MySQL connection pooling with JERSEY - mysql

Question

I'm developping a RESTful API with Jersey and MySQL.
I'm actually using the JDBC driver to connect to the database and I create a new connection everytime I want to acess it. As it clearly is a memory leakage, I started to implement the ServletContextClassclass but I don't know how to call the method when I need to get the result of a SQL query.
Here is how I did it wrong:
DbConnection.java
public class DbConnection {
public Connection getConnection() throws Exception {
try {
String connectionURL = "jdbc:mysql://root:port/path";
Connection connection = null;
Class.forName("com.mysql.jdbc.Driver").newInstance();
connection = DriverManager.getConnection(connectionURL, "root", "password");
return connection;
}
catch (SQLException e) {
throw e;
}
}
}
DbData.java
public ArrayList<Product> getAllProducts(Connection connection) throws Exception {
ArrayList<Product> productList = new ArrayList<Product>();
try {
PreparedStatement ps = connection.prepareStatement("SELECT id, name FROM product");
ResultSet rs = ps.executeQuery();
while (rs.next()) {
Product product = new Product();
product.setId(rs.getInt("id"));
product.setName(rs.getString("name"));
productList.add(product);
}
return productList;
} catch (Exception e) {
throw e;
}
}
Resource.java
#GET
#Path("task/{taskId}")
#Consumes(MediaType.APPLICATION_JSON)
public Response getInfos(#PathParam("taskId") int taskId) throws Exception {
try {
DbConnection database= new DbConnection();
Connection connection = database.getConnection();
Task task = new Task();
DbData dbData = new DbData();
task = dbData.getTask(connection, taskId);
return Response.status(200).entity(task).build();
} catch (Exception e) {
throw e;
}
}
Here is where I ended up trying to implement the new class:
ServletContextClass.java
public class ServletContextClass implements ServletContextListener {
public Connection getConnection() throws Exception {
try {
String connectionURL = "jdbc:mysql://root:port/path";
Connection connection = null;
Class.forName("com.mysql.jdbc.Driver").newInstance();
connection = DriverManager.getConnection(connectionURL, "root", "password");
return connection;
} catch (SQLException e) {
throw e;
}
}
public void contextInitialized(ServletContextEvent arg0) {
System.out.println("ServletContextListener started");
DbConnection database = new DbConnection();
try {
Connection connection = database.getConnection();
} catch (Exception e) {
e.printStackTrace();
}
}
public void contextDestroyed(ServletContextEvent arg0) {
System.out.println("ServletContextListener destroyed");
//con.close ();
}
}
But problem is, I don't know what to do next. Any help? Thanks

Answer 1

You need to set the Connection variable as an attribute of the ServletContext. Also, I would recommend using connection as a static class variable so you can close it in the contextDestroyed method.
You can retrieve the connection attribute in any of your servlets later on for doing your DB operations.
public class ServletContextClass implements ServletContextListener {
public static Connection connection;
public Connection getConnection(){
try {
String connectionURL = "jdbc:mysql://root:port/path";
Class.forName("com.mysql.jdbc.Driver").newInstance();
connection = DriverManager.getConnection(connectionURL, "root", "password");
} catch (SQLException e) {
// Do something
}
}
public void contextInitialized(ServletContextEvent arg0) {
System.out.println("ServletContextListener started");
getConnection();
arg0.getServletContext().setAttribute("connection", connection);
}
public void contextDestroyed(ServletContextEvent arg0) {
System.out.println("ServletContextListener destroyed");
try{
if(connection != null){
connection.close();
}
}catch(SQLException se){
// Do something
}
}
}
Finally access your connection attribute inside your Servlet (Resource). Make sure you pass #Context ServletContext to your Response method so you can access your context attributes.
#GET
#Path("task/{taskId}")
#Consumes(MediaType.APPLICATION_JSON)
public Response getInfos(#PathParam("taskId") int taskId, #Context ServletContext context) throws Exception {
try {
Connection connection = (Connection) context.getAttribute("connection");
Task task = new Task();
DbData dbData = new DbData();
task = dbData.getTask(connection, taskId);
return Response.status(200).entity(task).build();
} catch (Exception e) {
throw e;
}
}
Now that we have solved your current issue, we need to know what can go wrong with this approach.
Firstly, you are only creating one connection object which will be used everywhere. Imagine multiple users simultaneously accessing your API, the single connection will be shared among all of them which will slow down your response time.
Secondly, your connection to DB will die after sitting idle for a while (unless you configure MySql server not to kill idle connections which is not a good idea), and when you try to access it, you will get SQLExceptions thrown all over. This can be solved inside your servlet, you can check if your connection is dead, create it again, and then update the context attribute.
The best way to go about your Mysql Connection Pool will be to use a JNDI resource. You can create a pool of connections which will be managed by your servlet container. You can configure the pool to recreate connections if they go dead after sitting idle. If you are using Tomcat as your Servlet Container, you can check this short tutorial to get started with understanding the JNDI connection pool.