Develop Reference

Save a variable when the server is off

In fact I am making a Minecraft plugin and I was wondering how some plugins (without using DB) manage to keep information even when the server is off.
For example if we make a grade plugin and we create a different list or we stack the players who constitute each. When the server will shut down and restart afterwards, the lists will become empty again (as I initialized them).
So I wanted to know if anyone had any idea how to keep this information.

If a plugin want to save informations only for itself, and it don't need to make it accessible from another way (a PHP website for example), you can use YAML format.
Create the config file :
File usersFile = new File(plugin.getDataFolder(), "user-data.yml");
if(!usersFile.exists()) { // don't exist
usersFile.createNewFile();
// OR you can copy file, but the plugin should contains a default file
/*try (InputStream in = plugin.getResource("user-data.yml");
OutputStream out = new FileOutputStream(usersFile)) {
ByteStreams.copy(in, out);
} catch (Exception e) {
e.printStackTrace();
}*/
}
Load the file as Yaml content :
YamlConfiguration config = YamlConfiguration.loadConfiguration(usersFile);
Edit content :
config.set(playerUUID, myVar);
Save content :
config.save(usersFile);
Also, I suggest you to make I/O async (read & write) with scheduler.
Bonus:
If you want to make ONE config file per user, and with default config, do like that :
File oneUsersFile = new File(plugin.getDataFolder(), playerUUID + ".yml");
if(!oneUsersFile.exists()) { // don't exist
try (InputStream in = plugin.getResource("my-def-file.yml");
OutputStream out = new FileOutputStream(oneUsersFile)) {
ByteStreams.copy(in, out); // copy default to current
} catch (Exception e) {
e.printStackTrace();
}
}
YamlConfiguration userConfig = YamlConfiguration.loadConfiguration(oneUsersFile);
PS: the variable plugin is the instance of your plugin, i.e. the class which extends "JavaPlugin".

You can use PersistentDataContainers:
To read data from a player, use
PersistentDataContainer p = player.getPersistentDataContainer();
int blocksBroken = p.get(new NamespacedKey(plugin, "blocks_broken"), PersistentDataType.INTEGER); // You can also use DOUBLE, STRING, etc.
The Namespaced key refers to the name or pointer to the data being stored. The PersistentDataType refers to the type of data that is being stored, which can be any Java primitive type or String. To write data to a player, use
p.set(new NamespacedKey(plugin, "blocks_broken"), PersistentDataType.INTEGER, blocksBroken + 1);

