Example: Using JDBCQuery to query a table

//////////////////////////////////////////////////////////////////////////////////
//
// JDBCQuery example.  This program uses the IBM Toolbox for Java JDBC driver to
// query a table and output its contents.
//
// Command syntax:
//    JDBCQuery system collectionName tableName
//
// For example,
//    JDBCQuery MySystem qiws qcustcdt
//
//////////////////////////////////////////////////////////////////////////////////

import java.sql.*;

public class JDBCQuery
{



    // Format a string so that it has the specified width.
    private static String format (String s, int width)
    {
        String formattedString;

        // The string is shorter than specified width,
        // so we need to pad with blanks.
        if (s.length() < width) {
            StringBuffer buffer = new StringBuffer (s);
            for (int i = s.length(); i < width; ++i)
                buffer.append (" ");
            formattedString = buffer.toString();
        }

        // Otherwise, we need to truncate the string.
        else
            formattedString = s.substring (0, width);

        return formattedString;
    }



    public static void main (String[] parameters)
    {
        // Check the input parameters.
        if (parameters.length != 3) {
            System.out.println("");
            System.out.println("Usage:");
            System.out.println("");
            System.out.println("   JDBCQuery system collectionName tableName");
            System.out.println("");
            System.out.println("");
            System.out.println("For example:");
            System.out.println("");
            System.out.println("");
            System.out.println("   JDBCQuery mySystem qiws qcustcdt");
            System.out.println("");
            return;
        }

        String system           = parameters[0];
        String collectionName   = parameters[1];
        String tableName        = parameters[2];

        Connection connection   = null;

        try {

            // Load the IBM Toolbox for Java JDBC driver.
            DriverManager.registerDriver(new com.ibm.as400.access.AS400JDBCDriver());

            // Get a connection to the database.  Since we do not
            // provide a user id or password, a prompt will appear.
            connection = DriverManager.getConnection ("jdbc:as400://" + system);
            DatabaseMetaData dmd = connection.getMetaData ();

            // Execute the query.
            Statement select = connection.createStatement ();
            ResultSet rs = select.executeQuery (
               "SELECT * FROM " + collectionName + dmd.getCatalogSeparator() + tableName);

            // Get information about the result set.  Set the column
            // width to whichever is longer: the length of the label
            // or the length of the data.
            ResultSetMetaData rsmd = rs.getMetaData ();
            int columnCount = rsmd.getColumnCount ();
            String[] columnLabels = new String[columnCount];
            int[] columnWidths = new int[columnCount];
            for (int i = 1; i <= columnCount; ++i) {
                columnLabels[i-1] = rsmd.getColumnLabel (i);
                columnWidths[i-1] = Math.max (columnLabels[i-1].length(), rsmd.getColumnDisplaySize (i));
            }

            // Output the column headings.
            for (int i = 1; i <= columnCount; ++i) {
                System.out.print (format (rsmd.getColumnLabel(i), columnWidths[i-1]));
                System.out.print (" ");
            }
            System.out.println ();

            // Output a dashed line.
            StringBuffer dashedLine;
            for (int i = 1; i <= columnCount; ++i) {
                for (int j = 1; j <= columnWidths[i-1]; ++j)
                    System.out.print ("-");
                System.out.print (" ");
            }
            System.out.println ();

            // Iterate throught the rows in the result set and output
            // the columns for each row.
            while (rs.next ()) {
                for (int i = 1; i <= columnCount; ++i) {
                    String value = rs.getString (i);
                    if (rs.wasNull ())
                        value = "<null>";
                    System.out.print (format (value, columnWidths[i-1]));
                    System.out.print (" ");
                }
                System.out.println ();
            }

        }

        catch (Exception e) {
            System.out.println ();
            System.out.println ("ERROR: " + e.getMessage());
        }

        finally {

            // Clean up.
            try {
                if (connection != null)
                    connection.close ();
            }
            catch (SQLException e) {
                // Ignore.
            }
        }

        System.exit (0);
    }



}