Advanced Java 2 Platform HOW TO PROGRAM phần 6 pptx

14.2 14.4.1 MoneyTransfer EJB Home and Remote Interfaces The MoneyTransfer EJB demonstrates the need for distributed transactions and their implementation using bean-managed and containe

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Please refer to Section 14.3.2 for deployment instructions Recall that MathTool is a

stateless session EJB, so you must specify this in the deployment process Also, be sure to

specify an appropriate JNDI name (e.g., MathTool) for the MathTool EJB

MathToolClient (Fig 14.24) is an application client for the MathTool EJB The user interface consists of a JTextField into which the user can enter an integer, a JButton to invoke MathTool method getFactorial and a JButton to invoke MathTool method getFibonacciSeries The calculation results are displayed in a JTextArea.

The MathToolClient constructor (lines 29–45) invokes method Tool (line 35) to create a new instance of the MathTool EJB Line 38 invokes method createGUI to create and lay out GUI components for the application’s user interface Method createMathTool (lines 48–83) uses an InitialContext (line 53) to look

createMath-up the MathToolHome interface in the JNDI Directory (lines 56–57) Line 65 invokes MathToolHome method create to create a MathTool EJB instance.

Method getFactorialButton (lines 86–122) creates a JButton that, when pressed, invokes MathTool EJB method getFactorial Lines 100–104 parse the number entered in numberTextField and invoke method getFactorial of the MathTool remote interface Lines 107–108 display the factorial in resultsText- Area Lines 113–115 catch a RemoteException if there is an error invoking method getFactorial.

Method getFibonacciButton (lines 125–182) creates a JButton that, when clicked, invokes MathTool EJB method getFibonacciSeries Lines 140–145 parse the number entered in numberTextField and invoke method getFibonac- ciSeries of the MathTool remote interface Method getFibonacciSeries

returns an array of integers containing a Fibonacci series of the length specified by the

integer argument howMany Lines 148–168 build a StringBuffer containing the Fibonacci series and display the series in resultsTextArea.

14 // create new MathTool EJB

Fig 14.23 MathToolHome interface for creating MathTool EJBs.

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1 // MathToolClient.java

2 // MathToolClient is a GUI for calculating factorials and

3 // Fibonacci series using the MathTool EJB.

4 package com.deitel.advjhtp1.ejb.session.stateless.client; 5

6 // Java core libraries

22 private MathToolHome mathToolHome;

23 private MathTool mathTool;

25 private JTextArea resultsTextArea;

26 private JTextField numberTextField;

33 // create MathTool for calculating factorials

34 // and Fibonacci series

47 // create MathTool EJB instance

50 // lookup MathToolHome and create MathTool EJB

53 InitialContext initialContext = new InitialContext();

Fig 14.24 MathToolClient for interacting with MathTool EJB (part 1 of 6).

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69 // handle exception if MathTool EJB is not found

70 catch ( NamingException namingException ) {

74 // handle exception when creating MathTool EJB

75 catch ( RemoteException remoteException ) {

79 // handle exception when creating MathTool EJB

80 catch ( CreateException createException ) {

83 } // end method createMathTool

85 // create JButton for calculating factorial

86 private JButton getFactorialButton()

103 // get Factorial of number input by user

104 int result = mathTool.getFactorial( number ); 105

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106 // display results in resultsTextArea

112 // handle exception calculating factorial

124 // create JButton for generating Fibonacci series

125 private JButton getFibonacciButton()

139 // get number entered by user

140 int number = Integer.parseInt(

141 numberTextField.getText() );

142

143 // get Fibonacci series

144 int[] series = mathTool.getFibonacciSeries(

155 // append each number in series to buffer

156 for ( int i = 0 ; i < series.length; i++ ) { 157

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158 // do not add comma before first number

170 } // end try

171

172 // handle exception calculating series

184 // create lay out GUI components

185 public void createGUI()

186 {

187 // create JTextArea to show results

188 resultsTextArea = new JTextArea();

189 resultsTextArea.setLineWrap( true );

190 resultsTextArea.setWrapStyleWord( true );

191 resultsTextArea.setEditable( false );

192

193 // create JTextField for user input

194 numberTextField = new JTextField( 10 );

195

196 // create JButton for calculating factorial

197 JButton factorialButton = getFactorialButton();

198

199 // create JButton for generating Fibonacci series

200 JButton fibonacciButton = getFibonacciButton();

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211 // add input components to new JPanel

212 JPanel inputPanel = new JPanel( new FlowLayout() );

213 inputPanel.add( new JLabel( "Enter an integer: " ) );

214 inputPanel.add( numberTextField );

215

216 // add JButton components to new JPanel

217 JPanel buttonPanel = new JPanel( new FlowLayout() );

232 // get WindowListener for exiting application

233 private WindowListener getWindowListener()

