关于使用batik中出现“unable to make sense of URL for connection”的问题

使用batik来打开SVG文件时，用到如下代码来读取SVG文件：

JFrame frame;
    JSVGCanvas canvas;
    Document document;
    Window window;

    public SVGApplication() {
        frame = new JFrame();
        canvas = new JSVGCanvas();
        // Forces the canvas to always be dynamic even if the current
        // document does not contain scripting or animation.
        canvas.setDocumentState(JSVGCanvas.ALWAYS_DYNAMIC);
        canvas.addSVGLoadEventDispatcherListener
            (new SVGLoadEventDispatcherAdapter() {
                    public void svgLoadEventDispatchStarted
                        (SVGLoadEventDispatcherEvent e) {
                        // At this time the document is available...
                        document = canvas.getSVGDocument();
                        // ...and the window object too.
                        window = canvas.getUpdateManager().
                            getScriptingEnvironment().createWindow();
                        // Registers the listeners on the document
                        // just before the SVGLoad event is
                        // dispatched.
                        registerListeners();
                        // It is time to pack the frame.
                        frame.pack();
                    }
                });
       
        frame.addWindowListener(new WindowAdapter() {
                public void windowOpened(WindowEvent e) {
                    // The canvas is ready to load the base document
                    // now, from the AWT thread.
                    canvas.setURI("line.svg");                  
                }
            });

其中由于红色部分出错，引起了“unable to make sense of URL for connection”。这说明这个路径不可用。经过一翻折腾以后发现，应该改成：

canvas.setURI("file:/home/hjh/svg/line.svg");

这样，就可以读取了。开始不知道为什么这样就可以了。后来分析后发现，只“/home/hjh/svg/line.svg”这个是表示的操作系统的路径，而不是一个URL路径。必须要在前面加上“file:/”才行。WINDOWS下的也是如此。如果SVG文件存在C:/下。不能直接用“C:/line.svg”,而应该用“file:/C:/line.svg”才可以。