Add option to set Content-Length in JSON Views

MappingJackson2JsonView and MappingJacksonJsonView now provide an
option that will set the Content-Length header of JSON responses.
Use of the option implies buffering of the response and it must be
enabled explicitly.

Issue: SPR-7866

spring-webmvc/src/main/java/org/springframework/web/servlet/view/json/MappingJackson2JsonView.java

@@ -16,6 +16,8 @@
 
 package org.springframework.web.servlet.view.json;
 
+import java.io.ByteArrayOutputStream;
+import java.io.OutputStream;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
@@ -71,6 +73,7 @@ public class MappingJackson2JsonView extends AbstractView {
 
 	private boolean disableCaching = true;
 
+	private boolean updateContentLength = false;
 
 	/**
 	 * Construct a new {@code JacksonJsonView}, setting the content type to {@code application/json}.
@@ -199,6 +202,15 @@ public class MappingJackson2JsonView extends AbstractView {
 		this.disableCaching = disableCaching;
 	}
 
+	/**
+	 * Whether to update the 'Content-Length' header of the response. When set to
+	 * {@code true}, the response is buffered in order to determine the content
+	 * length and set the 'Content-Length' header of the response.
+	 * <p>The default setting is {@code false}.
+	 */
+	public void setUpdateContentLength(boolean updateContentLength) {
+		this.updateContentLength = updateContentLength;
+	}
 
 	@Override
 	protected void prepareResponse(HttpServletRequest request, HttpServletResponse response) {
@@ -215,9 +227,10 @@ public class MappingJackson2JsonView extends AbstractView {
 	protected void renderMergedOutputModel(Map<String, Object> model, HttpServletRequest request,
 			HttpServletResponse response) throws Exception {
 
+		OutputStream stream = this.updateContentLength ? createTemporaryOutputStream() : response.getOutputStream();
+
 		Object value = filterModel(model);
-		JsonGenerator generator =
-				this.objectMapper.getJsonFactory().createJsonGenerator(response.getOutputStream(), this.encoding);
+		JsonGenerator generator = this.objectMapper.getJsonFactory().createJsonGenerator(stream, this.encoding);
 
 		// A workaround for JsonGenerators not applying serialization features
 		// https://github.com/FasterXML/jackson-databind/issues/12
@@ -229,6 +242,10 @@ public class MappingJackson2JsonView extends AbstractView {
 			generator.writeRaw("{} && ");
 		}
 		this.objectMapper.writeValue(generator, value);
+
+		if (this.updateContentLength) {
+			writeToResponse(response, (ByteArrayOutputStream) stream);
+		}
 	}
 
 	/**

spring-webmvc/src/main/java/org/springframework/web/servlet/view/json/MappingJacksonJsonView.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2011 the original author or authors.
+ * Copyright 2002-2012 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.
@@ -16,6 +16,8 @@
 
 package org.springframework.web.servlet.view.json;
 
+import java.io.ByteArrayOutputStream;
+import java.io.OutputStream;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
@@ -73,6 +75,7 @@ public class MappingJacksonJsonView extends AbstractView {
 
 	private boolean disableCaching = true;
 
+	private boolean updateContentLength = false;
 
 	/**
 	 * Construct a new {@code JacksonJsonView}, setting the content type to {@code application/json}.
@@ -201,6 +204,16 @@ public class MappingJacksonJsonView extends AbstractView {
 		this.disableCaching = disableCaching;
 	}
 
+	/**
+	 * Whether to update the 'Content-Length' header of the response. When set to
+	 * {@code true}, the response is buffered in order to determine the content
+	 * length and set the 'Content-Length' header of the response.
+	 * <p>The default setting is {@code false}.
+	 */
+	public void setUpdateContentLength(boolean updateContentLength) {
+		this.updateContentLength = updateContentLength;
+	}
+
 
 	@Override
 	protected void prepareResponse(HttpServletRequest request, HttpServletResponse response) {
@@ -217,9 +230,10 @@ public class MappingJacksonJsonView extends AbstractView {
 	protected void renderMergedOutputModel(Map<String, Object> model, HttpServletRequest request,
 			HttpServletResponse response) throws Exception {
 
+		OutputStream stream = this.updateContentLength ? createTemporaryOutputStream() : response.getOutputStream();
+
 		Object value = filterModel(model);
-		JsonGenerator generator =
-				this.objectMapper.getJsonFactory().createJsonGenerator(response.getOutputStream(), this.encoding);
+		JsonGenerator generator = this.objectMapper.getJsonFactory().createJsonGenerator(stream, this.encoding);
 
