ch13.htm

corba比较入门级的介绍详细间接了corba访问发布各种细节。

can invoke the application at any given time). This method always takes <TT>String[]
args</TT> as a parameter (or the semantically equivalent <TT>String args[]</TT>).
The <TT>main()</TT> method of <TT>BankServerMain</TT> begins in line 11.</P>
<P>Before any CORBA objects are created, the ORB and BOA must be initialized, as
shown in lines 13-17.</P>
<P>Then the <TT>BankServerImpl</TT> object is created and registered with the BOA,
through the <TT>obj_is_ready()</TT> method, as seen in lines 19-23.</P>
<P>The <TT>impl_is_ready()</TT> method, called in line 27, enters the CORBA event
loop, passing incoming CORBA events to the appropriate objects.</P>
<P>Finally, in lines 28-35, a <TT>catch</TT> handler is added in case exceptions
are thrown by any of the methods called. The <TT>try...catch</TT> mechanism works
the same in Java as in C++.</P>
<P><TT>CORBAAlgorithms.java</TT>, appearing in Listing 13.3, contains a couple of
useful methods.</P>
<P>Note the use of the <TT>package</TT> statement in line 3. This indicates that
the <TT>CORBAAlgorithms</TT> class belongs to the <TT>util</TT> package.</P>
<P>Note also that <TT>contains()</TT>, which begins in line 10, is declared as a
<TT>static</TT> method. Such methods behave the same as in C++--that is, they exist
independently of any object instance and are invoked as freestanding functions rather
than as methods on objects.</P>
<P>As seen in lines 16-29, this method iterates through the provided <TT>Vector</TT>,
searching for an object for which <TT>_is_equivalent()</TT> (a standard CORBA method)
returns <TT>true</TT>. The next method, <TT>removeElement()</TT>, behaves similarly.


<BLOCKQUOTE>
	<P>
<HR>
<B>Warning: </B>Remember that the <TT>_is_equivalent()</TT> method returns <TT>true</TT>
	if it is known that two object references refer to the same object. It is possible
	for <TT>_is_equivalent()</TT> to return <TT>false</TT> even if two references are
	in fact equivalent; the only guarantee is that the method will never return <TT>true</TT>
	if the references are not equivalent. Use this method with caution. 
<HR>


