概观

使用Apache Batik加载和解析SVG文件.该解决方案在将SVG文件转换为MetaPost的初步阶段显示Java代码.这应该提供有关如何使用Java从SVG文件加载,解析和提取内容的一般概念.

图书馆

您将需要以下库：

batik-anim.jar

batik-awt-util.jar

batik-bridge.jar

batik-css.jar

batik-dom.jar

batik-ext.jar

batik-gvt.jar

batik-parser.jar

batik-script.jar

batik-svg-dom.jar

batik-svggen.jar

batik-util.jar

batik-xml.jar

xml-apis-ext.jar

加载SVG文件

主应用程序将SVG文件加载到DOM中,然后将DOM转换为SVG DOM. initSVGDOM()方法调用非常重要.在不调用initSVGDOM()的情况下,从DOM中提取SVG DOM元素的方法将不可用.

import java.io.File;

import java.io.IOException;

import java.net.URI;

import org.apache.batik.bridge.BridgeContext;

import org.apache.batik.bridge.DocumentLoader;

import org.apache.batik.bridge.GVTBuilder;

import org.apache.batik.bridge.UserAgent;

import org.apache.batik.bridge.UserAgentAdapter;

import org.apache.batik.dom.svg.SAXSVGDocumentFactory;

import org.apache.batik.dom.svg.SVGOMSVGElement;

import org.apache.batik.util.XMLResourceDescriptor;

import org.w3c.dom.Document;

import org.w3c.dom.NodeList;

/**

* Responsible for converting all SVG path elements into MetaPost curves.

*/

public class SVGMetaPost {

private static final String PATH_ELEMENT_NAME = "path";

private Document svgDocument;

/**

* Creates an SVG Document given a URI.

*

* @param uri Path to the file.

* @throws Exception Something went wrong parsing the SVG file.

*/

public SVGMetaPost( String uri ) throws IOException {

setSVGDocument( createSVGDocument( uri ) );

}

/**

* Finds all the path nodes and converts them to MetaPost code.

*/

public void run() {

NodeList pathNodes = getPathElements();

int pathNodeCount = pathNodes.getLength();

for( int iPathNode = 0; iPathNode < pathNodeCount; iPathNode++ ) {

MetaPostPath mpp = new MetaPostPath( pathNodes.item( iPathNode ) );

System.out.println( mpp.toCode() );

}

}

/**

* Returns a list of elements in the SVG document with names that

* match PATH_ELEMENT_NAME.

*

* @return The list of "path" elements in the SVG document.

*/

private NodeList getPathElements() {

return getSVGDocumentRoot().getElementsByTagName( PATH_ELEMENT_NAME );

}

/**

* Returns an SVGOMSVGElement that is the document's root element.

*

* @return The SVG document typecast into an SVGOMSVGElement.

*/

private SVGOMSVGElement getSVGDocumentRoot() {

return (SVGOMSVGElement)getSVGDocument().getDocumentElement();

}

/**

* This will set the document to parse. This method also initializes

* the SVG DOM enhancements, which are necessary to perform SVG and CSS

* manipulations. The initialization is also required to extract information

* from the SVG path elements.

*

* @param document The document that contains SVG content.

*/

public void setSVGDocument( Document document ) {

initSVGDOM( document );

this.svgDocument = document;

}

/**

* Returns the SVG document parsed upon instantiating this class.

*

* @return A valid, parsed, non-null SVG document instance.

*/

public Document getSVGDocument() {

return this.svgDocument;

}

/**

* Enhance the SVG DOM for the given document to provide CSS- and SVG-specific

* DOM interfaces.

*

* @param document The document to enhance.

* @link http://wiki.apache.org/xmlgraphics-batik/BootSvgAndCssDom

*/

private void initSVGDOM( Document document ) {

UserAgent userAgent = new UserAgentAdapter();

DocumentLoader loader = new DocumentLoader( userAgent );

BridgeContext bridgeContext = new BridgeContext( userAgent, loader );

bridgeContext.setDynamicState( BridgeContext.DYNAMIC );

// Enable CSS- and SVG-specific enhancements.

(new GVTBuilder()).build( bridgeContext, document );

}

/**

* Use the SAXSVGDocumentFactory to parse the given URI into a DOM.

*

* @param uri The path to the SVG file to read.

* @return A Document instance that represents the SVG file.

* @throws Exception The file could not be read.

*/

private Document createSVGDocument( String uri ) throws IOException {

String parser = XMLResourceDescriptor.getXMLParserClassName();

SAXSVGDocumentFactory factory = new SAXSVGDocumentFactory( parser );

return factory.createDocument( uri );

}

/**

* Reads a file and parses the path elements.

