Bug in pgjdbc2 ? org.postgresql.PG_Stream.flush(PG_Stream.java:355)

Hello,
I test a jsp script with ab -c 50 -n 10000 ( 50 simultan connection) an
sometimes I receive an exception:
An I/O error has occured while flushing the output - Exception:
java.net.SocketException: Socket closed Stack Trace:
java.net.SocketException: Socket closed at
java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:99) at
java.net.SocketOutputStream.write(SocketOutputStream.java:136) at
java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:69) at
java.io.BufferedOutputStream.flush(BufferedOutputStream.java:127) at
org.postgresql.PG_Stream.flush(PG_Stream.java:355) at
org.postgresql.core.QueryExecutor.sendQuery(QueryExecutor.java:135) at
org.postgresql.core.QueryExecutor.execute(QueryExecutor.java:64) at
org.postgresql.Connection.ExecSQL(Connection.java:398) at
org.postgresql.jdbc2.Statement.execute(Statement.java:130) at
org.postgresql.jdbc2.Statement.executeQuery(Statement.java:54) at
org.postgresql.jdbc2.PreparedStatement.executeQuery(PreparedStatement.java:99)
at _test__jsp._jspService(_test__jsp.java:102) at

This is test.jsp:
try
{

Class.forName("org.postgresql.Driver"); //load the driver
}
catch (ClassNotFoundException e)
{
eroare="Eroare 1"+e;
out.println(eroare);
return;
}

try
{

dbconn=DriverManager.getConnection("jdbc:postgresql://"+DB_HOST+"/"+DB_NAME,
DB_USER,DB_PASS);

dbmd = dbconn.getMetaData();
sql= new java.sql.PreparedStatement[10];

}
catch (SQLException e)
{
eroare="Eroare 2"+e;
out.println(eroare);
return ;
}
java.sql.ResultSet rez;
for (int j=0;j<10;j++)
{

try
{
sql[0] = dbconn.prepareStatement("select * from cat");
rez=sql[0].executeQuery();
}
catch (Exception e)
{
eroare="Eroare 3"+e;
out.println(eroare);
inchide();
return;
}

try{
while (rez.next())
{
out.println(", "+rez.getString("id"));
}
rez.close();
sql[0].close();

}
catch(Exception e)
{
inchide();
out.println("Eroare next"+e);
}
} //end for

try
{
dbconn.close();
}
catch(Exception e)
{
out.println("Eroare inc"+e);
}

out.println("OK");

Please, help me

Sorin