java - 使用 JRI 从 JSP 动态绘制 R 图

Question

我使用 R 来使用 JRI 绘制图表。我使用了以下代码:

Rengine re = new Rengine (new String [] {"--vanilla"}, false, null);
re.eval("jpeg('<filename>')";
re.eval("plot(x,y)");
re.eval("dev.off()");

并使用

从 jsp 调用生成的文件

 <\img src='<filename>'/>

是否可以动态绘制图形，而不是在“img”标签中保存和调用文件？我想在浏览器中显示图表。请提出建议。

Answer 1

您可以使用data URIs并内联图形:

library(base64enc)

# unique filename; you can specify tmpdir for the 
# location where the png will be written
this_file <- tempfile("supercoolplot", fileext=".png")

# make a png
png(file=this_file <- tempfile("supercoolplot", fileext=".png"), width=200, height=200, bg="transparent")
plot(sample(1:10, 10, replace=TRUE)) # randomize plot
rect(1,5,3,7,col="white")
dev.off()

# show you the file
print(this_file)

# encode the png
encoded_png <- sprintf("<img src='data:image/png;base64,%s'/>", base64encode(this_file))

# optionally remove the offending file
# if you use the tmpdir option then you can prbly leave the
# file there and serve it up via the <img/> tag directly
# vs encode it below
unlink(this_file)

# see what we did (only showing part of the string)
substr(encoded_png, 1, 80)

## [1] "<img src='data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAMgAAADICAYAAACtWK6eAAAD"

# prove it works (run this in your R Console / RStudio
htmltools::html_print(htmltools::HTML(encoded_png))

如上所述，您可以将 png(或您的情况下的 jpeg)输出到临时文件/目录，并(可选)在完成后将其删除。