Fix buffer issue when response buffering is active and a short results

deegree-services/deegree-services-commons/src/main/java/org/deegree/services/controller/utils/HttpResponseBuffer.java

@@ -315,6 +315,11 @@ public void flushBuffer() throws IOException {
 				throw new IOException(e);
 			}
 		}
+		if (printWriter != null) {
+			// NOTE flush on printWriter is required and flush() could trigger an error
+			// state if already closed. checkError() flushes stream if not closed
+			printWriter.checkError();
+		}
 		if (buffer != null) {
 			try {
 				buffer.flush();
@@ -359,7 +364,7 @@ public OutputStream getBuffer() {
 	 * This is a ServletOutputStream that uses our internal ByteArrayOutputStream to
 	 * buffer all data.
 	 */
-	private static class BufferedServletOutputStream extends ServletOutputStream {
+	static class BufferedServletOutputStream extends ServletOutputStream {
 
 		private final OutputStream buffer;
 

deegree-services/deegree-services-commons/src/test/java/org/deegree/services/controller/utils/HttpResponseBufferTest.java

@@ -0,0 +1,101 @@
+/*----------------------------------------------------------------------------
+ This file is part of deegree, http://deegree.org/
+ Copyright (C) 2001-2023 by:
+ - Department of Geography, University of Bonn -
+ and
+ - lat/lon GmbH -
+ and
+ - grit graphische Informationstechnik Beratungsgesellschaft mbH -
+
+ This library is free software; you can redistribute it and/or modify it under
+ the terms of the GNU Lesser General Public License as published by the Free
+ Software Foundation; either version 2.1 of the License, or (at your option)
+ any later version.
+ This library is distributed in the hope that it will be useful, but WITHOUT
+ ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
+ details.
+ You should have received a copy of the GNU Lesser General Public License
+ along with this library; if not, write to the Free Software Foundation, Inc.,
+ 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+
+ Contact information:
+
+ grit graphische Informationstechnik Beratungsgesellschaft mbH
+ Landwehrstr. 143, 59368 Werne
+ Germany
+ https://www.grit.de/
+
+ lat/lon GmbH
+ Aennchenstr. 19, 53177 Bonn
+ Germany
+ https://lat-lon.de/
+
+ Department of Geography, University of Bonn
+ Prof. Dr. Klaus Greve
+ Postfach 1147, 53001 Bonn
+ Germany
+ https://www.geographie.uni-bonn.de/deegree/
+
+ e-mail: info@deegree.org
+ ----------------------------------------------------------------------------*/
+package org.deegree.services.controller.utils;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.greaterThan;
+import static org.hamcrest.Matchers.is;
+import static org.hamcrest.Matchers.notNullValue;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import javax.servlet.http.HttpServletResponse;
+import javax.xml.stream.XMLStreamException;
+import org.deegree.commons.utils.io.StreamBufferStore;
+import org.junit.Test;
+import org.mockito.Mockito;
+
+public class HttpResponseBufferTest {
+
+	@Test
+	public void testPrintWriterFlushing() throws IOException {
+
+		HttpServletResponse response = mockHttpRequest();
+
+		HttpResponseBuffer buf = new HttpResponseBuffer(response, null);
+		StreamBufferStore store = (StreamBufferStore) buf.getBuffer();
+		assertThat(store, is(notNullValue()));
+		assertThat(store.size(), is(0));
+
+		buf.getWriter().write("ABC");
+		assertThat(store.size(), is(0));
+
+		buf.flushBuffer();
+		assertThat(store.size(), is(3));
+	}
+
+	@Test
+	public void testXMLWriterFlushing() throws IOException, XMLStreamException {
+
+		HttpServletResponse response = mockHttpRequest();
+
+		HttpResponseBuffer buf = new HttpResponseBuffer(response, null);
+		StreamBufferStore store = (StreamBufferStore) buf.getBuffer();
+		assertThat(store, is(notNullValue()));
+		assertThat(store.size(), is(0));
+
+		buf.getXMLWriter(); // will create a start document
+		assertThat(store.size(), is(0));
+
+		buf.flushBuffer();
+		assertThat(store.size(), is(greaterThan(0)));
+	}
+
+	private HttpServletResponse mockHttpRequest() throws IOException {
+		ByteArrayOutputStream bos = new ByteArrayOutputStream();
+
+		HttpServletResponse mock = Mockito.mock(HttpServletResponse.class);
+		Mockito.when(mock.getOutputStream()).thenReturn(new HttpResponseBuffer.BufferedServletOutputStream(bos));
+		return mock;
+	}
+
+}