Question

DOJO正在开发的项目中有一项新要求，即用户可以将图表导出为PNG图像。我进行了一项研究，发现了两个想法：

1，尝试在DOJO API中找到一个合适的方法直接导出到PNG图像（因为我与Ext JS类似，它提供了导出到图像的API方法），但是DOJO图表没有方法可以做到这一点

使用DOJO API（如dojox.fx或dojox.gfx）绘制图像，但这些不能生成图像。所以我放弃了这种方式。

2，使用第三方插件执行此操作。首先，我可以通过方法'dojox.gfx.utils.toSvg（chart.surface）.then'获取图表的表面内容，然后使用Apache的插件Batik将SVG内容转换为PNG图像。以下是我尝试的代码：

dojox.gfx.utils.toSvg(chart.surface).then(function(svg) {
    var args = {
        url : "chart/doExportChart.action",
        content : {
            svgContent : svg
        },
        handleAs : "json",
        load : function(response) {
            // Do something like exporting the responded image.
        },
        error : function(error) {
            // Error handling
        }
    };

    dojo.xhrPost(args);
    }, 
    function(error) {
        // Error handling
    }
);

方法doExportChart执行类似的操作：

JPEGTranscoder t = new JPEGTranscoder();

// Set the transcoding hints.
t.addTranscodingHint(JPEGTranscoder.KEY_QUALITY, new Float(.8));

// Create the transcoder input.
String svgURI = new File("c:/sample.svg").toURL().toString();
TranscoderInput input = new TranscoderInput(svgURI);

// Create the transcoder output.
OutputStream ostream = new FileOutputStream("c:/sample.jpg");
TranscoderOutput output = new TranscoderOutput(ostream);

 // Save the image.
 t.transcode(input, output);

// Flush and close the stream.
 ostream.flush();
ostream.close();

SVG sample.svg的内容如下：

svg xmlns=httpwww.w3.org2000svg width=1200 height=589defsrect fill=rgb(255, 255, 255) fill-opacity=1 stroke=none stroke-opacity=0 stroke-width=1 stroke-linecap=butt stroke-linejoin=miter stroke-miterlimit=4 x=41.5 y=13.666666666666666 width=1142 height=528.5 fill-rule=evenoddg transform=matrix(1.00000000,0.00000000,0.00000000,0.00000000,0.00000000,541.16666667)gpolyline fill=none fill-opacity=0 stroke=rgb(204, 204, 204) stroke-opacity=1 stroke-width=1.7 stroke-linecap=butt stroke-linejoin=miter stroke-miterlimit=4 points=42.50000000 14.66666667 90.00000000 242.63573883 137.50000000 191.97594502 185.00000000 126.84192440 232.50000000 242.63573883 280.00000000 201.02233677 327.50000000 159.40893471 375.00000000 541.16666667 422.50000000 343.95532646 470.00000000 220.92439863 517.50000000 146.74398625 565.00000000 224.54295533 612.50000000 240.82646048 660.00000000 110.55841924 707.50000000 249.87285223 755.00000000 161.21821306 802.50000000 195.59450172 850.00000000 320.43470790 897.50000000 318.62542955 945.00000000 282.43986254 992.50000000 286.05841924 1040.00000000 349.38316151 1087.50000000 210.06872852 1135.00000000 286.05841924 1182.50000000 329.48109966 stroke-dasharray=none polyline fill=none fill-opacity=0 stroke=rgb(191, 19, 19) stroke-opacity=1 stroke-width=1.5 stroke-linecap=butt stroke-linejoin=miter stroke-miterlimit=4 points=42.50000000 14.66666667 90.00000000 242.63573883 137.50000000 191.97594502 185.00000000 126.84192440 232.50000000 242.63573883 280.00000000 201.02233677 327.50000000 159.40893471 375.00000000 541.16666667 422.50000000 343.95532646 470.00000000 220.92439863 517.50000000 146.74398625 565.00000000 224.54295533 612.50000000 240.82646048 660.00000000 110.55841924 707.50000000 249.87285223 755.00000000 161.21821306 802.50000000 195.59450172 850.00000000 320.43470790 897.50000000 318.62542955 945.00000000 282.43986254 992.50000000 286.05841924 1040.00000000 349.38316151 1087.50000000 210.06872852 1135.00000000 286.05841924 1182.50000000 329.48109966 stroke-dasharray=none ggrect fill=rgb(255, 255, 255) fill-opacity=1 stroke=none stroke-opacity=0 stroke-width=1 stroke-linecap=butt stroke-linejoin=miter stroke-miterlimit=4 x=0 y=0 width=42.5 height=590 fill-rule=evenoddrect fill=rgb(255, 255, 255) fill-opacity=1 stroke=none stroke-opacity=0 stroke-width=1 stroke-linecap=butt stroke-linejoin=miter stroke-miterlimit=4 x=1182.5 y=0 width=18.5 height=591 fill-rule=evenoddrect fill=rgb(255, 255, 255) fill-opacity=1 stroke=none stroke-opacity=0 stroke-width=1 stroke-linecap=butt stroke-linejoin=miter stroke-miterlimit=4 x=0 y=0 width=1201 height=14.666666666666666 fill-rule=evenoddrect fill=rgb(255, 255, 255) fill-opacity=1 stroke=none stroke-opacity=0 stroke-width=1 stroke-linecap=butt stroke-linejoin=miter stroke-miterlimit=4 x=0 y=541.1666666666666 width=1201 height=49.83333333333333 fill-rule=evenoddgline fill=none fill-opacity=0 stroke=rgb(51, 51, 51) stroke-opacity=1 stroke-width=1 stroke-linecap=butt stroke-linejoin=miter stroke-miterlimit=4 x1=42.5 y1=541.1666666666666 x2=1182.5 y2=541.1666666666666 stroke-dasharray=none ggline fill=none fill-opacity=0 stroke=rgb(51, 51, 51) stroke-opacity=1 stroke-width=1 stroke-linecap=butt stroke-linejoin=miter stroke-miterlimit=4 x1=42.5 y1=541.1666666666666 x2=42.5 y2=14.666666666666666 stroke-dasharray=none line fill=none fill-opacity=0 stroke=rgb(102, 102, 102) stroke-opacity=1 stroke-width=1 stroke-linecap=butt stroke-linejoin=miter stroke-miterlimit=4 x1=42.5 y1=427.1821305841924 x2=36.5 y2=427.1821305841924 stroke-dasharray=none text fill=rgb(51, 51, 51) fill-opacity=1 stroke=none stroke-opacity=0 stroke-width=1 stroke-linecap=butt stroke-linejoin=miter stroke-miterlimit=4 x=32.5 y=430.91546391752576 text-anchor=end text-decoration=none rotate=0 kerning=auto text-rendering=optimizeLegibility font-style=normal font-variant=normal font-weight=normal font-size=7pt font-family=Tahoma fill-rule=evenodd100textline fill=none fill-opacity=0 stroke=rgb(102, 102, 102) stroke-opacity=1 stroke-width=1 stroke-linecap=butt stroke-linejoin=miter stroke-miterlimit=4 x1=42.5 y1=246.25429553264598 x2=36.5 y2=246.25429553264598 stroke-dasharray=none text fill=rgb(51, 51, 51) fill-opacity=1 stroke=none stroke-opacity=0 stroke-width=1 stroke-linecap=butt stroke-linejoin=miter stroke-miterlimit=4 x=32.5 y=249.9876288659793 text-anchor=end text-decoration=none rotate=0 kerning=auto text-rendering=optimizeLegibility font-style=normal font-variant=normal font-weight=normal font-size=7pt font-family=Tahoma fill-rule=evenodd200textline fill=none fill-opacity=0 stroke=rgb(102, 102, 102) stroke-opacity=1 stroke-width=1 stroke-linecap=butt stroke-linejoin=miter stroke-miterlimit=4 x1=42.5 y1=65.32646048109962 x2=36.5 y2=65.32646048109962 stroke-dasharray=none text fill=rgb(51, 51, 51) fill-opacity=1 stroke=none stroke-opacity=0 stroke-width=1 stroke-linecap=butt stroke-linejoin=miter stroke-miterlimit=4 x=32.5 y=69.05979381443295 text-anchor=end text-decoration=none rotate=0 kerning=auto text-rendering=optimizeLegibility font-style=normal font-variant=normal font-weight=normal font-size=7pt font-family=Tahoma fill-rule=evenodd300textgsvg

