Develop Reference

Java: How do I get a unique serial ID for the computer that will never change

I am making a program that requires a unique serial ID for the computer that is running the program. It needs to never change (or change very rarely AND the user has to know when it will change in advance). Also I need it to either work on Linux, Mac and Windows (maybe even Solaris) or one way for each.
I have tried this...
try
{
Process process = Runtime.getRuntime().exec(new String[]
{
"wmic", "bios", "get", "serialnumber"
});
process.getOutputStream().close();
Scanner sc = new Scanner(process.getInputStream());
String property = sc.next();
String serial = sc.next();
System.out.println(property + ": " + serial);
} catch(IOException e)
{
e.printStackTrace();
}
but WMIC is only on windows. But other than that, it's perfect.
Just a way to do that on a Mac and in Linux would be perfect

There is no computer serial number, even if there were, the client's software could be modified to send any number. You could somehow incorporate the network card's media access control address (MAC address), but that can be altered by software, or the card could be swapped out, or there could be multiple cards.
About the only thing you can do for a voting application is to use secure hardware that contains a unique number that can't be copied coupled with encryption. This is what smartcards do.

Create a database / execute a bunch of mysql statements from Java

I have a library that needs to create a schema in MySQL from Java. Currently, I have a dump of the schema that I just pipe into the mysql command. This works okay, but it is not ideal because:
It's brittle: the mysql command needs to be on the path: usually doesn't work on OSX or Windows without additional configuration.
Also brittle because the schema is stored as statements, not descriptively
Java already can access the mysql database, so it seems silly to depend on an external program to do this.
Does anyone know of a better way to do this? Perhaps...
I can read the statements in from the file and execute them directly from Java? Is there a way to do this that doesn't involve parsing semicolons and dividing up the statements manually?
I can store the schema in some other way - either as a config file or directly in Java, not as statements (in the style of rails' db:schema or database.yml) and there is a library that will create the schema from this description?
Here is a snippet of the existing code, which works (when mysql is on the command line):
if( db == null ) throw new Exception ("Need database name!");
String userStr = user == null ? "" : String.format("-u %s ", user);
String hostStr = host == null ? "" : String.format("-h %s ", host);
String pwStr = pw == null ? "" : String.format("-p%s ", pw);
String cmd = String.format("mysql %s %s %s %s", hostStr, userStr, pwStr, db);
System.out.println(cmd + " < schema.sql");
final Process pr = Runtime.getRuntime().exec(cmd);
new Thread() {
public void run() {
try (OutputStream stdin = pr.getOutputStream()) {
Files.copy(f, stdin);
}
catch (IOException e) { e.printStackTrace(); }
}
}.start();
new Thread() {
public void run() {
try (InputStream stdout = pr.getInputStream() ) {
ByteStreams.copy(stdout, System.out);
}
catch (IOException e) { e.printStackTrace(); }
}
}.start();
int exitVal = pr.waitFor();
if( exitVal == 0 )
System.out.println("Create db succeeded!");
else
System.out.println("Exited with error code " + exitVal);

The short answer (as far as i know) is no.
You will have to do some parsing of the file into separate statements.
I have faced the same situation and you can find many questions on this topic here on SO.
some like here will show a parser. others can direct to tools Like this post from apache that can convert the schema to an xml format and then can read it back.
My main intention when writing this answer is to tell that I chose to use the command line in the end.
extra configuration: maybe it is an additional work but you can do it by config or at runtime based on the system you are running inside. you do the effort one time and you are done
depending on external tool: it is not as bad as it seems. you have some benefits too.
1- you don't need to write extra code or introduce additional libraries just for parsing the schema commands.
2- the tool is provided by the vendor. it is probably more debugged and tested than any other code that will do the parsing.
3- it is safer on the long run. any additions or changes in the format of dump that "might" break the parser will most probably be supported with the tool that comes with the database release. you won't need to do any change in your code.
4- the nature of the action where you are going to use the tool (creating schema) does not suggest frequent usage, minimizing the risk of it becoming a performance bottle neck.
I hope you can find the best solution for your needs.

Check out Yank, and more specifically the code examples linked to on that page. It's a light-weight persistence layer build on top of DBUtils, and hides all the nitty-gritty details of handling connections and result sets. You can also easily load a config file like you mentioned. You can also store and load SQL statements from a properties file and/or hard code the SQL statements in your code.

