Fix using system default charset in view rendering

Prior to this commit, FreeMarkerView used the system default charset to
render. This commit switches this by defaulting to UTF-8, if no charset
is specified in the content type.

 - Add contentType parameter to AbstractView.renderInternal, used to
 determine the charset contained therein
 - Adds a defaultCharset property to AbstractView and
 ViewResolverSupport.

spring-web-reactive/src/main/java/org/springframework/web/reactive/result/view/AbstractView.java

@@ -16,6 +16,8 @@
 
 package org.springframework.web.reactive.result.view;
 
+import java.nio.charset.Charset;
+import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.LinkedHashMap;
 import java.util.List;
@@ -45,6 +47,8 @@ public abstract class AbstractView implements View, ApplicationContextAware {
 
 	private final List<MediaType> mediaTypes = new ArrayList<>(4);
 
+	private Charset defaultCharset = StandardCharsets.UTF_8;
+
 	private ApplicationContext applicationContext;
 
 
@@ -73,6 +77,24 @@ public abstract class AbstractView implements View, ApplicationContextAware {
 		return this.mediaTypes;
 	}
 
+	/**
+	 * Set the default charset for this view, used when the
+	 * {@linkplain #setSupportedMediaTypes(List) content type} does not contain one.
+	 * Default is {@linkplain StandardCharsets#UTF_8 UTF 8}.
+	 */
+	public void setDefaultCharset(Charset defaultCharset) {
+		Assert.notNull(defaultCharset, "'defaultCharset' must not be null");
+		this.defaultCharset = defaultCharset;
+	}
+
+	/**
+	 * Return the default charset, used when the
+	 * {@linkplain #setSupportedMediaTypes(List) content type} does not contain one.
+	 */
+	public Charset getDefaultCharset() {
+		return this.defaultCharset;
+	}
+
 	@Override
 	public void setApplicationContext(ApplicationContext applicationContext) {
 		this.applicationContext = applicationContext;
@@ -104,7 +126,7 @@ public abstract class AbstractView implements View, ApplicationContextAware {
 		}
 
 		Map<String, Object> mergedModel = getModelAttributes(model, exchange);
-		return renderInternal(mergedModel, exchange);
+		return renderInternal(mergedModel, contentType, exchange);
 	}
 
 	/**
@@ -127,11 +149,12 @@ public abstract class AbstractView implements View, ApplicationContextAware {
 	 * Subclasses must implement this method to actually render the view.
 	 * @param renderAttributes combined output Map (never {@code null}),
 	 * with dynamic values taking precedence over static attributes
-	 * @param exchange current exchange
-	 * @return {@code Mono} to represent when and if rendering succeeds
+	 * @param contentType the content type selected to render with which should
+	 * match one of the {@link #getSupportedMediaTypes() supported media types}.
+	 *@param exchange current exchange  @return {@code Mono} to represent when and if rendering succeeds
 	 */
 	protected abstract Mono<Void> renderInternal(Map<String, Object> renderAttributes,
-			ServerWebExchange exchange);
+			MediaType contentType, ServerWebExchange exchange);
 
 
 	@Override

spring-web-reactive/src/main/java/org/springframework/web/reactive/result/view/UrlBasedViewResolver.java

@@ -13,6 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 package org.springframework.web.reactive.result.view;
 
 import java.util.Locale;
@@ -194,6 +195,7 @@ public class UrlBasedViewResolver extends ViewResolverSupport implements ViewRes
 	protected AbstractUrlBasedView createUrlBasedView(String viewName) {
 		AbstractUrlBasedView view = (AbstractUrlBasedView) BeanUtils.instantiateClass(getViewClass());
 		view.setSupportedMediaTypes(getSupportedMediaTypes());
+		view.setDefaultCharset(getDefaultCharset());
 		view.setUrl(getPrefix() + viewName + getSuffix());
 		return view;
 	}

spring-web-reactive/src/main/java/org/springframework/web/reactive/result/view/ViewResolverSupport.java

@@ -16,6 +16,8 @@
 
 package org.springframework.web.reactive.result.view;
 
+import java.nio.charset.Charset;
+import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.List;
 
@@ -38,6 +40,8 @@ public abstract class ViewResolverSupport implements ApplicationContextAware, Or
 
 	private List<MediaType> mediaTypes = new ArrayList<>(4);
 
+	private Charset defaultCharset = StandardCharsets.UTF_8;
+
 	private ApplicationContext applicationContext;
 
 	private int order = Integer.MAX_VALUE;
@@ -67,6 +71,25 @@ public abstract class ViewResolverSupport implements ApplicationContextAware, Or
 		return this.mediaTypes;
 	}
 