Access is denied for writing to ApplicationResources.properties file

For bilingual support in an application I am working on, we are using Spring messaging which uses two files, ApplicationResources.properties and ApplicationResources_fr.properties. This works well.
Now I am trying to expand on this by making it a little more dynamic. The application will read key value pairs from the database and insert them, which gives me the following error:
java.io.FileNotFoundException: \ApplicationResources.properties (Access is denied)
I am able to check on the key value pairs so I know the path I am using is correct. I have also checked the files in Eclipse properties by right clicking, and by visiting the actual file on my system, and they are not read-only. I do not believe they are encrypted because I am able to open and view with notepad++.
Here is my testing code which shows I can view them
Properties test_prop = null;
InputStream is = null;
try {
test_prop = new Properties();
is = this.getClass().getResourceAsStream(en_path);
test_prop.load(is);
Set<Object> keys = test_prop.keySet();
boolean key_found = false;
for(Object k:keys) {
String key = (String)k;
if(key.equals("f12345"))
{
key_found=true;
break;
}
}
System.out.println("Language Properties Test in DAO:" + (key_found? "Key Found" : "Key not found"));
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (NullPointerException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
Here is where I try to write to the file, and get the error:
ResultSet rs = null;
try (
Connection connection = jdbcTemplate.getDataSource().getConnection();
CallableStatement callableStatement = connection.prepareCall(test_prod_cur);
)
{
callableStatement.registerOutParameter(1, OracleTypes.CURSOR);
callableStatement.executeUpdate();
rs = (ResultSet) callableStatement.getObject(1);
while (rs.next())
{
String thead = rs.getString(1);
//System.out.println(thead + " " + rs.getString(2) + " " + rs.getString(3));
en_prop.setProperty(keyheader+thead, rs.getString(2));
fr_prop.setProperty(keyheader+thead, rs.getString(3));
}
}
catch (SQLException e)
{
System.out.println("SQLException - bilingual values - CLUDAOImpl");
System.out.println(e.getMessage());
}
//add to properties files
//*
try (OutputStream en_os = new FileOutputStream(en_path);)
{
en_prop.store(en_os, null);
} catch (IOException e) {
e.printStackTrace();
}
try(OutputStream fr_os = new FileOutputStream(en_path);)
{
fr_prop.store(fr_os, null);
} catch (IOException e) {
e.printStackTrace();
}
So the database query is successful, that was tested with the commented out system.out.println. It is the following lines that end up throwing the error:
en_prop.store(en_os, null);
fr_prop.store(fr_os, null);
Update: I did a search on the java.util.Properties which lead me to the javadocs on it and wow does that simplify many things. I can now grab a property value or check if the key exists in 6 lines of code (not counting try catch).
Properties prop = null;
InputStream is = null;
this.prop = new Properties();
is = this.getClass().getResourceAsStream(path);
prop.load(is);
this.prop.getProperty("key name"); //returns value of key, or null
this.prop.containsKey("key name"); //returns true if key exists
Update2: There is an issue using java.util.Properties and that is you lose all formatting of the original file, so white-space, comments, and ordering are all lost. In another answer someone suggested using Apache's Commons Configuration API. I plan on trying it out.

So I ended up creating a class to handle interactions with the ApplicationResources(_fr).properties files instead of doing it in the DAO. This was because I plan on using it in more places. I also started using methods from the java.util.Properties Javadocs which proved very helpful and simplified many areas.
Below is my new file write/properties store code.
try (
OutputStream en_os = new FileOutputStream(getClass().getResource(en_path).getFile(),false);
OutputStream fr_os = new FileOutputStream(getClass().getResource(fr_path).getFile(), false);
)
{
en_prop.store(en_os, null);
fr_prop.store(fr_os, null);
} catch (IOException e) {
e.printStackTrace();
}
Lets compare the new and original OutputStreams:
OutputStream en_os = new FileOutputStream(getClass().getResource(en_path).getFile(),false); //new
OutputStream en_os = new FileOutputStream(en_path); //original, Access is Denied
This answer is incomplete for the following reasons.
I am unable to explain why the original method failed and resulted in a "Access is denied error".
More concerning reason to me, this doesnt actually alter the file I am expecting or wanting. I expected to alter the file that appears in my project navigator, but when viewed changes are not observed. If I use an absolute path (C:\...) and overwrite the file then I can alter it as expected, but this path would have to be changed as servers are changed and its bad programming and dangerous. This working method is altering some kind of temp or running file (as confirmed via the path as the file that shows the new values is in the tmp0 folder). After some testing, this temporary file is overwritten on startup only when the original file has been changed, otherwise the new values persist across application starting.
I am also unsure as to the scope of this file. I am unable to tell if all users interacting with the website would cause changes to the same file. If all users are interacting with the file, then potential leakage across sessions could occur. It is also possible that each session has isolated values and could lead to missing information. I suspect that all users are interacting with the same resource but have not performed the testing required to be absolutely positive about this. UPDATE: I have confirmed that all users interact with the same temporary file.

Problems with setting text to a textField

I am creating a client-server chat application and I intend required to store the username for a better user experience.As soon as I fire the main method, the load() method is called.This method sets the user name automatically by reading from the configurations file.The configuration file is not null (I have the user name stored). But the textField is not updating.Any ideas?Here is my load method:
public static void load()
{
Properties prop = new Properties();
InputStream input = null;
try {
input = new FileInputStream("config.properties");
prop.load(input);
textField.setText(prop.getProperty("user")); //not updating!!!!
} catch (IOException ex) {
ex.printStackTrace();
} finally {
if (input != null) {
try {
input.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}

Thanks for your help, guys.I figured out the problem.Actually, I had declared textfield as:
static JTextField textField=new JTextField();
outside main() and then again as:
textField=new JTextField();
inside the constructor.I removed the one inside the constructor and it solved the problem.
Once again thank you all for your help.

