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I am currently in a Distributed Systems Implementation class. My
group has created a project, which is a food ordering system. It is
coded in Java and uses Microsoft Access to make tables for the users,
orders, and items. In this class, we are required to connect our
program to two servers, one primary and another back-up. Our
professor expects the back-up server to be readily available on
another computer if the primary server fails on the first computer.
Can anyone explain to me how I would link my java coded proram with
access to two servers?
Thanks
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try to connect to server1 - if it fails try server2.
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How can i start windows calcultor from a java code...
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Rather unclear here. Do you mean to start the windows calc program?
If yes, then have a look at launching external processes from java; check using this site[^].
Panic, Chaos, Destruction.
My work here is done.
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hi everybody 
i'm trying to write a program that uses "brute force" to decrypt an encrypted message (using AES), where I only have the first 96-bits of the 128-bit secret key
when i complie i got this exception:
Exception in thread "main" javax.crypto.BadPaddingException: Given final block not properly padded
my code:
public static byte[] encrypt (byte[] plainText , SecretKeySpec spc)<br />
throws NoSuchAlgorithmException,GeneralSecurityException {<br />
Cipher cipher = Cipher.getInstance("AES");<br />
cipher.init(Cipher.ENCRYPT_MODE,spc);<br />
byte[] cipherText = cipher.doFinal( plainText);<br />
return cipherText ;<br />
}<br />
<br />
public static byte[] decrypt (byte[] cipherText , SecretKeySpec spec)<br />
throws NoSuchAlgorithmException,GeneralSecurityException {<br />
Cipher cipher = Cipher.getInstance("AES");<br />
cipher.init(Cipher.DECRYPT_MODE, spec);<br />
byte[] plainText = cipher.doFinal(cipherText);<br />
return plainText ;<br />
}<br />
<br />
public static void readfile(RandomAccessFile file, byte[] bytes) throws Exception<br />
{<br />
file.seek(0);<br />
int offset = 0;<br />
int numRead = 0;<br />
while (offset < bytes.length<br />
&& (numRead=file.read(bytes, offset, bytes.length-offset)) >= 0) {<br />
offset += numRead;<br />
}<br />
}<br />
<br />
public static void main(String[] args) throws Exception {<br />
try<br />
{<br />
RandomAccessFile cipherfile = new RandomAccessFile( "ciphertext2.dat", "r" );<br />
<br />
byte[] bytes = new byte[(int)cipherfile.length()];<br />
readfile(cipherfile,bytes);<br />
<br />
RandomAccessFile file = new RandomAccessFile( "partial-key.dat", "r" );<br />
byte[] keybytes = new byte[(int)file.length()+4];<br />
readfile(file,keybytes);<br />
for(int i=0;i<256;i++)<br />
{<br />
keybytes[12]=(byte)i;<br />
for(int j=0;j<256;j++)<br />
{<br />
keybytes[13]=(byte)j;<br />
for(int k=0;k<265;k++)<br />
{<br />
keybytes[14]=(byte)k;<br />
for(int l=0;l<265;l++)<br />
{<br />
keybytes[15]=(byte)l;<br />
SecretKeySpec key = new SecretKeySpec(keybytes, "AES");<br />
byte[] plain=new byte[(int)cipherfile.length()];<br />
plain=decrypt (bytes,key);<br />
for (int y=0;y<=plain.length;y++)<br />
System.out.print((char)plain[y]);<br />
}<br />
}<br />
}<br />
}<br />
<br />
file.close();<br />
<br />
cipherfile.close();<br />
}<br />
catch ( FileNotFoundException e)<br />
{<br />
System.out.println(e);<br />
}<br />
catch ( IOException e)<br />
{<br />
System.out.println(e);<br />
}<br />
}<br />
thanks in advance![Rose | [Rose]](https://codeproject.freetls.fastly.net/script/Forums/Images/rose.gif)
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mesho wrote: for(int k=0;k<265;k++)
Are you sure this should be 265?
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sorry, it was a typing error
what about my exception?any idea? 
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mesho wrote: sorry, it was a typing error
Are you still getting the same error after correcting this? It looks like your encrypted data may be incorrect.
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yes
i don't think that the problem is with encrypted data
how about reading encrypted data, and key?
is there any mistake?
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mesho wrote: i don't think that the problem is with encrypted data
That is what the Padding Exception seems to be saying! You may need to look at the encryption side to see how the data looks at the end and then make certain that you reconstruct it in the same way during the decryption phase. Obviously if your key is wrong this may also affect the result.
