Java基础之线程——使用执行器（UsingExecutors)

控制台程序。

在这个版本的银行示例中，把借款和贷款事务创建为在不同线程中执行的任务，它们把事务提交给职员。创建事务的任务是Callable<>任务，因为它们需要返回已为每个账户创建的借款或贷款事务的总额。

 // Defines a customer account
 public class Account {
   // Constructor
   public Account(int accountNumber, int balance) {
     this.accountNumber = accountNumber;                                // Set the account number
     this.balance = balance;                                            // Set the initial balance
   }

   // Return the current balance
   public int getBalance() {
     return balance;
   }

   // Set the current balance
   public void setBalance(int balance) {
     this.balance = balance;
   }

   public int getAccountNumber() {
     return accountNumber;
   }

   @Override
   public String toString() {
     return "A/C No. " + accountNumber + " : $" + balance;
   }

   private int balance;                                                 // The current account balance
   private int accountNumber;                                           // Identifies this account
 }

 // Bank account transaction types
 public enum TransactionType {DEBIT, CREDIT }

 public class Transaction {
   // Constructor
   public Transaction(Account account, TransactionType type, int amount) {
     this.account = account;
     this.type = type;
     this.amount = amount;
   }

   public Account getAccount() {
     return account;
   }

   public TransactionType getTransactionType() {
     return type;
   }

   public int getAmount() {
     return amount;
   }
   @Override
   public String toString() {
     return type + " A//C: " + ": $" + amount;
   }

   private Account account;
   private int amount;
   private TransactionType type;
 }

 // Define the bank

 public class Bank {
   // Perform a transaction
   public void doTransaction(Transaction transaction) {
     synchronized(transaction.getAccount()) {
       int balance = 0;
       switch(transaction.getTransactionType()) {
         case CREDIT:
           System.out.println("Start credit of " +
                   transaction.getAccount() + " amount: " +
                   transaction.getAmount());

             // Get current balance
             balance = transaction.getAccount().getBalance();

             // Credits require a lot of checks...
             try {
               Thread.sleep(100);

             } catch(InterruptedException e) {
               System.out.println(e);
             }
             balance += transaction.getAmount();                        // Increment the balance
             transaction.getAccount().setBalance(balance);              // Restore account balance
             System.out.println("  End credit of " +
                     transaction.getAccount() + " amount: " +
                     transaction.getAmount());
             break;
         case DEBIT:
             System.out.println("Start debit of " +
                     transaction.getAccount() + " amount: " +
                     transaction.getAmount());

             // Get current balance
             balance = transaction.getAccount().getBalance();

             // Debits require even more checks...
             try {
               Thread.sleep(150);

             } catch(InterruptedException e) {
               System.out.println(e);
             }
             balance -= transaction.getAmount();                        // Decrement the balance...
             transaction.getAccount().setBalance(balance);              // Restore account balance

             System.out.println("  End debit of " +
                     transaction.getAccount() + " amount: " +
                     transaction.getAmount());
             break;

         default:                                                       // We should never get here
           System.out.println("Invalid transaction");
           System.exit(1);
       }
     }
   }
 }

 import java.util.List;
 import java.util.Collections;
 import java.util.LinkedList;

 public class Clerk implements Runnable {
   // Constructor
   public Clerk(int ID, Bank theBank) {
     this.ID = ID;
     this.theBank = theBank;                                            // Who the clerk works for
   }

   // Receive a transaction
   synchronized public boolean doTransaction(Transaction transaction) {
     if(inTray.size() >= maxTransactions)
       return false;
     inTray.add(transaction);                                           // Add transaction to the list
     return true;
   }

   // The working clerk...
    public void run() {
     while(true) {
       while(inTray.size() == 0) {                                      // No transaction waiting?
         try {
           Thread.sleep(200);                                           // then take a break
           if(inTray.size() != 0) {
             break;
           } else {
             return;
           }
         } catch(InterruptedException e) {
           System.out.println("Clerk "+ ID + "\n" + e);
           return;
         }
       }
       theBank.doTransaction(inTray.remove(0));
       if(Thread.interrupted()) {
         System.out.println("Interrupt flag for Clerk " + ID + " set. Terminating.");
         return;
       }
     }
   }

   int ID;
   private Bank theBank;
   private List<Transaction> inTray =                                   // The in-tray holding transactions
                    Collections.synchronizedList(new LinkedList<Transaction>());
   private int maxTransactions = 8;                                     // Maximum transactions in the in-tray
 }

