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JSP mysql connections not closing, however in Java class it does

I am developing a web application using Java, JSP, MySQL. I cannot get the MySQL connections to close in the JSP, yet it works in a Java class. I have the following code:
A. First I have a class to get the ResultSet when running a get query as follows:
public static ResultSet get(String query) {
ResultSet rs = null;
try {
Class.forName(JDBC_DRIVER);
connection = DriverManager.getConnection(DB_URL + DB_NAME, USERNAME, PASSWORD);
statement = connection.createStatement();
rs = statement.executeQuery(query);
} catch (ClassNotFoundException | SQLException ex) {
ex.printStackTrace();
}
return rs;
}
B. I have a java class using the above to return the MySQL results in objects as follows:
public static <E> E getByFromOtherRS(E element, List<String> columns, String tableName, String whereColumn, String whereValue, Method getFromRS) {
try {
String query = "Select * from " + tableName + " where " + whereColumn + "='" + whereValue + "';";
ResultSet rs = SQLAccessor.get(query);
while (rs.next()) {
try {
element = (E) getFromRS.invoke(element, rs);
} catch (IllegalAccessException | IllegalArgumentException | InvocationTargetException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
} catch (SQLException ex) {
} finally {
try {
SQLAccessor.getConnection().close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
return element;
}
C. I then use the above in the below class. When I run the main method I get the result as expected. Also, when I do
show status like '%onn%'
in the MySQL shell the number of Threads_connected are the same as before running the code.
public static void main(String[] args) {
Gson gson = new Gson();
System.out.println(gson.toJson(getUserByUsername()));
}
public static User getUserByUsername() {
User user = Accessor.getByFromOtherRS(new User(), Accessor.getColumns("user"), "user", "username", "linda", Accessor.getFromRSMethod(UserAccessor.class));
return user;
}
D. The problem is with the JSP. I have the below code in the JSP. I get the user email correctly, but the problem is with the MySQL - when I run the same command as above the number of Threads_connected are now 17 more.
<%
User user = DatabaseAccessor.getUserByUsername();
System.out.println(user.getEmail());
%>
Any help in this regard will be greatly appreciated.

Can't see the full code...
Given the code snippet, it will be better if you issue 'close' to the connection in a finally block to ensure it gets closed.
finally {
if (connection!=null) { connection.close();}
}

use one jdbc connection class for all classes java

i have been using this JDBC conection in all of my class that had to run query but i created a new class which i dont want the constructor with a parameter of the DConnection from JDBC Class(main Database Class).
but i keep on getting NullPointExceptions. Can anyway figur out what that problem may be.
Thanks.
public class UsersDao {
// associating the Database Connection objekt
private DConnector connector;
private final Connection myConn;
// Constructor
public UsersDao() throws CZeitExceptionHand,SQLException {
myConn = connector.getConnenction();
}
public boolean updateUsers(String mitarb, int mid) throws SQLException{
// PreparedStatement myStmt = null;
Statement stmt = myConn.createStatement();
try {
String myStmt = "SELECT Bly "
+ "" + mid + ";";
return stmt.execute(myStmt);
} finally {
close(stmt);
}
}
Example like this Method which is working but in different class
String[][] getAllTheWorkers(DConnector connector) throws CZeitExceptionHand {
try {
Connection connect = connector.getConnenction();
Statement stmt = connect.createStatement();
ResultSet result = stmt.executeQuery("SELECT ");
result.last();
int nt = result.getRow();
result.beforeFirst();
}
return results;
} catch (SQLException e) {
throw new CZeitExceptionHand("Error: " + e);
}
}

The object does not seem to be initialized.
Can you please post which method is not working and from where it is invoked ?
P.S : Unable to add a comment - that is why have answered !

How do I call data from a table in a database into a java class in netbeans?