244 // handle exception when removing MathTool EJB

245 catch ( RemoveException removeException ) {

246 removeException.printStackTrace();

247 System.exit( -1 );

248 }

249

250 // handle exception when removing MathTool EJB

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14.4 EJB Transactions

The Java 2 Enterprise Edition supports distributed transactions A distributed transaction

is a transaction that includes multiple databases or multiple application servers For ple, a distributed transaction could transfer funds from an account at one bank into an ac-count at another bank atomically

exam-J2EE supports two methods for defining transaction boundaries: bean-managed action demarcation and container-managed transaction demarcation Bean-managed

trans-transaction demarcation requires the EJB developer to code the trans-transaction boundaries

manually in the EJBs using the Java Transaction API (JTA) Container-managed

transac-tion demarcatransac-tion allows the EJB deployer to specify transactransac-tion boundaries declarativelywhen deploying EJBs

Software Engineering Observation 14.2

Entity EJBs may use only container-managed transaction demarcation. 14.2

14.4.1 MoneyTransfer EJB Home and Remote Interfaces

The MoneyTransfer EJB demonstrates the need for distributed transactions and their

implementation using bean-managed and container-managed transaction demarcation In

this example, we transfer money from an account at BankABC to an account at BankXYZ.

We first withdraw money from an account at BankABC and then deposit the same amount

at BankXYZ Transactions are needed to ensure that the money is “put back” in the

Bank-264 MathToolClient client = new MathToolClient();

265 }

266 }

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ABC account if the deposit at BankXYZ fails We also need to ensure that if the withdrawal from BankABC fails, the money is not deposited at BankXYZ.

The MoneyTransfer remote interface (Fig 14.25) provides methods for

transfer-ring money between accounts and for getting the balances of accounts at two different

banks Method transfer (line 15) transfers the given amount of money from an account

at BankABC to an account at BankXYZ Method getBankABCBalance (line 18) returns the account balance at BankABC Method getBankXYZBalance (line 21) returns the account balance at BankXYZ Interface MoneyTransferHome (Fig 14.26) provides method create (lines 15–16) for creating MoneyTransfer EJB instances.

14 // transfer amount from BankABC to BankXYZ

15 public void transfer( double amount ) throws RemoteException;

17 // get BankABC account balance

18 public double getBankABCBalance() throws RemoteException;

20 // get BankXYZ account balance

21 public double getBankXYZBalance() throws RemoteException;

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14.4.2 Bean-Managed Transaction Demarcation

Bean-managed transaction demarcation requires the EJB developer to code the transaction

boundaries manually in the EJBs Bean-managed transaction demarcation may be usedonly with session EJBs

MoneyTransferEJB (Fig 14.27) implements the MoneyTransfer remote

inter-face using bean-managed transaction demarcation to ensure atomicity of the database

updates in method transfer (lines 26–81) Lines 29–30 create a UserTransaction Line 34 begins the transaction by invoking UserTransaction method begin All statements after the transaction begins are part of the transaction until the transaction is committed or rolled back

14 // create MoneyTransfer EJB

15 public MoneyTransfer create() throws RemoteException,

1 // MoneyTransferEJB.java

2 // MoneyTransferEJB is a stateless session EJB for transferring

3 // funds from an Account at BankABC to an Account at BankXYZ

4 // using bean-managed transaction demarcation.

24

25 // transfer funds from BankABC to BankXYZ

26 public void transfer( double amount ) throws EJBException

28 // create transaction for transferring funds

29 UserTransaction transaction =

Fig 14.27 MoneyTransferEJB implementation of MoneyTransfer remote

interface using bean-managed transaction demarcation (part 1 of 6).Fig 14.26 MoneyTransferHome interface for creating MoneyTransfer

EJBs (part 2 of 2)

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37 // catch exception if method begin fails

40 // throw EJBException indicating transaction failed

44 // transfer funds from account in BankABC to account

45 // in BankXYZ using bean-managed transaction demarcation

72 // handle exception when rolling back transaction

73 catch ( SystemException systemException ) {

74 throw new EJBException( systemException );

77 // throw EJBException indicating transaction failed

82

interface using bean-managed transaction demarcation (part 2 of 6)

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83 // get balance of Account at BankABC

84 public double getBankABCBalance() throws EJBException

89 // select balance for Account # 12345

90 String select = "SELECT balance FROM Account " +

106 // handle exception when getting Account balance

107 catch ( SQLException sqlException ) {

108 throw new EJBException( sqlException );

110

111 } // end method getBankABCBalance

112

113 // get balance of Account at BankXYZ

114 public double getBankXYZBalance() throws EJBException

115 {

117 try {

118

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135

152 // create MoneyTransfer instance

154

155 // remove MoneyTransfer instance

156 public void ejbRemove() throws EJBException

157 {

158 closeDatabaseResources();

