title: Why do I get the below error while loading the xlsx package in R?
body: <pre><code>&gt; library(xlsx)
  Error : .onAttach failed in attachNamespace() for 'xlsx', details:
    call: .jnew("org/apache/poi/xssf/usermodel/XSSFWorkbook")
    error: java.lang.NoClassDefFoundError
  Error: package or namespace load failed for ‘xlsx’
  </code></pre>
  
  <p>Is there any requirement in JDK that I am missing?</p>
  
  <p>Also in the same breath, I keep getting a different kind of error in another Windows system like below, which says it can't find the dlls of Java software, despite Java being installed and environment variables set.</p>
  
  <pre><code>&gt; library(xlsx)
  Loading required package: rJava
  Error : .onLoad failed in loadNamespace() for 'rJava', details:
    call: inDL(x, as.logical(local), as.logical(now), ...)
    error: unable to load shared object 'E:/R Project/Softwares/R-  3.1.2/library/rJava/libs/x64/rJava.dll':
    LoadLibrary failure:  The specified module could not be found.
  
  Error: package ‘rJava’ could not be loaded
  </code></pre>