Sending a password to a Java Process

I am trying to access SVN through the process command in Java as part of a larger GUI to see what files are on the SVN. After much research, I have significantly refined my methods, however I still cannot accomplish it. If I run the code in the GUI, it just hangs. To discover what that problem was, I simplified it and ran it as a console program. When I ran it there, it displayed a request for my GNOME keyring. My code enters the password but the console does not seem to accept it. My code follows:
public class SvnJavaTest{
public static void main(String[] args){
try {
String[] commands = {"svn", "ls", "https://svnserver"};
Process beginProcess = Runtime.getRuntime().exec(commands, null, new File("/home/users/ckorb/Desktop"));
BufferedReader br = new BufferedReader(new InputStreamReader(beginProcess.getInputStream()));
BufferedWriter write = new BufferedWriter(new OutputStreamWriter(beginProcess.getOutputStream()));
write.write("password");
write.flush();
String line=br.readLine();
while (line != null){
System.out.println(line);
line =br.readLine();
}
br.close();
write.close();
beginProcess.waitFor();
} catch (IOException e1) {
e1.printStackTrace();
} catch (InterruptedException ie) {
ie.printStackTrace();
}
}
}
I don't get any errors running this and if I type in my password manually into the console and then run it, it works because it remembers my password. I have looked and found that there are some packages that would automatically enter my keyring on login but that isn't really an option. Thank you very much.

The main problem with a solution like this is that you don't really have control over stdin and stdout. A malicious person can wrap the svn command with a shell script that makes a copy of the stdin (thereby capturing all the passwords your program transmits). While shell's flexibility makes it great in so many ways, it is the same flexibility that you are connecting to, and you'd better be comfortable with it (and it's consequences).
That is the real reason why it is better to use a Java API to use the client, there's a much smaller chance of injecting code which captures sensitive data (and better error reporting).

Use the SVN Kit library instead.

Better to use svn java API (there are several, I am not sure which one is better), it's more straightforward solution.
Answering you question - you could provide auth info in the url: https://username:password#svnserver

Query Windows Search from Java

I would like to get to query Windows Vista Search service directly ( or indirectly ) from Java.
I know it is possible to query using the search-ms: protocol, but I would like to consume the result within the app.
I have found good information in the Windows Search API but none related to Java.
I would mark as accepted the answer that provides useful and definitive information on how to achieve this.
Thanks in advance.
EDIT
Does anyone have a JACOB sample, before I can mark this as accepted?
:)

You may want to look at one of the Java-COM integration technologies. I have personally worked with JACOB (JAva COm Bridge):
http://danadler.com/jacob/
Which was rather cumbersome (think working exclusively with reflection), but got the job done for me (quick proof of concept, accessing MapPoint from within Java).
The only other such technology I'm aware of is Jawin, but I don't have any personal experience with it:
http://jawinproject.sourceforge.net/
Update 04/26/2009:
Just for the heck of it, I did more research into Microsoft Windows Search, and found an easy way to integrate with it using OLE DB. Here's some code I wrote as a proof of concept:
public static void main(String[] args) {
DispatchPtr connection = null;
DispatchPtr results = null;
try {
Ole32.CoInitialize();
connection = new DispatchPtr("ADODB.Connection");
connection.invoke("Open",
"Provider=Search.CollatorDSO;" +
"Extended Properties='Application=Windows';");
results = (DispatchPtr)connection.invoke("Execute",
"select System.Title, System.Comment, System.ItemName, System.ItemUrl, System.FileExtension, System.ItemDate, System.MimeType " +
"from SystemIndex " +
"where contains('Foo')");
int count = 0;
while(!((Boolean)results.get("EOF")).booleanValue()) {
++ count;
DispatchPtr fields = (DispatchPtr)results.get("Fields");
int numFields = ((Integer)fields.get("Count")).intValue();
for (int i = 0; i < numFields; ++ i) {
DispatchPtr item =
(DispatchPtr)fields.get("Item", new Integer(i));
System.out.println(
item.get("Name") + ": " + item.get("Value"));
}
System.out.println();
results.invoke("MoveNext");
}
System.out.println("\nCount:" + count);
} catch (COMException e) {
e.printStackTrace();
} finally {
try {
results.invoke("Close");
} catch (COMException e) {
e.printStackTrace();
}
try {
connection.invoke("Close");
} catch (COMException e) {
e.printStackTrace();
}
try {
Ole32.CoUninitialize();
} catch (COMException e) {
e.printStackTrace();
}
}
}
To compile this, you'll need to make sure that the JAWIN JAR is in your classpath, and that jawin.dll is in your path (or java.library.path system property). This code simply opens an ADO connection to the local Windows Desktop Search index, queries for documents with the keyword "Foo," and print out a few key properties on the resultant documents.
Let me know if you have any questions, or need me to clarify anything.
Update 04/27/2009:
I tried implementing the same thing in JACOB as well, and will be doing some benchmarks to compare performance differences between the two. I may be doing something wrong in JACOB, but it seems to consistently be using 10x more memory. I'll be working on a jcom and com4j implementation as well, if I have some time, and try to figure out some quirks that I believe are due to the lack of thread safety somewhere. I may even try a JNI based solution. I expect to be done with everything in 6-8 weeks.
Update 04/28/2009:
This is just an update for those who've been following and curious. Turns out there are no threading issues, I just needed to explicitly close my database resources, since the OLE DB connections are presumably pooled at the OS level (I probably should have closed the connections anyway...). I don't think I'll be any further updates to this. Let me know if anyone runs into any problems with this.
Update 05/01/2009:
Added JACOB example per Oscar's request. This goes through the exact same sequence of calls from a COM perspective, just using JACOB. While it's true JACOB has been much more actively worked on in recent times, I also notice that it's quite a memory hog (uses 10x as much memory as the Jawin version)
public static void main(String[] args) {
Dispatch connection = null;
Dispatch results = null;
try {
connection = new Dispatch("ADODB.Connection");
Dispatch.call(connection, "Open",
"Provider=Search.CollatorDSO;Extended Properties='Application=Windows';");
results = Dispatch.call(connection, "Execute",
"select System.Title, System.Comment, System.ItemName, System.ItemUrl, System.FileExtension, System.ItemDate, System.MimeType " +
"from SystemIndex " +
"where contains('Foo')").toDispatch();
int count = 0;
while(!Dispatch.get(results, "EOF").getBoolean()) {
++ count;
Dispatch fields = Dispatch.get(results, "Fields").toDispatch();
int numFields = Dispatch.get(fields, "Count").getInt();
for (int i = 0; i < numFields; ++ i) {
Dispatch item =
Dispatch.call(fields, "Item", new Integer(i)).
toDispatch();
System.out.println(
Dispatch.get(item, "Name") + ": " +
Dispatch.get(item, "Value"));
}
System.out.println();
Dispatch.call(results, "MoveNext");
}
} finally {
try {
Dispatch.call(results, "Close");
} catch (JacobException e) {
e.printStackTrace();
}
try {
Dispatch.call(connection, "Close");
} catch (JacobException e) {
e.printStackTrace();
}
}
}

