Java SE (Java Platform, Standard Edition)

I am learning the Java tools and policy to create some local browser application for personal use. So I signed a jar file with jarsigner, keytool and policytool and still trying to figure out why my browser application cannot read a simple local text file.

My question are

1. Why use java policy tool (policytool.exe)? If I signed a .jar with keytool and jarsigner, do I really need java policytool to write a policy?

2. What is the maximum validity days? 365? or more? Do I need to sign again when validity expire?
3. I don't want any of my local browser application gets to internet but only work with local files (read, write, or execute). how do I do that?
4. how to use java security policy to grant access to the jar applet? where do I place and import the policy file so the hosting web browser and the applet can work?

My java applet is a simple class that read a text line from a local file in the same folder, and pass the result to a calling web browser Javascript.

Currently the result in the web page is the error message below, even though the jar is signed correctly.

access denied (java.io.FilePermission hello.txt read)

Someone please help and enlight the newbie!