159 }

160

161 // passivate MoneyTransfer instance

162 public void ejbPassivate() throws EJBException

163 {

165 }

166

167 // activate MoneyTransfer instance

168 public void ejbActivate() throws EJBException

169 {

170 openDatabaseResources();

171 }

172

173 // close database Connections and PreparedStatements

174 private void closeDatabaseResources() throws EJBException

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186 // close database Connections

194 // handle exception closing database connections

198

199 } // end method closeDatabaseResources

200

201 // open database Connections and create PreparedStatements

202 private void openDatabaseResources() throws EJBException

204 // look up the BankABC and BankXYZ DataSources and create

205 // Connections for each

206 try {

207 Context initialContext = new InitialContext();

208

209 // get DataSource reference from JNDI directory

210 DataSource dataSource = ( DataSource )

224 String withdrawal = "UPDATE Account SET balance = " +

225 "balance - ? WHERE accountID = 12345" ;

232 String deposit = "UPDATE Account SET balance = " +

233 "balance + ? WHERE accountID = 54321" ;

234

235 depositStatement =

236 bankTwoConnection.prepareStatement( deposit );

237

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Lines 48–51 withdraw the given transfer amount from an account in the BankABC database Lines 53–56 deposit the given transfer amount in an account in the BankXYZ database Both of these updates are part of the transaction begun on line 34 even though they are in separate databases Line 59 commits the transaction to save the

updates to each database

Lines 65–79 catch any Exceptions thrown from lines 46–61 Line 69 invokes UserTransaction method rollback to undo any updates that were made within the transaction boundaries This rollback ensures that if any critical part of method transfer failed, all of the changes made in both databases are undone to ensure the

integrity of the data Lines 73–75 catch a SystemException, which is thrown by UserTransaction method rollback if the rollback fails Lines 74 and 78 throw EJBExceptions to aid in debugging the application

Methods getBankABCBalance (lines 84–111) and getBankXYZBalance (lines 114–141) execute simple SQL SELECT statements to retrieve the balances of the accounts at each bank Methods setSessionContext (lines 144–150) and ejbActi- vate (lines 168–171) invoke method openDatabaseResources (lines 202–250) to create Connections and PreparedStatements for each database for use throughout the lifetime of the MoneyTransfer EJB instance Methods ejbRemove (lines 156– 159) and ejbPassivate (lines 162–165) invoke method closeDatabaseRe- sources (lines 174–199) to close the Connections and PreparedStatements.

14.4.3 Container-Managed Transaction Demarcation

Container-managed transaction demarcation allows the EJB developer to implement an

EJB without specifying transaction boundaries The EJB deployer provides transaction marcation semantics declaratively when deploying the application

de-MoneyTransferEJB (Fig 14.28) implements the MoneyTransfer remote face using container-managed transaction demarcation Method transfer (lines 25–51)

inter-is similar to method transfer in Fig 14.27 Note, however, that thinter-is version of method transfer does not declare any transaction boundaries, as this is now the responsibility

238 } // end try

239

240 // handle exception if DataSource not found in directory

242 throw new EJBException( namingException );

244

245 // handle exception getting Connection to DataSource

248 }

249

250 } // end method openDatabaseResources

251 }

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of the EJB deployer The EJB deployer specifies the transaction semantics using one of thesix transaction types listed in Fig 14.29

1 // MoneyTransferEJB.java

2 // MoneyTransferEJB is a stateless session EJB for transferring

3 // funds from an Account at BankABC to an Account at BankXYZ

4 // using container-managed transaction demarcation.

5 package com.deitel.advjhtp1.ejb.transactions.containermanaged; 6

7 // Java core libraries

23

24 // transfer funds from BankABC to BankXYZ

25 public void transfer( double amount ) throws EJBException

27 // transfer funds from account in BankABC to account in

28 // BankXYZ using container-managed transaction demarcation

43 // handle exception withdrawing and depositing

interface using container-managed transaction demarcation (part 1 of 5)

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46 // throw EJBException to indicate transfer failed

47 // and roll back container-managed transaction

52

54 public double getBankABCBalance() throws EJBException

81 } // end method getBankABCBalance

82

84 public double getBankXYZBalance() throws EJBException

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98 // get first record in ResultSet and return balance

122 // create MoneyTransfer instance

124

125 // remove MoneyTransfer instance

126 public void ejbRemove() throws EJBException

127 {

129 }

130

131 // passivate MoneyTransfer instance

132 public void ejbPassivate() throws EJBException

133 {

135 }

136

137 // activate MoneyTransfer instance

138 public void ejbActivate() throws EJBException

139 {

140 openDatabaseResources();

141 }

142

143 // close database Connections and PreparedStatements

144 private void closeDatabaseResources() throws EJBException

145 {

146 // close database resources

147 try {

148

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164 // handle exception closing database connections