As few posts here suggest you can bridge between Java and .NET or COM using commercial or free frameworks like JACOB, JNBridge, J-Integra etc..
Actually I had an experience with with one of these third parties (an expensive one :-) ) and I must say I will do my best to avoid repeating this mistake in the future. The reason is that it involves many "voodoo" stuff you can't really debug, it's very complicated to understand what is the problem when things go wrong.
The solution I would suggest you to implement is to create a simple .NET application that makes the actual calls to the windows search API. After doing so, you need to establish a communication channel between this component and your Java code. This can be done in various ways, for example by messaging to a small DB that your application will periodically pull. Or registering this component on the machine IIS (if exists) and expose simple WS API to communicate with it.
I know that it may sound cumbersome but the clear advantages are: a) you communicate with windows search API using the language it understands (.NET or COM) , b) you control all the application paths.

Any reason why you couldn't just use Runtime.exec() to query via search-ms and read the BufferedReader with the result of the command? For example:
public class ExecTest {
public static void main(String[] args) throws IOException {
Process result = Runtime.getRuntime().exec("search-ms:query=microsoft&");
BufferedReader output = new BufferedReader(new InputStreamReader(result.getInputStream()));
StringBuffer outputSB = new StringBuffer(40000);
String s = null;
while ((s = output.readLine()) != null) {
outputSB.append(s + "\n");
System.out.println(s);
}
String result = output.toString();
}
}

There are several libraries out there for calling COM objects from java, some are opensource (but their learning curve is higher) some are closed source and have a quicker learning curve. A closed source example is EZCom. The commercial ones tend to focus on calling java from windows as well, something I've never seen in opensource.
In your case, what I would suggest you do is front the call in your own .NET class (I guess use C# as that is closest to Java without getting into the controversial J#), and focus on making the interoperability with the .NET dll. That way the windows programming gets easier, and the interface between Windows and java is simpler.
If you are looking for how to use a java com library, the MSDN is the wrong place. But the MSDN will help you write what you need from within .NET, and then look at the com library tutorials about invoking the one or two methods you need from your .NET objects.
EDIT:
Given the discussion in the answers about using a Web Service, you could (and probably will have better luck) build a small .NET app that calls an embedded java web server rather than try to make .NET have the embedded web service, and have java be the consumer of the call. For an embedded web server, my research showed Winstone to be good. Not the smallest, but is much more flexible.
The way to get that to work is to launch the .NET app from java, and have the .NET app call the web service on a timer or a loop to see if there is a request, and if there is, process it and send the response.

How to allow running only one instance of a Java program at a time?

