java导出pdf报告之七：合并两个png图片

对于此项，主要是为了实现绿色小圆点根据动态数据显示在不同的位置，如下图所示：

然后做了两个png图片，一个是绿色的小圆点，一个是下方的低中高矩形图片（设置颜色部分和文字部分比例2:1，低中高比例1:2:1）

刚开始实现是直接在图形图片上画圆点图片，结果发现圆点的颜色给丢了。

private String mergePicture(String srcPicture,String iconPicture,Double pos,String name) throws Exception {
        BufferedImage d = ImageIO.read(new FileInputStream(srcPicture));  //长方形
        BufferedImage b = ImageIO.read(new FileInputStream(iconPicture));  //圆点
        Graphics2D g = d.createGraphics();
            g.setRenderingHint(RenderingHints.KEY_INTERPOLATION,RenderingHints.VALUE_INTERPOLATION_BILINEAR);
        g.drawImage(b, (int)(d.getWidth()*0.96), d.getHeight()/3 - b.getHeight()/2, null);
        g.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER));

        g.dispose();
        String filePath = picturePath + REPORT + "/" + name;
        ImageIO.write(d, "png", new File(filePath));
        return filePath;
}

生成的图片如下：

后来改变了一下思路，先是创建一个透明画布，然后再透明画布上分别画矩形图片和圆点图片

private String mergePicture(String srcPicture,String iconPicture,Double pos,String name) throws Exception {
        BufferedImage d = ImageIO.read(new FileInputStream(srcPicture)); //长方形
        BufferedImage b = ImageIO.read(new FileInputStream(iconPicture));  //圆点
        //创建透明画布
        BufferedImage bi = new BufferedImage(d.getWidth(),d.getHeight(),BufferedImage.TYPE_INT_RGB);
        Graphics2D g = bi.createGraphics();
        bi = g.getDeviceConfiguration().createCompatibleImage(d.getWidth(),d.getHeight(),Transparency.TRANSLUCENT);
        g.dispose();

        //将矩形图片画到透明画布上
        g = bi.createGraphics();
        g.setRenderingHint(RenderingHints.KEY_INTERPOLATION,RenderingHints.VALUE_INTERPOLATION_BILINEAR);
        g.drawImage(d,0,0,null);

        //将圆点图片画到画布上
        //圆点图象的路径 水印一般为gif或者png的，这样可设置透明度
        ImageIcon imgIcon = new ImageIcon(b);
        //得到Image对象。
        Image con = imgIcon.getImage();
        g.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_ATOP,1f));
        //表示水印图片的坐标位置(x,y)
        g.drawImage(con, (int)(d.getWidth()*pos/100), d.getHeight()/3 - b.getHeight()/2, null);
        g.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER));
        g.dispose();

        String filePath = picturePath + REPORT + "/" + name;
        ImageIO.write(bi, "png", new File(filePath));
        return filePath;
    }

以上方法完美解决问题，并实现了想要的效果