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Java Newsletters Archive: 17
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JavaFAQ Home » Java Newsletters
***********************************************
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ *
* > The Java FAQ
Daily Tips, weekly publication < *
*
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ *
*
* Issue No: 17 27
December 2000
* http://www.javafaq.nu/java
*
*
* Please
recommend our FREE "100 Java Tips" book and us to your
* friends and
colleagues!
* http://javafaq.nu/java/advert/our_book.shtml
***********************************************
Table
of Contents
1. I don't know anything about security... Part 2.
2. I
guess what I'm asking is "Is java.util.Hashtable
thread safe?"
3. Is
there any way to run code after the VM has been
instructed to exit?
4.
Why would anyone use AWT and not Swing today?
5. I'm working on a java
project and looking for a better
API that can generate PDF, work with Excel,
Word documents...
6. Where can I find Java --> Native code
compilers?
7. I have a directory having class files arranged in package
hierarcy. How can I make the executable of this whole
directory?
***********************************************
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Tip
1 Q: I need to read C: est.doc for example and store it
somewhere for my
future use. I don't know anything about security.
Part 2, Part 1 was
published last week.
Answer :
I think they want you to go out and buy
a cert from Verisign or
Thawte, etc. You can also generate your own signing
certificate
through openSSL, or some other package, but, if you do, you'll
need to have them import it into their database as a trusted signer.
This can be done with a simple Perl script which sends the
certificate
with a header of:
"Content-Type: application/x-x509-ca-cert"
You must also
add some code to your applet to use the Netscape
way of signing. You can
download the file 'capsapi_classes.zip'
from Netscape. This file contains
the Netscape Capabilities API.
Basically, all you need to do is import the
package and enable
privileges as you need them. It is important to enable
privileges
in the same method (ie. same frame stack)
in which you are
going to use them. You cannot just enable all
the privileges you need in the
init method of your applet. The
code looks something like
this:
import netscape.security.*;
public void MyMethod() {
try
{
PrivilegeManager.enablePrivilege("UniversalFileRead");
FileInputStream
fis = new FileInputStream("myfile");
} catch (Exception e)
{
System.out.println(e);
}
} // end MyMethod
You'll need to add
'capsapi_classes.zip' to the archive attribute
of your applet tag. I also
believe it is possible to grant
privileges to a codebase in Netscape without
signing. This is
done by editing the 'prefs.js' file on the client.
Obviously,
this is not possible on the internet, but, for an intranet
environment, this could be a solution. Anyway, when an applet
tries to
enable a privilege, the Netscape browser will pop up a
window asking the
user if they wish to grant the privilege. This
decision can be
persistent.
The user can manage the privileges they have granted by clicking
on the padlock icon in the bottom left corner of their browser
window,
and selecting the "Java/JavaScript" section.
If your users may be using
Microsoft IE as well as Netscape,
you'll have to learn the Microsoft
security API. I haven't done
this yet, but I believe it is possible to code
an applet so that
it will work in either browser.
Another alternative is
to code different versions of the applet,
and build the page containing the
applet dynamically, based on
the "User-Agent". I have found that it is
possible in IE to grant
universal privileges to an applet, even if it is not
signed, but
I sure wouldn't recommend doing that.
***********************************************
Tip
2 Q: I guess what I'm asking is "Is java.util.Hashtable
thread
safe?"
It's been a while since I've used hashtables for anything
significant, but I seem to recall the get() and put()
methods being
synchronized.
The JavaDocs don't reflect this. They simply say that the
class
Hashtable is synchronized. What can I assume? If several threads
access the hashtable at the same time (assuming they are not
modifying
the same entry), the operations will succeed, right?
I guess what I'm asking
is "Is java.util.Hashtable thread safe?"
A: That is right! It is
recommendable, if you have questions like
these, always look at source for
the api, it's freely
available.
***********************************************
Tip
3 Q: Is there any way to run code after the VM has been
instructed to
exit?
A: In 1.3, you can use Runtime.addShutdownHook(Thread
hook)
***********************************************
Tip
4 Q: Why would anyone use AWT and not Swing today?
A: There are several
handheld devices that do not have a lot of
memory or CPU power available,
AWT is more suitable for them
(Smaller footprint).
Tip
5 Q: I'm working on a java project and looking for a better
API that can
generate PDF, work with Excel, Word documents...
Where can I find
it?
Answer: We have a list
here:
http://www.javafaq.nu/java/office/index.shtml
***********************************************
Tip
6 Q: Where can I find Java --> Native code compilers?
Answer: We just
published a list of Java products that lets you do
Java --> Native code
compilation:
http://javafaq.nu/java/staff/staff.shtml
***********************************************
Tip
7 Q: I have a directory having class files arranged in package
hierarcy. How
can I make the executable of this whole directory?
Any application
available for that in Windows NT environment.
Answer: Make a JAR file out
of it and add a manifest file that
indicates which main() method of which
class must be called.
Double-clicking this JAR file will run your
application.
The
Java FAQ Daily Tips is a newsletter that is only sent to those
who have
specifically subscribed to it.
Copyright (c) 2000 John
Andersson
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