Parse Java source code file into PSI file and do some operations on the PSI elements

Hi,

Is it possible to parse a java source code file (like a path of the file) and convert it into a PSI file so that I could iterate over the PSI elements in it? 

I saw a few similar posts and tried their approaches. For example in below, a PsiManager is used to create (or find) the virtual file. However, a "Project project" parameter is needed ("mProject" in the below example) and I do not know how to get that parameter. Could someone shed some light on this?  

Thank you! :)

The code below is obtained from https://gist.github.com/agaricusb/4367023

if (!virtualFile.isDirectory() && "java".equalsIgnoreCase(virtualFile.getExtension()) ) {
 
PsiManager psiMgr = PsiManager.getInstance(mProject);
PsiFile file = psiMgr.findFile(virtualFile);
if (!(file instanceof PsiJavaFile) ) {
 
PsiJavaFile jFile = PsiJavaFile)psiMgr.getElementFactory().createFileFromText("temp.java", file.getText());
 
// do whatever you want with your PsiJavaFile
}