 		// A workaround for JsonGenerators not applying serialization features
 		// https://github.com/FasterXML/jackson-databind/issues/12
@@ -231,6 +245,10 @@ public class MappingJacksonJsonView extends AbstractView {
 			generator.writeRaw("{} && ");
 		}
 		this.objectMapper.writeValue(generator, value);
+
+		if (this.updateContentLength) {
+			writeToResponse(response, (ByteArrayOutputStream) stream);
+		}
 	}
 
 	/**

spring-webmvc/src/test/java/org/springframework/web/servlet/view/json/MappingJackson2JsonViewTests.java

@@ -59,7 +59,7 @@ import com.fasterxml.jackson.databind.ser.Serializers;
  * @author Arjen Poutsma
  * @author Rossen Stoyanchev
  */
-public class MappingJackson2JsonViewTest {
+public class MappingJackson2JsonViewTests {
 
 	private MappingJackson2JsonView view;
 
@@ -94,6 +94,7 @@ public class MappingJackson2JsonViewTest {
 		model.put("bindingResult", createMock("binding_result", BindingResult.class));
 		model.put("foo", "bar");
 
+		view.setUpdateContentLength(true);
 		view.render(model, request, response);
 
 		assertEquals("no-cache", response.getHeader("Pragma"));
@@ -104,6 +105,7 @@ public class MappingJackson2JsonViewTest {
 
 		String jsonResult = response.getContentAsString();
 		assertTrue(jsonResult.length() > 0);
+		assertEquals(jsonResult.length(), response.getContentLength());
 
 		validateResult();
 	}
@@ -137,9 +139,11 @@ public class MappingJackson2JsonViewTest {
 		model.put("bindingResult", createMock("binding_result", BindingResult.class));
 		model.put("foo", bean);
 
+		view.setUpdateContentLength(true);
 		view.render(model, request, response);
 
 		assertTrue(response.getContentAsString().length() > 0);
+		assertEquals(response.getContentAsString().length(), response.getContentLength());
 
 		validateResult();
 	}

spring-webmvc/src/test/java/org/springframework/web/servlet/view/json/MappingJacksonJsonViewTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2010 the original author or authors.
+ * Copyright 2002-2012 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.
@@ -52,7 +52,7 @@ import org.springframework.validation.BindingResult;
  * @author Jeremy Grelle
  * @author Arjen Poutsma
  */
-public class MappingJacksonJsonViewTest {
+public class MappingJacksonJsonViewTests {
 
 	private MappingJacksonJsonView view;
 
@@ -87,6 +87,7 @@ public class MappingJacksonJsonViewTest {
 		model.put("bindingResult", createMock("binding_result", BindingResult.class));
 		model.put("foo", "bar");
 
+		view.setUpdateContentLength(true);
 		view.render(model, request, response);
 
 		assertEquals("no-cache", response.getHeader("Pragma"));
@@ -97,6 +98,7 @@ public class MappingJacksonJsonViewTest {
 
 		String jsonResult = response.getContentAsString();
 		assertTrue(jsonResult.length() > 0);
+		assertEquals(jsonResult.length(), response.getContentLength());
 
 		validateResult();
 	}
@@ -130,9 +132,11 @@ public class MappingJacksonJsonViewTest {
 		model.put("bindingResult", createMock("binding_result", BindingResult.class));
 		model.put("foo", bean);
 
+		view.setUpdateContentLength(true);
 		view.render(model, request, response);
 
 		assertTrue(response.getContentAsString().length() > 0);
+		assertEquals(response.getContentAsString().length(), response.getContentLength());
 
 		validateResult();
 	}

src/dist/changelog.txt

@@ -25,7 +25,8 @@ Changes in version 3.2 M1
 * support access to all URI vars via @PathVariable Map<String, String>
 * add "excludedExceptions" property to SimpleUrlHandlerMapping
 * add CompositeRequestCondition for use with multiple custom request mapping conditions
-* add option to configure custom MessageCodesResolver through WebMvcConfigurer
+* add ability to configure custom MessageCodesResolver through the MVC Java config
+* add option in MappingJacksonJsonView for setting the Content-Length header
 
 Changes in version 3.1.1 (2012-02-16)
 -------------------------------------