*

* @param args args[0] - Filename to parse.

* @throws IOException Error reading the SVG file.

*/

public static void main( String args[] ) throws IOException {

URI uri = new File( args[0] ).toURI();

SVGMetaPost converter = new SVGMetaPost( uri.toString() );

converter.run();

}

}

注意：除非另有说明,否则调用initSVGDOM()应该是Batik的默认行为.唉,它不是,发现这个宝石意味着在他们的网站上阅读documentation buried.

解析SVG DOM

解析SVG DOM是相对微不足道的. toCode()方法是该类的主力：

import org.apache.batik.dom.svg.SVGItem;

import org.apache.batik.dom.svg.SVGOMPathElement;

import org.w3c.dom.Node;

import org.w3c.dom.svg.SVGPathSegList;

/**

* Responsible for converting an SVG path element to MetaPost. This

* will convert just the bezier curve portion of the path element, not

* its style. Typically the SVG path data is provided from the "d" attribute

* of an SVG path node.

*/

public class MetaPostPath extends MetaPost {

private SVGOMPathElement pathElement;

/**

* Use to create an instance of a class that can parse an SVG path

* element to produce MetaPost code.

*

* @param pathNode The path node containing a "d" attribute (output as MetaPost code).

*/

public MetaPostPath( Node pathNode ) {

setPathNode( pathNode );

}

/**

* Converts this object's SVG path to a MetaPost draw statement.

*

* @return A string that represents the MetaPost code for a path element.

*/

public String toCode() {

StringBuilder sb = new StringBuilder( 16384 );

SVGOMPathElement pathElement = getPathElement();

SVGPathSegList pathList = pathElement.getNormalizedPathSegList();

int pathObjects = pathList.getNumberOfItems();

sb.append( ( new MetaPostComment( getId() ) ).toString() );

for( int i = 0; i < pathObjects; i++ ) {

SVGItem item = (SVGItem)pathList.getItem( i );

sb.append( String.format( "%s%n", item.getValueAsString() ) );

}

return sb.toString();

}

/**

* Returns the value for the id attribute of the path element. If the

* id isn't present, this will probably throw a NullPointerException.

*

* @return A non-null, but possibly empty String.

*/

private String getId() {

return getPathElement().getAttributes().getNamedItem( "id" ).getNodeValue();

}

/**

* Typecasts the given pathNode to an SVGOMPathElement for later analysis.

*

* @param pathNode The path element that contains curves, lines, and other

* SVG instructions.

*/

private void setPathNode( Node pathNode ) {

this.pathElement = (SVGOMPathElement)pathNode;

}

/**

* Returns an SVG document element that contains path instructions (usually

* for drawing on a canvas).

*

* @return An object that contains a list of items representing pen

* movements.

*/

private SVGOMPathElement getPathElement() {

return this.pathElement;

}

}

建立

编译因环境而异.类似于以下的脚本应该有所帮助：

#!/bin/bash

mkdir -p ./build

javac -cp ./lib/* -d ./build ./source/*.java

确保将所有.jar文件放入./lib目录中.将源文件放入./source目录.

跑

创建一个脚本(或批处理文件)来执行该程序：

#!/bin/bash

java -cp ./lib/*:./build SVGMetaPost $1

产量

对包含有效SVG路径的文件运行时,会产生：

$./run.sh stripe/trigon.svg

% path8078-6

M 864.1712 779.3069

C 864.1712 779.3069 868.04065 815.6211 871.4032 833.4621

C 873.4048 844.08203 874.91724 855.0544 879.0846 864.82227

C 884.24023 876.9065 895.2377 887.9899 900.0184 897.3661

C 904.7991 906.7422 907.3466 918.3257 907.3466 918.3257

C 907.3466 918.3257 892.80817 887.6536 864.1712 887.3086

C 835.53424 886.9637 820.9958 918.3257 820.9958 918.3257

C 820.9958 918.3257 823.6176 906.59644 828.32404 897.3661

C 833.0304 888.1356 844.10223 876.9065 849.2578 864.82227

C 853.4252 855.05444 854.9376 844.08203 856.93915 833.4621

C 860.3017 815.6211 864.17114 779.3069 864.17114 779.3069

z

从这里开始,应该清楚如何使用Java将SVG路径数据读入相应的SVG对象.

附录

请注意,从SVG转换为MetaPost的最简单方法是：

>将SVG转换为PDF(例如,使用Inkscape或rsvg-convert).

>使用pstoedit将PDF转换为MetaPost.