java. Lang. outofmemoryerror: Java heap space error when executing millions of queries

In my application, I need to perform millions of queries on MySQL database The code is as follows:

for (int i=0; i< num_rows ; i++) {
   String query2="select id from mytable where x='"+ y.get(i) "'";              
   Statement stmt2 = Con0.createStatement(ResultSet.TYPE_FORWARD_ONLY,ResultSet.CONCUR_READ_ONLY);     
   ResultSet rs2 = stmt2.executeQuery(query2);    
   ... // process result in rs2
   rs2.close(); 
}

Where num_ Rows is about 2 million After the 600k loop, Java reports an error and exits:

What's wrong with my code? How can I avoid such mistakes?

Thank you in advance!

Solution

Declaration is not a good method here Try the following code:

PreparedStatement pre = Con0.prepareStatement("select id from mytable where x=?");

for (int i=0; i< num_rows ; i++) {
   pre.setString(1,y.get(i));
   ResultSet rs2 = pre.executeQuery();
   ... // process result in rs2
   rs2.close(); 
   pre.clearParameters();
}
pre.close();