168

169 } // end method closeDatabaseConnections

170

171 // open database Connections and create PreparedStatements

172 private void openDatabaseResources() throws EJBException

174 // look up the BankABC and BankXYZ DataSources and create

175 // Connections for each

176 try {

177 Context initialContext = new InitialContext();

178

179 // get DataSource reference from JNDI directory

180 DataSource dataSource = ( DataSource )

194 String withdrawal = "UPDATE Account SET balance = " +

195 "balance - ? WHERE accountID = 12345" ;

196

197 withdrawalStatement =

198 bankOneConnection.prepareStatement( withdrawal );

199

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Line 66 throws an EJBException in response to any SQLException thrown from lines 29–41 The EJBContainer rolls back the current transaction when method transfer throws an EJBException (line 48).

Figure 14.29 lists the available transaction types for container-managed persistence.The deployer specifies the transaction type for each business method when deploying theapplication

200 // prepare deposit statment for account #54321 at

201 // BankXYZ

202 String deposit = "UPDATE Account SET balance = " +

203 "balance + ? WHERE accountID = 54321" ;

210 // handle exception if DataSource not found in directory

212 throw new EJBException( namingException );

214

215 // handle exception getting Connection to DataSource

218 }

219

220 } // end method openDatabaseConnections

221 }

Transaction Type Description

NotSupported Method does not support transactions The EJB container suspends the

exist-ing transaction context if the method is invoked within a transaction context

Required Method requires a transaction The EJB container creates a new transaction if

the method is invoked without an existing transaction context and commits the transaction at the end of the method

Supports Method supports transactions The EJB container will not create a new

transac-tion if the method is invoked without an existing transactransac-tion context, but will execute the method as part of an existing transaction context if one is available

RequiresNew Method requires a new transaction The EJB container suspends the existing

transaction context and starts a new transaction if the method is invoked as part of another transaction

Fig 14.29

Fig 14.29 Transaction types for container-managed transaction demarcation

(part 1 of 2)

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14.4.4 MoneyTransfer EJB Client

MoneyTransferEJBClient (Fig 14.30) provides a user interface for interacting with

the MoneyTransfer EJB Lines 24–26 declare JTextFields to display the account balances and accept a user-input transfer amount Line 34 invokes method create- MoneyTransfer to create a new MoneyTransfer EJB instance Line 37 invokes method createGUI to create and lay out GUI components for the application The GUI consists of JTextFields for displaying account balances and inputting the transfer amount and a JButton for transferring funds Line 40 invokes method displayBal- ances to display the current account balances at BankABC and BankXYZ.

Method createMoneyTransfer (lines 47–80) uses the MoneyTransferHome interface to create a MoneyTransfer EJB instance Line 51 creates an InitialCon- text for locating the MoneyTransfer EJB in the JNDI directory Lines 54–59 invoke InitialContext method lookup to get a remote reference to the MoneyTrans- ferHome interface Line 62 creates a new MoneyTransfer EJB instance by invoking MoneyTransferHome method create.

Method getTransferButton (lines 108–142) creates a JButton to transfer funds from BankABC to BankXYZ Lines 120–124 read the transfer amount from the user and invoke MoneyTransfer method transfer Line 127 invokes method displayBalances to update the display with the new account balances

Mandatory The method must execute in an existing transaction context The EJB

con-tainer throws a TransactionRequiredException if the method is

invoked without a valid transaction context

Never The method must not execute in a transaction context The EJB container

throws a RemoteException if the method is invoked inside a transaction

context

1 // MoneyTransferEJBClient.java

2 // MoneyTransferEJBClient is a client for interacting with

3 // the MoneyTransfer EJB.

Fig 14.30 MoneyTransferEJBClient for interacting with

MoneyTransfer EJB (part 1 of 6).

Transaction Type Description

Fig 14.29

Fig 14.29 Transaction types for container-managed transaction demarcation

(part 2 of 2)

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24 private JTextField bankABCBalanceTextField;

25 private JTextField bankXYZBalanceTextField;

26 private JTextField transferAmountTextField;

46 // create MoneyTransferEJB for transferring money

47 private void createMoneyTransfer( String JNDIName )

53 // lookup MoneyTransfer EJB

54 Object homeObject = context.lookup( JNDIName );

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65

66 // handle exception when looking up MoneyTransfer EJB

70

72 catch ( CreateException createException ) {

80 } // end method createMoneyTransfer

82 // display balance in account at BankABC

83 private void displayBalances()

87 // get and display BankABC Account balance

88 double balance = moneyTransfer.getBankABCBalance();

100 // handle exception when invoke MoneyTransfer EJB methods

107 // create button to transfer funds between accounts

108 private JButton getTransferButton()

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117 try {

118

119 // get transfer amount from JTextField

120 double amount = Double.parseDouble(

121 transferAmountTextField.getText() ); 122

130 // handle exception when transferring money

144 // create and lay out GUI components

145 private void createGUI()

