Polish "Add support for documenting request part payload fields"

- Rebase on latest code, and make use of new support for the same
  TemplatedSnippet producing multiple snippets with different names
  from the same template
- Expand the documentation
- Apply code formatting
- Add support for relaxed documentation of a request part's fields

Closes gh-270

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

@@ -0,0 +1,48 @@
+/*
+ * 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.mockmvc;
+
+import org.springframework.http.MediaType;
+import org.springframework.mock.web.MockMultipartFile;
+import org.springframework.test.web.servlet.MockMvc;
+
+import static org.springframework.restdocs.mockmvc.MockMvcRestDocumentation.document;
+import static org.springframework.restdocs.mockmvc.RestDocumentationRequestBuilders.fileUpload;
+import static org.springframework.restdocs.payload.PayloadDocumentation.fieldWithPath;
+import static org.springframework.restdocs.payload.PayloadDocumentation.requestPartFields;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
+
+public class RequestPartPayload {
+
+	private MockMvc mockMvc;
+
+	public void response() throws Exception {
+		// tag::payload[]
+		MockMultipartFile image = new MockMultipartFile("image", "image.png", "image/png",
+				"<<png data>>".getBytes());
+		MockMultipartFile metadata = new MockMultipartFile("metadata", "",
+				"application/json", "{ \"version\": \"1.0\"}".getBytes());
+
+		this.mockMvc.perform(fileUpload("/images").file(image).file(metadata)
+					.accept(MediaType.APPLICATION_JSON))
+			.andExpect(status().isOk())
+			.andDo(document("image-upload", requestPartFields("metadata", // <1>
+					fieldWithPath("version").description("The version of the image")))); // <2>
+		// end::payload[]
+	}
+
+}

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

@@ -0,0 +1,48 @@
+/*
+ * 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.restassured;
+
+import java.io.File;
+import java.util.HashMap;
+import java.util.Map;
+
+import com.jayway.restassured.RestAssured;
+import com.jayway.restassured.specification.RequestSpecification;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.springframework.restdocs.payload.PayloadDocumentation.fieldWithPath;
+import static org.springframework.restdocs.payload.PayloadDocumentation.requestPartFields;
+import static org.springframework.restdocs.restassured.RestAssuredRestDocumentation.document;
+
+public class RequestPartPayload {
+
+	private RequestSpecification spec;
+
+	public void response() throws Exception {
+		// tag::payload[]
+		Map<String, String> metadata = new HashMap<>();
+		metadata.put("version", "1.0");
+		RestAssured.given(this.spec).accept("application/json")
+			.filter(document("image-upload", requestPartFields("metadata", // <1>
+					fieldWithPath("version").description("The version of the image")))) // <2>
+			.when().multiPart("image", new File("image.png"), "image/png")
+					.multiPart("metadata", metadata).post("images")
+			.then().assertThat().statusCode(is(200));
+		// end::payload[]
+	}
+
+}