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。

<TT>174:     public void requestUpdateService(Account account) throws</TT>
<TT>175:             InvalidAccountException {</TT>
<TT>176: </TT>
<TT>177:         // First check to see if the Account is with this Bank.</TT>
<TT>178:         if (!CORBAAlgorithms.contains(myAccounts, account)) {</TT>
<TT>179: </TT>
<TT>180:             // Invalid Account; throw an exception.</TT>
<TT>181:             System.out.println(&quot;BankImpl: Attempted to delete &quot; +</TT>
<TT>182:                     &quot;invalid Account.&quot;);</TT>
<TT>183:             throw new InvalidAccountException();</TT>
<TT>184:         }</TT>
<TT>185: </TT>
<TT>186:         // If we got this far, the Account must exist with this</TT>
<TT>187:         // Bank, so we can proceed.</TT>
<TT>188:         mySubscribedAccounts.addElement(account._duplicate());</TT>
<TT>189:     }</TT>
<TT>190: </TT>
<TT>191:     // Return the next available account number.</TT>
<TT>192:     protected String getNextAccountNumber() {</TT>
<TT>193: </TT>
<TT>194:         return &quot;Account&quot; + myNextAccountNumber++;</TT>
<TT>195:     }</TT>
<TT>196: </TT>
<TT>197:     // Return the current date in the form &quot;Mmm DD YYYY&quot;.</TT>
<TT>198:     protected String getCurrentDate() {</TT>
<TT>199: </TT>
<TT>200:         SimpleDateFormat format = new SimpleDateFormat(&quot;MMM dd &quot; +</TT>
<TT>201:                 &quot;yyyy&quot;);</TT>
<TT>202:         return format.format(new Date());</TT>
<TT>203:     }</TT>
</FONT></PRE>
<P><TT>204: }</TT>
<H4><FONT COLOR="#000077">Listing 13.9. UpdateAccountThread.java.</FONT></H4>
<PRE><FONT COLOR="#0066FF">
<TT> 1: // UpdateAccountThread.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: import idlGlobal.Customer;</TT>
<TT> 8: </TT>
<TT> 9: public class UpdateAccountThread extends Thread {</TT>
<TT>10: </TT>
<TT>11:     // The Accounts to be updated by this thread.</TT>
<TT>12:     Vector myAccounts;</TT>
<TT>13: </TT>
<TT>14:     public UpdateAccountThread(Vector accounts) {</TT>
<TT>15: </TT>
<TT>16:         myAccounts = accounts;</TT>
<TT>17:     }</TT>
<TT>18: </TT>
<TT>19:     protected UpdateAccountThread() {</TT>
<TT>20: </TT>
<TT>21:     }</TT>
<TT>22: </TT>
<TT>23:     public void run() {</TT>
<TT>24: </TT>
<TT>25:         // Do this forever (or until the thread is killed).</TT>
<TT>26:         while (true) {</TT>
<TT>27: </TT>
<TT>28:             // Sleep for one minute between updates.</TT>
<TT>29:             try {</TT>
<TT>30:                 sleep(60000);</TT>
<TT>31:             } catch (InterruptedException ex) {</TT>
<TT>32:             }</TT>
<TT>33: </TT>
<TT>34:             // Iterate through each Account...</TT>
<TT>35:             Enumeration e = myAccounts.elements();</TT>
<TT>36:             while (e.hasMoreElements()) {</TT>
<TT>37:                 Account account = (Account)e.nextElement();</TT>
<TT>38: </TT>
<TT>39:                 // Iterate through each Customer associated with</TT>
<TT>40:                 // the Account...</TT>
<TT>41:                 Customer[] customers = account.getCustomers();</TT>
<TT>42:                 for (int i = 0; i &lt; customers.length; i++) {</TT>
<TT>43: </TT>
