futuretask用法及使用场景介绍

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(); 
    // 创建任务集合 
    List<FutureTask<Integer>> taskList = new ArrayList<FutureTask<Integer>>(); 
    // 创建线程池 
    ExecutorService exec = Executors.newFixedThreadPool(5); 
    for (int i = 0; i < 10; i++) { 
      // 传入Callable对象创建FutureTask对象 
      FutureTask<Integer> ft = new FutureTask<Integer>(inst.new ComputeTask(i, ""+i)); 
      taskList.add(ft); 
      // 提交给线程池执行任务，也可以通过exec.invokeAll(taskList)一次性提交所有任务; 
      exec.submit(ft); 
    } 
    System.out.println("所有计算任务提交完毕, 主线程接着干其他事情！"); 
    // 开始统计各计算线程计算结果 
    Integer totalResult = 0; 
    for (FutureTask<Integer> ft : taskList) { 
      try { 
        //FutureTask的get方法会自动阻塞,直到获取计算结果为止 
        totalResult = totalResult + ft.get(); 
      } catch (InterruptedException e) { 
        e.printStackTrace(); 
      } catch (ExecutionException e) { 
        e.printStackTrace(); 
      } 
    } 
    // 关闭线程池 
    exec.shutdown(); 
    System.out.println("多任务计算后的总结果是:" + 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("生成子线程计算任务: "+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秒钟，观察主线程行为，预期的结果是主线程会继续执行，到要取得FutureTask的结果是等待直至完成。 
      Thread.sleep(5000); 
      System.out.println("子线程计算任务: "+taskName+" 执行完成!"); 
      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{ 
      //创建 Connection 
      Connection conn = createConnection(); 
      connectionPool.put(key, conn); 
      return conn; 
    } 
  } 
  finally{ 
    lock.unlock(); 
  } 
} 
//创建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(); 
  } 
} 
//创建Connection 
private Connection createConnection(){ 
  return null; 
}