com.jayway.restassured.RestAssured;
@@ -72,4 +73,27 @@ public class Payload {
 		.then().assertThat().statusCode(is(200));
 	}
 
+	public void descriptorReuse() throws Exception {
+		FieldDescriptor[] book = new FieldDescriptor[] {
+				fieldWithPath("title").description("Title of the book"),
+				fieldWithPath("author").description("Author of the book") };
+
+		// tag::single-book[]
+		RestAssured.given(this.spec).accept("application/json")
+			.filter(document("book", responseFields(book))) // <1>
+			.when().get("/books/1")
+			.then().assertThat().statusCode(is(200));
+		// end::single-book[]
+
+		// tag::book-array[]
+		RestAssured.given(this.spec).accept("application/json")
+			.filter(document("books", responseFields(
+				fieldWithPath("[]").description("An array of books")) // <1>
+				.andWithPrefix("[].", book))) // <2>
+		.when().get("/books/1")
+		.then().assertThat().statusCode(is(200));
+		// end::book-array[]
+
+	}
+
 }