<TT>44:                     try {</TT>
<TT>45:                         // Send an update message to each Customer.</TT>
<TT>46:                         customers[i].updateAccountBalance(account,</TT>
<TT>47:                                 account.balance());</TT>
<TT>48:                     } catch (Exception ex) {</TT>
<TT>49: </TT>
<TT>50:                         // Ignore any exceptions that occur.</TT>
<TT>51:                     }</TT>
<TT>52:                 }</TT>
<TT>53:             }</TT>
<TT>54:         }</TT>
<TT>55:     }
56: }</TT></FONT></PRE>
<H4><FONT COLOR="#000077">Listing 13.10. BankMain.java.</FONT></H4>
<PRE><FONT COLOR="#0066FF"><TT> 1: // BankMain.java</TT>
<TT> 2: </TT>
<TT> 3: import org.omg.CORBA.BOA;</TT>
<TT> 4: import org.omg.CORBA.ORB;</TT>
<TT> 5: </TT>
<TT> 6: import idlGlobal.BankServer;</TT>
<TT> 7: import idlGlobal.BankServerHelper;</TT>
<TT> 8: </TT>
<TT> 9: public class BankMain {</TT>
<TT>10: </TT>
<TT>11:     public static ORB myORB;</TT>
<TT>12:     public static BOA myBOA;</TT>
<TT>13: </TT>
<TT>14:     public static void main(String[] args) {</TT>
<TT>15: </TT>
<TT>16:         // Check the number of arguments; there should be exactly</TT>
<TT>17:         // one.</TT>
<TT>18:         if (args.length != 1) {</TT>
<TT>19:             System.out.println(&quot;Usage: Bank &lt;bankname&gt;&quot;);</TT>
<TT>20:             return;</TT>
<TT>21:         }</TT>
<TT>22: </TT>
<TT>23:         // Assign the Bank name to the first argument.</TT>
<TT>24:         String bankName = args[0];</TT>
<TT>25: </TT>
<TT>26:         BankServer bankServer;</TT>
<TT>27:         BankImpl bank;</TT>
<TT>28: </TT>
<TT>29:         try {</TT>
<TT>30: </TT>
<TT>31:             // Initialize the ORB and BOA.</TT>
<TT>32:             myORB = ORB.init(args, null);</TT>
<TT>33:             myBOA = myORB.BOA_init();</TT>
<TT>34: </TT>
<TT>35:             // Create an BankImpl object and register it with the</TT>
<TT>36:             // ORB.</TT>
<TT>37:             bank = new BankImpl(bankName);</TT>
<TT>38:             myBOA.obj_is_ready(bank);</TT>
<TT>39: </TT>
<TT>40:             // Bind to a BankServer.</TT>
<TT>41:             bankServer = BankServerHelper.bind(myORB);</TT>
<TT>42:             System.out.println(&quot;BankImpl: Successfully bound to &quot; +</TT>
<TT>43:                     &quot;BankServer.&quot;);</TT>
<TT>44:         } catch (Exception ex) {</TT>
<TT>45: </TT>
<TT>46:             // The bind attempt failed...</TT>
<TT>47:             System.out.println(&quot;BankImpl: Unable to bind to &quot; +</TT>
<TT>48:                     &quot;BankServer.&quot;);</TT>
<TT>49:             return;</TT>
<TT>50:         }</TT>
<TT>51: </TT>
<TT>52:         try {</TT>
<TT>53: </TT>
<TT>54:             // Register with the BankServer.</TT>
<TT>55:             bankServer.registerBank(bank);</TT>
<TT>56: </TT>
<TT>57:             // Wait for CORBA events.</TT>
<TT>58:             myBOA.impl_is_ready();</TT>
<TT>59:         } catch (Exception ex) {</TT>
<TT>60: </TT>
<TT>61:             // The registerBank() attempt failed...</TT>
<TT>62:             System.out.println(&quot;BankImpl: Unable to register &quot; +</TT>
<TT>63:                     &quot;Bank:&quot;);</TT>