146 {

147 // create JTextFields for user input and display

148 bankABCBalanceTextField = new JTextField( 10 );

156 // create button to transfer between accounts

157 JButton transferButton = getTransferButton();

158

159 // layout user interface

160 Container contentPane = getContentPane();

161 contentPane.setLayout( new GridLayout( 3 2 ) );

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174 // get WindowListener for exiting application

175 private WindowListener getWindowListener()

176 {

177 // remove MoneyTransfer EJB when user exits application

178 return new WindowAdapter() {

187 // handle exception removing MoneyTransfer EJB

188 catch ( RemoveException removeException ) {

189 removeException.printStackTrace();

190 System.exit( 1 );

191 }

192

193 // handle exception removing MoneyTransfer EJB

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Figure 14.30 shows three screen captures of MoneyTransferEJBClient Enter any legal value in the text field and press the Transfer button This causes the EJB to

update the database entries The client then updates its GUI to reflect the new account ances

bal-Fig 14.30 MoneyTransferEJBClient for interacting with

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14.4.5 Deploying the MoneyTransfer EJB

The MoneyTransfer EJB accesses two databases that store account information The

examples use the Cloudscape DBMS introduced in Chapter 8, JDBC Follow the directions

in Section 8.5 to set up the databases for the MoneyTransfer EJB The SQL script for the databases, transactions.sql, is on the CD-ROM that accompanies this book If

you have not already done so, please see Appendix E for instructions on integrating scape with the J2EE 1.2.1 reference implementation Add the following

Cloud-|jdbc/BankABC|jdbc:cloudscape:rmi:BankABC;create=true;|jdbc/ BankXYZ|jdbc:cloudscape:rmi:BankXYZ;create=true;

to the jdbc.datasources property in the file fault.properties

C:\j2sdkee1.2.1\config\de-Deploying each versions of the MoneyTransfer EJB is very similar to deploying the other session EJBs When deploying the MoneyTransfer EJB, we must create

resource references to the two databases in the New Enterprise Bean Wizard (Fig 14.31)

Click the Add button to add a new resource reference Fill in the Coded Name and JNDI Name fields with jdbc/BankABC for the BankABC database (Fig 14.32) and jdbc/ BankXYZ for the BankXYZ database (Fig 14.33) In the Transaction Management dialog of the New Enterprise Bean Wizard select Bean-Managed Transactions for the bean-managed version of MoneyTransferEJB (Fig 14.34) or Container-Man- aged Transactions for the container-managed version of MoneyTransferEJB

(Fig 14.35) For the container-managed EJB, select a transaction type for each method (seeSection 14.4.3 for information about transaction types) The rest of the deployment is thesame as the deployment of the other session EJBs Be sure to run the Cloudscape server

before executing MoneyTransferEJBClient.

Fig 14.31

Fig 14.31 Resource References dialog of New Enterprise Bean Wizard.

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14.5 Internet and World Wide Web Resources

TheServerSide.com is an online community for J2EE developers There are forums, articles and

other resources for building applications with J2EE

SUMMARY

• Every EJB consists of a remote interface, a home interface and an EJB implementation

• The remote interface declares business methods that clients of the EJB may invoke The home

in-terface provides create methods for creating new instances of the EJB, finder methods for

find-ing instances of the EJB and remove methods for removfind-ing instances of the EJB The EJB implementation defines the business methods declared in the remote interface and the create, remove and finder methods of the home interface

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• EJBs have a complex life cycle that is managed by an EJB container The EJB container createsclasses that implement the home and remote interfaces.

• The J2EE specification defines six roles for implementing enterprise systems Each role is sible for producing some part of an enterprise application

respon-• The remote interface for an EJB declares the business methods that clients of the EJB may invoke

The remote interface must extend interface javax.ejb.EJBObject.

• Each method of the remote interface is required to declare that it throws Exception Each method also may throw application-specific exceptions—for example, an IllegalArgumentException if a provided argument does not meet certain criteria.

java.rmi.Remote-• The home interface for an EJB declares methods for creating, removing and finding EJB instances

The home interface must extend interface javax.ejb.EJBHome.

• Depending on the EJB type (i.e., session or entity), the container invokes EJB implementation

meth-ods that correspond to methmeth-ods create and remove and finder methmeth-ods of the home interface

• The EJB implementation defines the business methods declared in the EJB remote interface and

the create, remove and finder methods declared in the EJB home interface The EJB

imple-mentation must also implement the methods of interface javax.ejb.SessionBean for sion EJBs, or interface javax.ejb.EntityBean for entity EJBs

ses-• The EJB container manages the life cycle, client interactions and method invocations, transactions,security and exceptions of an EJB Clients of an EJB do not interact directly with the EJB When

a client invokes a business method of the EJB’s remote interface, the invocation goes first to theEJB container, which then delegates the business method invocation to the EJB implementation

• Session EJBs exist for the duration of a client’s session Each session EJB instance is associatedwith a single client Session EJBs can manipulate data in a database, but unlike entity EJBs, ses-sion EJBs are not persistent and do not represent database data directly

• Stateful session EJBs maintain state information between business method invocations For ple, a stateful session EJB could maintain information about a customer’s shopping cart while thecustomer browses an on-line store

exam-• Interface SessionContext extends interface EJBContext, which provides methods for

ob-taining information about the EJB container

• The EJB container invokes method ejbCreate when a client invokes a create method in the home interface The EJB implementation must provide an ejbCreate method for each create method declared in the home interface The ejbCreate methods must have the same number and types of arguments as their corresponding create methods

• The EJB container invokes method ejbRemove in response to an invocation of method remove

in the home interface

• The EJB container invokes method ejbPassivate when it determines that the EJB is no longer

needed in memory

• The EJB container invokes method ejbActivate to restore an EJB instance that the container

passivated previously The EJB container activates an EJB instance if a client invokes a businessmethod of that EJB instance

• RMI-IIOP allows RMI objects to interact with CORBA components, which communicate using

the Internet Inter-Orb Protocol (IIOP) CORBA is a language-independent framework for

build-ing distributed systems To enable interoperability among EJBs and CORBA components, EJBscommunicate using RMI-IIOP We discuss CORBA and RMI-IIOP in detail in Chapter 22

• Stateless session EJBs maintain no state information between business method invocations As aresult, any stateless session EJB instance can be used to respond to any client’s request This im-proves the performance of stateless session EJBs over stateful session EJBs

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• The Java 2 Enterprise Edition supports distributed transactions A distributed transaction is a action that is applied across multiple databases or across multiple EJB servers

trans-• J2EE supports two methods for defining transaction boundaries: bean-managed transaction marcation and container-managed transaction demarcation Bean-managed transaction demarca-tion requires the EJB developer to code the transaction boundaries manually in the EJBs, using theJava Transaction Services Container-managed transaction demarcation allows the EJB deployer

de-to specify transaction boundaries declaratively when deploying EJBs

• Bean-managed transaction demarcation requires the EJB developer to code the transaction aries manually in the EJBs Bean-managed transaction demarcation may be used only with sessionEJBs

bound-• Container-managed transaction demarcation allows the EJB developer to implement an EJB out specifying transaction boundaries The EJB deployer provides transaction demarcation seman-tics declaratively when deploying the application

with-TERMINOLOGY

SELF-REVIEW EXERCISES

14.1 What are the two main types of session EJBs? What is the primary difference between them?

14.2 What three Java objects must the EJB developer provide for each EJB?

14.3 What are the responsibilities of the EJB container?

14.4 How does a client get a remote reference to an EJB instance?

14.5 What types of transaction demarcation can EJBs use? What are the benefits of each type?

ANSWERS TO SELF-REVIEW EXERCISES

14.1 There are stateful session EJBs and stateless session EJBs Stateful session EJBs maintainstate information between business method invocations in a client’s session Stateless session EJBsmaintain no state information between business method invocations

application server Internet Inter-Orb Protocol (IIOP)

bean-managed transaction demarcation J2EE (Java 2 Enterprise Edition)

business methods Java Transaction Services (JTS)

container-managed transaction demarcation java.rmi.RemoteException

CORBA (Common Object Request

Broker Architecture)

java:comp/env naming context javax.ejb.EJBHome

distributed transaction javax.ejb.SessionBean

EJB container JNDI (Java Naming and Directory

Interface) directoryEJB implementation

EJB server least recently used

Enterprise JavaBeans (EJBs) SessionContext interface

entity EJB stateful session EJB

home interface stateless session EJB

IllegalArgumentException

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14.2 The EJB developer must provide a remote interface, a home interface and the EJB tation

implemen-14.3 The EJB container is responsible for managing the life cycle of the EJB The EJB containercreates classes to implement the home and remote interfaces, and delegates business method invoca-tions to the developer-supplied EJB implementation The EJB container also provides runtime re-sources, such as database connections and transactions, as well as life-cycle management

14.4 A client looks up the EJB’s home interface in a JNDI directory For session EJBs, the client

then invokes one of the home interface’s create methods For entity EJBs, the client can invoke

one of the home interface’s create methods or finder methods.

