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javamysqltomcatconnection-pooling
krackmoe
krackmoe

Reputation: 1763

Where to initialize Connection Pooling, java tomcat

I have read this page: http://www.javaranch.com/journal/200601/JDBCConnectionPooling.html

The approach of Method Scope Connections seems quite good for me. But i have one Question, when do i init the JDBCServlet class? Every time i want a connection? Because i thought that everytime i want a connection i just call getConnection()...

public class JDBCServlet extends HttpServlet {

  private DataSource datasource;

  public void init(ServletConfig config) throws ServletException {
    try {
      // Look up the JNDI data source only once at init time
      Context envCtx = (Context) new InitialContext().lookup("java:comp/env");
      datasource = (DataSource) envCtx.lookup("jdbc/MyDataSource");
    }
    catch (NamingException e) {
      e.printStackTrace();
    }
  }

  private Connection getConnection() throws SQLException {
    return datasource.getConnection();
  }

  public void doGet (HttpServletRequest req, HttpServletResponse res) throws ServletException {
    Connection connection=null;
    try {
      connection = getConnection();
      ..<do JDBC work>..
    } 
    catch (SQLException sqlException) {
      sqlException.printStackTrace();
    }
    finally {
      if (connection != null) 
        try {connection.close();} catch (SQLException e) {}
      }
    }
  }
}

Upvotes: 0

Views: 3840

Answers (3)

Gigaquad
Gigaquad

Reputation: 153

The JDBCServlet servlet is invoked when you navigate to a link where the servlet is mapped to.

So you dont have to do anything apart apart from the mapping from URL to servlet which is done in the web.xml.

the web container then create the instance of the servlet by using init method and then call doGet.

This is a PDF for a servlet tutorial with tomcat, but the basics are the same.

http://www.tutorialspoint.com/servlets/servlets_tutorial.pdf

look at the servlet deployment section

for the DBUtil Class this is a good example. 

public class DBUtil {

private static DataSource dataSource;

static {
    try {
        dataSource = new InitialContext().lookup("jdbc/MyDataSource");
    } catch (NamingException e) { 
        throw new ExceptionInInitializerError("'jdbc/MyDataSource' not found in JNDI", e);
    }
}

public static Connection getConnection() {
    return dataSource.getConnection();
}

}

This gives your class that can be used by all servlets in your Web Application.

you wil call the DBUtil class by 

try {
    connection = DBUtil.getConnection();
    statement = connection.prepareStatement("SELECT id, foo, bar FROM table");
    resultSet = statement.executeQuery();

   //Do what you need to do. 

} finally {
    if (resultSet != null) try { resultSet.close(); } catch (SQLException ignore) {}
    if (statement != null) try { statement.close(); } catch (SQLException ignore) {}
    if (connection != null) try { connection.close(); } catch (SQLException ignore) {}
}

Upvotes: 2

Martin Spamer
Martin Spamer

Reputation: 5585

Servlets are initialised by the Container which will call init as required and defined by the web.xml configuration file.

Use the Apache Tomcat JDBC Connection pools which does the same in a standard way.

Upvotes: 1

Alastair McCormack
Alastair McCormack

Reputation: 27704

There's many connection pooling libraries including MySQL's own. Many people use C3P0 which is very mature.

The common idea is that you define the Datasource in the server container and access the JNDI reference from your code. During the servlet init you're just looking up the datasource so this is the ideal place to do this. This will not use any connections until you actually perform an action.

See Tomcat DBCP for a good intro and if you wish to use C3P0 C3P0 Tomcat Configuration

Upvotes: 0

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