<TT>64:             System.out.println(ex);</TT>
<TT>65:             return;</TT>
<TT>66:         }</TT>
<TT>67: </TT>
<TT>68:         // When this point is reached, the application is finished.</TT>
<TT>69:         return;</TT>
<TT>70:     }
71: }</TT> </FONT></PRE>
<P>Here are highlights from the various classes that implement the <TT>Bank</TT>
server application. First, note the implementation for <TT>getCustomers()</TT> in
<TT>AccountImpl.java</TT> (refer to lines 60-71 of Listing 13.4).</P>
<P>Notice the relative simplicity with which objects are copied from <TT>Vectors</TT>
into arrays. First, an array of the appropriate size is created (in line 62), and
the contents of the <TT>Vector</TT> are copied into it with a single method call:
<TT>copyInto()</TT> (line 63). Because these are outbound CORBA objects, they must
be <TT>_duplicate()</TT>d, which is the reason for the subsequent iteration across
the <TT>Vector</TT>, as in lines 65-68.</P>
<P>Next, note the constructor of <TT>BankImpl</TT> (lines 34-46 of Listing 13.8).</P>
<P>In the constructor, an <TT>UpdateAccountThread</TT> object is created (which you'll
get a closer look at in a moment) and started. For simple threads, this is all that
Java requires: Create a <TT>Thread</TT> object, and call <TT>start()</TT> on that
object. Now, look at the <TT>UpdateAccountThread</TT> itself, beginning in line 9
of Listing 13.9.</P>
<P>One way to implement threads in Java is to create a class that derives from <TT>java.lang.Thread</TT>
(or simply <TT>Thread</TT>), as <TT>UpdateAccountThread</TT> does. The next step
is to implement the <TT>run()</TT> method. The actual workings of the <TT>UpdateAccountThread.run()</TT>
method are self-explanatory.</P>
<P>Finally, notice in <TT>BankMain.java</TT> how an application binds to a CORBA
object (refer to Listing 13.10). Again, the ORB is initialized (lines 31-33).</P>
<P>Sometime after the ORB and BOA are initialized, <TT>BankMain</TT> uses the <TT>bind()</TT>
method of <TT>BankServerHelper</TT> to bind to a <TT>BankServer</TT> object, as in
line 41. (Recall again that <TT>bind()</TT> is nonstandard and is used here for simplicity.)
<H4><FONT COLOR="#000077">ATM</FONT></H4>
<P>The implementation of the <TT>ATM</TT> server, consisting of <TT>ATMImpl.java</TT>
and <TT>ATMMain.java</TT>, appears in Listings 13.11 and 13.12. This is clear-cut
and contains no surprises.
<H4><FONT COLOR="#000077">Listing 13.11. ATMImpl.java.</FONT></H4>
<PRE><FONT COLOR="#0066FF"><TT> 1: // ATMImpl.java</TT>
<TT> 2: </TT>
<TT> 3: import idlGlobal.Account;</TT>
<TT> 4: import idlGlobal.ATMCard;</TT>
<TT> 5: </TT>
<TT> 6: import idlGlobal.AuthorizationException;</TT>
<TT> 7: import idlGlobal.InsufficientFundsException;</TT>
<TT> 8: import idlGlobal.InvalidAmountException;</TT>
<TT> 9: </TT>
<TT>10: public class ATMImpl extends idlGlobal._ATMImplBase {</TT>
<TT>11: </TT>
<TT>12:     private String myName;</TT>
<TT>13: </TT>
<TT>14:     public ATMImpl(String name) {</TT>
<TT>15: </TT>
<TT>16:         myName = new String(name);</TT>
<TT>17:     }</TT>
<TT>18: </TT>
<TT>19:     private ATMImpl() {</TT>
<TT>20: </TT>
<TT>21:         myName = new String();</TT>
<TT>22:     }</TT>
<TT>23: </TT>
<TT>24:     public String name() {</TT>
