MappingJackson(2)JsonView allows subclasses to access the ObjectMapper and to override content writing

Issue: SPR-7619

Author: jhoeller

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2013 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.
@@ -17,6 +17,7 @@
 package org.springframework.web.servlet.view.json;
 
 import java.io.ByteArrayOutputStream;
+import java.io.IOException;
 import java.io.OutputStream;
 import java.util.Collections;
 import java.util.HashMap;
@@ -27,7 +28,6 @@
 
 import com.fasterxml.jackson.core.JsonEncoding;
 import com.fasterxml.jackson.core.JsonGenerator;
-import com.fasterxml.jackson.core.util.DefaultPrettyPrinter;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.SerializationFeature;
 
@@ -48,13 +48,15 @@
  * @author Jeremy Grelle
  * @author Arjen Poutsma
  * @author Rossen Stoyanchev
+ * @author Juergen Hoeller
  * @since 3.1.2
  * @see org.springframework.http.converter.json.MappingJackson2HttpMessageConverter
  */
 public class MappingJackson2JsonView extends AbstractView {
 
 	/**
-	 * Default content type. Overridable as bean property.
+	 * Default content type: "application/json".
+	 * Overridable through {@link #setContentType}.
 	 */
 	public static final String DEFAULT_CONTENT_TYPE = "application/json";
 
@@ -75,8 +77,9 @@ public class MappingJackson2JsonView extends AbstractView {
 
 	private boolean updateContentLength = false;
 
+
 	/**
-	 * Construct a new {@code JacksonJsonView}, setting the content type to {@code application/json}.
+	 * Construct a new {@code MappingJackson2JsonView}, setting the content type to {@code application/json}.
 	 */
 	public MappingJackson2JsonView() {
 		setContentType(DEFAULT_CONTENT_TYPE);
@@ -85,38 +88,44 @@ public MappingJackson2JsonView() {
 
 
 	/**
-	 * Sets the {@code ObjectMapper} for this view.
-	 * If not set, a default {@link ObjectMapper#ObjectMapper() ObjectMapper} is used.
-	 * <p>Setting a custom-configured {@code ObjectMapper} is one way to take further control
-	 * of the JSON serialization process. For example, an extended {@code SerializerFactory}
-	 * can be configured that provides custom serializers for specific types. The other option
-	 * for refining the serialization process is to use Jackson's provided annotations on the
-	 * types to be serialized, in which case a custom-configured ObjectMapper is unnecessary.
+	 * Set the {@code ObjectMapper} for this view.
+	 * If not set, a default {@link ObjectMapper#ObjectMapper() ObjectMapper} will be used.
+	 * <p>Setting a custom-configured {@code ObjectMapper} is one way to take further control of
+	 * the JSON serialization process. The other option is to use Jackson's provided annotations
+	 * on the types to be serialized, in which case a custom-configured ObjectMapper is unnecessary.
 	 */
 	public void setObjectMapper(ObjectMapper objectMapper) {
 		Assert.notNull(objectMapper, "'objectMapper' must not be null");
 		this.objectMapper = objectMapper;
 		configurePrettyPrint();
 	}
 
-	private void configurePrettyPrint() {
-		if (this.prettyPrint != null) {
-			this.objectMapper.configure(SerializationFeature.INDENT_OUTPUT, this.prettyPrint);
-		}
+	/**
+	 * Return the {@code ObjectMapper} for this view.
+	 */
+	public final ObjectMapper getObjectMapper() {
+		return this.objectMapper;
 	}
 
 	/**
-	 * Set the {@code JsonEncoding} for this converter.
+	 * Set the {@code JsonEncoding} for this view.
 	 * By default, {@linkplain JsonEncoding#UTF8 UTF-8} is used.
 	 */
 	public void setEncoding(JsonEncoding encoding) {
 		Assert.notNull(encoding, "'encoding' must not be null");
 		this.encoding = encoding;
 	}
 
+	/**
+	 * Return the {@code JsonEncoding} for this view.
+	 */
+	public final JsonEncoding getEncoding() {
+		return this.encoding;
+	}
+
 	/**
 	 * Indicates whether the JSON output by this view should be prefixed with <tt>"{} && "</tt>.
-	 * Default is false.
+	 * Default is {@code false}.
 	 * <p>Prefixing the JSON string in this manner is used to help prevent JSON Hijacking.
 	 * The prefix renders the string syntactically invalid as a script so that it cannot be hijacked.
 	 * This prefix does not affect the evaluation of JSON, but if JSON validation is performed
@@ -127,12 +136,11 @@ public void setPrefixJson(boolean prefixJson) {
 	}
 