</BLOCKQUOTE>

<H4><FONT COLOR="#000077">Bank</FONT></H4>
<P>Listings 13.4-10 contain the definitions of the Java classes that implement the
<TT>Bank</TT> functionality. You'll see that the functionality provided by these
classes mirrors their counterparts from previous chapters.
<H4><FONT COLOR="#000077">Listing 13.4. AccountImpl.java.</FONT></H4>
<PRE><FONT COLOR="#0066FF"><TT>  1: // AccountImpl.java</TT>
<TT>  2: </TT>
<TT>  3: import java.util.Enumeration;</TT>
<TT>  4: import java.util.Vector;</TT>
<TT>  5: </TT>
<TT>  6: import idlGlobal.Customer;</TT>
<TT>  7: </TT>
<TT>  8: import idlGlobal.InsufficientFundsException;</TT>
<TT>  9: import idlGlobal.InvalidAmountException;</TT>
<TT> 10: </TT>
<TT> 11: public class AccountImpl extends idlGlobal._AccountImplBase {</TT>
<TT> 12: </TT>
<TT> 13:     // This Account's account number.</TT>
<TT> 14:     private String myAccountNumber;</TT>
<TT> 15: </TT>
<TT> 16:     // This Account's creation date.</TT>
<TT> 17:     private String myCreationDate;</TT>
<TT> 18: </TT>
<TT> 19:     // This Account's balance.</TT>
<TT> 20:     private float myBalance;</TT>
<TT> 21: </TT>
<TT> 22:     // This Account's list of owners (which are Customers).</TT>
<TT> 23:     private Vector myOwners;</TT>
<TT> 24: </TT>
<TT> 25:     public AccountImpl(String accountNumber, String creationDate,</TT>
<TT> 26:             float initialBalance, Customer customer) {</TT>
<TT> 27: </TT>
<TT> 28:         super(accountNumber);</TT>
<TT> 29: </TT>
<TT> 30:         myAccountNumber = new String(accountNumber);</TT>
<TT> 31:         myCreationDate = new String(creationDate);</TT>
<TT> 32:         myBalance = initialBalance;</TT>
<TT> 33:         myOwners = new Vector();</TT>
<TT> 34:         myOwners.addElement(customer._duplicate());</TT>
<TT> 35:     }</TT>
<TT> 36: </TT>
<TT> 37:     protected AccountImpl() {</TT>
<TT> 38: </TT>
<TT> 39:         myAccountNumber = new String();</TT>
<TT> 40:         myCreationDate = new String();</TT>
<TT> 41:         myBalance = 0.0f;</TT>
<TT> 42:         myOwners = new Vector();</TT>
<TT> 43:     }</TT>
<TT> 44: </TT>
<TT> 45:     public String accountNumber() {</TT>
<TT> 46: </TT>
<TT> 47:         return myAccountNumber;</TT>
<TT> 48:     }</TT>
<TT> 49: </TT>
<TT> 50:     public String creationDate() {</TT>
<TT> 51: </TT>
<TT> 52:         return myCreationDate;</TT>
<TT> 53:     }</TT>
<TT> 54: </TT>
<TT> 55:     public float balance() {</TT>
<TT> 56: </TT>
<TT> 57:         return myBalance;</TT>
<TT> 58:     }</TT>
<TT> 59: </TT>
<TT> 60:     public Customer[] getCustomers() {</TT>
<TT> 61: </TT>
<TT> 62:         Customer[] list = new Customer[myOwners.size()];</TT>
<TT> 63:         myOwners.copyInto(list);</TT>
<TT> 64: </TT>
<TT> 65:         Enumeration e = myOwners.elements();</TT>
<TT> 66:         while (e.hasMoreElements()) {</TT>
<TT> 67:             ((Customer)e.nextElement())._duplicate();</TT>
<TT> 68:         }</TT>
<TT> 69: </TT>
<TT> 70:         return list;</TT>
<TT> 71:     }</TT>
<TT> 72: </TT>
<TT> 73:     public float withdraw(float amount) throws</TT>
<TT> 74:             InvalidAmountException, InsufficientFundsException {</TT>
<TT> 75: </TT>
<TT> 76:         // Disallow the withdrawal of negative amounts and throw an</TT>
<TT> 77:         // exception if this is attempted.</TT>
<TT> 78:         if (amount &lt; 0.0) {</TT>
<TT> 79:             System.out.println(&quot;AccountImpl: Attempted to &quot; +</TT>
<TT> 80:                     &quot;withdraw invalid amount.&quot;);</TT>
<TT> 81:             throw new InvalidAmountException();</TT>
<TT> 82:         }</TT>
<TT> 83: </TT>
<TT> 84:         // Disallow withdrawal of an amount greater than the</TT>
<TT> 85:         // current balance and throw an exception if this is</TT>
<TT> 86:         // attempted.</TT>
<TT> 87:         if (amount &gt; myBalance) {</TT>
<TT> 88:             System.out.println(&quot;AccountImpl: Insufficient funds to&quot;</TT>
<TT> 89:                     + &quot; withdraw specified amount.&quot;);</TT>
<TT> 90:             throw new InsufficientFundsException();</TT>
<TT> 91:         }</TT>
<TT> 92: </TT>
<TT> 93:         myBalance -= amount;</TT>
<TT> 94: </TT>
<TT> 95:         return myBalance;</TT>
<TT> 96:     }</TT>
<TT> 97: </TT>
<TT> 98:     public float deposit(float amount) throws</TT>
<TT> 99:             InvalidAmountException {</TT>
<TT>100: </TT>
<TT>101:         // Disallow the deposit of negative amounts and throw an</TT>
<TT>102:         // exception if this is attempted.</TT>
<TT>103:         if (amount &lt; 0.0) {</TT>
<TT>104:             System.out.println(&quot;AccountImpl: Attempted to deposit &quot;</TT>
<TT>105:                     + &quot;invalid amount.&quot;);</TT>
<TT>106:             throw new InvalidAmountException();</TT>
<TT>107:         }</TT>