<TT>25: </TT>
<TT>26:         return myName;</TT>
<TT>27:     }</TT>
<TT>28: </TT>
<TT>29:     public void name(String name) {</TT>
<TT>30: </TT>
<TT>31:         myName = new String(name);</TT>
<TT>32:     }</TT>
<TT>33: </TT>
<TT>34:     public float withdraw(ATMCard card, Account account, short pin,</TT>
<TT>35:             float amount) throws AuthorizationException,</TT>
<TT>36:             InvalidAmountException, InsufficientFundsException {</TT>
<TT>37: </TT>
<TT>38:         System.out.println(&quot;ATM: Authorizing Account for &quot; +</TT>
<TT>39:                 &quot;withdrawal.&quot;);</TT>
<TT>40:         if (pin != card.pin() || !card.isAuthorized(account)) {</TT>
<TT>41: </TT>
<TT>42:             // Incorrect PIN or card not authorized; throw an</TT>
<TT>43:             // exception.</TT>
<TT>44:             System.out.println(&quot;  Authorization failed.&quot;);</TT>
<TT>45:             throw new AuthorizationException();</TT>
<TT>46:         }</TT>
<TT>47: </TT>
<TT>48:         System.out.println(&quot;  Authorization succeeded; forwarding &quot;</TT>
<TT>49:                 + &quot;withdrawal request to Account.&quot;);</TT>
<TT>50:         return account.withdraw(amount);</TT>
<TT>51:     }</TT>
<TT>52: </TT>
<TT>53:     public float deposit(ATMCard card, Account account, short pin,</TT>
<TT>54:             float amount) throws AuthorizationException,</TT>
<TT>55:             InvalidAmountException {</TT>
<TT>56: </TT>
<TT>57:         System.out.println(&quot;ATM: Authorizing Account for &quot; +</TT>
<TT>58:                 &quot;deposit.&quot;);</TT>
<TT>59:         if (pin != card.pin() || !card.isAuthorized(account)) {</TT>
<TT>60: </TT>
<TT>61:             // Incorrect PIN or card not authorized; throw an</TT>
<TT>62:             // exception.</TT>
<TT>63:             System.out.println(&quot;  Authorization failed.&quot;);</TT>
<TT>64:             throw new AuthorizationException();</TT>
<TT>65:         }</TT>
<TT>66: </TT>
<TT>67:         System.out.println(&quot;  Authorization succeeded; forwarding &quot;</TT>
<TT>68:                 + &quot;deposit request to Account.&quot;);</TT>
<TT>69:         return account.deposit(amount);</TT>
<TT>70:     }</TT>
<TT>71: </TT>
<TT>72:     public float getBalance(ATMCard card, Account account, short</TT>
<TT>73:             pin) throws AuthorizationException {</TT>
<TT>74: </TT>
<TT>75:         System.out.println(&quot;ATM: Authorizing Account for &quot; +</TT>
<TT>76:                 &quot;balance.&quot;);</TT>
<TT>77:         if (pin != card.pin() || !card.isAuthorized(account)) {</TT>
<TT>78: </TT>
<TT>79:             // Incorrect PIN or card not authorized; throw an</TT>
<TT>80:             // exception.</TT>
<TT>81:             System.out.println(&quot;  Authorization failed.&quot;);</TT>
<TT>82:             throw new AuthorizationException();</TT>
<TT>83:         }</TT>
<TT>84: </TT>
<TT>85:         System.out.println(&quot;  Authorization succeeded; forwarding &quot;</TT>
<TT>86:                 + &quot;balance request to Account.&quot;);</TT>
<TT>87:         return account.balance();</TT>
<TT>88:     }
89: }</TT></FONT></PRE>
<H4><FONT COLOR="#000077">Listing 13.12. ATMMain.java.</FONT>