To add on to what Andreas Fester said above. You should first do a check on the file, if it exists or not, this will allow you to verify you are pointing to the right directory in the case the root of the project. Also add a clause saying something like if(prop.getProperty("user")==null){//handle null} then also try using textField.append("text"); just to see a different method and then verify by doing System.out.println("TextField: "+textField.getText()) to see if it is setting the text
If anything look at this demo given by oracle to use textfield. Also its a good practice to know when to separate member variable (belongs to instance) or class variables(static), I would avoid static like in the demo provided.
hope this helps.

How to know whether a string path is Web URL or a File based

I have a text field to acquire location information (String type) from User. It could be file directory based (e.g. C:\directory) or Web url (e.g. http://localhost:8008/resouces). The system will read some predetermined metadata file from the location.
Given the input string, how can I detect the nature of the path location whether it is a file based or Web URL effectively.
So far I have tried.
URL url = new URL(location); // will get MalformedURLException if it is a file based.
url.getProtocol().equalsIgnoreCase("http");
File file = new File(location); // will not hit exception if it is a url.
file.exist(); // return false if it is a url.
I am still struggling to find a best way to tackle both scenarios. :-(
Basically I would not prefer to explicitly check the path using the prefix such as http:// or https://
Is there an elegant and proper way of doing this?

You can check if the location starts with http:// or https://:
String s = location.trim().toLowerCase();
boolean isWeb = s.startsWith("http://") || s.startsWith("https://");
Or you can use the URI class instead of URL, URI does not throw MalformedURLException like the URL class:
URI u = new URI(location);
boolean isWeb = "http".equalsIgnoreCase(u.getScheme())
|| "https".equalsIgnoreCase(u.getScheme())
Although new URI() may also throw URISyntaxException if you use backslash in location for example. Best way would be to either use prefix check (my first suggestion) or create a URL and catch MalformedURLException which if thrown you'll know it cannot be a valid web url.

If you're open to the use of a try/catch scenario being "elegant", here is a way that is more specific:
try {
processURL(new URL(location));
}
catch (MalformedURLException ex){
File file = new File(location);
if (file.exists()) {
processFile(file);
}
else {
throw new PersonalException("Can't find the file");
}
}
This way, you're getting the automatic URL syntax checking and, that failing, the check for file existence.

you can try:
static public boolean isValidURL(String urlStr) {
try {
URI uri = new URI(urlStr);
return uri.getScheme().equals("http") || uri.getScheme().equals("https");
}
catch (Exception e) {
return false;
}
}
note that this will return false for any other reason that invalidates the url, ofor a non http/https url: a malformed url is not necessarily an actual file name, and a good file name can be referring to a non exisiting one, so use it in conjunction with you file existence check.

public boolean urlIsFile(String input) {
if (input.startsWith("file:")) return true;
try { return new File(input).exists(); } catch (Exception e) {return false;}
}
This is the best method because it is hassle free, and will always return true if you have a file reference. For instance, other solutions don't and cannot cover the plethora of protocol schemes available such as ftp, sftp, scp, or any future protocol implementations. So this one is the one for all uses and purposes; with the caveat of the file must exist, if it doesn't begin with the file protocol.
if you look at the logic of the function by it's name, you should understand that, returning false for a non existent direct path lookup is not a bug, that is the fact.

