[Web Chart系列之六] canvas Chart 导出图文件

前言

博主正在参加CSDN2013年度博客之星评选，如果这篇文章对您有用，请投他一票：

投票地址：http://vote.blog.csdn.net/blogstaritem/blogstar2013/oscar999

不胜感激^^

[Web Chart系列之六] canvas Chart 导出图文件

Chart 导出的原理很基本方法，在上一篇已经有介绍过。

对于Extjs 来说，在 Ext.chart.Chart 这个类直接有提供一个 save( [config] ) 的方法， 调用这个方法， 就可以在browser 下载当前这个chart 的对应格式的图形文件。

chart.save({
     type: 'image/png'
});

这里使用的技术是把数据传递到服务器端， 由服务器端产生图再传到前端。

所以， 在调用save 这个方法的时候， 你会发现， 请求会访问http://svg.sencha.io/ 这个地址。

曾经， 大概在 2013 的年中的时候， 这个地址都可以访问， 当时不知何时， 这个地址的访问就会报 503 (Service Unavailable)的错误了。

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" alt="" />

这样的话， 原本可以work 的chart 导出功能， 现在就不行了。

网上搜索一下， 是说部分版本已经不提供这个服务了。

不管如何， 讲自己的服务放在别的地方， 总也不踏实， 是否可以开发出这种服务呢？

原理

首先看一看， chart.save 时，前端传递了那些参数：

aaarticlea/png;base64,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" alt="" />

参数有四个：

width 和 height 应该是图片的大小

type 应该是图的保存格式

svg  传递的就是xml方式的svg 格式的数据。

所以问题归结为一点： 在服务端如何解析这个svg 格式的数据并生成图片文件？

解决方法

看懂这些svg 数据， 并使用基本API生成一个图片不失为一种解法？

但是对java 语言来说， 是否已经存在第三方包来帮我们直接做这种事呢？

答案之一就是：

Batik

Batik是使用
svg格式图片来实现各种功能的应用程序以及Applet提供的一个基于java的工具包。

它是属于 Apache软件基金会 的一个项目， 应该是值得信赖的。

项目主页：  http://xmlgraphics.apache.org/batik/

下载地址：http://mirrors.cnnic.cn/apache/xmlgraphics/batik/、

开发步骤：

1. 下载batik-1.7.zip （ 目前的最新版） 并解压

2. 把根目录， lib 和 extensions 目录下的所有lib 包拷入项目的web lib 中。(可以选择)

3. 写一个servlet   ImageExportService.java

/**
* author:oscar999
*/
import java.io.IOException;
import java.io.OutputStream;
import java.io.StringReader;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.batik.transcoder.TranscoderException;
import org.apache.batik.transcoder.TranscoderInput;
import org.apache.batik.transcoder.TranscoderOutput;
import org.apache.batik.transcoder.image.JPEGTranscoder;
import org.apache.batik.transcoder.image.PNGTranscoder;

public class ImageExportService extends HttpServlet {

	/**
	 *
	 */
	private static final long serialVersionUID = 1L;

	/**
	 * Post File to Client
	 * Input Parameters:
	 *  type(image type, as png, jpeg),
	 *  svg(svg string, post by extjs),
	 *  filename(save file name)
	 */
	@Override
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException,
			IOException {

		String type = request.getParameter("type");
		String svg = request.getParameter("svg");
		String filename = "chart";
		if( request.getParameter("filename")!=null&&request.getParameter("filename").length()>0)
		{
			filename = request.getParameter("filename");
		}

		String postfix;
		if ("image/jpeg".equals(type)) {
			response.setContentType("image/jpeg");
			postfix = "jpg";
		} else {
			response.setContentType("image/png");
			postfix = "png";
		}
		response.setHeader("Content-Disposition", "attachment; filename=" + filename + "." + postfix);

		StringReader stringReader = new StringReader(svg);
		OutputStream out = response.getOutputStream();

		try {
			TranscoderInput input = new TranscoderInput(stringReader);
			TranscoderOutput output = new TranscoderOutput(out);

			if ("image/jpeg".equals(type)) {
				new JPEGTranscoder().transcode(input, output);
			} else {
				new PNGTranscoder().transcode(input, output);
			}

		} catch (TranscoderException e) {
			throw new ServletException(e);
		}
	}

}

4.  在 web.xml 中配置此servlet 的请求路径

  <servlet>
  	<servlet-name>ImageExportService</servlet-name>
  	<servlet-class>com.XXX.ImageExportService</servlet-class>
  </servlet>
  <servlet-mapping>
      <servlet-name>ImageExportService</servlet-name>
      <url-pattern>/ImageExportService</url-pattern>
  </servlet-mapping>

5.  让Extjs 的Chart.save 切换到新的服务器。

Ext.draw.engine.ImageExporter.defaultUrl = 'ImageExportService';

(注意， 这部分是写在web端的， 可以放在 Ext.onReady 里面)

6. 全部完成， 写个例子测试一下

//author: oscar999
<script type="text/javascript">
var chart;
var panel1;
Ext.require(['*']);
Ext.onReady(function() {

	Ext.draw.engine.ImageExporter.defaultUrl = '/'+WEB_PROJECT_NAME+'/ImageExportService';

	var store = Ext.create('Ext.data.JsonStore', {
	    fields: ['name', 'data'],
	    data: [
	        { 'name': 'metric one',   'data':100000 },
	        { 'name': 'metric two',   'data': 7 },
	        { 'name': 'metric three', 'data': 5 },
	        { 'name': 'metric four',  'data': 2 },
	        { 'name': 'metric five',  'data':27 }
	    ]
	});

	var chart = Ext.create('Ext.chart.Chart', {
	    renderTo: Ext.getBody(),
	    width: 500,
	    height: 300,
	    animate: true,
	    store: store,
	    axes: [{
	        type: 'Numeric',
	        position: 'bottom',
	        fields: ['data'],
	        label: {
	            renderer: Ext.util.Format.numberRenderer('0,0')
	        },
	        title: 'Sample Values',
	        grid: true,
	        minimum: 0
	    }, {
	        type: 'Category',
	        position: 'left',
	        fields: ['name'],
	        title: 'Sample Metrics'
	    }],
	    series: [{
	        type: 'bar',
	        axis: 'bottom',
	        highlight: true,
	        tips: {
	          trackMouse: true,
	          width: 140,
	          height: 28,
	          renderer: function(storeItem, item) {
	            this.setTitle(storeItem.get('name') + ': ' + storeItem.get('data') + ' views');
	          }
	        },
	        label: {
	          display: 'insideEnd',
	            field: 'data',
	            renderer: Ext.util.Format.numberRenderer('0'),
	            orientation: 'horizontal',
	            color: '#333',
	            'text-anchor': 'middle'
	        },
	        xField: 'name',
	        yField: 'data'
	    }]
	});

	Ext.MessageBox.confirm('Confirm Download', 'Would you like to download the chart as an image?', function(choice){
	    if(choice == 'yes'){
	        chart.save({
	            type: 'image/png',
	            filename:'testfile'
	        });
	    }
	});

});
</script>

跨浏览器处理

可能想到会有一个问题， IE 的低版本还只是支持vml 绘图， 那在这些版本的IE中， 导出图是否就不行了呢？

其实不用担心， Extjs 已经帮我们处理好了， 即使在这些版本的IE中， 传递到服务器的也是 svg  格式的数据。

(另外发现的一点是， 如果要传入自己定义的参数, 比如filename 等， 直接从save 中可能不行，可以考虑从呼叫url 传入)