Resolve #248: support default namespace in SimpleXmlDecoder

If the namespace map contains an entry with the empty string as its key
then the URL in the value of this entry  will be added as
`xmlns="http://example.org/value-url"` to the root element.

Author: cboehme

src/main/java/org/culturegraph/mf/stream/converter/xml/SimpleXmlEncoder.java

@@ -64,7 +64,7 @@ public final class SimpleXmlEncoder extends DefaultStreamPipe<ObjectReceiver<Str
 	private static final String END_CLOSE_ELEMENT = ">";
 
 	private static final String XML_HEADER = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n";
-	private static final String XMLNS_MARKER = " xmlns:";
+	private static final String XMLNS_MARKER = " xmlns";
 
 	private final StringBuilder builder = new StringBuilder();
 
@@ -189,7 +189,10 @@ private void writeHeader() {
 		builder.append(rootTag);
 		for (final Entry<String, String> entry : namespaces.entrySet()) {
 			builder.append(XMLNS_MARKER);
-			builder.append(entry.getKey());
+			if (!entry.getKey().isEmpty()) {
+				builder.append(':');
+				builder.append(entry.getKey());
+			}
 			builder.append(BEGIN_ATTRIBUTE);
 			writeEscaped(builder, entry.getValue());
 			builder.append(END_ATTRIBUTE);

src/test/java/org/culturegraph/mf/stream/converter/xml/SimpleXmlEncoderTest.java

@@ -21,6 +21,9 @@
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 
+import java.util.HashMap;
+import java.util.Map;
+
 import org.culturegraph.mf.framework.DefaultObjectReceiver;
 import org.junit.Before;
 import org.junit.Test;
@@ -90,6 +93,30 @@ public void shouldWrapAllRecordsInOneRootTagtIfSeparateRootsIsFalse() {
 				getResultXml());
 	}
 
+	@Test
+	public void shouldAddNamespaceToRootElement() {
+		final Map<String, String> namespaces = new HashMap<String, String>();
+		namespaces.put("ns", "http://example.org/ns");
+		simpleXmlEncoder.setNamespaces(namespaces);
+
+		emitEmptyRecord();
+
+		assertEquals("<?xml version=\"1.0\" encoding=\"UTF-8\"?><records xmlns:ns=\"http://example.org/ns\"><record /></records>",
+				getResultXml());
+	}
+
+	@Test
+	public void shouldAddNamespaceWithEmptyKeyAsDefaultNamespace() {
+		final Map<String, String> namespaces = new HashMap<String, String>();
+		namespaces.put("", "http://example.org/ns");
+		simpleXmlEncoder.setNamespaces(namespaces);
+
+		emitEmptyRecord();
+
+		assertEquals("<?xml version=\"1.0\" encoding=\"UTF-8\"?><records xmlns=\"http://example.org/ns\"><record /></records>",
+				getResultXml());
+	}
+
 	private void emitTwoRecords() {
 		simpleXmlEncoder.startRecord("X");
 		simpleXmlEncoder.literal(TAG, VALUE);
@@ -100,6 +127,12 @@ private void emitTwoRecords() {
 		simpleXmlEncoder.closeStream();
 	}
 
+	private void emitEmptyRecord() {
+		simpleXmlEncoder.startRecord("");
+		simpleXmlEncoder.endRecord();
+		simpleXmlEncoder.closeStream();
+	}
+
 	private String getResultXml() {
 		return resultCollector.toString().replaceAll("[\\n\\t]", "");
 	}