R 安装包遇到问题（一） loadNamespace()里算'rJava'时.onLoad失败了 rJava 包的安装与载入

> library(xlsx)
Error: package or namespace load failed for ‘xlsx’:
 loadNamespace()里算'rJava'时.onLoad失败了，详细内容：
  调用: fun(libname, pkgname)
  错误: JAVA_HOME cannot be determined from the Registry
> library(rJava)
Error: package or namespace load failed for ‘rJava’:
 loadNamespace()里算'rJava'时.onLoad失败了，详细内容：
  调用: fun(libname, pkgname)
  错误: JAVA_HOME cannot be determined from the Registry
> install.packages("rJava")
trying URL 'https://mirrors.tongji.edu.cn/CRAN/bin/windows/contrib/3.5/rJava_0.9-10.zip'
Content type 'application/zip' length 826966 bytes (807 KB)
downloaded 807 KB

package ‘rJava’ successfully unpacked and MD5 sums checked

The downloaded binary packages are in
	C:\Users\muzhitiehe\AppData\Local\Temp\Rtmp6Xz8mD\downloaded_packages
> library(xlsx)
Error: package or namespace