Connection pool in java

I create a pool of connections, but mysql swears at a large number of connections, as I understand it is necessary to close the connection after its use. But isn't a connection pool created for this purpose, to keep a certain number of connections for quick access to them from different streams? Please tell me what I'm doing wrong, maybe I misunderstand the mechanism of the pool of connections?

package ObjectPool; import java.sql.Connection; import java.sql.DriverManager; import java.sql.SQLException; import java.util.ArrayList; public class PoolController { ArrayList<Connection> conpool=new ArrayList<Connection>(); public int instancescount=0; int maxinstancescount=100; int ex=0; public PoolController() throws ClassNotFoundException{ Class.forName("org.sqlite.JDBC"); } public Connection add(){ Connection con=null; try { con=DriverManager.getConnection("jdbc:mysql://localhost:3306/lesson","root"); conpool.add(con); instancescount++; } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } return con; } public Connection getconnection(){ Connection con=null; if(conpool.size()>0){ con=conpool.get(conpool.size()-1); conpool.remove(conpool.size()-1);}else { if(instancescount<=maxinstancescount){ ex++; //System.out.println(ex); con=add(); }else{ synchronized(conpool){ while(conpool.size()<=0){ try {conpool.wait();} catch (InterruptedException e) {} } } } } return con; } public void release(Connection con){ synchronized(conpool){ conpool.add(con); conpool.notify(); } } } 

I run several threads for simultaneous access to databases:

  package DataSourcepackage; import java.beans.PropertyVetoException; import java.io.IOException; import java.sql.Connection; import java.sql.SQLException; import java.sql.Statement; import ObjectPool.PoolController; public class Mainthread extends Thread { DataSource ds; int count; PoolController poolcontroller; public Mainthread(PoolController poolcontroller,int count) throws IOException, SQLException, PropertyVetoException{ this.poolcontroller=poolcontroller; this.count=count; start(); } public void run(){ Connection con=poolcontroller.getconnection(); Statement stmt; try { stmt = con.createStatement(); String query="INSERT INTO lesson.tele2 VALUES ('asd',"+count+",'eq')"; stmt.executeUpdate(query); poolcontroller.release(con); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } } } 

this is the main class from which 500 threads start:

 package DataSourcepackage; import java.beans.PropertyVetoException; import java.io.IOException; import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; import java.util.Calendar; import ObjectPool.PoolController; public class experiment { public static void main(String [] args) throws SQLException, ClassNotFoundException, IOException, PropertyVetoException{ PoolController pool=new PoolController(); long startTime = System.currentTimeMillis(); for(int i=0;i<500;i++){ new Mainthread(pool,i); } } } 

throws such an exception:

 com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Data source rejected establishment of connection, message from server: "Too many connections" at sun.reflect.GeneratedConstructorAccessor33.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at java.lang.reflect.Constructor.newInstance(Constructor.java:423) at com.mysql.jdbc.Util.handleNewInstance(Util.java:425) at com.mysql.jdbc.Util.getInstance(Util.java:408) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:918) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:897) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:886) at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1040) at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2253) at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2284) at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2083) at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:806) at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47) at sun.reflect.GeneratedConstructorAccessor27.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at java.lang.reflect.Constructor.newInstance(Constructor.java:423) at com.mysql.jdbc.Util.handleNewInstance(Util.java:425) at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:410) at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:328) at java.sql.DriverManager.getConnection(DriverManager.java:664) at java.sql.DriverManager.getConnection(DriverManager.java:247) at ObjectPool.PoolController.add(PoolController.java:20) at ObjectPool.PoolController.getconnection(PoolController.java:39) at DataSourcepackage.Mainthread.run(Mainthread.java:21)