<TT>108: </TT>
<TT>109:         myBalance += amount;</TT>
<TT>110: </TT>
<TT>111:         return myBalance;</TT>
<TT>112:     }
113: }</TT></FONT></PRE>
<H4><FONT COLOR="#000077">Listing 13.5. ATMCardImpl.java.</FONT></H4>
<PRE><FONT COLOR="#0066FF"><TT> 1: // ATMCardImpl.java</TT>
<TT> 2: </TT>
<TT> 3: import java.util.Enumeration;</TT>
<TT> 4: import java.util.Vector;</TT>
<TT> 5: </TT>
<TT> 6: import idlGlobal.Account;</TT>
<TT> 7: </TT>
<TT> 8: import idlGlobal.InvalidAccountException;</TT>
<TT> 9: </TT>
<TT>10: import util.CORBAAlgorithms;</TT>
<TT>11: </TT>
<TT>12: public class ATMCardImpl extends idlGlobal._ATMCardImplBase {</TT>
<TT>13: </TT>
<TT>14:     // This ATMCard's Personal Identification Number (PIN).</TT>
<TT>15:     private short myPIN;</TT>
<TT>16: </TT>
<TT>17:     // The Accounts which are authorized for use with this ATMCard.</TT>
<TT>18:     private Vector myAccounts;</TT>
<TT>19: </TT>
<TT>20:     public ATMCardImpl(short pin, Account initialAccount) {</TT>
<TT>21: </TT>
<TT>22:         myPIN = pin;</TT>
<TT>23:         myAccounts = new Vector();</TT>
<TT>24:         myAccounts.addElement(initialAccount._duplicate());</TT>
<TT>25:     }</TT>
<TT>26: </TT>
<TT>27:     private ATMCardImpl() {</TT>
<TT>28: </TT>
<TT>29:         myPIN = 0;</TT>
<TT>30:         myAccounts = new Vector();</TT>
<TT>31:     }</TT>
<TT>32: </TT>
<TT>33:     public void pin(short pin) {</TT>
<TT>34: </TT>
<TT>35:         myPIN = pin;</TT>
<TT>36:     }</TT>
<TT>37: </TT>
<TT>38:     public short pin() {</TT>
<TT>39: </TT>
<TT>40:         return myPIN;</TT>
<TT>41:     }</TT>
<TT>42: </TT>
<TT>43:     public Account[] getAccounts() {</TT>
<TT>44: </TT>
<TT>45:         Account[] list = new Account[myAccounts.size()];</TT>
<TT>46:         myAccounts.copyInto(list);</TT>
<TT>47: </TT>
<TT>48:         Enumeration e = myAccounts.elements();</TT>
<TT>49:         while (e.hasMoreElements()) {</TT>
<TT>50:             ((Account)e.nextElement())._duplicate();</TT>
<TT>51:         }</TT>
<TT>52: </TT>
<TT>53:         return list;</TT>
<TT>54:     }</TT>
<TT>55: </TT>
<TT>56:     public void addAccount(Account account) throws</TT>
<TT>57:             InvalidAccountException {</TT>
<TT>58: </TT>
<TT>59:         if (isAuthorized(account)) {</TT>
<TT>60: </TT>
<TT>61:             // Account has already been added, so throw an</TT>
<TT>62:             // exception.</TT>
<TT>63:             throw new InvalidAccountException();</TT>
<TT>64:         }</TT>
<TT>65: </TT>
<TT>66:         // Add the created Account at the end of the list.</TT>
<TT>67:         myAccounts.addElement(account._duplicate());</TT>
<TT>68:     }</TT>
<TT>69: </TT>
<TT>70:     public void removeAccount(Account account) throws</TT>
<TT>71:             InvalidAccountException {</TT>
<TT>72: </TT>
<TT>73:         if (!isAuthorized(account)) {</TT>
<TT>74: </TT>
<TT>75:             // Invalid Account; throw an exception.</TT>
<TT>76:             throw new InvalidAccountException();</TT>
<TT>77:         }</TT>
<TT>78: </TT>
<TT>79:         // Delete the given Account.</TT>
<TT>80:         CORBAAlgorithms.removeElement(myAccounts, account);</TT>
<TT>81:         account._release();</TT>
<TT>82:     }</TT>
<TT>83: </TT>
<TT>84:     public boolean isAuthorized(Account account) {</TT>
<TT>85: </TT>
<TT>86:         return CORBAAlgorithms.contains(myAccounts, account);</TT>
<TT>87:     }
88: }</TT></FONT></PRE>
<H4><FONT COLOR="#000077">Listing 13.6. CheckingAccountImpl.java.</FONT></H4>
<PRE><FONT COLOR="#0066FF"><TT> 1: // CheckingAccountImpl.java</TT>
<TT> 2: </TT>
<TT> 3: import idlGlobal.Customer;</TT>
<TT> 4: </TT>
<TT> 5: import idlGlobal.InsufficientFundsException;</TT>
<TT> 6: import idlGlobal.InvalidAmountException;</TT>
<TT> 7: </TT>
<TT> 8: public class CheckingAccountImpl extends idlGlobal.</TT>
<TT> 9:         _CheckingAccountImplBase {</TT>
<TT>10: </TT>
<TT>11:     // The AccountImpl to which most of this CheckingAccountImpl's</TT>
<TT>12:     // functionality is delegated.</TT>
<TT>13:     private AccountImpl myAccount;</TT>
<TT>14: </TT>
<TT>15:     public CheckingAccountImpl(String accountNumber, String</TT>
<TT>16:             creationDate, float initialBalance, Customer customer)</TT>
<TT>17:             {</TT>
<TT>18: </TT>
<TT>19:         myAccount = new AccountImpl(accountNumber, creationDate,</TT>
<TT>20:                 initialBalance, customer);</TT>
<TT>21:     }</TT>
<TT>22: </TT>
<TT>23:     protected CheckingAccountImpl() {</TT>
<TT>24: </TT>
<TT>25:     }</TT>
<TT>26: </TT>
<TT>27:     public String accountNumber() {</TT>
<TT>28: </TT>
<TT>29:         return myAccount.accountNumber();</TT>
<TT>30:     }</TT>
<TT>31: </TT>
<TT>32:     public String creationDate() {</TT>
<TT>33: </TT>
<TT>34:         return myAccount.creationDate();</TT>
<TT>35:     }</TT>
<TT>36: </TT>