Java File.exists and other File operations returning wrong results for an existing File (network, macosx)

The filesystem AirportHDD is mounted (AFP) from the beginning and the file exists when I start this little program.
I tried to figure out the whole day why the following is not working, but couldnt find any solution:
public static void main(String[] arguments)
{
while(1==1)
{
File f=new File(
"/Volumes/AirportHDD/test/lock.csv");
System.out.println(f.exists());
AmySystem.sleep(100);
}
}
the output is:
true, true, ...
as soon as I remove the file from a different computer (AirportHDD is a mounted harddisk over network) then the output keeps saying:
true, true, ...
when I open the finder and goto this directory the output changes to: false, false, ...
when the file is added again (via another pc) the output is still:
false, false, ...
but if you open the finder again and click on the directory and finder shows the existing file, the output changes suddenly to: false, true, true, true, ...
NOTE:
also all other file operations like opening for read are failing as long as java 'thinks' the file is not there
if the program itself is creating and deleting the files then problem is not occurring
just found out while testing that with samba sharing everything is ok, but with AFP it just wont work
is there a way to tell java to do the same thing as finder, like a refresh, or do not try to cache, whatever?

I think you might be looking for the WatchService. Oracle was also kind enough to provide a tutorial.
Because the longevity of these links aren't guaranteed, I'll edit in an example code in a couple of minutes. I just wanted to let you know I think I found something in case you want to start looking at it for yourself.
UPDATE
Following the linked tutorial, I came up with code like this. I'm not sure it'll work (don't have time to test it), but it might be enough to get you started. The WatchService also has a take() method that will wait for events, which means you could potentially assume the file's existence (or lack thereof) based on the last output you gave. That will really depend on what this program will be interacting with.
If this works, good. If not, maybe we can figure out how to fix it based on whatever errors you're getting. Or maybe someone else will come along and give a better version of this code (or better option altogether) if they're more acquainted with this than I am.
public static void main(String[] arguments) {
Path path = Paths.get("/Volumes/AirportHDD/test/lock.csv");
WatchService watcher = FileSystems.getDefault().newWatchService();
WatchKey key = null;
try {
key = path.register(watcher,
ENTRY_CREATE,
ENTRY_DELETE);
} catch (IOException x) {
System.err.println(x);
}
while(true) {//I tend to favor this infinite loop, but that's just preference.
key = watcher.poll();
if(key != null) {
for (WatchEvent<?> event: key.pollEvents()) {
WatchEvent.Kind<?> kind = event.kind();
if (kind == OVERFLOW || kind == ENTRY_DELETE) {
System.out.println(false);
}
else if (kind == ENTRY_CREATE) {
System.out.println(true);
}
}//for(all events)
}//if(file event occured)
else {
File f=new File(path);
System.out.println(f.exists());
}//else(no file event occured)
AmySystem.sleep(100);
}//while(true)
}//main() method

Here is a JUnit test that shows the problem
The problem still happens using Samba on OSX Mavericks. A possible reason
is explaned by the statement in:
http://appleinsider.com/articles/13/06/11/apple-shifts-from-afp-file-sharing-to-smb2-in-os-x-109-mavericks
It aggressively caches file and folder properties and uses opportunistic locking to enable better caching of data.
Please find below a checkFile that will actually attempt to read a few bytes and forcing a true file access to avoid the caching misbehaviour ...
JUnit test:
/**
* test file exists function on Network drive
* #throws Exception
*/
#Test
public void testFileExistsOnNetworkDrive() throws Exception {
String testFileName="/Volumes/bitplan/tmp/testFileExists.txt";
File testFile=new File(testFileName);
testFile.delete();
for (int i=0;i<10;i++) {
Thread.sleep(50);
System.out.println(""+i+":"+OCRJob.checkExists(testFile));
switch (i) {
case 3:
// FileUtils.writeStringToFile(testFile, "here we go");
Runtime.getRuntime().exec("/usr/bin/ssh phobos /usr/bin/touch "+testFileName);
break;
}
}
}
checkExists source code:
/**
* check if the given file exists
* #param f
* #return true if file exists
*/
public static boolean checkExists(File f) {
try {
byte[] buffer = new byte[4];
InputStream is = new FileInputStream(f);
if (is.read(buffer) != buffer.length) {
// do something
}
is.close();
return true;
} catch (java.io.IOException fnfe) {
}
return false;
}

The problem is the network file system AFP. With the use of SAMBA everything works like expected.
Maybe the OS returns the wrong file info in OSX with the use of AFP in these scenarios.