first time posting so sorry if my question is slightly strange.
So I have a project in school that requires us to create java classes using netbeans that open up a window with three options, check stock, purchase item and update stock.
We had a class called stockdata that held the details of 5 different items for us to use in our three classes to check, purchase and update items. The latest stage of our coursework requires us to create a derby database and enter the items into a table.
I have done this with no issues but I am having a problem getting the items from the table back into my classes to use. We were given the following code but I can't get it to work, even using the commented hints.
package stock;
// Skeleton version of StockData.java that links to a database.
// NOTE: You should not have to make any changes to the other
// Java GUI classes for this to work, if you complete it correctly.
// Indeed these classes shouldn't even need to be recompiled
import java.sql.*; // DB handling package
import java.io.*;
import org.apache.derby.drda.NetworkServerControl;
public class StockData {
private static Connection connection;
private static Statement stmt;
static {
// standard code to open a connection and statement to an Access database
try {
NetworkServerControl server = new NetworkServerControl();
server.start(null);
// Load JDBC driver
Class.forName("org.apache.derby.jdbc.EmbeddedDriver");
//Establish a connection
String sourceURL = "jdbc:derby://localhost:1527/"
+ new File("UserDB").getAbsolutePath() + ";";
connection = DriverManager.getConnection(sourceURL, "use", "use");
stmt = connection.createStatement();
} // The following exceptions must be caught
catch (ClassNotFoundException cnfe) {
System.out.println(cnfe);
} catch (SQLException sqle) {
System.out.println(sqle);
} catch (Exception e) {
System.out.println(e);
}
}
// You could make methods getName, getPrice and getQuantity simpler by using an auxiliary
// private String method getField(String key, int fieldNo) to return the appropriate field as a String
public static String getName(String key) {
try {
// Need single quote marks ' around the key field in SQL. This is easy to get wrong!
// For instance if key was "11" the SELECT statement would be:
// SELECT * FROM Stock WHERE stockKey = '11'
ResultSet res = stmt.executeQuery("SELECT * FROM Stock WHERE stockKey = '" + key + "'");
if (res.next()) { // there is a result
// the name field is the second one in the ResultSet
// Note that with ResultSet we count the fields starting from 1
return res.getString(2);
} else {
return null;
}
} catch (SQLException e) {
System.out.println(e);
return null;
}
}
public static double getPrice(String key) {
// Similar to getName. If no result, return -1.0
return 0;
}
public static int getQuantity(String key) {
// Similar to getName. If no result, return -1
return 0;
}
// update stock levels
// extra is +ve if adding stock
// extra is -ve if selling stock
public static void update(String key, int extra) {
// SQL UPDATE statement required. For instance if extra is 5 and stockKey is "11" then updateStr is
// UPDATE Stock SET stockQuantity = stockQuantity + 5 WHERE stockKey = '11'
String updateStr = "UPDATE Stock SET stockQuantity = stockQuantity + " + extra + " WHERE stockKey = '" + key + "'";
System.out.println(updateStr);
try {
stmt.executeUpdate(updateStr);
} catch (SQLException e) {
System.out.println(e);
}
}
// close the database
public static void close() {
try {
connection.close();
} catch (SQLException e) {
// this shouldn't happen
System.out.println(e);
}
}
}
Sorry if this seems a stupid question but I am fairly new to Java and was making good progress until this roadblock.
Thanks in advance!
Alex

Searching for "java sql" on Google delivers this link: https://docs.oracle.com/javase/tutorial/jdbc/basics/processingsqlstatements.html
From a connection you can create a statement (you can find this in the link and in your code) , then fetch a result set and loop over that with rs.next(). That should get your started.
Of course you have to make sure that the driver and database are there/running, just saying...

Here netbeans has nothing to do with database. This is a Java-based integrated development environment(IDE) that will help you to reduce syntactic error.
public void dataAccess(){
try {
String connectionUrl = "suitable connection url as per your database";
Connection con = null;
Statement stmt = null;
ResultSet rs = null;
Class.forName("JDBC driver name as per your database");
con = DriverManager.getConnection(connectionUrl, userName, password);
String SQL = "SQL query as per your criteria";
stmt = con.createStatement();
rs = stmt.executeQuery(query);
while (rs.next()) {
// look into ResultSet api and use method as per your requirement
}
rs.close();
}
catch (Exception e) {
//log error message ;
}
}