然后运行上面的代码错误遇到：

Exception in thread "main" org.apache.batik.transcoder.TranscoderException: null
Enclosed Exception:
Content is not allowed in prolog.
    at org.apache.batik.transcoder.XMLAbstractTranscoder.transcode(XMLAbstractTranscoder.java:136)
    at org.apache.batik.transcoder.SVGAbstractTranscoder.transcode(SVGAbstractTranscoder.java:156)
    at com.ibm.crl.poc.util.PocImageUtil.main(PocImageUtil.java:142)

我按照http://xmlgraphics.apache.org/batik/using/transcoder.html的官方示例执行第二个解决方案。我不知道，希望有人给我指导。非常感谢。

Answer 1

如果您的目的是支持旧浏览器，那么使用svg根本就不是一种选择。 2006年以后的大多数浏览器版本都有一些基本的支持 - 但是对于Internet Explorer IE8和旧版需要插件来呈现SVG内容。

@ Batik异常;它看起来像外部源解析失败（有错误搜索此问题和样式语法）。在上面的在线工具中很难阻止任何内容，但是尝试下载xmlns并将其作为sample.svg在同一域中提供（或尝试将其保留）为proposed here

除非你要求图像具有相同的外观和感觉，否则这种方法可能略有偏差。您可以使用用于图表的系列，而不是转换SVG，为JFreeChart或类似创建情节。

无论哪种方式，你都不能指望javascript生成PNG，所涉及的算法是......鼓励一下：）

最后一个选项是让您的图表在一个框架中呈现，使页面非常简单并快速渲染（创建一个dojolayer以避免100多个请求）。然后，一旦客户端请求图像导出，从服务器端获取此帧的“快照”。这将确保存在对SVG的支持并提供序列化结果。例如：

客户机侧：

<iframe
     width=700
     height=400
     src="chart/doRenderChart.action?unid=howto_identify_graph"></iframe>

服务器端，一旦用户点击“导出”：

doExportAction(HttpServletRequest req, HttpServletResponse resp) throws IOException {
   String chart = req.getParameter('url') 
         = "chart/doRenderChart.action?unid=howto_identify_graph";
   int width = 700;
   int height = 400;
   File f = File.createTempFile("prefix",null,myDir);
   String tmpfile = f.getName();
   f.delete();
   Process p=Runtime.getRuntime().exec("/path/to/bin/wkhtmltoimage "+
        "--crop-h " + height + 
        " --crop-w " + height + " " +
          chart + 
        " -f png " + 
          tmpfile
   ); 
   p.waitFor();
   // get and serve 'tmpfile' contents
}

以下是WKHtmlToXX

的项目

如何将dojox.charting.Chart转换为PNG图像供用户导出？

1 个答案: