Trying to use JFreeChart using JSP/Servles; issues with JDBCCategoryDataset and CategoryDataset

Question

i am trying to connect to a database and execute a query in a servlet. I am following this example JFreeChart Example. If you look at the readData() method, it returns a CategoryDataset when it originally was a JDBCCategoryDataset. I get an error until i cast it do a CategoryDataset. When i run the code, it doesn't work, telling me it cannot cast. Any help would be much appreciated!

Answer 1

Because JDBCCategoryDataset implements the CategoryDataset interface, no cast should be required in the assignment: CategoryDataset data = readData(); I get the following chart from the variation of readData() outlined below. I suspect that you have another problem.

private CategoryDataset readData() { 

    JDBCCategoryDataset data = null; 
    Connection con; 
     try { 
        con = DriverManager.getConnection("jdbc:h2:mem:test", "", ""); 
        data = new JDBCCategoryDataset(con); 
        String sql = "select TYPE_NAME, PRECISION "
            + "from INFORMATION_SCHEMA.TYPE_INFO "
            + "where PRECISION BETWEEN 1 AND 12"; 
        data.executeQuery(sql); 
        con.close(); 
    } 
    … 
    return data; 
 }