add homedir() fcn, use java user.home with envvar fallback

Author: scivision

+stdlib/+fileio/expanduser.m

@@ -6,11 +6,7 @@
 
 expanded = p;
 
-if ispc
-  home = getenv('USERPROFILE');
-else
-  home = getenv('HOME');
-end
+home = stdlib.fileio.homedir();
 
 if ~isempty(home)
   i = startsWith(expanded, "~");

+stdlib/+fileio/homedir.m

@@ -0,0 +1,27 @@
+function home = homedir()
+
+persistent h;
+
+if ~isempty(h)
+  home = h;
+  return
+end
+
+try
+   home = string(java.lang.System.getProperty("user.home"));
+catch excp
+    % if Java not available use env vars, else error
+    if excp.identifier ~= "MATLAB:undefinedVarOrClass"
+      error("stdlib:fileio:homedir", excp.message)
+    end
+
+    if ispc
+      home = getenv('USERPROFILE');
+    else
+      home = getenv('HOME');
+    end
+end
+
+h = home;
+
+end