package futuretask; 
import java.util.ArrayList; 
import java.util.List; 
import java.util.concurrent.Callable; 
import java.util.concurrent.ExecutionException; 
import java.util.concurrent.ExecutorService; 
import java.util.concurrent.Executors; 
import java.util.concurrent.FutureTask; 
public class FutureTaskForMultiCompute { 
  public static void main(String[] args) { 
    FutureTaskForMultiCompute inst=new FutureTaskForMultiCompute(); 
    // 創(chuàng)建任務(wù)集合 
    List<FutureTask<Integer>> taskList = new ArrayList<FutureTask<Integer>>(); 
    // 創(chuàng)建線程池 
    ExecutorService exec = Executors.newFixedThreadPool(5); 
    for (int i = 0; i < 10; i++) { 
      // 傳入Callable對(duì)象創(chuàng)建FutureTask對(duì)象 
      FutureTask<Integer> ft = new FutureTask<Integer>(inst.new ComputeTask(i, ""+i)); 
      taskList.add(ft); 
      // 提交給線程池執(zhí)行任務(wù)，也可以通過exec.invokeAll(taskList)一次性提交所有任務(wù); 
      exec.submit(ft); 
    } 
    System.out.println("所有計(jì)算任務(wù)提交完畢, 主線程接著干其他事情！"); 
    // 開始統(tǒng)計(jì)各計(jì)算線程計(jì)算結(jié)果 
    Integer totalResult = 0; 
    for (FutureTask<Integer> ft : taskList) { 
      try { 
        //FutureTask的get方法會(huì)自動(dòng)阻塞,直到獲取計(jì)算結(jié)果為止 
        totalResult = totalResult + ft.get(); 
      } catch (InterruptedException e) { 
        e.printStackTrace(); 
      } catch (ExecutionException e) { 
        e.printStackTrace(); 
      } 
    } 
    // 關(guān)閉線程池 
    exec.shutdown(); 
    System.out.println("多任務(wù)計(jì)算后的總結(jié)果是:" + totalResult); 
  } 
  private class ComputeTask implements Callable<Integer> { 
    private Integer result = 0; 
    private String taskName = ""; 
    public ComputeTask(Integer iniResult, String taskName){ 
      result = iniResult; 
      this.taskName = taskName; 
      System.out.println("生成子線程計(jì)算任務(wù): "+taskName); 
    } 
    public String getTaskName(){ 
      return this.taskName; 
    } 
    @Override 
    public Integer call() throws Exception { 
      // TODO Auto-generated method stub 
      for (int i = 0; i < 100; i++) { 
        result =+ i; 
      } 
      // 休眠5秒鐘，觀察主線程行為，預(yù)期的結(jié)果是主線程會(huì)繼續(xù)執(zhí)行，到要取得FutureTask的結(jié)果是等待直至完成。 
      Thread.sleep(5000); 
      System.out.println("子線程計(jì)算任務(wù): "+taskName+" 執(zhí)行完成!"); 
      return result; 
    } 
  } 
} 

private Map<String, Connection> connectionPool = new HashMap<String, Connection>(); 
private ReentrantLock lock = new ReentrantLock(); 
public Connection getConnection(String key){ 
  try{ 
    lock.lock(); 
    if(connectionPool.containsKey(key)){ 
      return connectionPool.get(key); 
    } 
    else{ 
      //創(chuàng)建 Connection 
      Connection conn = createConnection(); 
      connectionPool.put(key, conn); 
      return conn; 
    } 
  } 
  finally{ 
    lock.unlock(); 
  } 
} 
//創(chuàng)建Connection 
private Connection createConnection(){ 
  return null; 
} 

private ConcurrentHashMap<String,FutureTask<Connection>>connectionPool = new ConcurrentHashMap<String, FutureTask<Connection>>(); 
public Connection getConnection(String key) throws Exception{ 
  FutureTask<Connection>connectionTask=connectionPool.get(key); 
  if(connectionTask!=null){ 
    return connectionTask.get(); 
  } 
  else{ 
    Callable<Connection> callable = new Callable<Connection>(){ 
      @Override 
      public Connection call() throws Exception { 
        // TODO Auto-generated method stub 
        return createConnection(); 
      } 
    }; 
    FutureTask<Connection>newTask = new FutureTask<Connection>(callable); 
    connectionTask = connectionPool.putIfAbsent(key, newTask); 
    if(connectionTask==null){ 
      connectionTask = newTask; 
      connectionTask.run(); 
    } 
    return connectionTask.get(); 
  } 
} 
//創(chuàng)建Connection 
private Connection createConnection(){ 
  return null; 
}