chapter 101© copyright janson industries 2011 database access ▮ jdbc ▮ db access objects ▮...

chapter 10 1© copyright Janson Industries 2011

Database Access

▮ JDBC

▮ DB Access objects

▮ Encapsulation

▮ Abstract classes

▮ CRUD


Database Access

▮ Need DBMS-specific software (called a driver) to access the various DBMSs

▮ Why? Java follows a DB access protocol called JDBC (Java DB Connectivity)

▮ None of the DBMSs directly support JDBC▮ However each DBMS vendor supplies a

driver

▮ The driver converts JDBC requests to the DBMS’s protocol


Drivers

Drivers

DBMS Java Pgm

DB2OracleODBC

JDBC


Drivers

▮ ODBC (Open DB Connectivity) is the MS Access DBMS’s protocol

▮ sun.jdbc.odbc.JdbcOdbcDriver, the driver class, is included in the JRE (and RAD)

▮ For DB2 and Oracle you must download the driver and include in classpath

▮ The headache with Access is you must define the DB as an ODBC data source


Drivers

▮ For Access: DB must reside and be defined as an ODBC data source on the computer where the application will run

▮ To run in RAD or as an application this means on the client

▮ To run on a server, this means on the computer that is acting as the server

▮ An Access DB cannot be accessed remotely


Drivers

▮ For other DBMS’s:

▮ Download the driver

▮ Set the class path to point to the driver

▮ To run in RAD: change the Java Build Path

▮ To run on a client or server: change that computer’s classpath environment variable to point to the driver


Running on client

▮ For instance to access DB2 on a IBM Power System:

ADDENVVAR ENVVAR(CLASSPATH) VALUE('/QIBM/ProdData/Http/Public/jt400/lib/jt400.zip')

▮ On a Windows PC, change the set classpath to include jt400.zip

path=c:\jdk\binSet classpath=.;\jdk\lib\tools.jar;c:\jtopen\lib\jt400.jar


Accessing a DB

▮ In a java pgm, 4 things, several steps:

▮ 1. Register/load the driver

▮ 2. Get a Connection object, using the DriverManager class

▮ 3. Create a Statement object, using the Connection object

▮ 4. Define and execute SQL statements, using the Statement object


Accessing a DB

▮ The Class class (yikes!) allows you to register/load the driver

▮ A DriverManager allows you to get a Connection object

▮ A Connection allows you to create a Statement object


Register/load the driver

▮ Instead of “instantiating an object of the driver”, load (register) the driver in the JVM with the “class loader”:

▮ Essentially returns a driver object (of the type specified) as a Class object and makes it available to the JVM

▮ Just like getInstance(), another way to create an object

Class.forName(“com.ibm.db2.jdbc.app.DB2Driver”)


Connection Object

▮ A DBMS connection must be established (even if the Java application is running on the same machine as the DBMS)

▮ To create a Connection must specify the

▮ Driver to be used

▮ DB (possibly including a URL or IP address)

▮ Optionally, a user ID and PW


DB Identifier

▮ Identified as: driver:subprotocol:subname

▮ Optional subprotocol ids a DB connectivity mechanism (supported by the driver)

▮ The subname ids the DB and its syntax depends on the protocol and subprotocol

▮ If specifying a network address as the subname, follow the standard naming convention of: //hostname:port/subsubname

▮ Subsubname has unique internal syntax

static String url = ("jdbc:db2:subprotocol:subname);


DB URL

▮ For MS Access on Windows

▮ For Oracle

▮ For DB2 on an IBM Power System

static String url = ("jdbc:odbc:TNT Database”);

static String url = ("jdbc:as400:1.2.3.4”);

static String url=("jdbc:oracle:thin:@1.2.3.4:1521:SID”);


Properties Object

▮ Properties hold information for the driver

▮ Each driver expects its own set of info

▮ Most drivers expect user ID and password (not MS Access)

▮ You can create a property object and then set the values

static Properties p = new Properties();

: : :

p.put("naming", "sql");

p.put("user", "rjanson");

p.put("password", “jeter");

File namingconvention


▮ Create a Connection object with the DriverManager’s static getConnection method

▮ Pass the String url and Properties object

▮ DriverManager searches for a suitable driver from those that were loaded (e.g., those that were registered with the .forName method) based on the protocol

con = DriverManager.getConnection(url, p);

Get a Connection Object


Statement Object

▮ Created with the Connection object’s createStatement method

▮ Primary methods to perform SQL instructions:▮ executeQuery – SQL Select command▮ executeUpdate – SQL Insert, Delete,

Updatestmt.executeUpdate("INSERT INTO TNTDB.CUSTOMER " +

"VALUES(1, 'Joe Customer', '1 Main St.', " +

"'Jacksonville, FL 32233')");

Statement stmt = con.createStatement();


Java Changes

▮ Add the following:

to access SQL related objects such as:▮ ResultSet

▮ Statement

▮ Connection

▮ SQLException

import java.sql.*;


Result Sets

▮ All data is returned by a SQL select statement as a ResultSet object

▮ A result set is comprised of a:

▮ Table that is comprised of▮ Rows/records▮ Columns/fields

▮ A pointer/cursor that is used to move between the rows


Result Sets

▮ Have a variety of methods to retrieve field data

▮ getXXX(field identifier) - where XXX is the data type (Int, String, etc.)

▮ Field can be identified by the field name or the column number

▮ Column number more efficient

▮ Field name better for documentation


Result Sets

▮ .next() increments pointer to next row/record▮ Initially pointer set before the first row, so

must .next() to “prime the read”▮ Returns a Boolean value indicating

whether there is a record or not

▮ .previous(), .last()

▮ .relative(#) moves pointer # number of rows


Result Set & Choice Example

try {

stmt = conn.createStatement();

select = "SELECT School FROM Schools ORDER BY School";

rs = stmt.executeQuery(select);

while (rs.next()){

schoolsCB.addItem(rs.getString(1));

}

stmt.close();

}

catch (SQLException sqlex) {

sqlex.printStackTrace();

System.out.println("\nSQL exception on query\n"); }

Populates Choicewith school names


Encapsulation

▮ Many terms used to describe:

▮ Transparency

▮ Information hiding

▮ Implementation ignorance

▮ Programmers have an “interface” to an object with no idea of how it works


Encapsulation

▮ Someone knows how to drive:▮ Turn the key

▮ Step on gas pedal

▮ Steer

▮ Step on brake pedal

▮ The driver doesn’t have to know how the car works or any of its internal components


Encapsulation

▮ Many methods and data are hidden from the user/application

▮ Changes to the class (variables and methods) do not affect users of the class

▮ Data accessible only through publicly defined methods


Encapsulation

DATA

Getters

SettersRules

Constructors


Encapsulation

▮ If programmers can’t directly access the data, their applications can’t screw it up!!

▮ PUBLIC methods comprise the interface

▮ PRIVATE methods for internal functions and non-user fields


Encapsulate a File/Table

▮ Define a class for the file (ex. TransTable)

▮ In the class, define private variables for each field in the file

▮ For each private variable:▮ Define a getter method▮ Define a setter with validation functions

▮ Define CRUD functions▮ Define functions to return associated

objects (customer purchase orders)▮ Define business functions (getTotal)


Business Change

▮ Selling to schools via purchase orders

▮ Have a DB called Sales with a table called TxTable

▮ Will create a new class to encapsulate TxTable called TransTable

▮ Need a new frame to add PO sales info


PO Sale

▮ Create a new POSale Frame to input PO sale transaction info

Chapter 10 30© copyright Janson Industries 2011

In class assg

Sales DB

User

Sales Info TxTable

EmptyFrame

Creates

PO Sale Sales Info

Sales Info

TransTable


This new class will eventually have all

these methods


How to Encapsulate a File▮ TransTable class will encapsulate the

TxTable file (with these fields)▮ School – char 25▮ Customer – char 30▮ PurchDate – char 10▮ ItemName – char 30▮ Qty – long integer (4 bytes)▮ Price – currency▮ PayDate – char 10▮ PONum – char 15▮ Comments - memo▮ PaidAmt – currency

34chapter 10 © copyright Janson Industries 2011

import java.util.*;

import java.util.Date;

import java.sql.*;

import java.text.DateFormat;

public class TransTable {

private String school;

private String customer;

private String purchDate;

private String itemName;

private int qty;

private double price;

private String payDate;

private String pONum;

private String comments;

private double paidAmt;

How to Encapsulate a File

▮ Define a private variable for each field

Need to import various date classes and the sql

package



Need date variables/objects

Need DBMSvariables/

objects

Create getters



public void setQty(int qty) {

this.qty = qty;}

public void setPrice(double price) {

this.price = price;}

public void setComments(String comments) {

this.comments = comments;}

public void setPaidAmt(double paidAmt) {

this.paidAmt = paidAmt;}

public void setPurchDate() {

this.purchDate = String.valueOf(dfShort.format(date));}

public void setPayDate() {

this.payDate = String.valueOf(dfShort.format(date));}

public void setSchool(String school) throws InvalidLengthException {

if (school.length() > 25)

throw new InvalidLengthException("School", school, 25);

this.school = school;}

Create setters (some with validation functions)



public void setCustomer(String customer) throws InvalidLengthException {

if (customer.length() > 30)

throw new InvalidLengthException("Customer", customer, 30);

this.customer = customer;

}

public void setPONum(String pONum) throws InvalidLengthException {

if (pONum.length() > 15)

throw new InvalidLengthException("PO Number", pONum, 15);

this.pONum = pONum;

}

public void setItemName(String itemName) throws InvalidLengthException {

if (itemName.length() > 30)

throw new InvalidLengthException("Item Name", itemName, 30);

this.itemName = itemName;}

}

Create and use a new Exception subclass


InvalidLengthException class

public class InvalidLengthException extends Exception {

public InvalidLengthException(String field, String value, int length)

{ super("The value entered for " + field + ": " + value +

", is too big. \nMax length is " + length + ".");

} // end of constructor for InvalidLengthException

/** \n command line control */

public static void main(String args[]) {

System.out.println("Welcome to class invalidLengthException");

} // end main

} // end of class InvalidLengthException


CRUD

▮ We need functions to Create, Read, Update and Delete transactions

▮ The create function is done with a simple default constructor (a constructor with no arguments)

▮ When invoked, this creates a TransTable object with all the private fields

public TransTable() {}


CRUD

▮ Of course, a calling program will have to set all the values

▮ And a write function will have to be executed to make the transaction info persistent

▮ In addition, need connection variables in order to do any reads/writes


Application Probs

▮ We are executing the same SQL statement many times

▮ Statement is translated into ML every time executed

▮ Very inefficient

▮ Solution: PreparedStatement


Prepared Statement

▮ A predefined/translated SQL statement

▮ Before executing, supply data for the statement

▮ More efficient

▮ Already created the variable as follows :

static PreparedStatement psAddTT = null;


Prepared Statement

▮ Need a prepared statement object

▮ Retrieved from the connection object

▮ Therefore need a connection object

▮ The ?’s “hold” the place for the data values

psAddTT = con.prepareStatement("INSERT INTO EXAMPLES." +

"CUSTMAST VALUES(?, ?, ?, ?)");


private void init() {

if (conn == null) {

try {

Class.forName(driver);

p.put("naming", "sql");

p.put("user", "anonymous");

p.put("password", "guest");

conn = DriverManager.getConnection(url, p);

} catch (ClassNotFoundException e) {

System.out.println("couldn't find jdbc/odbc driver");

e.printStackTrace();

System.exit(1);

} catch (SQLException e) {

System.out.println("couldn't connect");


System.exit(1);

}

} }

init creates connection to DB

init


...and creates the statement objects needed to access

data in the DB

init


Access a DB

▮ Need to call init from all constructors

▮ Change null constructor to run init

▮ Time to test, add the following main method and run as Java app

public TransTable() {init();}

public static void main(String[] args) {

TransTable tt = new TransTable();

System.out.println("Created a TransTable object");

}


Never defined the DB as an ODBC data source


Click Start, Control Panel, Administrative Tools

Data Sources (ODBC)

Click Add


Select Microsoft Access Driver and click Finish


If Access Driver doesn’t appear and you are running 64 bit Win7, here are links on work

around:http://answers.microsoft.com/en-us/office/forum/office_2007-excel/no-odbc-drivers-

available-for-excel-or-access-in/001c234b-dfd5-4378-a325-c4f1482fb6fd

http://stackoverflow.com/questions/6721702/windows-7-64-bit-odbc-drivers-for-ms-access-missing


Specify Sales and click Select

Locate and select the DB file then click OK


Click OK

© copyright Janson Industries 2011chapter 10 53Click OK

Sales appears in Data Source list


Test again


PO Sale

▮ Encapsulating TransTable will make other classes (like POSale) that use the DB simpler

▮ Created a new PO Sale Frame to capture PO sale transaction info


import java.awt.Frame;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

import java.awt.event.WindowEvent;

import java.awt.event.WindowListener;import java.awt.Dimension;import java.awt.Label;import java.awt.Rectangle;import java.awt.TextField;import java.awt.Button;import java.awt.Point;

public class POSale extends Frame implements ActionListener, WindowListener {

private static final long serialVersionUID = 1L;

private Button addBtn = null; private Label custNameLbl = null;

private TextField custNameTF = null; private Label itemNameLbl = null;

private TextField itemNameTF = null; private Label qtyLbl = null;

private TextField qtyTF = null; private Label priceLbl = null;

private TextField priceTF = null; private Label resultLbl = null;

private Label schoolLbl = null; private TextField schoolTF = null;

private Label commentLbl = null; private TextField commentsTF = null;

private TextField pONumTF = null; private Label pONumLbl = null;

POSale

Visual components


public void windowActivated(WindowEvent e) {}

public void windowClosed(WindowEvent e) {}

public void windowClosing(WindowEvent e) {

this.dispose();}

public void windowDeactivated(WindowEvent e) {}

public void windowDeiconified(WindowEvent e) {}

public void windowIconified(WindowEvent e) {}

public void windowOpened(WindowEvent e) {}

private Button getAddBtn() { if (addBtn == null) {

addBtn = new Button();addBtn.setLabel("Add");addBtn.setLocation(new Point(237, 178));addBtn.setSize(new Dimension(60, 23));addBtn.addActionListener(this);

} return addBtn;}

private TextField getCustNameTF() {

if (custNameTF == null) {

custNameTF = new TextField();

custNameTF.setBounds(new Rectangle(147, 45, 140, 23));

}

return custNameTF;

}

Window Listenermethods

Visual component

getters


private TextField getItemNameTF() { if (itemNameTF == null) {

itemNameTF = new TextField();

itemNameTF.setBounds(new Rectangle(147, 78, 140, 23));}

return itemNameTF; }

private TextField getQtyTF() { if (qtyTF == null) {

qtyTF = new TextField();

qtyTF.setBounds(new Rectangle(108, 111, 32, 23)); }

return qtyTF; }

private TextField getPriceTF() { if (priceTF == null) {

priceTF = new TextField();

priceTF.setBounds(new Rectangle(199, 111, 60, 23)); }

return priceTF;}

private TextField getSchoolTF() { if (schoolTF == null) {

schoolTF = new TextField();

schoolTF.setBounds(new Rectangle(389, 45, 113, 23)); }

return schoolTF;}

private TextField getCommentsTF() { if (commentsTF == null) {

commentsTF = new TextField();

commentsTF.setBounds(new Rectangle(389, 79, 113, 55));}

return commentsTF;}

private TextField getPONumTF() { if (pONumTF == null) {

pONumTF = new TextField();

pONumTF.setBounds(new Rectangle(331, 111, 47, 23)); }

return pONumTF;}

Remaining visual

componentgetters


Salepublic POSale() {

super();

initialize();

}

private void initialize() {pONumLbl = new Label(); pONumLbl.setBounds(new Rectangle(265, 111, 62, 23));

pONumLbl.setText("PO Num:"); commentLbl = new Label();

commentLbl.setBounds(new Rectangle(307, 78, 71, 23)); commentLbl.setText("Comments:");

schoolLbl = new Label(); schoolLbl.setBounds(new Rectangle(325, 45, 53, 23));

schoolLbl.setText("School: "); resultLbl = new Label();

resultLbl.setBounds(new Rectangle(14, 145, 508, 23)); resultLbl.setAlignment(Label.CENTER);

resultLbl.setText(""); priceLbl = new Label();

priceLbl.setBounds(new Rectangle(147, 111, 45, 23)); priceLbl.setText("Price:");

qtyLbl = new Label(); qtyLbl.setBounds(new Rectangle(39, 111, 45, 23));

qtyLbl.setText("Quantity:"); itemNameLbl = new Label();

itemNameLbl.setBounds(new Rectangle(61, 78, 79, 23)); itemNameLbl.setText("Item Name:");

custNameLbl = new Label(); custNameLbl.setBounds(new Rectangle(31, 45, 109, 23));

custNameLbl.setText("Customer Name:");

this.setLayout(null); this.setSize(535, 214); this.setTitle("PO Sale");

this.setVisible(true); this.add(getAddBtn(), null); this.add(custNameLbl, null);

this.add(getCustNameTF(), null); this.add(itemNameLbl, null);

this.add(getItemNameTF(), null); this.add(qtyLbl, null);

this.add(getQtyTF(), null); this.add(priceLbl, null); this.add(getPriceTF(), null);

this.add(resultLbl, null); this.add(schoolLbl, null); this.add(getSchoolTF(), null);

this.add(commentLbl, null); this.add(getCommentsTF(), null);

this.add(getPONumTF(), null); this.add(pONumLbl, null); addWindowListener(this);

}

Null constructor that calls initialize

Defines labels, then frame

▮ And a main to test

▮ Speaking of test, code an actionPerformed to:▮ Create a TransTable object▮ Populate the object with info entered

in Frame▮ Clear the frame text fields▮ Display info from TransTable objectchapter 10 60© copyright Janson Industries 2011

Sale


new POSale();

}


public void actionPerformed(ActionEvent e) {

TransTable newSale = new TransTable();

try {

newSale.setCustomer(custNameTF.getText());

newSale.setSchool(schoolTF.getText());

newSale.setPONum(pONumTF.getText());

newSale.setItemName(itemNameTF.getText());

newSale.setPrice(Double.valueOf(priceTF.getText()).doubleValue());

newSale.setComments(commentsTF.getText());

newSale.setQty(Integer.valueOf(qtyTF.getText()).intValue());

newSale.setPurchDate();

custNameTF.setText(""); schoolTF.setText("");

pONumTF.setText(""); priceTF.setText("");

commentsTF.setText(""); qtyTF.setText(""); itemNameTF.setText("");

System.out.println("Successfully created a TransTable object for PO Num:" + newSale.getPONum());

}

catch (InvalidLengthException err) {

System.out.println("\nLength exception: \n"+err.getMessage());

}

}

Creates newSale,

retrieves info from frame, sets

props

Proves object exists by displaying PO Num

Clears TFs


Run POSale, enter a PO Num, click Add


Success!


PO Sale

▮ Might be nice if we put the info in the database table

▮ Need to finish CRUD functions in TransTable

▮ PO Sale will invoke the U of CRUD


Prepared Statement

▮ In TransTable, before the insert can be performed, must supply values to the prepared statement:

psAddTT.setString(1, School);

psAddTT.setString(2, CustName);

psAddTT.setString(3, PurchDate);

: : :

psAddTT.executeUpdate();


Prepared Statement

▮ Of course, the variables CustName, etc. had to be set to some values

▮ POSale does this after it creates the TransTable object (newSale)

newSale.setSchool(schoolTF.getText());

newSale.setCustName (custNameTF.getText());

newSale.setPurchDate();

: : : : :


Update (in TransTable)

public void write() {

try {

psAddTT.setString(1, school);

psAddTT.setString(2, customer);

psAddTT.setString(3, purchDate);

psAddTT.setString(4, itemName);

psAddTT.setInt(5, qty);

psAddTT.setDouble(6, price);

psAddTT.setString(7, pONum);

psAddTT.setString(8, comments);

psAddTT.setDouble(9, 0);

psAddTT.executeUpdate(); }

catch (SQLException e) {

System.err.println("General SQL exception.");

System.err.println(e.getMessage()); }

}

Sets paid amount to zero


POSale must invoke write in actionPerformed

Put out a user msg and comment out the test println


PO Sale

▮ Notice that POSale doesn’t worry about connections.

▮ There are no:▮ Drivers▮ Driver managers▮ Connection objects▮ Prepared statements

▮ Encapsulating the file makes the client class’ logic/coding simpler!!


Now when we run POSale, enter info, & click Add…


…the info is inserted into the table


Paying a PO

▮ Need the ability to mark a PO as paid

▮ New POPay frame will:

▮ Display a list of outstanding PO's with PO #, school, and date

▮ When user selects a PO, POPay (using the TransTable object) updates pay date and paid amt


Paying a PO

User

Framew/ POs

Creates

OutstandingPOs

TransTable

dummyTT

POPay

Sales DB

TransTable

PO’s where paidAmt = 0


For each unpaid PO display PO#, School & PO Date

When you click on one...


...the PayDate and PaidAmt are updated...


Paying a PO

Sales DB

User

SelectedPO

TransTable

Createsw/ selected PO #

realPO

Select PO info

Paid date& amount

POPay

Pay

TransTable

1

2

34

5


read(String whereClause)

▮ There can be many read functions:▮ A read for a key value (a single record)▮ A read for all records in a table▮ A read for records based on a condition

▮ Therefore the actual read method needs to accept a where clause

▮ Other methods need to create the where clause and pass to read()



▮ Because the SQL read statement will be dynamically built can't use a prepared statement

▮ Must use a regular statement object

▮ That's why we created a variable

▮ And in init, created the statement object

private Statement stmt;



TransTable(String poNum)

▮ To retrieve a single record, create a constructor that accepts a key value

▮ Will build read to retrieve records based on a Where condition, so need a method to pass a null Where

▮ POPay only wants outstanding PO's ▮ Need a method to pass a where clause

that has the condition paid amount = 0



▮ The select statement simply returns a result set

▮ TransTable needs to: ▮ Assign the result set to a result set

variable▮ Retrieve data from the result set and set

the TransTable object properties

▮ read method will assign result set

▮ Will create a getDataFromRS method to get data and assign to properties


Read

private ResultSet rs;

: : : :

private void read(String whereClause) {

try {

String select = "SELECT * FROM TxTable " +

whereClause;

rs = stmt.executeQuery(select);

rs.next();

} catch (SQLException sqlex) {


System.out.println("\nSQL exception on Select\n");

}

}

read accepts a where clause if the where clause is blank, will retrieve all

records

"Priming read"


Single Record Read

public TransTable(String ponum) {

this();

try {

this.read(" WHERE PONum = '" + ponum + "'");

this.getDataFromRS();

rs.close();

stmt.close();


System.out.println("SQL exceptions");


System.exit(1);

}

}

Builds where clause, executes read & getDataFromRS

Invokes the null constructor – why?

House cleaning, closes rs and statement


getDataFromRS

private void getDataFromRS() {

try { school = rs.getString(1);

customer = rs.getString(2);

purchDate = rs.getString(3);

itemName = rs.getString(4);

qty = rs.getInt(5);

price = rs.getDouble(6);

payDate = rs.getString(7);

pONum = rs.getString(8);

comments = rs.getString(9);

paidAmt = rs.getDouble(10);

}

catch (SQLException sqlex) {


System.out.println("\nSQL exception on rs get\n");

} }


Other methods needed

▮ Still need:

▮ A delete function (not going to show/do)

▮ A getAll method

▮ Related business functions

▮ getOutStandingPOs method ▮ pass where clause of paidAmt = 0

▮ setPOPaid method

▮ Then must create POPay

▮ Passes a null where clause so all POs will be returned

▮ Pretty simple but notice it returns a result set

▮ This means the invoking object must handle the result set


Get all POs

public ResultSet getAllPOs()

{

if (conn==null) { init();}

read("");

return rs;

}

▮ Again, pretty simple but it also returns a result set

▮ This means the invoking object (POPay) must handle the result set


Outstanding POs

public ResultSet getOutStandingPOs()

{

if (conn==null) { init();}

read("WHERE PaidAmt = 0");

return rs;

}

▮ Will test with following main method


Outstanding POs


TransTable tt = new TransTable();

ResultSet rsTest = tt.getOutStandingPOs();

try {

System.out.println("Got the first PO " + rsTest.getString(8));

} catch (SQLException sqlex) {


System.out.println("SQL exception on rs get");

}

}

▮ Need to update just the PayDate and PaidAmt fields

▮ Needed another statement variable

▮ In init, created & assigned statement object

▮ Then create two new methods:▮ One to build the SQL update statement▮ One to perform the update


Updating (in TransTable)

private Statement updateStmt;

updateStmt = conn.createStatement();


Updating (in TransTable)public void setPOPaid() {

this.setPayDate();

String totalCost = String.valueOf(qty * price);

String update = "Update TxTable Set PayDate = '" +

this.payDate + "', PaidAmt = " +

totalCost + “ WHERE PONum = '" +

this.pONum + "'";

this.update(update);

}

public void update(String sqlupdate) {

try {

updateStmt.executeUpdate(sqlupdate);

}

catch (SQLException e) {

System.err.println("General SQL exception.");

System.err.println(e.getMessage());

}

}


POPay Frame

▮ Initially will display all outstanding POs

▮ User selects one

▮ POPay then:

▮ Creates a new TransTable object for the selected PO

▮ Invokes the setPOPaid method


Assuming we have the data above


For each unpaid PO display PO#, School & PO Date

When you click on one...


...message displayed and list box cleared…


...the PayDate and PaidAmt are updated


Running again would show that the PO was updated


import java.awt.Frame; import java.awt.event.ItemEvent;

import java.awt.event.ItemListener; import java.awt.event.WindowEvent;

import java.awt.event.WindowListener; import java.sql.ResultSet;

import java.sql.SQLException; import java.awt.List;

import java.awt.Rectangle; import java.awt.Label;

public class POPay extends Frame implements WindowListener, ItemListener {

private static final long serialVersionUID = 1L;

ResultSet rs;

private List outstandingPOLB = null;

private Label label = null;

public void windowActivated(WindowEvent e) {}

public void windowClosed(WindowEvent e) {}

public void windowClosing(WindowEvent e) {

this.dispose();

}

public void windowDeactivated(WindowEvent e) {}

public void windowDeiconified(WindowEvent e) {}

public void windowIconified(WindowEvent e) {}

public void windowOpened(WindowEvent e) {}

POPay Frame

2 visual comps (list & label) & a

result set

Window listener

methods


public POPay() {

super();

TransTable dummyTT = new TransTable();

rs = dummyTT.getOutStandingPOs();

initialize();

}

POPay Constructor

Creates a TransTable object and retrieves

outstanding POs


private void initialize() {

label = new Label();

label.setBounds(new Rectangle(5, 141, 291, 23));

label.setAlignment(Label.CENTER);

label.setText("Select the PO to be paid");

this.setLayout(null);

this.setSize(300, 200);

this.setTitle("Pay a PO");

this.setVisible(true);

this.add(getOutstandingPOLB(), null);

this.add(label, null);

addWindowListener(this);

}

Initialize (in POPay)

Defines label and frame and gets the

list


▮ Need to add outstanding PO's to the list

▮ Tie an item listener to the list

List (in POPay)


private List getOutstandingPOLB() {

if (outstandingPOLB == null) {

outstandingPOLB = new List();

outstandingPOLB.setBounds(new Rectangle(35, 66, 229, 64));

outstandingPOLB.addItemListener(this);

try {

do {

outstandingPOLB.add(rs.getString(8) +

" " + rs.getString(1) +

" " + rs.getString(3));

} while (rs.next());



}

}

return outstandingPOLB;

}

List (in POPay)

RAD generates code to create, size and position

Programmer adds listener & loop to retrieve PO info from result set &

add to list


POPay

▮ This is a good time to test that:

▮ Connection works

▮ All outstanding POs are displayed


POPay pay = new POPay();

}


Looking good!


▮ itemStateChanged method must:

▮ Retrieve the selected item from LB

▮ Extract the PO # from the selected item

▮ Create a TransTable object for the PO #

▮ Invoke setPOPaid

▮ Clear the list

▮ Display the paid message

Item State Changed


public void itemStateChanged (ItemEvent e) {

String selectedPO = outstandingPOLB.getSelectedItem();

int index = 0;

String pONum =

String.valueOf(selectedPO.charAt(index));

index++;

while(!(String.valueOf(selectedPO.charAt(index)).

equals(" "))) {

pONum = pONum +

String.valueOf(selectedPO.charAt(index));

index++;

}

TransTable realPO = new TransTable(pONum);

realPO.setPOPaid();

label.setText("PO# " + realPO.getPONum() + " paid");

outstandingPOLB.removeAll();

}

Retrieve PO info, get first char, assign to PO#

Loop through till a space is encountered – space means end of the

PO# reached

Point to next char

Create TransTable and invoke setPOPaid

Build and display message and clear POs from list


Run and select PO # 82634

To verify:Check that PayDate and PaidAmt are updated

Run again and only 2 POs should be shown


Enterprise Data

▮ Rarely use MS Access to store sizable amount of data

▮ Can consist of many DBs with many tables▮ Thousands of tables not unusual

▮ Tables stored and possibly moved between different types of DBMS:

▮

▮ DB2, Oracle, SQL Server, ...


Enterprise Data

▮ Defining connection info and objects in each "encapsulating" (i.e. table/file) class redundant

▮ Takes up more space

▮ Longer to make changes

▮ Greater chance of error when making changes

▮ Inheritance can help!▮


Inheritance

▮ By creating superclasses, we can reduce the amount of duplicate code

▮ For instance, all the connection variables and methods:▮ variables (url, password, driver, etc.)▮ conn ▮ init

▮ Define in one DBMS-type superclass and have table/file classes inherit them


Abstract types

▮ A subclass (or implementing class) must have methods with the same signature as its superclass' abstract methods

▮ E.g. abstract methods are "behind" the WindowListener methods▮ All those methods you were forced to

code, are defined as abstract methods in the WindowListener class

▮ A class can also be defined as abstract▮ abstract classes cannot be instantiated


Inheritance

▮ Remember the steps to encapsulate a file:▮ Define a class for the file

▮ Define private variables for each field in the file

▮ Define a getter and setter for each private variable

▮ Define CRUD functions

▮ Define functions to return associated objects (getOutStandingPOs())

▮ Define business functions (setPOPaid())


Inheritance

▮ We can enforce consistency across all the encapsulating classes by creating “abstract” methods that define the encapsulation interface method’s signatures in a superclass

▮ I.e. define abstract CRUD methods in the superclass so that all subclasses must code CRUD methods the same way


▮ DBFile class will define:▮ Common variables and functions▮ Abstract standard interface methods

▮ Individual DBMS classes define:▮ Unique values for that DBMS type

▮ Individual Table classes define:▮ Unique values for the table▮ Standard interface methods▮ Unique functions for that table

Multiple DBMS Example


DBFileconn, url, driver, user, pw, etc.

private init();abstract delete(),write(), update(), read()

AccessFiledriver = ("sun.

jdbc.odbc.

JdbcOdbcDriver")

user =

pw =

DB2Filedriver = ("com.

ibm.as400.access

.AS400JDBCDriver")

user =

pw =

is a is a

OracleFiledriver= “oracle

.jdbc.driver.

OracleDriver”)

user =

pw =

Multiple DBMS Example


Database Example

▮ We’ll create an abstract DBFile class to…

▮ Define connection variables// DBFile

import java.util.*;

import java.sql.*;

abstract class DBFile {

Connection conn = null;

String url = null;

String user, pw;

Properties p = new Properties();

String driver = null;

public boolean connExists = false;

Abstract classes

cannot be instantiated!!


Database Example

▮ … and to…▮ Create a common connection method

initpublic void init() { if (conn == null) { try {

Class.forName(driver); p.put("naming", "sql");

p.put("user", user); p.put("password", pw);

conn = DriverManager.getConnection(url, p);

} catch (ClassNotFoundException e) {

System.out.println("couldn't find driver");

e.printStackTrace(); System.exit(1);



e.printStackTrace(); System.exit(1); } } }


Database Example

▮ … and to:▮ Enforce CRUD

▮ Protected allow subclasses access▮ Even if in a different package

protected abstract void write();

protected abstract void update(String sqlStmt);

protected abstract void read(String whereClause);

protected abstract void delete(String sqlStmt);

protected abstract void getDataFromRS();

}


Database Example

▮ You can have many different types of databases at many different locations▮ Local Access DB’s▮ Remote Oracle DB’s▮ Remote DB2 DB’s

▮ Need subclasses to define each “type” of DB’s (or multiple DBMS of same type on different machines) unique connection values▮ Driver, URL, PW, ID


AccessFile Class

abstract class AccessFile extends DBFile {

public AccessFile () {

url = "jdbc:odbc:Sales";

driver = "sun.jdbc.odbc.JdbcOdbcDriver";

user = "anonymous";

pw = "guest";

}

}Also defined as abstract

classes


DB2File Class

▮ Have to get the correct driver

▮ JTOpen available (on website) or free at:▮ http://sourceforge.net/projects/jt400/

files/JTOpen-full/7.3/jtopen_7_3.zip/download

// DB2File

abstract class DB2File extends DBFile {

public DB2File() {

url = "jdbc:as400://207.203.206.4/Sales";

driver = "com.ibm.as400.access.AS400JDBCDriver";

user = "bjanson";

pw = "jeter"; }

}


Oracle File Class

▮ Have to get the correct driver

▮ OracleDriver on website or free at:▮ http://www.oracle.com/technology/

software/tech/java/sqlj_jdbc/index.html// Oracle File

abstract class OracleFile extends DBFile {

public OracleFile() {

url = "jdbc:oracle:thin:@207.203.206.4:1521:SID";

driver = "oracle.jdbc.driver.OracleDriver";

user = "bjanson";

pw = "jeter"; }

}


DBFilepublic init();abstract delete, write, update, read

AccessFiledriver =

user =

pw =

TransTable

is a

Customer

is a is a

Database Example


TransTable Changes

▮ TransTable is a subclass of AccessFile and AccessFile variables are inherited

▮ TransTable doesn’t define init() or variables (i.e. url) instead inherits from DBFile

import java.util.*;

: : :

public class TransTable extends AccessFile {

: : : :

//static Connection conn = null;

//static String url = ("jdbc:odbc:Sales");

//static Properties p = new Properties();

//static String driver = ("sun.jdbc.odbc.JdbcOdbcDriver");//private String userid = new String("student99");//private String pw = new String("pinrut");


TransTable Changes

▮ Comment out old init

▮ Must still run init (inherited init) and create various statement objects

public TransTable() {

init();

try {

if (psAddTT == null) {

psAddTT = conn.prepareStatement("INSERT INTO "

+ "TxTable(School, Customer, PurchDate, ItemName, Qty,"

+ "Price, PONum, Comments, PaidAmt) VALUES(?, ?, ?, ?, ?, ?, ?, ?, ?)");

}


TransTable Changes

if (stmt == null) {


}

if (updateStmt == null) {

updateStmt = conn.createStatement();

}




System.exit(1);

}

}

protected void getDataFromRS() {...

protected void read(String whereClause) {...


TransTable Class

▮ Have a small problem with TransTable: we never defined a delete method

▮ This is the error message when you don’t code a required abstract method:

▮ What should you do?


