Java 如何加载和解析 SVG 文档

How to load and parse SVG documents

提问by Dave Jarvis

Background

背景

There are number of unanswered questions related to reading and parsing SVG paths:

有许多与读取和解析 SVG 路径相关的未解决问题：

• Easiest way to read in svg path data with Java?
• Re: parsing a svg file using batik svg parser
• How to convert SVG Path (SVGOMPathElement) to array of points?

• 使用 Java 读取 svg 路径数据的最简单方法？
• 回复：使用蜡染 svg 解析器解析 svg 文件
• 如何将 SVG 路径 (SVGOMPathElement) 转换为点数组？

Problem

问题

The SVG pathelement contains a data attribute(d). Sometimes it is necessary to load, parse, and extract just the path information from an SVG file.

SVGpath元素包含一个数据属性( d)。有时需要从 SVG 文件加载、解析和提取路径信息。

Question

题

How do you load, parse, and extract SVG path information from an SVG file?

如何从 SVG 文件中加载、解析和提取 SVG 路径信息？

采纳答案by Dave Jarvis

Overview

概述

Load and parse SVG files using Apache Batik. The solution shows Java code in the preliminary stages of converting an SVG file to MetaPost. This should provide a general idea for how to load, parse, and extract content from SVG files using Java.

使用Apache Batik加载和解析 SVG 文件。该解决方案显示了在将 SVG 文件转换为 MetaPost 的初步阶段中的 Java 代码。这应该提供有关如何使用 Java 从 SVG 文件加载、解析和提取内容的总体思路。

Libraries

图书馆

You will need the following libraries:

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

Load SVG File

加载 SVG 文件

The main application loads the SVG file into DOM, then converts the DOM to an SVG DOM. The initSVGDOM()method call is extremely important. Without calling initSVGDOM(), the methods for extracting SVG DOM elements from the DOM would not be available.

主应用程序将 SVG 文件加载到 DOM，然后将 DOM 转换为 SVG DOM。该initSVGDOM()方法的调用是非常重要的。如果不调用initSVGDOM()，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();
  }
}

Note: Calling initSVGDOM()should be Batik's default behaviour unless otherwise specified. Alas, it isn't, and discovering this gem means reading documentation buriedon their website.

注意：initSVGDOM()除非另有说明，否则调用应该是 Batik 的默认行为。唉，它不是，发现这个宝石意味着阅读埋在他们网站上的文档。

Parse SVG DOM

解析 SVG DOM

Parsing the SVG DOM is then relatively trivial. The toCode()method is the workhorse of the class:

解析 SVG DOM 就相对简单了。该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;
  }
}

Build

建造

Compiling will vary from environment to environment. A script similar to the following should help:

编译会因环境而异。类似于以下的脚本应该会有所帮助：

#!/bin/bash
mkdir -p ./build
javac -cp ./lib/* -d ./build ./source/*.java

Be sure to put all the .jarfiles into the ./libdirectory. Put the source files into the ./sourcedirectory.

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

Run

跑

Create a script (or batch file) to execute the program:

创建一个脚本（或批处理文件）来执行程序：

#!/bin/bash
java -cp ./lib/*:./build SVGMetaPost 

Output

输出

When run against a file containing a valid SVG path, this produces:

当针对包含有效 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

From here it should be clear how to read SVG path data into their corresponding SVG objects.

从这里应该清楚如何将 SVG 路径数据读入其相应的 SVG 对象。

Addendum

附录

Note that the simplest way to convert from SVG to MetaPostis:

请注意，从 SVG 转换为MetaPost的最简单方法是：

1. Convert SVG to PDF (e.g., using Inkscapeor rsvg-convert).
2. Convert PDF to MetaPost using pstoedit.

1. 将 SVG 转换为 PDF（例如，使用Inkscape或rsvg-convert）。
2. 使用 .pdf 将 PDF 转换为 MetaPost pstoedit。