前些天接了个需求, 需要推送产品 日/月/季 度榜单到群给大佬们看, 方便大佬们决策
飞书可以推送图片
所以技术方案定为根据数据生成图片
用node + puppeteer.js做了一版, 但是要另外起个服务, 且要跑在有显卡的服务器上
于是就用java实现了一遍 ( 有两个方式, 倾向于用cssbox )

思路如下

1: 样式有前端些( 毕竟java程序员大多数都很头疼css )
2: 把模板渲染成页面, 然后生成一张图

三个依赖 pom.xml

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-freemarker</artifactId>
        </dependency>
        <dependency>
            <groupId>org.xhtmlrenderer</groupId>
            <artifactId>core-renderer</artifactId>
            <version>R8</version>
        </dependency>
        <dependency>
            <groupId>net.sf.cssbox</groupId>
            <artifactId>cssbox</artifactId>
            <version>4.12</version>
        </dependency>

核心工具类 FreemarkerUtils.class

import freemarker.template.Configuration;
import freemarker.template.Template;
import freemarker.template.TemplateException;
import freemarker.template.TemplateExceptionHandler;
import org.fit.cssbox.css.CSSNorm;
import org.fit.cssbox.css.DOMAnalyzer;
import org.fit.cssbox.io.DocumentSource;
import org.fit.cssbox.io.StreamDocumentSource;
import org.fit.cssbox.layout.BrowserCanvas;
import org.springframework.stereotype.Component;
import org.w3c.dom.Document;
import org.xhtmlrenderer.swing.Java2DRenderer;
import org.xhtmlrenderer.util.FSImageWriter;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.*;
import java.nio.charset.StandardCharsets;
import java.util.UUID;

@Component
public class FreemarkerUtils {

    private static String fileUrl = FreemarkerUtils.class.getResource("/").getPath();

    public static String getTemplate(String template, Object object) throws IOException, TemplateException {
        Configuration cfg = new Configuration(Configuration.VERSION_2_3_25);
        String templatePath = fileUrl + "html/";
        cfg.setDirectoryForTemplateLoading(new File(templatePath));
        cfg.setDefaultEncoding("UTF-8");
        cfg.setTemplateExceptionHandler(TemplateExceptionHandler.RETHROW_HANDLER);
        cfg.setLogTemplateExceptions(false);
        Template temp = cfg.getTemplate(template);
        StringWriter stringWriter = new StringWriter();
        temp.process(object, stringWriter);
        stringWriter.flush();
        stringWriter.close();
        return stringWriter.getBuffer().toString();
    }

    public BufferedImage turnImage(String template, Object object, Integer width, Integer height) throws Exception {
        String html = getTemplate(template, object);

        // 转文档
        byte[] bytes=html.getBytes();
        ByteArrayInputStream bin = new ByteArrayInputStream(bytes);
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document document = builder.parse(bin);
        /*
        画笔生成图
         */
        DOMAnalyzer da = new DOMAnalyzer(document);
        // 创建一个字节流
        InputStream is = new ByteArrayInputStream(html.getBytes(StandardCharsets.UTF_8));
        DocumentSource docSource = new StreamDocumentSource(is, null, "text/html; charset=utf-8");
        // 设置样式属性
        da.attributesToStyles();
        da.addStyleSheet(null, CSSNorm.stdStyleSheet(), DOMAnalyzer.Origin.AGENT);
        da.addStyleSheet(null, CSSNorm.userStyleSheet(), DOMAnalyzer.Origin.AGENT);
        da.addStyleSheet(null, CSSNorm.formsStyleSheet(), DOMAnalyzer.Origin.AGENT);
        da.getStyleSheets();

        // 转图片
        BrowserCanvas contentCanvas = new BrowserCanvas(da.getRoot(), da, docSource.getURL());
        contentCanvas.createLayout(new Dimension(width, height));
//        contentCanvas.setSize(width, height);
//        contentCanvas.setAutoSizeUpdate(false);
        // 生成图片
        BufferedImage img = contentCanvas.getImage();

        /*
            Rendere文档生成图
        */
//        Java2DRenderer renderer = new Java2DRenderer(document, width, height);
//        BufferedImage img = renderer.getImage();

//        final FSImageWriter imageWriter = new FSImageWriter();
//        imageWriter.setWriteCompressionQuality(1.0f);
//        // 生成图片名字
//        String uuid = UUID.randomUUID().toString();
//        //输出路径
//        imageWriter.write(img, "E:\\8080server\\img\\" + uuid + ".jpg");
        return img;

    }

}

调用 LaunchPlanTopToImgHandleJob.class

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.awt.image.BufferedImage;

@Service
public class LaunchPlanTopToImgHandleJob {
    @Autowired
    FreemarkerUtils freemarkerUtils;
    public BufferedImage createByFtlToImg (Object object, String type, Integer width, Integer height) throws Exception {
        String template = "";
        BufferedImage img = null;
        switch (type){
            // 模板
            default: template = "index.ftl";
                img = freemarkerUtils.turnImage(template, object, width, height);
        }
        return img;
    }
}

至此完成,

至此完成,

目前已知坑点是对css3支持很差, 但其实css2已经可以满足大部分样式要求了
部署到Linux系统上发现 中文乱码
解决方案如下

1. cd /usr/share/fonts
2. 把字体包解压进去 https://pan.baidu.com/s/110yjyPIOCyudejPz5ZM0xw 提取码：6666
3. 执行 yum install mkfontscale
4. 执行 mkfontscale
5. 执行 mkfontscale
6. 执行 fc-cache
7. 重启服务
8. 模板文件加上以下css样式

html{
      font-family: "Microsoft YaHei", "Microsoft YaHei UI", "FangSong", "SimSun", "微软雅黑","sans-serif";
}