 	/**
-	 * Whether to use the {@link DefaultPrettyPrinter} when writing JSON.
+	 * Whether to use the default pretty printer when writing JSON.
 	 * This is a shortcut for setting up an {@code ObjectMapper} as follows:
 	 * <pre>
 	 * ObjectMapper mapper = new ObjectMapper();
 	 * mapper.configure(SerializationFeature.INDENT_OUTPUT, true);
-	 * converter.setObjectMapper(mapper);
 	 * </pre>
 	 * <p>The default value is {@code false}.
 	 */
@@ -141,6 +149,12 @@ public void setPrettyPrint(boolean prettyPrint) {
 		configurePrettyPrint();
 	}
 
+	private void configurePrettyPrint() {
+		if (this.prettyPrint != null) {
+			this.objectMapper.configure(SerializationFeature.INDENT_OUTPUT, this.prettyPrint);
+		}
+	}
+
 	/**
 	 * Set the attribute in the model that should be rendered by this view.
 	 * When set, all other model attributes will be ignored.
@@ -160,7 +174,7 @@ public void setModelKeys(Set<String> modelKeys) {
 	/**
 	 * Return the attributes in the model that should be rendered by this view.
 	 */
-	public Set<String> getModelKeys() {
+	public final Set<String> getModelKeys() {
 		return this.modelKeys;
 	}
 
@@ -179,7 +193,7 @@ public void setRenderedAttributes(Set<String> renderedAttributes) {
 	 * @deprecated use {@link #getModelKeys()} instead
 	 */
 	@Deprecated
-	public Set<String> getRenderedAttributes() {
+	public final Set<String> getRenderedAttributes() {
 		return this.modelKeys;
 	}
 
@@ -212,6 +226,7 @@ public void setUpdateContentLength(boolean updateContentLength) {
 		this.updateContentLength = updateContentLength;
 	}
 
+
 	@Override
 	protected void prepareResponse(HttpServletRequest request, HttpServletResponse response) {
 		setResponseContentType(request, response);
@@ -227,34 +242,21 @@ protected void prepareResponse(HttpServletRequest request, HttpServletResponse r
 	protected void renderMergedOutputModel(Map<String, Object> model, HttpServletRequest request,
 			HttpServletResponse response) throws Exception {
 
-		OutputStream stream = this.updateContentLength ? createTemporaryOutputStream() : response.getOutputStream();
-
+		OutputStream stream = (this.updateContentLength ? createTemporaryOutputStream() : response.getOutputStream());
 		Object value = filterModel(model);
-		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
-		if (this.objectMapper.isEnabled(SerializationFeature.INDENT_OUTPUT)) {
-			generator.useDefaultPrettyPrinter();
-		}
-
-		if (this.prefixJson) {
-			generator.writeRaw("{} && ");
-		}
-		this.objectMapper.writeValue(generator, value);
-
+		writeContent(stream, value, this.prefixJson);
 		if (this.updateContentLength) {
 			writeToResponse(response, (ByteArrayOutputStream) stream);
 		}
 	}
 
 	/**
-	 * Filters out undesired attributes from the given model.
+	 * Filter out undesired attributes from the given model.
 	 * The return value can be either another {@link Map} or a single value object.
 	 * <p>The default implementation removes {@link BindingResult} instances and entries
 	 * not included in the {@link #setRenderedAttributes renderedAttributes} property.
 	 * @param model the model, as passed on to {@link #renderMergedOutputModel}
-	 * @return the object to be rendered
+	 * @return the value to be rendered
 	 */
 	protected Object filterModel(Map<String, Object> model) {
 		Map<String, Object> result = new HashMap<String, Object>(model.size());
@@ -267,4 +269,27 @@ protected Object filterModel(Map<String, Object> model) {
 		return (this.extractValueFromSingleKeyModel && result.size() == 1 ? result.values().iterator().next() : result);
 	}
 
+	/**
+	 * Write the actual JSON content to the stream.
+	 * @param stream the output stream to use
+	 * @param value the value to be rendered, as returned from {@link #filterModel}
+	 * @param prefixJson whether the JSON output by this view should be prefixed
+	 * with <tt>"{} && "</tt> (as indicated through {@link #setPrefixJson})
+	 * @throws IOException if writing failed
+	 */
+	protected void writeContent(OutputStream stream, Object value, boolean prefixJson) throws IOException {
+		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
+		if (this.objectMapper.isEnabled(SerializationFeature.INDENT_OUTPUT)) {
+			generator.useDefaultPrettyPrinter();
+		}
+
+		if (prefixJson) {
+			generator.writeRaw("{} && ");
+		}
+		this.objectMapper.writeValue(generator, value);
+	}
+
 }