Question

I’m using Axis2 with Apache Tomcat. I need the clients of the web service to be able to query a database, so I found on the internet that, by adding the following resource to the Tomcat’s context, it will automatically create a connection pool:

Resource name="jdbc/TestDB" auth="Container"
               type="javax.sql.DataSource" 
               removeAbandoned="true" 
               removeAbandonedTimeout="30"
               maxActive="80"   
               maxIdle="30"
               maxWait="10000"
               username="user"
               password=""
               driverClassName="org.postgresql.Driver"
               url = "jdbc:postgresql://localhost:5432/mydb"
               useUnicode="true"
               characterEncoding="utf-8"
               characterSetResults="utf8"
               validationQuery="/* ping */ SELECT 1" 

It seems to be working, but now what I want to do is reuse the same PreparedStatement, so it won’t be parsed every time a client makes a request. So, I made the PreparedStatement static for all client connections and when I create it, i invoke statement.setPoolable(true), which, from what I understand, is redundant (a PreparedStatement is already poolable). I hoped that this way, the PreparedStatement won’t be tied to a single connection. Still, I get the error:

java.sql.SQLException: org.apache.tomcat.dbcp.dbcp.DelegatingPreparedStatement with address * is closed.

The weird thing is, if i call statement.isClosed() before i make any set, it returns false. Then, I set something and it throws that exception.

The code is:

try {
        Connection conn;

        Context envCtx = (Context) new InitialContext().lookup("java:comp/env");

        DataSource ds = (DataSource) envCtx.lookup("jdbc/TestDB");
        conn = ds.getConnection();    

        if(statement == null){
        //statement is static, so it won't be null at the second call                
            statement = conn.prepareStatement(query);
            statement.setPoolable(true);        
        }
        if(statement.isClosed()){
            statement = conn.prepareStatement(query);
            //it never gets here
        }
        else{
            Logger.getLogger(HelloAxisWorld.class.getName()).log(Level.INFO, "STATEMENT IS NOT CLOSED", new Object());  
            //it always gets here
        }

        statement.setString(1, par1); //here, the second call throws an exception
        ResultSet rs = statement.executeQuery();
        while (rs.next()) {
            cur_value = rs.getInt("cur_value");
        }         
        rs.close();

        conn.close();

    }catch (Exception ex) {            
        Logger.getLogger(HelloAxisWorld.class.getName()).log(Level.SEVERE, null, ex);          
    }

I don’t understand why does statement.isClosed return false, but then the exception says it is closed. Maybe this is not the way to reuse a preparedStatement, but then how can i do it? I read that, if I call conn.prepareStatement on the same query, jdbc will return the PreparedStatement from cache (it will not be parsed again), but I’m not sure if it’s true.

Answer 1

There is a project called c3p0 which was made specifically to handle one of the cases you are having. The website is here https://sourceforge.net/projects/c3p0/ and here http://www.mchange.com/projects/c3p0/ It handles data-source JNDI binding, connection pooling and statement pooling. There also is a reference on stackoverflow on someone using this library with servlets what-is-a-good-strategy-for-caching-prepared-statements-in-tomcat