14.5 EJBs can use either bean-managed or container-managed transaction demarcation managed transaction demarcation allows the developer to have fine-grained control over transactionboundaries Container-managed transaction demarcation simplifies the EJB implementation by al-lowing the EJB deployer to specify transaction boundaries declaratively at deployment time

Bean-EXERCISES

14.1 Stateless session EJBs offer a performance advantage over stateful session beans Convertthe example of Fig 14.3, Fig 14.4, Fig 14.5 and Fig 14.6 from a stateful session EJB to a statelesssession EJB

14.2 Add a new recursive business method power( base, exponent ) to the MathTool

EJB (Fig 14.21, Fig 14.22, Fig 14.23) that, when invoked, returns

base exponent

For example, power( 3, 4 ) = 3 * 3 * 3 * 3 If the exponent is not an integer greater than or

equal to 1, throw an IllegalArgumentException [Hint: The recursion step would use the

relationship

base exponent = base · base exponent – 1

and the terminating condition occurs when exponent is equal to 1 because

base 1 = base

Modify the client in Fig 14.24 to enable the user to enter the base and exponent.]

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15 Entity EJBs

Objectives

• To understand how entity EJBs represent persistent

data.

• To understand synchronization issues between EJBs

and database data.

• To understand the life-cycle of an entity EJB.

• To understand the advantages and disadvantages of

container-managed and bean-managed persistence.

There is nothing more requisite in business than dispatch.

Joseph Addison

All meanings, we know, depend on the key of interpretation.

George Eliot

Event that are predestined require but little management

They manage themselves They slip into place while we sleep,

and suddenly we are aware that the thing we fear to attempt,

is already accomplished.

Amelia Barr

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15.1 Introduction

A fundamental part of an enterprise application is the information tier, which maintains

data for the application In this chapter, we introduce entity EJBs, which enable developers

to build object-based representations of information-tier data, such as data stored in a tional database EJB containers provide advanced features that simplify developing entityEJBs For example, based on information provided at deployment time (e.g., SQL queries),

rela-an entity EJB’s container crela-an generate code automatically for storing rela-and retrieving datarepresented by the EJB For entity EJBs that represent more complex data (e.g., data stored

in multiple database tables), the programmer can implement code for storing and retrievingthe data manually

In this chapter, we present two versions of an entity EJB that represents a companyemployee The first version demonstrates an entity EJB that uses JDBC to persist data to arelational database The second version takes advantage of the container’s ability tomanage data storage and retrieval to simplify the EJB implementation After completingthis chapter, you will be able to build and deploy entity EJBs through which business-logiccomponents, such as session EJBs (Chapter 14), can access data in the information tier

15.2 Entity EJB Overview

Each entity EJB instance represents a particular unit of data, such as a record in a database

table There are two types of entity EJBs—those that use bean-managed persistence and those that use container-managed persistence Entity EJBs that use bean-managed persis-

tence must implement code for storing and retrieving data from the persistent data sourcesthey represent For example, an entity EJB that uses bean-managed persistence might usethe JDBC API to store and retrieve data in a relational database Entity EJBs that use con-tainer-managed persistence rely on the EJB container to implement the data-access calls totheir persistent data sources The deployer must supply information about the persistentdata source when deploying the EJB

Outline

15.1 Introduction

15.2 Entity EJB Overview

15.3 Employee Entity EJB

15.4 Employee EJB Home and Remote Interfaces

15.5 Employee EJB with Bean-Managed Persistence

15.5.1 Employee EJB Implementation

15.5.2 Employee EJB Deployment

15.6 Employee EJB with Container-Managed Persistence

15.7 Employee EJB Client

15.8 Internet and World Wide Web Resources

Summary • Terminology • Self-Review Exercises • Answers to Self-Review Exercises • Exercises

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Entity EJBs provide create methods for creating new EJB instances, remove

methods for removing EJB instances and finder methods for finding EJB instances For

entity EJBs that represent information in a database, each create method performs INSERT operations to create new records in the database, and each remove method per-

forms DELETE operations to remove records from the database Each finder method

locates entity EJB instances that conform to certain search criteria (e.g using SELECT

oper-ations) We discuss each of these method types throughout the chapter

15.3 Employee Entity EJB

In the following sections, we build an entity EJB that represents an Employee We vide two implementations of the Employee EJB The first implementation (Section 15.5) uses bean-managed persistence to store and retrieve Employee information in an under-

pro-lying database The second implementation (Section 15.6) uses container-managed

persis-tence Both of these implementations use the same Employee remote interface and EmployeeHome interface, which we present in Section 15.4.

We use the Cloudscape database for storing Employee data To create the Employee database, run the SQL script employee.sql that is on the CD-ROM that

accompanies the book Please see Chapter 8, JDBC, for instructions on running SQL scripts

in Cloudscape To configure the J2EE reference implementation to use the Employee

database, append the text

|jdbc/Employee|jdbc:cloudscape:rmi:Employee;create=true

to the end of the jdbc.datasources property in the J2EE default.properties

configuration file

15.4 Employee EJB Home and Remote Interfaces

The Employee remote interface (Fig 15.1) provides methods for setting and getting ployee information Note that interface Employee extends interface EJBObject (line 11) This is a requirement for all EJB remote interfaces The Employee remote interface

Em-provides set and get methods for each Employee property, including the

socialSecu-rityNumber, firstName, lastName, title and salary There is no set method for property employeeID because employeeID is the primary key Each set and get method

throws a RemoteException This is required of all methods in the remote interface.

