Add support for reusing a snippet to document common elements

This commit updates all of the Snippet implementations that take one
or more descriptors to provide an and method that can be used to
create a new Snippet that has additional descriptors.

Closes gh-168

docs/src/docs/asciidoc/documenting-your-api.adoc

@@ -445,6 +445,45 @@ When documenting HTTP Headers, the test will fail if a documented header is not
 the request or response.
 
 
+
+[[documenting-your-api-reusing-snippets]]
+=== Reusing snippets
+
+It's common for an API that's being documented to have some features that are common
+across several of its resources. To avoid repetition when documenting such resources a
+`Snippet` configured with the common elements can be reused.
+
+First, create the `Snippet` that describes the common elements. For example:
+
+[source,java,indent=0]
+----
+include::{examples-dir}/com/example/SnippetReuse.java[tags=field]
+----
+
+Second, use this snippet and add further descriptors that are resource-specific. For
+example:
+
+[source,java,indent=0,role="primary"]
+.MockMvc
+----
+include::{examples-dir}/com/example/mockmvc/MockMvcSnippetReuse.java[tags=use]
+----
+<1> Reuse the `pagingLinks` `Snippet` calling `and` to add descriptors that are specific
+	to the resource that is being documented.
+
+[source,java,indent=0,role="secondary"]
+.REST Assured
+----
+include::{examples-dir}/com/example/restassured/RestAssuredSnippetReuse.java[tags=use]
+----
+<1> Reuse the `pagingLinks` `Snippet` calling `and` to add descriptors that are specific
+	to the resource that is being documented.
+
+The result of the example is that links with the rels `first`, `last`, `next`, `previous`,
+`alpha`, and `bravo` are all documented.
+
+
+
 [[documenting-your-api-constraints]]
 === Documenting constraints
 

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

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2012-2016 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.hypermedia.LinksSnippet;
+
+import static org.springframework.restdocs.hypermedia.HypermediaDocumentation.linkWithRel;
+import static org.springframework.restdocs.hypermedia.HypermediaDocumentation.links;
+
+public class SnippetReuse {
+
+	// tag::field[]
+	protected final LinksSnippet pagingLinks = links(
+			linkWithRel("first").optional().description("The first page of results"),
+			linkWithRel("last").optional().description("The last page of results"),
+			linkWithRel("next").optional().description("The next page of results"),
+			linkWithRel("prev").optional().description("The previous page of results"));
+	// end::field[]
+
+}

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

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2012-2016 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.mockmvc;
+
+import com.example.SnippetReuse;
+
+import org.springframework.http.MediaType;
+import org.springframework.test.web.servlet.MockMvc;
+
+import static org.springframework.restdocs.hypermedia.HypermediaDocumentation.linkWithRel;
+import static org.springframework.restdocs.mockmvc.MockMvcRestDocumentation.document;
+import static org.springframework.restdocs.mockmvc.RestDocumentationRequestBuilders.get;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
+
+public class MockMvcSnippetReuse extends SnippetReuse {
+	
+	private MockMvc mockMvc;
+	
+	public void documentation() throws Exception {
+		// tag::use[]
+		this.mockMvc.perform(get("/").accept(MediaType.APPLICATION_JSON))
+			.andExpect(status().isOk())
+			.andDo(document("example", this.pagingLinks.and( // <1>
+					linkWithRel("alpha").description("Link to the alpha resource"),
+					linkWithRel("bravo").description("Link to the bravo resource"))));
+		// end::use[]
+	}
+
+}

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

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2012-2016 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.restassured;
+
+import com.example.SnippetReuse;
+import com.jayway.restassured.RestAssured;
+import com.jayway.restassured.specification.RequestSpecification;
+
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.springframework.restdocs.hypermedia.HypermediaDocumentation.linkWithRel;
+import static org.springframework.restdocs.restassured.RestAssuredRestDocumentation.document;
+
+public class RestAssuredSnippetReuse extends SnippetReuse {
+	
+	private RequestSpecification spec;
+	
+	public void documentation() throws Exception {
+		// tag::use[]
+		RestAssured.given(this.spec)
+			.accept("application/json")
+			.filter(document("example", this.pagingLinks.and( // <1>
+					linkWithRel("alpha").description("Link to the alpha resource"),
+					linkWithRel("bravo").description("Link to the bravo resource"))))
+			.get("/").then().assertThat().statusCode(is(200));
+		// end::use[]
+	}
+
+}