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Hey all,
let me start off by saying that I'm not totally sure of whether or not I'm phrasing my question right, but here goes. I'm trying to make a trading card game, and I want to make it expandable (not to mention I don't want to hard code the cards into the game). I was brainstorming the best way to have different cards (represented as objects) and let them have different actions in their methods (for example, onPlay() and onDiscard() will have different implementations for different cards). What I want to be able to do is, on initiation, have the program load these cards into an array of AbstractCard (which all card objects will implement), from which the game can use as its database of cards. At first, I thought of storing the actions in a text file, and then having the card determine its action based on what was saved in the text file. However, I quickly realized how messy that would be, and had a different idea. Perhaps I could create a different class for each card, and compile them all separately and put them in a location on the hard drive. The program would then check that directory and load all the compiled classes it finds there, declare objects from them, and put them in the AbstractCard array (to me, this sounds similar to what a plug-in system does).
So, my question(s) is(are), is this a good way of going about this? If so, how should I implement it? With regards to the implementation, this sounds kind of like reflection, but I have no experience in that area and so am not sure how to go about doing that.
Thanks,
Chuck Murphy
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Inheritance is your friend! This is the classic example of using it.
Start with your nice basic abstract class:
abstract class Card
{
private String description;
Card(String description)
{
this.description = description;
}
abstract void onPlay();
abstract void onDiscard();
}
Then for each type of card you need, have another class:
class RealCard extend Card
{
RealCard()
{
super("This is a real card");
}
void onPlay()
{
}
void onDiscard()
{
}
}
That is the better way to design things.
The second part of how to store the objects is covered by a simple enough idea - serialization. Get your card classes right and hard code them to start with, then worry about the persistaance; it should be relatively easy.
Panic, Chaos, Destruction.
My work here is done.
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Well, you see, I'm already doing that, I'm just looking for how to offer users the ability to create their own cards and add them to the game, without needing to get the source, add some classes, and recompile the game. Also, assume here that these users are trusted, I know someone could stick some malicious code in one of these user-created cards if I follow this method 
Here's some psuedo-code:
LinkedList<AbstractCard> lstAllCards = new LinkedList<AbstractCard>();
for each file in directory "user_cards/"
{
if file is a java class
{
AbstractCard newCard = file.instantiate()
lstAllCards.add(newCard);
}
}
From what I've read of reflection, the way to do this might be to try this:
AbstractCard newCard = Class.forName(fileName).newInstance();
Also, after reading this, I may want to have the card list be a LinkedList<Class>, not a LinkedList<AbstractCard>, so that I can instantiate new cards at will without having to refer back to these initial instances. Am I on the right track?
EDIT: angle brackets weren't showing up for the generics, replaced them with "& lt;" and "& gt";
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I have searched high and low (and yes - even in the jCIFS library) on how to share a directory/folder in Java. I have seen it done in C# (the language I am more familiar with), but have not been able to figure out how to do it in Java. Please, Java experts please help me out and point me in the right direction!
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I don't think you can because this is OS-specific behaviour. You could use JNI to call a Windows API or shell out to run NET SHARE, but I as far as I am aware you can't do it directly from within Java.
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Oh no! Thank you so much for replying. The project I am working on has to work on multiple platforms (Window, Mac, Linux, Unix, etc).
I guess we might have to do it differently for each platform we connect to - I forgot to mention that I wanted to do it remotely. I am able to create a directory using the jCIFS library.
Do you know of a way to remotely determine what OS is running on machine we connect to - that is another issue I have yet to determine if is possible.
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I'm working on a servelet project. I use database connection (jdbc odbc) when I try to access data into database, I get HTTP status 500 error
java.lang.NullPointerException
checkpps.doGet(checkpps.java:61)
javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
line 61 in my code is : statement = link.createStatement();
any body could help me please???
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At the risk of stating the obvious, link is null. More than that I cannot say, because I don't know what link is or how you get hold of it.
