Future+Callable異步查詢

Future+Callable異步查詢

• Future (java.util.concurrent)
  表示異步計算的結果。提供了檢查計算是否完成的方法，以等待計算的完成，並獲取計算的結果。

• Callable (java.util.concurrent)
  Callable類似於Runnable，兩者都是爲那些其實例可能被另一個線程執行的類設計的。兩者的區別是：Runnable不會反會返回結果，無法拋出經過檢查的異常；Callable可以有返回值，返回值可以被Future拿到，能夠拋出經過檢查的異常。

  /**
   * 異步回調：
   *  Future
   *  Callable<T>
   */
  public class AsynchronousCallback {
  
      public static void main(String[] args) {
          String[] addresss = {"北京市","上海市"};
  
          List<Future<List<UserEntity>>> futureList = new ArrayList<>();
          for (String address: addresss) {
              futureList.add(ThreadPoolExecutorFactory.executor.submit(new TaskCallable(address)));
          }
  
          List<UserEntity> users = new ArrayList<>();
          for (Future<List<UserEntity>> user: futureList) {
              try {
              	//獲取future中的返回值
                  List<UserEntity> list = user.get();
                  if (!CollectionUtils.isEmpty(list)){
                      users.addAll(list);
                  }
              } catch (InterruptedException e) {
                  e.printStackTrace();
              } catch (ExecutionException e) {
                  e.printStackTrace();
              }
          }
          System.out.println(users);
      }
  }
  

• 實現Callable， call方法中調用查詢數據接口

  class TaskCallable implements Callable<List<UserEntity>> {
  
      private String address;
  
      public TaskCallable(String address) {
          this.address = address;
      }
  
      @Override
      public List<UserEntity> call() throws InterruptedException {
          System.out.println(address);
          UserServiceImpl userService = new UserServiceImpl();
          List<UserEntity> userServiceById = userService.findById(address);
          return userServiceById;
      }
  }
  

• 返回結果

  北京市
  上海市
  [UserEntity{id=1, username='小紅', sex='女', age=18, address='北京市'}, UserEntity{id=2, username='小剛', sex='男', age=18, address='北京市'}, UserEntity{id=3, username='小青', sex='女', age=18, address='北京市'}, UserEntity{id=4, username='小率', sex='男', age=18, address='北京市'}, UserEntity{id=4, username='小率', sex='男', age=18, address='北京市'}, UserEntity{id=6, username='小1', sex='女', age=18, address='上海市'}, UserEntity{id=7, username='小2', sex='男', age=18, address='上海市'}, UserEntity{id=8, username='小3', sex='女', age=18, address='上海市'}, UserEntity{id=9, username='小4', sex='男', age=18, address='上海市'}, UserEntity{id=10, username='小5', sex='男', age=18, address='上海市'}]