A Simple Example

The following java program illustrates the concept of Data Object, Key,Table,and Manager being used together to extract data.

To run this java program, see the environment and compilation example.

//This is a deconstruction of DBUtils/jExamples/jReadDB.java
//for completeness, code that is unimportant to the discussion but
//necessary to run the example is typeset in this color



import java.sql.SQLException;

import emitter.DictEntry;
import jdbc.SQLEmitter;
import key.CalibKey;
import manager.ManagerCreationVisitor;
import manager.DefaultDBMS;
import manager.Table;
import manager.TableManager;
/**
 * Usage: java jReadDB    [jdbc URL] [jdbc driver]
 * Sample program for the jDBManager API.
 * This program fills either ORACLE or MSQL nTables tables, with nRows CMPChEl
 * instances (or with whatever you prefer to provide) and then reads back some
 * of them.
 * The attribute (row) name and the component (subdetector) names are
 * defined as two static strings below.
 * The username and password to log into the DBMS can be defined as java propert
ies
 * DefaultsDBMS class provides valid default values (on cdfsga) for all
 * these variables.
 * @version 0.0.1 20 April 1999
 * @author Paolo Calafiura (PCalafiura@lbl.gov
)
 */


public class jReadDB {

  //the entry at the top of the dictionary


//needed to construct a Dictionary, and then later a Manager
//see  TESTDicts.java
//to see what actually gets instantiated

  //the Dictionary
  static String topDictName = "TESTDicts";


  static public void main(String args[]) {
    int i,j; //favourite iterators

    //parse command line

    //the third arg (database_name) is passed to the DefaultDBMS which
    //builds a database connection using data in the iomap.txt file and
    //also handles the two  optional arguments.
    DefaultDBMS defDB =  null;
    try {
      if( args.length == 3 ) {
        defDB =  new DefaultDBMS(args[2]);
      } else if( args.length == 4 ) {
        defDB =  new DefaultDBMS(args[2], args[3]);
      } else if( args.length == 5 ) {
        defDB =  new DefaultDBMS(args[2], args[3], args[4]);
      } else {
        //print a usage message
        System.err.println("Usage: java jDBManager run version database_nam
e [jdbc_URL] [jdbc_driver]");
        System.exit(1);
      }
    } catch (Exception e) {
      e.printStackTrace();
      System.out.println(e);
      System.exit(2);
    }

    int run = Integer.parseInt(args[0],10);  //total number of sets
    int version = Integer.parseInt(args[1],10); //group size of each set


    // Connect to the database
    try {
      defDB.createConnection();
      System.out.println("Connected to the database.");
    } catch( Exception e ) {
      System.err.println(e);
      e.printStackTrace();
      System.exit(4);
    }

    //
    //create the Managers navigating the dictionary
    //

    //now load the dictionary top entry
    DictEntry topDict = null;
    try {

      //create the Dictionary
      Class c = Class.forName(topDictName);
      topDict = (DictEntry)c.newInstance(); //default const

      System.out.println("jDBManager: top dictionary entry is class: " +
                         topDictName);
    } catch (Exception e) {
      e.printStackTrace();
      System.out.println(e);
      throw new Error("Class " + topDictName + " not found");
    }

   //make a ManagerCreationVisitor 
   ManagerCreationVisitor mcVisitor = new ManagerCreationVisitor(defDB,
                                                              topDictName);

   //introduce the visitor to the dictionary
   topDict.accept(mcVisitor);


   //make the Manager
   TableManager[] iom = mcVisitor.makeTableManager("CMPChEl");

   if (iom.length<1)
      throw new Error("No attributes found in tree generated from " + topDictNam
e);
    //
    // now lets put some stuff into the (pre-existing!) CMPChEl tables
    //

    int iComp = 0;



    try {

      //make a table row
      CMPChEl ttable = new CMPChEl();
      //make a  container of row objects
      Table cont = new Table(ttable.getClass());
      //make a key
      CalibKey qk = new CalibKey(run,version);
      //make manager perform io on the database table
      iom[0].doGet(qk, cont);
      System.out.println(cont.niceOutputFormat());


    } catch (Exception e) {
      System.err.println(e);
      e.printStackTrace();
      System.exit(7);
    }

  } //end of main