I need to prevent users from starting my Java application (WebStart Swing app) multiple times. So if the application is already running it shouldn't be possible to start it again or show a warning / be closed again.
Is there some convenient way to achieve this? I thought about blocking a port or write sth to a file. But hopefully you can access some system properties or the JVM?
btw. target platform is Windows XP with Java 1.5

I think your suggestion of opening a port to listen when you start your application is the best idea.
It's very easy to do and you don't need to worry about cleaning it up when you close your application. For example, if you write to a file but someone then kills the processes using Task Manager the file won't get deleted.
Also, if I remember correctly there is no easy way of getting the PID of a Java process from inside the JVM so don't try and formulate a solution using PIDs.
Something like this should do the trick:
private static final int PORT = 9999;
private static ServerSocket socket;
private static void checkIfRunning() {
try {
//Bind to localhost adapter with a zero connection queue
socket = new ServerSocket(PORT,0,InetAddress.getByAddress(new byte[] {127,0,0,1}));
}
catch (BindException e) {
System.err.println("Already running.");
System.exit(1);
}
catch (IOException e) {
System.err.println("Unexpected error.");
e.printStackTrace();
System.exit(2);
}
}
This sample code explicitly binds to 127.0.0.1 which should avoid any firewall warnings, as any traffic on this address must be from the local system.
When picking a port try to avoid one mentioned in the list of Well Known Ports. You should ideally make the port used configurable in a file or via a command line switch in case of conflicts.

As the question states that WebStart is being used, the obvious solution is to use javax.jnlp.SingleInstanceService.
This service is available in 1.5. Note that 1.5 is currently most of the way through its End Of Service Life period. Get with Java SE 6!

I think that the better idea would be to use file lock (quite an old idea :) ). Since Java 1.4 a new I/O library was introduced, that allows file locking.
Once the application starts it tries to acquire lock on a file (or create it if does not exist), when the application exits the lock is relased. If application cannot acquire a lock, it quits.
The example how to do file locking is for example in Java Developers Almanac.
If you want to use file locking in Java Web Start application or an applet you need to sing the application or the applet.

You can use JUnique library. It provides support for running single-instance java application and is open-source.
http://www.sauronsoftware.it/projects/junique/
See also my full answer at How to implement a single instance Java application?

We do the same in C++ by creating a kernal mutex object and looking for it at start up. The advantages are the same as using a socket, ie when the process dies/crashes/exits/is killed, the mutex object is cleaned up by the kernel.
I'm not a Java programmer, so I am not sure whether you can do the same kind of thing in Java?

I've create the cross platform AppLock class.
http://mixeddev.info/articles/2015/02/01/run-single-jvm-app-instance.html
It is using file lock technique.
Update. At 2016-10-14 I've created package compatible with maven/gradle https://github.com/jneat/jneat and explained it here http://mixeddev.info/articles/2015/06/01/synchronize-different-jvm-instances.html

You could use the registry, although this halfheartedly defeats the purpose of using a high-level language like java. At least your target platform is windows =D

Try JUnique:
String appId = "com.example.win.run.main";
boolean alreadyRunning;
try {
JUnique.acquireLock(appId);
alreadyRunning = false;
} catch (AlreadyLockedException e) {
alreadyRunning = true;
}
if (alreadyRunning) {
Sysout("An Instance of this app is already running");
System.exit(1);
}

I've seen so many of this questions and I was looking to solve the same problem in a platform independent way that doesn't take the chance to collide with firewalls or get into socket stuff.
So, here's what I did:
import java.io.File;
import java.io.IOException;
/**
* This static class is in charge of file-locking the program
* so no more than one instance can be run at the same time.
* #author nirei
*/
public class SingleInstanceLock {
private static final String LOCK_FILEPATH = System.getProperty("java.io.tmpdir") + File.separator + "lector.lock";
private static final File lock = new File(LOCK_FILEPATH);
private static boolean locked = false;
private SingleInstanceLock() {}
/**
* Creates the lock file if it's not present and requests its deletion on
* program termination or informs that the program is already running if
* that's the case.
* #return true - if the operation was succesful or if the program already has the lock.<br>
* false - if the program is already running
* #throws IOException if the lock file cannot be created.
*/
public static boolean lock() throws IOException {
if(locked) return true;
if(lock.exists()) return false;
lock.createNewFile();
lock.deleteOnExit();
locked = true;
return true;
}
}
Using System.getProperty("java.io.tmpdir") for the lockfile path makes sure that you will always create your lock on the same place.
Then, from your program you just call something like:
blah blah main(blah blah blah) {
try() {
if(!SingleInstanceLock.lock()) {
System.out.println("The program is already running");
System.exit(0);
}
} catch (IOException e) {
System.err.println("Couldn't create lock file or w/e");
System.exit(1);
}
}
And that does it for me. Now, if you kill the program it won't delete the lock file but you can solve this by writing the program's PID into the lockfile and making the lock() method check if that process is already running. This is left as an assingment for anyone interested. :)