svggen: customizable serialization in SVGGraphics2D (#132)

Some people have complained that the SVG output by Batik's `SVGGraphics2D` is ugly or too big, see BATIK-502 or BATIK-1337. This commit introduces:

- A public serializer that has general validity.
- A new `XmlSerializer` interface that can be used to customize the serialization. Its default methods mimic what the previous code did.
- A `CompactXmlSerializer` implementation which significantly decreases the size of the output files.
- Methods for setting and getting a custom serializer to `SVGGeneratorContext`.

Author: carlosame

echosvg-svggen/src/main/java/io/sf/carte/echosvg/svggen/CompactXmlSerializer.java

@@ -0,0 +1,92 @@
+/*
+
+   See the NOTICE file distributed with this work for additional
+   information regarding copyright ownership.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+
+package io.sf.carte.echosvg.svggen;
+
+import java.io.IOException;
+import java.io.Writer;
+
+import org.w3c.dom.DocumentType;
+import org.w3c.dom.Node;
+
+/**
+ * Compact SVG serialization.
+ */
+public class CompactXmlSerializer implements XmlSerializer {
+
+	@Override
+	public void serializeXML(Node node, Writer writer, boolean escaped)
+			throws IOException, SVGGraphics2DRuntimeException {
+		XmlWriter.IndentWriter iwriter = new XmlWriter.IndentWriter(writer) {
+
+			@Override
+			public void printIndent() throws IOException {
+			}
+
+		};
+
+		XmlWriter xmlWri = new XmlWriter(iwriter, escaped) {
+
+			@Override
+			protected void writeXml(DocumentType docType) throws IOException {
+				IndentWriter out = getWriter();
+				out.write("<!DOCTYPE ");
+				out.write(docType.getName());
+
+				String publicId = docType.getPublicId();
+				if (publicId != null) {
+					out.write(" PUBLIC '");
+					out.write(publicId);
+					out.write('\'');
+				}
+
+				String systemId = docType.getSystemId();
+				if (systemId != null) {
+					out.write(" '");
+					out.write(systemId);
+					out.write('\'');
+				}
+
+				out.write('>');
+			}
+
+		};
+
+		xmlWri.writeXml(node);
+	}
+
+	@Override
+	public void writeDocumentType(Writer out, String name, String publicId, String systemId)
+			throws IOException {
+		out.write("<!DOCTYPE ");
+		out.write(name);
+		if (publicId != null) {
+			out.write(" PUBLIC '");
+			out.write(publicId);
+			out.write('\'');
+		}
+		if (systemId != null) {
+			out.write(" '");
+			out.write(systemId);
+			out.write('\'');
+		}
+		out.write('>');
+	}
+
+}

echosvg-svggen/src/main/java/io/sf/carte/echosvg/svggen/ErrorConstants.java

@@ -46,7 +46,7 @@ public interface ErrorConstants {
 	String ERR_ACI = "AttributedCharacterIterator not supported yet";
 
 	// XmlWriter
-	String ERR_PROXY = "proxy should not be null";
+	String ERR_WRITER = "Writer should not be null";
 	String INVALID_NODE = "Unable to write node of type ";
 
 	// DOMGroup/TreeManager

echosvg-svggen/src/main/java/io/sf/carte/echosvg/svggen/SVGGeneratorContext.java

@@ -117,6 +117,8 @@ public class SVGGeneratorContext implements ErrorConstants {
 	 */
 	private Integer compressionLevel = null;
 
+	private XmlSerializer xmlSerializer = null;
+
 	/**
 	 * Class to describe the GraphicContext defaults to be used. Note that this
 	 * class does *not* contain a default for the initial transform, as this
@@ -473,4 +475,23 @@ public final String doubleString(double value) {
 		}
 	}
 
+	/**
+	 * Get the object to use in SVG serialization.
+	 * 
+	 * @return the SVG serializer, or {@code null} if the default should be used.
+	 */
+	public XmlSerializer getXmlSerializer() {
+		return xmlSerializer;
+	}
+
+	/**
+	 * Set the object to use in SVG serialization.
+	 * 
+	 * @param xmlSerializer the SVG serializer, or {@code null} if the default
+	 *                      should be used.
+	 */
+	public void setXmlSerializer(XmlSerializer xmlSerializer) {
+		this.xmlSerializer = xmlSerializer;
+	}
+
 }

echosvg-svggen/src/main/java/io/sf/carte/echosvg/svggen/SVGGraphics2D.java

@@ -448,15 +448,31 @@ public void stream(Element svgRoot, Writer writer, boolean useCss, boolean escap
 			//
 			svgRoot.setAttributeNS(XMLNS_NAMESPACE_URI, XMLNS_PREFIX, SVG_NAMESPACE_URI);
 
