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.

Active Directory - search by specifying a search filter and search controls and no context

I followed this tutorial to search in active directory.
Sample code :
class SearchSubtree {
public static void main(String[] args) {
Hashtable<String, Object> env = new Hashtable<String, Object>(11);
env
.put(Context.INITIAL_CONTEXT_FACTORY,
"com.sun.jndi.ldap.LdapCtxFactory");
env.put(Context.PROVIDER_URL, "ldap://localhost:389/o=JNDITutorial");
try {
DirContext ctx = new InitialDirContext(env);
String[] attrIDs = { "sn", "telephonenumber", "golfhandicap", "mail" };
SearchControls ctls = new SearchControls();
ctls.setReturningAttributes(attrIDs);
ctls.setSearchScope(SearchControls.SUBTREE_SCOPE);
String filter = "(&(sn=Geisel)(mail=*))";
NamingEnumeration answer = ctx.search("", filter, ctls);
// Print the answer
ctx.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
But NameNotFoundException is thrown at
NamingEnumeration answer = ctx.search("", filter, ctls);
But when I pass, "DC=extldap,DC=com" as first argument, code works fine.
Is there any issue with the tutorial? Can first argument not be empty string? Or is this a limitation with Active Directory?

Generally speaking, for LDAP servers you always need a root context to start your search from. Basically, you are doing the equivalent of trying to search a SQL database without specifying a database or table name.
Some server implementations may allow an empty context (I know iPlanet used to allow it in some cases) but these are exceptions to the rule.
The javadoc for DirContext.search() says:
Searches in the named context or object for entries that satisfy the
given search filter. Performs the search as specified by the search
controls.
See search(Name, String, SearchControls) for details.
Parameters:
name the name of the context or object to search
...
Usually, in Active Directory it is fine to start searching from the domain root, which is always DC=<your>,DC=<domain>.
That is why your second search works.

error while creating adminclient for websphere 7.0.0.11

I need to develop an application for managing WebSphere Application Server v7.0.0.11. I explored a bit and found out that we can use Mbeans. Actually I need to create something similar as Web-sphere's web console.
My problem is that the application should be in C# .net so is there any connector/Adapter to invoke web-sphere's management API. Please point me in right direction.
I am a C#.net developer and a total newbie in java/websphere, I tried creating Admin Client Example from IBM site by using packages found at IBM/Webshpere/Cimrepos directory. The name of Jar file is com.ibm.wplc.was_7.0.0.11.jar I unzipped that jar file in the same folder.
So now My App is starts, connects to websphere successfully and finds mbean on the nodeAgent. The problem I am facing in invoking mbean. I am getting following error message.
exception invoking launchProcess : javax.management.ReflectionExcetion: Target Method not found com.ibm.ws.management.nodeagent.NodeAgent.launchProcess
I am using following url for list of mbean
http://pic.dhe.ibm.com/infocenter/wasinfo/v7r0/index.jsp?topic=/com.ibm.websphere.javadoc.doc/web/mbeanDocs/index.html
i tried using different methods from nodeAgent mbean but no joy , I am always getting same exception "method not found".
Following is the code snipped for invoking launchprocess
private void invokeLaunchProcess(String serverName)
{
// Use the launchProcess operation on the NodeAgent MBean to start
// the given server
String opName = "launchProcess";
String signature[] = { "java.lang.String" };
String params[] = { serverName };
boolean launched = false;
try
{
Boolean b = (Boolean)adminClient.invoke(nodeAgent, opName, params, null);
launched = b.booleanValue();
if (launched)
System.out.println(serverName + " was launched");
else
System.out.println(serverName + " was not launched");
}
catch (Exception e)
{
System.out.println("Exception invoking launchProcess: " + e);
}
}
Full Code could be found on following link
http://pic.dhe.ibm.com/infocenter/wasinfo/v6r0/index.jsp?topic=%2Fcom.ibm.websphere.express.doc%2Finfo%2Fexp%2Fae%2Ftjmx_develop.html
Please let me know what I am doing wrong, do i need to include some other package ? I browsed com.ibm.wplc.was_7.0.0.11.jar, there isn't any folder named nodeagent in com\ibm\ws\managemnt. I found the same jar file in Appserver\runtimes library.
Any help is greatly appreciated, Thanks in Advance.
Getting Mbean
private void getNodeAgentMBean(String nodeName)
{
// Query for the ObjectName of the NodeAgent MBean on the given node
try
{
String query = "WebSphere:type=NodeAgent,node=" + nodeName + ",*";
ObjectName queryName = new ObjectName(query);
Set s = adminClient.queryNames(queryName, null);
if (!s.isEmpty())
nodeAgent = (ObjectName)s.iterator().next();
else
{
System.out.println("Node agent MBean was not found");
System.exit(-1);
}
}
catch (MalformedObjectNameException e)
{
System.out.println(e);
System.exit(-1);
}
catch (ConnectorException e)
{
System.out.println(e);
System.exit(-1);
}catch (Exception e){
e.printStackTrace();
System.exit(-1);
}
System.out.println("Found NodeAgent MBean for node " + nodeName);
}

It seems my problem was with adminClient.invoke method I wasn't passing parameters correctly. It got fixed after having correct parameters. I hope this helps if someone is having same problem.

How to synchronize placing an object in JNDI across processes?

I am trying to place an object in JNDI, so that only one of the progam should be able to place it in JNDI. is there any global lock that can be used in J2EE environment. Is RMI can be used for this purpose? please provide any reference links. Thanks in advance.
Also, what is NameAlreadyBoundexception? I am trying to use it as a method to synchronize, i.e, only one program places it in JNDI and if other trying to bind should get that exception.
But when i am testing the multiple binding I am not getting the Exception.And second binding is done. look up is giving the second object bound. here is my code:
public class TestJNDI {
private static String JNDI_NAME = "java:comp/env/test/something";
public static void main(String[] args) throws NamingException {
Hashtable<String, String> env = new Hashtable<String, String>();
env.put(Context.INITIAL_CONTEXT_FACTORY,"weblogic.jndi.WLInitialContextFactory");
env.put(Context.PROVIDER_URL,"t3://127.0.0.1:7001");
Context ctx = new InitialContext(env);
System.out.println("Initial Context created");
String obj1 = "obj1";
String obj2 = "obj2";
try{
ctx.bind(JNDI_NAME, obj1);
System.out.println("Bind Sucess");
}catch(NameAlreadyBoundException ne ){
// already bound
System.out.println("Name already bound");
}
ctx.close();
Context ctx2 = new InitialContext(env);
try{
// Second binding to the same name not giving the Exception??
ctx2.bind(JNDI_NAME, obj2);
System.out.println("Re Bind Sucess");
}catch(NameAlreadyBoundException ne ){
// already bound
System.out.println("Name already bound");
}
String lookedUp = (String) ctx2.lookup(JNDI_NAME);
System.out.println("LookedUp Object"+lookedUp);
ctx2.close();
}
}

When you close the first content ctx1 you release any objects bound to it see : Context
So your second context has nothing to do with the first one.