11 public interface Employee extends EJBObject {

Fig 15.1 Employee remote interface for setting and getting Employee

information (part 1 of 2)

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An EJB instance represents a particular row in the corresponding database table Thehome interface for an entity EJB represents the table as a whole The home interface pro-

vides finder methods for locating particular rows in the table and create methods for

inserting new records Interface EmployeeHome (Fig 15.2) provides finder method

findByPrimaryKey (lines 15–16) to locate instances of the Employee EJB based on

a primary key The primary key for the Employee EJB is the employeeID Method findByPrimaryKey throws a FinderException if the Employee with the given primaryKey cannot be found Method create (lines 19–20) creates new instances of the Employee EJB Method create throws a CreateException if there is a

problem with creating the EJB instance

12

13 // get Employee ID

15

16 // set social security number

19

20 // get social security number

23

24 // set first name

27

28 // get first name

30

31 // set last name

34

35 // get last name

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Method findByPrimaryKey is one type of finder method for entity EJBs Every

entity EJB must have a findByPrimaryKey method that takes the entity EJB’s

primary-key class as an argument Entity EJBs also can define additional finder methods A finder

method name must begin with findBy and should end with the name of property to be

used as the search criteria For example, a finder method for finding Employees based on the title property would be named findByTitle A finder method for finding

Employee s within a certain salary range would be named findBySalaryRange.

15.5 Employee EJB with Bean-Managed Persistence

This section describes the Employee EJB with bean-managed persistence and deploying the EJB This bean-managed implementation uses JDBC to store Employee data in an un-

derlying database

15.5.1 Employee EJB Implementation

Figure 15.3 shows the Employee EJB implementation using bean-managed persistence Class EmployeeEJB implements interface EntityBean (line 15) All entity EJB implementations must implement interface EntityBean Line 17 declares an Entity- Context reference for the EJB’s EntityContext The EntityContext provides the EJB with information about the container in which the EJB is deployed The Connec- tion object (line 18) is the EJB’s Connection to the Employee database Lines 20–

25 declare private member variables that cache data retrieved from the database and

up-dates from the client

14 // find Employee with given primary key

16 throws RemoteException, FinderException;

17

18 // create new Employee EJB

20 throws RemoteException, CreateException;

Fig 15.2 EmployeeHome interface for finding and creating Employee EJBs.

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1 // EmployeeEJB.java

2 // EmployeeEJB is an entity EJB that uses bean-managed

3 // persistence to persist Employee data in a database.

17 private EntityContext entityContext;

18 private Connection connection;

19

21 private String socialSecurityNumber;

23 private String lastName;

25 private Double salary;

33 // set social security number

34 public void setSocialSecurityNumber( String number )

36 socialSecurityNumber = number;

39 // get social security number

40 public String getSocialSecurityNumber()

45 // set first name

46 public void setFirstName( String name )

48 firstName = name;

Fig 15.3 EmployeeEJB implementation of Employee remote interface using

bean-managed persistence (part 1 of 8)

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51 // get first name

52 public String getFirstName()

54 return firstName;

57 // set last name

63 // get last name

93 // create new Employee

94 public Integer ejbCreate( Integer primaryKey )

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102 // create INSERT statement

103 String insert = "INSERT INTO Employee " +

113 // execute INSERT and close PreparedStatement

120 // throw EJBException if INSERT fails

122 throw new CreateException( sqlException.getMessage() );

123 }

124 } // end method ejbCreate

125

126 // do post-creation tasks when creating new Employee

127 public void ejbPostCreate( Integer primaryKey ) {}

128

129 // remove Employee information from database

130 public void ejbRemove() throws RemoveException

139 // create DELETE statement

140 String delete = "DELETE FROM Employee WHERE " +

150 // execute DELETE and close PreparedStatement

151 deleteStatement.executeUpdate();

152 deleteStatement.close();

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154

155 // throw new EJBException if DELETE fails

157 throw new RemoveException( sqlException.getMessage() );

158 }

159 } // end method ejbRemove

160

161 // store Employee information in database

162 public void ejbStore() throws EJBException

171 // create UPDATE statement

172 String update = "UPDATE Employee SET " +

189 // execute UPDATE and close PreparedStatement

190 updateStatement.executeUpdate();

191 updateStatement.close();

193

194 // throw EJBException if UPDATE fails

197 }

198 } // end method ejbStore

199

200 // load Employee information from database

201 public void ejbLoad() throws EJBException

202 {

203 // get Employee record from Employee database table

204 try {

205

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