Develop Reference

How do I determine the host from my Java applet?

I have developed an applet that needs to read in a data file from the user. I have the user pick the file outside the applet and upload it, I then move a copy of the file to the applet folder so I can access it with the applet with only sandbox security. My problem arises from the fact that I run the applet on several hosts. How can I determine the correct host this applet was downloaded from so I can connect to the proper host for the correct data file?

See the Applet.getCodeBase() & getDocumentBase() methods.

Connecting to a sql database from an applet on the server, do you use localhost or the actual ip

I am trying to connect to a database on my website from a java applet.
When I try from eclipse, it says that there was a communications link failure and that the driver has not received any packets from the server. Is that because only applets on the actual server can connect to a database?
So I exported it as a jar and I personally signed it and uploaded it to my website. Then using as embed tag, I put it in my webpage.
<div id="blah">
<embed id="Math"
type="application/x-java-applet"
width="810" height="600"
archive="mathG.jar,mysql-connector-java-5.1.23-bin.jar"
code="com.mathg.math.MathG"
codebase="test"
pluginspage="http://java.com/download/"/>
Is that the proper way to put the applet on the site? The applet shows up and it works on the webpage, but when I press a button to connect to the database, it says that it couldn't connect.
I tried using both localhost and the actual ip in my java code to try to connect, but neither works.

Putting the IP address of the database server is preferred; localhost should only be used for quick & dirty local tests. It's unlikely that you'll deploy an app or database on localhost.
This is a very bad idea. No applet should have direct access to a database from the internet. All that data is exposed.
A better idea is to put a servlet in-between the applet and database. Deploy the servlet by exposing it to the internet; put the database behind a firewall and only open its port to the servlet. Let the servlet handle authentication, validation, binding, and interacting with the database. Users will be much better off with this design.

Connection to a remote database through an Applet

I made a applet that includes JDBC sql connector.
On my pc I can connect to the database on my server, so that works.
But when I put the applet in my browser it doesn't work.
When I load JDBC with it, it gives me an error.
And when I don't load the archive it does loads, but it doesn't connect.
Now my qeustion is.
How to connect ?
and is it possible some how to hide my database account info.
Because if I use mywebsite/java/UCP.class I can open it and I can read the password of my database account out of it...
So maybe somebody can help me with this?

For security reasons it would be better to create a web endpoint that mediates between your applet and your database.
More information here:
Execute jdbc applet in browser
and here:
http://www.stanford.edu/dept/itss/docs/oracle/10g/java.101/b10979/applet.htm

java.net.SocketPermission in Applet

I'm developing an applet that requires to save a text file on the server. After wrestling with this problem for a while I stumbled on the internet on the Lynlin.class which can send files using ftp connection. That works fine provided I add to my C:\Program Files\Java\jre7\lib\security\java.policy file a following line:
permission java.net.SocketPermission "192.168.33.15:*", "connect, accept ,resolve, listen";
If I try to run this applet from the computer that did not have the java.policy file edited I get the following error:
java.security.AccessControlException: access denied
("java.net.SocketPermission" "192.168.33.15:21" "connect,resolve")*
Does anybody know how could I get rid of this problem other than editing java.policy file at each and every computer that will be using this applet?
Just to claryfy:
my applet at the moment is not signed, but the server with which it tries to send a file is the same at which the applet is located
the http and ftp server are microsoft IIS running on the Windows Server 2003 (ip 192.168.33.15)

The exact URL is "\pwaidc9...
That's not a URL. It is a Windows UNC file name. You downloaded the applet from a file system, not a TCP host at all, so you can't connect to it with a socket.
Sign the applet.

As EJP alluded to, the address delivering the applet, and the address of the server, seem to be different to the JRE that is running the applet.
It is necessary to access the HTML via the server (an http://.. address).

There is no way for an applet to do network connections without explicit permissions to allow such activity in the client machine environment. This is so for the security of the client machine. All applets by default run in a restricted sandboxed environment.

File upload on server

I have created an applet which creates a file on running it. But when I run my applet via server, it fails.
Is there any possible way to create a file on server with applet?
EDIT:I am creating a sound record applet which works fine when I run the applet in browser locally.It actually creates a file of recorded sound,but when I run the same applet on server,it does not create file.Is it because the server does not allow you to do so?
Is there any possible solution so that the file can be created?

File objects always point to a location (that may not exist) on the client machine.
To store something on a server, it would require some server side functionality to accept the bytes and create a (server-side) File. That might be done with PHP, servlets/JSP, ASP etc. Once the server-side is organized to accept the bytes, the applet can connect to it and push the sound recording through.

Java Applets are run on the client machine. Once you invoke the page containing an applet, the applet gets downloaded to the client's machine and runs. Hence it will not get access to the server.