Try something like this
String filePath = new File("").getAbsolutePath();
filePath.concat("path to the property file");
So your new file points to the path where it is created, usually your project home folder.
[EDIT]
As @cmc said,
String basePath = new File("").getAbsolutePath();
System.out.println(basePath);
String path = new File("src/main/resources/conf.properties")
.getAbsolutePath();
System.out.println(path);
Both give the same value.