 // Generates transactions for clerks
 import java.util.Random;
 import java.util.Vector;
 import java.util.concurrent.Callable;

 public class TransactionSource implements Callable<int[]> {

   public TransactionSource(TransactionType type, int maxTrans, Vector<Account> accounts, Vector<Clerk> clerks) {
     this.type = type;
     this.maxTrans = maxTrans;
     this.accounts = accounts;
     this.clerks = clerks;
     totals = new int[accounts.size()];
   }

   // The source of transactions
   public int[] call() {
     // Create transactions randomly distributed between the accounts
     Random rand = new Random();
     Transaction transaction = null;                                    // Stores a transaction
     int amount = 0;                                                    // Stores an amount of money
     int select = 0;                                                    // Selects an account
     boolean done = false;
     for(int i = 1 ; i <= maxTrans ; ++i) {
       // Generate a random account index for  operation
       select = rand.nextInt(accounts.size());
       amount = 50 + rand.nextInt(26);                                  // Generate amount of $50 to $75
       transaction = new Transaction(accounts.get(select),              // Account
                                     type,                              // Transaction type
                                     amount);                           //  of amount
       totals[select] += amount;                                        // Keep total tally for account
       done = false;
       while(true) {
         // Find a clerk to do the transaction
         for(Clerk clerk : clerks) {
           if(done = clerk.doTransaction(transaction))
             break;
         }
         if(done) {
           break;
         }

         // No clerk was free so wait a while
         try {
           Thread.sleep(10);
         } catch(InterruptedException e) {
           System.out.println(" TransactionSource\n" + e);
           return totals;
         }
       }
       if(Thread.interrupted()) {
         System.out.println("Interrupt flag for "+ type + " transaction source set. Terminating.");
         return totals;
       }
     }
     return totals;
   }

   private TransactionType type;
   private int maxTrans;
   private Vector<Account> accounts;
   private Vector<Clerk> clerks;
   private int[] totals;
 }

 import java.util.Vector;
 import java.util.concurrent.Executors;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Future;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.TimeUnit;

 public class UsingExecutors {

     public static void main(String[] args) {
       int[] initialBalance = {500, 800};                               // The initial account balances
       int[] totalCredits = new int[initialBalance.length];             // Two different cr totals
       int[] totalDebits = new int[initialBalance.length];              // Two different db totals
       int transactionCount = 20;                                       // Number of debits and of credits
       int clerkCount = 2;

       // Create the account, the bank, and the clerks...
       Bank theBank = new Bank();                                       // Create a bank
       Vector<Clerk> clerks = new Vector<Clerk>();                      // Stores the clerk
       Vector<Account> accounts = new Vector<Account>();                // Stores the accounts

       for(int i = 0 ; i < clerkCount ; ++i) {
         clerks.add(new Clerk(i+1, theBank));                           // Create the clerks
       }

       for(int i = 0 ; i < initialBalance.length; ++i) {
         accounts.add(new Account(i+1, initialBalance[i]));             // Create accounts
         totalCredits[i] = totalDebits[i] = 0;
       }

       ExecutorService threadPool = Executors.newCachedThreadPool();

       // Create and start the transaction source threads
       Future<int[]> credits = threadPool.submit(new TransactionSource(TransactionType.CREDIT, transactionCount, accounts, clerks));
       Future<int[]> debits = threadPool.submit(new TransactionSource(TransactionType.DEBIT, transactionCount, accounts, clerks));

       // Create and start the clerk threads
       for(Clerk clerk : clerks) {
         threadPool.submit(clerk);
       }
       try {
         totalCredits = credits.get();
         totalDebits = debits.get();
       } catch(ExecutionException e) {
         System.out.println(e.getCause());
       } catch(InterruptedException e) {
         System.out.println(e);
       }

     // Orderly shutdown when all threads have ended
     threadPool.shutdown();
     try {
       threadPool.awaitTermination(10L, TimeUnit.SECONDS);
     } catch(InterruptedException e) {
       System.out.println(e);
     }

     if(threadPool.isTerminated()) {
       System.out.println("\nAll clerks have completed their tasks.\n");
     } else {
       System.out.println("\nClerks still running - shutting down anyway.\n");
       threadPool.shutdownNow();
     }

     // Now output the results
     for(int i = 0 ; i < accounts.size() ; ++i) {
       System.out.println("Account Number:"+accounts.get(i).getAccountNumber()+"\n"+
          "Original balance    : $" + initialBalance[i] + "\n" +
          "Total credits       : $" + totalCredits[i] + "\n" +
          "Total debits        : $" + totalDebits[i] + "\n" +
          "Final balance       : $" + accounts.get(i).getBalance() + "\n" +
          "Should be           : $" + (initialBalance[i]
                                    + totalCredits[i]
                                    - totalDebits[i]) + "\n");
     }
   }
 }