Verify that POPay still works


TransTable Class


▮ If we moved TxTable from Access to DB2 on an IBM Power System…

▮ …just change TransTable to extend DB2File

DB2Fileurl=

driver =

user =

pw =

is a

TransTable

is a


TransTable DB2 Class

// TransTable.java

import java.sql.*;

public class TransTable extends DB2File{



init();....}

protected void delete(String whereClause) { }

No communication variables to

change

“Got around” abstract delete method


TransTable Class


▮ If we moved TxTable from DB2 on an IBM Power System to Oracle…

▮ …just change TransTable to extend OracleFile

OracleFileurl=

driver =

user =

pw =

is a

TransTable

is a


TransTable DB2 Class

// TransTable.java

import java.sql.*;

public class TransTable extends OracleFile{



init();....}

protected void delete(String whereClause) { }

No communication variables to

change


TxTable DB2 Table

CREATE TABLE sales.txtable

(school char(25),

customer char(30),

purchdate char(10),

qty int,

itemname char(30),

price double,

paydate char(10),

ponum char(15),

comments char(100),

paidamt double)

Assuming the table was created

using this SQL


TransTable Class

Do table classes or methods have any idea TxTable was moved?


DB2 Table

▮ DB2 driver must be downloaded▮ jtopen folder on class website

▮ To run in RAD, driver must be added to Java Build Path

▮ Right click project and select properties

▮ Select Java Build Path

▮ Click Libraries tab


Click Add External Jars...


Drill down to the jtopen/lib folder and select jt400.jar

Click Open then OK


jt400.jar added to project


Run POSale, input a new PO


DB2 Table


In Class Assg

▮ Create a class DispEmp that:

▮ Retrieves the contents of TNTDB.employee

▮ Displays the contents on a frame


DB Problems

▮ If you get a Unhandled exceptions msg:

Unhandled exceptionType=Segmentation error vmState=0x00040000J9Generic_Signal_Number=00000004 ExceptionCode=c0000005 ExceptionAddress=738B72D7 ContextFlags=0001003fHandler1=7FEFA0C0 Handler2=7FECC180 InaccessibleAddress=00000000EDI=00000000 ESI=70B52000 EAX=00000000 EBX=00000000ECX=00000020 EDX=00000000EIP=738B72D7 ESP=6F77DDD4 EBP=6F77DDD8 EFLAGS=00010202GS=0000 FS=003B ES=0023 DS=0023Module=C:\Windows\WinSxS\x86_microsoft.vc80.crt_1fc8b3b9a1e18e3b_8.0.50727.4927_none_d08a205e442db5b5\MSVCR80.dllModule_base_address=738A0000 Offset_in_DLL=000172d7Target=2_40_20110401_055940 (Windows 7 6.1 build 7600)CPU=x86 (8 logical CPUs) (0xcf5d5000 RAM)----------- Stack Backtrace -----------_strnicmp+0x7c (0x738B72D7 [MSVCR80+0x172d7])_strnicmp+0xe9 (0x738B7344 [MSVCR80+0x17344])(0x713042BE [ACECORE+0x42be])---------------------------------------JVMDUMP006I Processing dump event "gpf", detail "" - please wait.JVMDUMP032I JVM requested System dump using 'K:\JavaBookWS\CE\core.20110331.160455.6620.0001.dmp' in response to an eventJVMDUMP010I System dump written to K:\JavaBookWS\CE\core.20110331.160455.6620.0001.dmpJVMDUMP032I JVM requested Snap dump using 'K:\JavaBookWS\CE\Snap.20110331.160455.6620.0002.trc' in response to an eventJVMDUMP010I Snap dump written to K:\JavaBookWS\CE\Snap.20110331.160455.6620.0002.trcJVMDUMP032I JVM requested Java dump using 'K:\JavaBookWS\CE\javacore.20110331.160455.6620.0003.txt' in response to an eventJVMDUMP010I Java dump written to K:\JavaBookWS\CE\javacore.20110331.160455.6620.0003.txtJVMDUMP013I Processed dump event "gpf", detail "".


Dumps can be accessed from within RAD


DB Problems

▮ Open the “dump” text file and scroll down to find the stack trace


Access Assg

▮ On the class web site is an Access DB called TNTDB that you can download

▮ TNTDB has 2 tables

▮ employee (with employee 111)

▮ shipment


The tables are defined as follows:


Access Assg

▮ You’ll need to:▮ Download the DB▮ Define the DB as an ODBC data

source

▮ Define the ▮ driver as

sun.jdbc.odbc.JdbcOdbcDriver▮ URL as jdbc:odbc:TNT Database▮ userid as anonymous▮ password as guest


DB2 Assg

▮ At PLEIONE.SEALINC.ORG is a DB2 database/schema on an IBM Power System called TNTDB

▮ TNTDB has 2 tables▮ Employee (has emps 111, 222, 333)▮ Shipment (has 7, 111, 8888)

▮ Your UserID is student99, and PW is pinrut ▮ Don’t forget about the driver!!


Oracle Assg

▮ Can only be accessed from on-campus!▮ Must use driver ojdbc14.zip on class

website

▮ Define URL as:jdbc:oracle:thin:@stora:1521:sora10

▮ In SQL, don’t reference TNTDB▮ Employee (has one emp, 999)▮ Shipment (has one shipment, 999)

▮ Your UserID is Scott, and PW is TIGER

chapter 101© copyright janson industries 2011 database access ▮ jdbc ▮ db access objects ▮...

Documents

driver object

copyright janson industries

driver class

connection object

class object

db access protocol

statement object

dbmss protocol slide