Hibernate exception occured after running few min in server
org.hibernate.exception.GenericJDBCException: Cannot open connection
at org.hibernate.exception.SQLStateConverter.handledNonSpecificException(SQLStateConverter.java:103)
at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:91)
at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43)
at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:29)
at org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:420)
at org.hibernate.jdbc.ConnectionManager.getConnection(ConnectionManager.java:144)
at org.hibernate.jdbc.JDBCContext.connection(JDBCContext.java:119)
at org.hibernate.transaction.JDBCTransaction.begin(JDBCTransaction.java:57)
at org.hibernate.impl.SessionImpl.beginTransaction(SessionImpl.java:1326)
at FetchCoeff.testing(FetchCoeff.java:37)
at UDPServer.main(UDPServer.java:70)
Caused by: java.sql.SQLException: Connections could not be acquired
from the underlying database!
at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:106)
at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:529)
at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection(AbstractPoolBackedDataSource.java:128)
at org.hibernate.connection.C3P0ConnectionProvider.getConnection(C3P0ConnectionProvider.java:35)
at org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:417)
... 6 more
Caused by: com.mchange.v2.resourcepool.CannotAcquireResourceException:
A ResourcePool could not acquire a resource from its primary factory
or source.
at com.mchange.v2.resourcepool.BasicResourcePool.awaitAvailable(BasicResourcePool.java:1319)
at com.mchange.v2.resourcepool.BasicResourcePool.prelimCheckoutResource(BasicResourcePool.java:557)
at com.mchange.v2.resourcepool.BasicResourcePool.checkoutResource(BasicResourcePool.java:477)
at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:525)
... 9 more
Exception in thread "main" java.lang.NullPointerException
at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1009)
at java.lang.Float.parseFloat(Float.java:439)
at ConvertReadings.Convertd(ConvertReadings.java:39)
at UDPServer.main(UDPServer.java:73)

xml file
<hibernate-configuration>
<session-factory>
<property name="connection.driver_class">
com.mysql.jdbc.Driver
</property>
<property name="connection.url">
jdbc:mysql://localhost:3306/praxeye1
</property>
<property name="connection.username">
enviromote
</property>
<property name="connection.password">
enviromote123
</property>
<property name="dialect">
org.hibernate.dialect.MySQLDialect
</property>
<property name="c3p0.validate">
true
</property>
<property name="current_session_context_class">
thread
</property>
<property name="hibernate.cache.provider_class">
org.hibernate.cache.NoCacheProvider
</property>
<property name="c3p0.min_size">
5
</property>
<property name="c3p0.max_size">
100
</property>
<property name="c3p0.timeout">
0
</property>
<property name="c3p0.max_statements">
0
</property>
<property name="c3p0.idle_test_period">
3000
</property>
<property name="c3p0.acquire_increment">
3
</property>

<property name="hibernate.connection.provider_class">
org.hibernate.connection.C3P0ConnectionProvider
</property>
<property name="show_sql">false</property>
<mapping resource="SensorReadings.hbm.xml"/>
</session-factory>
</hibernate-configuration>

hibernate code
public class FetchCoeff {

public String[] testing(String x, String y) {
Session session= null ;
Transaction tx= null;
String c[] = new String[30];


System.out.println("entering main");
Configuration cfg= new Configuration();
cfg.configure("Hibernate.cfg.xml");
System.out.println("configuration is done");
session = cfg.buildSessionFactory().openSession();
System.out.println("connection got");
try{
tx = session.beginTransaction();
String q= "SELECT d.c1, d.c0, d.DevID, d.SensorType FROM SensorReadings d WHERE d.DevID= :DevID AND d.SensorType= :SensorType";
Query query = session.createQuery(q);
query.setParameter("DevID",x);
query.setParameter("SensorType", y);
System.out.println("query executed");
for(Iterator it=query.iterate();it.hasNext();){
Object[] ob = (Object[]) it.next();
System.out.println("Coefficent 1 is :" + ob[0]);
System.out.println("Coefficent 0 is :" + ob[1]);
System.out.println("Device ID is : " + ob[2]);
System.out.println("Sensor type is : " + ob[3]);
c[1]= (String)ob[0];
c[0]= (String)ob[1];
tx.commit();
session.close();
}
}catch(HibernateException e){
System.out.println("Hibernate exception occured");
e.printStackTrace();
}catch(Exception d){
System.out.println("exception occured");
d.printStackTrace();
}
finally
{
//session.close();
}
return c;
}
}

converting part

public class ConvertReadings {
public String Convertd(String a, String b, String c1, String c0 ) throws Exception
{
Converter con= new Converter();
int x;
double i = Float.parseFloat(a);
if (b.equalsIgnoreCase("HUM"))
{
double c=Float.parseFloat(c1);
double d=Float.parseFloat(c0);
x=con.convert(c, d, i);
return String.valueOf(x);
}
else if (b.equalsIgnoreCase("CO"))
{
double c=Float.parseFloat(c1);;
double d=Float.parseFloat(c0);
x=con.convert(c, d, i);
return String.valueOf(x);
}

public class Converter {
public int convert(double c, double d, double i){
int x;
i = (c * i) + d;
x = (int) (Math.ceil(i));
return x;
}

}


final running code
DatagramSocket serverSocket = new DatagramSocket(20001);
byte[] receiveData = new byte[1024];
while (true)
{
DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
serverSocket.receive(receivePacket);
String sentence = new String(receivePacket.getData(), 0, receivePacket.getLength());
System.out.println(sentence);
try
{
InetAddress IPAddress = receivePacket.getAddress();
int port = receivePacket.getPort();
System.out.println("The Client IP Address and Port Number is" + IPAddress + port);// displaying the above 2 line o/p

String s[] = sentence.split(",");
Calendar currentDate = Calendar.getInstance(); // NEW

SimpleDateFormat sdfDestination = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss"); // NEW
// parse the date into another format

String strDate = sdfDestination.format(currentDate.getTime()); // NEW
s[2] = strDate; // NEW

if (s[0].equalsIgnoreCase(pwd))
{
s[0] = "password secret";
System.out.println(s.length);
j = 4;
while (j != s.length)
{
a = sm.sensorMap(s[j]);
System.out.println(a);
String ab[] = a.split(",");
b = ab[0];
c = ab[1];
String coeff[] =fc.testing(s[1], b);// here i am getting problem

String conv = cr.Convertd(s[j + 1], b, coeff[1], coeff[0]); // even here i am getting exception

String sql = "INSERT INTO readings_db (DevID,Date,Time,SensorPNo,SensorType,Reading,ConvertedReading) values('"
+ s[1]
+ "','"
+ s[2]
+ "','"
+ s[3]
+ "','"
+ c
+ "','"
+ b
+ "','"
+ s[j + 1]
+ "','"
+ conv + "')";

storageHandler.store(sql); //Gives the sql to persist to the handler.
j += 2;
}
sentence += " " + cal.getTime();
}
for (int i = 0; i < s.length; i++)
{
System.out.println(s[i]);
}
}// end of try block
catch (ArrayIndexOutOfBoundsException e)
{
System.out.println(e);
}// end of catch block

}

}
}