+	/**
+	 * Set the default charset for this view, used when the
+	 * {@linkplain #setSupportedMediaTypes(List) content type} does not contain one.
+	 * Default is {@linkplain StandardCharsets#UTF_8 UTF 8}.
+	 */
+	public void setDefaultCharset(Charset defaultCharset) {
+		Assert.notNull(defaultCharset, "'defaultCharset' must not be null");
+		this.defaultCharset = defaultCharset;
+	}
+
+	/**
+	 * Return the default charset, used when the
+	 * {@linkplain #setSupportedMediaTypes(List) content type} does not contain one.
+	 */
+	public Charset getDefaultCharset() {
+		return this.defaultCharset;
+	}
+
+
 	@Override
 	public void setApplicationContext(ApplicationContext applicationContext) {
 		this.applicationContext = applicationContext;

spring-web-reactive/src/main/java/org/springframework/web/reactive/result/view/freemarker/FreeMarkerView.java

@@ -13,14 +13,17 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 package org.springframework.web.reactive.result.view.freemarker;
 
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.OutputStreamWriter;
 import java.io.Writer;
+import java.nio.charset.Charset;
 import java.util.Locale;
 import java.util.Map;
+import java.util.Optional;
 
 import freemarker.core.ParseException;
 import freemarker.template.Configuration;
@@ -37,6 +40,7 @@ import org.springframework.beans.factory.BeanFactoryUtils;
 import org.springframework.beans.factory.NoSuchBeanDefinitionException;
 import org.springframework.context.ApplicationContextException;
 import org.springframework.core.io.buffer.DataBuffer;
+import org.springframework.http.MediaType;
 import org.springframework.web.reactive.result.view.AbstractUrlBasedView;
 import org.springframework.web.server.ServerWebExchange;
 
@@ -158,7 +162,8 @@ public class FreeMarkerView extends AbstractUrlBasedView {
 	}
 
 	@Override
-	protected Mono<Void> renderInternal(Map<String, Object> renderAttributes, ServerWebExchange exchange) {
+	protected Mono<Void> renderInternal(Map<String, Object> renderAttributes, MediaType contentType,
+			ServerWebExchange exchange) {
 		// Expose all standard FreeMarker hash models.
 		SimpleHash freeMarkerModel = getTemplateModel(renderAttributes, exchange);
 		if (logger.isDebugEnabled()) {
@@ -167,8 +172,8 @@ public class FreeMarkerView extends AbstractUrlBasedView {
 		Locale locale = Locale.getDefault(); // TODO
 		DataBuffer dataBuffer = exchange.getResponse().bufferFactory().allocateBuffer();
 		try {
-			// TODO: pass charset
-			Writer writer = new OutputStreamWriter(dataBuffer.asOutputStream());
+			Charset charset = getCharset(contentType).orElse(getDefaultCharset());
+			Writer writer = new OutputStreamWriter(dataBuffer.asOutputStream(), charset);
 			getTemplate(locale).process(freeMarkerModel, writer);
 		}
 		catch (IOException ex) {
@@ -181,6 +186,10 @@ public class FreeMarkerView extends AbstractUrlBasedView {
 		return exchange.getResponse().writeWith(Flux.just(dataBuffer));
 	}
 
+	private static Optional<Charset> getCharset(MediaType mediaType) {
+		return mediaType != null ? Optional.ofNullable(mediaType.getCharset()) : Optional.empty();
+	}
+
 	/**
 	 * Build a FreeMarker template model for the given model Map.
 	 * <p>The default implementation builds a {@link SimpleHash}.

spring-web-reactive/src/test/java/org/springframework/web/reactive/result/view/UrlBasedViewResolverTests.java

@@ -13,6 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 package org.springframework.web.reactive.result.view;
 
 import java.util.Locale;
@@ -22,6 +23,7 @@ import org.junit.Test;
 import reactor.core.publisher.Mono;
 
 import org.springframework.context.support.StaticApplicationContext;
+import org.springframework.http.MediaType;
 import org.springframework.web.server.ServerWebExchange;
 
 import static org.junit.Assert.assertNotNull;
@@ -61,7 +63,8 @@ public class UrlBasedViewResolverTests {
 		}
 
 		@Override
-		protected Mono<Void> renderInternal(Map<String, Object> attributes, ServerWebExchange exchange) {
+		protected Mono<Void> renderInternal(Map<String, Object> attributes, MediaType contentType,
+				ServerWebExchange exchange) {
 			return Mono.empty();
 		}
 	}