Add flush method to ServerHttpResponse

This is useful to make sure response headers are written to the
underlying response. It is also useful in conjunction with long
running, async requests and HTTP streaming, to ensure the Servlet
response buffer is sent to the client without additional delay and
also causes an IOException to be raised if the client has gone away.

spring-web/src/main/java/org/springframework/http/server/AsyncServletServerHttpRequest.java

@@ -116,21 +116,35 @@ public class AsyncServletServerHttpRequest extends ServletServerHttpRequest
 	// Implementation of AsyncListener methods
 	// ---------------------------------------------------------------------
 
+	@Override
 	public void onStartAsync(AsyncEvent event) throws IOException {
 	}
 
+	@Override
 	public void onError(AsyncEvent event) throws IOException {
 	}
 
+	@Override
 	public void onTimeout(AsyncEvent event) throws IOException {
-		for (Runnable handler : this.timeoutHandlers) {
-			handler.run();
+		try {
+			for (Runnable handler : this.timeoutHandlers) {
+				handler.run();
+			}
+		}
+		catch (Throwable t) {
+			// ignore
 		}
 	}
 
+	@Override
 	public void onComplete(AsyncEvent event) throws IOException {
-		for (Runnable handler : this.completionHandlers) {
-			handler.run();
+		try {
+			for (Runnable handler : this.completionHandlers) {
+				handler.run();
+			}
+		}
+		catch (Throwable t) {
+			// ignore
 		}
 		this.asyncContext = null;
 		this.asyncCompleted.set(true);

spring-web/src/main/java/org/springframework/http/server/ServerHttpResponse.java

@@ -17,6 +17,7 @@
 package org.springframework.http.server;
 
 import java.io.Closeable;
+import java.io.IOException;
 
 import org.springframework.http.HttpOutputMessage;
 import org.springframework.http.HttpStatus;
@@ -35,6 +36,11 @@ public interface ServerHttpResponse extends HttpOutputMessage, Closeable {
 	 */
 	void setStatusCode(HttpStatus status);
 
+	/**
+	 * TODO
+	 */
+	void flush() throws IOException;
+
 	/**
 	 * Close this response, freeing any resources created.
 	 */

spring-web/src/main/java/org/springframework/http/server/ServletServerHttpResponse.java

@@ -80,6 +80,13 @@ public class ServletServerHttpResponse implements ServerHttpResponse {
 		return this.servletResponse.getOutputStream();
 	}
 
+	@Override
+	public void flush() throws IOException {
+		writeCookies();
+		writeHeaders();
+		this.servletResponse.flushBuffer();
+	}
+
 	public void close() {
 		writeCookies();
 		writeHeaders();