-			svgRoot.setAttributeNS(XMLNS_NAMESPACE_URI, XMLNS_PREFIX + ":" + XLINK_PREFIX, XLINK_NAMESPACE_URI);
+			svgRoot.setAttributeNS(XMLNS_NAMESPACE_URI, XMLNS_PREFIX + ":" + XLINK_PREFIX,
+					XLINK_NAMESPACE_URI);
 
 			DocumentFragment svgDocument = svgRoot.getOwnerDocument().createDocumentFragment();
 			svgDocument.appendChild(svgRoot);
 
-			if (useCss)
+			if (useCss) {
 				SVGCSSStyler.style(svgDocument);
+			}
+
+			XmlSerializer xmlWri = getGeneratorContext().getXmlSerializer();
+
+			if (xmlWri == null) {
+				xmlWri = new XmlSerializer() {
+				};
+			}
+
+			// <?xml version="1.0" encoding="..."?>
+			// Should end with a newline so the serializer starts at column 1
+			writeDocumentHeader(writer);
+
+			// Write DOCTYPE declaration here.
+			xmlWri.writeDocumentType(writer, SVG_SVG_TAG, SVG_PUBLIC_ID, SVG_SYSTEM_ID);
+			xmlWri.serializeXML(svgDocument, writer, escaped);
 
-			XmlWriter.writeXml(svgDocument, writer, escaped);
 			writer.flush();
 		} catch (SVGGraphics2DIOException e) {
 			// this catch prevents from catching an SVGGraphics2DIOException
@@ -466,6 +482,12 @@ public void stream(Element svgRoot, Writer writer, boolean useCss, boolean escap
 			generatorCtx.getErrorHandler().handleError(e);
 		} catch (IOException io) {
 			generatorCtx.getErrorHandler().handleError(new SVGGraphics2DIOException(io));
+		} catch (SVGGraphics2DRuntimeException e) {
+			// this catch prevents from catching an SVGGraphics2DRuntimeException
+			// and wrapping it again in another SVGGraphics2DRuntimeException
+			generatorCtx.getErrorHandler().handleError(e);
+		} catch (RuntimeException e) {
+			generatorCtx.getErrorHandler().handleError(new SVGGraphics2DRuntimeException(e));
 		} finally {
 			// Restore the svgRoot to its original tree position
 			if (rootParent != null) {
@@ -478,6 +500,17 @@ public void stream(Element svgRoot, Writer writer, boolean useCss, boolean escap
 		}
 	}
 
+	private void writeDocumentHeader(Writer out) throws IOException {
+		String encoding = null;
+
+		if (out instanceof OutputStreamWriter) {
+			OutputStreamWriter osw = (OutputStreamWriter) out;
+			encoding = XmlWriter.java2std(osw.getEncoding());
+		}
+
+		XmlWriter.writeXmlHeader(out, encoding);
+	}
+
 	/**
 	 * Invoking this method will return a set of definition element that contain all
 	 * the definitions referenced by the attributes generated by the various

echosvg-svggen/src/main/java/io/sf/carte/echosvg/svggen/XmlSerializer.java

@@ -0,0 +1,72 @@
+/*
+
+   See the NOTICE file distributed with this work for additional
+   information regarding copyright ownership.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+ */
+
+package io.sf.carte.echosvg.svggen;
+
+import java.io.IOException;
+import java.io.Writer;
+
+import org.w3c.dom.Node;
+
+/**
+ * XML serializer.
+ * 
+ * <p>
+ * Implementations should be able to correctly serialize SVG.
+ * </p>
+ */
+public interface XmlSerializer {
+
+	/**
+	 * Serialize the given XML node to the given writer.
+	 * <p>
+	 * Callers of this method should catch {@code RuntimeException} in addition to
+	 * the {@link SVGGraphics2DRuntimeException}.
+	 * </p>
+	 * 
+	 * @param node    the node to serialize.
+	 * @param writer  the writer to write the serialization output.
+	 * @param escaped defines if the characters in Text nodes and attribute values
+	 *                should be escaped.
+	 * @throws IOException                   if an I/O error occurs.
+	 * @throws SVGGraphics2DRuntimeException or other runtime exception if the node
+	 *                                       hierarchy is inconsistent or contains
+	 *                                       unknown nodes.
+	 */
+	default void serializeXML(Node node, Writer writer, boolean escaped)
+			throws IOException, SVGGraphics2DRuntimeException {
+		XmlWriter xmlWri = new XmlWriter(writer, escaped);
+		xmlWri.writeXml(node);
+	}
+
+	/**
+	 * Serialize a document type with the given identifiers.
+	 * 
+	 * @param writer   the writer to write the serialization output.
+	 * @param name     the document type name.
+	 * @param publicId the public identifier, or {@code null} if none.
+	 * @param systemId the system identifier, or {@code null} if none.
+	 * @throws IOException if an I/O error occurs.
+	 */
+	default void writeDocumentType(Writer writer, String name, String publicId, String systemId)
+			throws IOException {
+		XmlWriter.writeDocumentType(writer, name, publicId, systemId);
+	}
+
+}