Error S1000 trying to execute more MySql queries in a Java Application

I have a problem trying to execute more than one query into my Java Application code.
I have a procedure that is called in main and is in the class "Fant":
public void XXX(){
Connectivity con=new Connectivity(); // this class set up the data for the connection to db; if ( !con.connect() ) {
System.out.println("Error during connection.");
System.out.println( con.getError() );
System.exit(0);
}
ArrayList<User> blabla=new ArrayList<User>();
blabla=this.getAllUsers(con);
for (User u:blabla)
{
try {
Connectivity coni=new Connectivity();//start a new connection each time that i perform a query
Statement t;
t = coni.getDb().createStatement();
String query = "Select count(*) as rowcount from berebe.baraba";
ResultSet rs = t.executeQuery(query);
int numPrenotazioni=rs.getInt("rowcount");
rs.close(); //close resultset
t.close(); //close statement
coni.getDb().close(); //close connection
}
}
catch (SQLException e)
{
System.err.println("SQLState: " +
((SQLException)e).getSQLState());
System.err.println("Error Code: " +
((SQLException)e).getErrorCode());
}
}
}
The called function is defined as:
ArrayList<User> getAllUsers(Connectivity con) {
try{
ArrayList<User> userArrayList=new ArrayList<User>();
String query = "Select idUser,bubu,lala,sisi,gogo,gg from berebe.sasasa";
Statement t;
t = con.getDb().createStatement();
ResultSet rs = t.executeQuery(query);
while (rs.next())
{
User utente=new User(....); //user fields got from query
userArrayList.add(utente);
}
rs.close();
t.close();
con.disconnect(); //disconnect the connection
return userArrayList;
} catch (SQLException e) {
}
return null;
}
The main is:
public static void main(String[] argv) {
ArrayList<User> users=new ArrayList<User>();
System.out.println("-------- MySQL JDBC Connection Testing ------------");
Fant style = new Fant();
style.XXX();
}
The query performed into "getAllusers" is executed and into the arraylist "blabla" there are several users; the problem is that the second query that needs the count is never executed.
The MYSQlState given when running is= "S1000" and the SQLERROR is "0".
Probably i'm mistaking on connections issues but i'm not familiar with statements,connections,resultsets.
Thank you.

You might forget to call rs.next() before getting the result form it in XXX()methods as shown below:
ResultSet rs = t.executeQuery(query);
// call rs.next() first here
int numPrenotazioni=rs.getInt("rowcount");

SQLite JDBC get on resultset always returns null resp. 0

In the following code, I execute a query on a SQLite JDBC connection via the executeRestitutionalQuery(String query) method:
public static ArrayList<Metadata> findMetadata(String name, String text, String after, String before, String repPath)
throws SQLException, ClassNotFoundException {
ArrayList<Metadata> data = new ArrayList<Metadata>();
boolean needADD = false;
String query = "SELECT * from " + TABLE_NAME_METADATA;
...
query += " ORDER BY timestamp DESC;";
ResultBundle bundle = executeRestitutionalQuery(query);
ResultSet result = bundle.getResultSet();
while(result.next()){
Metadata metadata = new Metadata(result.getLong("id"), result.getString("name"), Timestamp.valueOf(result.getString("timestamp")),
result.getInt("filesNo"), result.getLong("size"), result.getString("description"), -1);
data.add(metadata);
}
closeStatementAndResultSet(bundle.getStatement(), bundle.getResultSet());
return data;
}
private static ResultBundle executeRestitutionalQuery(String query) throws SQLException, ClassNotFoundException{
Connection connection = null;
Statement statement = null;
ResultSet result = null;
ResultBundle bundle = null;
try{
connection = getConnection();
statement = connection.createStatement();
statement.executeUpdate(query);
connection.commit();
result = statement.executeQuery(query);
bundle = new ResultBundle(statement, result);
}finally{
if(connection != null){
try{
connection.close();
}catch (Exception e){
/* ignored */
}
}
}
return bundle;
}
private static void closeStatementAndResultSet(Statement statement, ResultSet result){
if(result != null){
try{
result.close();
}catch (Exception e){
// ignored
}
}
if(statement != null){
try{
statement.close();
}catch (Exception e){
// ignored
}
}
}
The ResultBundle class is just used to summarize the resultset and the statement. It looks like this:
public class ResultBundle {
private final Statement statement;
private final ResultSet result;
public ResultBundle(Statement statement, ResultSet result){
this.result = result;
this.statement = statement;
}
public Statement getStatement(){
return statement;
}
public ResultSet getResultSet(){
return result;
}
}
The problem is, that every call to result.getLong(), result.getString() etc. returns null resp. 0. I can't understand why. The queries should all be okay, as the code was running fine before I had to do some refactoring. Could the problem arise from the ResultBundle-class? What am I not seeing here?

Statements and ResultSets are "live" objects, living only as long as their connection. The executeRestitutionalQuery returns a ResultBundle, whose result and statement members are implicitly closed on return when the connection is closed in the finally block.
try {
...
}finally{
if(connection != null){
try{
connection.close(); // <---- here's the problem
}catch (Exception e){
/* ignored */
}
}
}
By the time, the caller of executeRestitutionalQuery can lay its hand on the resource bundle, the connection has been closed, and the result set is "dead".

I would say this is a bad design.
A better one would keep the SQL objects in tight scope, map results into a collection or object and immediately close all those scarce resources. Not only will the data be available to clients, but you'll avoid nasty problems with connection and cursors exhausted. It'll scale better, too.