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import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;
public class checkpps extends HttpServlet{
private Statement statement;
private Connection link;
private String URL = "jdbc:odbc:quiz";
String name;
public void init() throws ServletException
{
super.init();
try{
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
link = DriverManager.getConnection("jdbc:odbc:quiz","sara", "sara");
}
catch (ClassNotFoundException e1){
System.out.println("driver not found");
}
catch (SQLException e2){
System.out.println("error in connection");
}
}
public void doGet ( HttpServletRequest req,
HttpServletResponse res) throws ServletException, IOException {
res.setContentType ("text/html");
PrintWriter out= res.getWriter();
String city = req.getParameter("city");
String ppsnum = req.getParameter("ppsno");
try {
statement = link.createStatement();
ResultSet result = statement.executeQuery("SELECT * FROM player");
while(result.next())
{
out.println("<p>" + result.getString("ppsno"));
}
}
catch (SQLException e)
{
System.out.println("error statement");
}
}
public void destroy()
{
try {
link.close();
}
catch (Exception e) {
System.out.println("error on closing!!");
e.printStackTrace();
System.exit(1);
}
}
}
as you see in my code, I'm trying to connect to database (MS Access) and link is my connection name. seems my connection has problem for some reason but still couldn't solve it. I have created DSN by the way.
any help?
modified on Wednesday, November 11, 2009 8:51 AM
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Which MSOffice you are using. And r you sure that you have selected the correct driver type.
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Hey Everyone
I am learning Java and would like to know how to get started on writing a piece of code that takes a collection of objects (which are answers from a form) and save it in a file (xml or .txt)
the FORM can be design from any visual editor (Flex, SWING, HTML, JSP etc...)
but once the form has been filled out, I want to save all the answers in a xml or .txt file
Any help would be greatly appreciated
thanks
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public void saveAnswers()
{
try
{
FileWriter fw = new FileWriter("Questions.txt");
PrintWriter pw = new PrintWriter(fw);
pw.println(textBox1.getText());
pw.println(textBox2.getText());
pw.println(textBox3.getText());
pw.println(textBox4.getText());
pw.flush();
}
}catch(Exception e)
{
System.out.println(e);
}
}
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Hi all,
Actually, i have developed a java application that connects with Ms Access database. now i want to deploy this application. is there a way i can bundle my database inside the jar. if not please suggest some appropriate way ( a step by step procedure)
thanx
regards
Adeel
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Is there a Java validator out there that can validate against the proposed W3C XSD v1.1 specification? I am currently validating against an XSD v1.0, but would like to add a number of assert statements and conditional attributes. If it helps, my current validation against XSD v1.0 is performed as follows (assume xsdFullPath and xmlFullPath are already defined):
parserFactory = javax.xml.parsers.DocumentBuilderFactory.newInstance();
parserFactory.setNamespaceAware(true);
parserFactory.setXIncludeAware( true);
parserFactory.setFeature('http://apache.org/xml/features/xinclude/fixup-base-uris',false);
parserFactory.setFeature('http://apache.org/xml/features/xinclude/fixup-language' ,false);
parser = parserFactory.newDocumentBuilder();
parser.setErrorHandler(org.xml.sax.helpers.DefaultHandler());
document = parser.parse(xmlFullPath);
xmldom = javax.xml.transform.dom.DOMSource(document);
factory = javax.xml.validation.SchemaFactory.newInstance(...
javax.xml.XMLConstants.W3C_XML_SCHEMA_NS_URI);
schemaFile = javax.xml.transform.stream.StreamSource(xsdFullPath);
schema = factory.newSchema(schemaFile);
validator = schema.newValidator();
validator.validate(xmldom);Thanks,
Sounds like somebody's got a case of the Mondays
-Jeff
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I have a simple question, I developed a java application, which runs on Oracle application server and Oracle database. This application depends on multiple JSPs on which multiple users can access a single JSP in the same time, some problems occurs due to the excessive usage of this application and I have some questions about them:
1. Is there any danger or disadvantages in connecting to the database using the jdbc directly from the JSP ?!!
2. An error occurs almost once a week (most probably at the point of time when an excessive usage happens). This error stops the users from submitting or accessing the some JSPs. I ran the following query on the DB to find any locked items:
SELECT o.owner, o.object_name, o.object_type, o.last_ddl_time, o.status,l.session_id, l.oracle_username, l.locked_mode
FROM dba_objects o, gv$locked_object l
WHERE o.object_id = l.object_id;
I found that the table I use to select from in the halted JSPs is a result of this query.
In order to solve this problem temporarily, i use the sql developer to add a record to this table and commit, i find that the problem is solved and the halted jsps involved are running.
These are the exceptions that appears in the log files of the application server right after I press commit:
a.java.lang.IllegalStateException: Session was invalidated (all the time)
b.java.sql.SQLException: Closed Connection (some times)
I do not know exactly where to start debugging, since i use synchronization in all of my code. Also I made sure that each user accessing the same JSP has a separate connection.
Thanks in advance
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