尝试从迭代器中删除SelectionKey时抛出UnsupportedOperationException

Question

下面的代码显示了一小块代码，它试图接受来自客户端的连接（使用java NIO的典型实现），但是当我尝试从Iterator中删除SelectionKey时，它会抛出异常。

此代码与Jenkov tutorial和另一个Acceptor (line 270) SocketServer from Apache Kafka非常相似。

  override def run(): Unit = {

    this.logger.info("Acceptor started.")

    super.run()

    this.serverSocketChannel.register(this.selector, SelectionKey.OP_ACCEPT)

    while (this.isRunning) {

      val readyKeys = this.selector.select(500)

      if (readyKeys > 0) {

        val selectedKeys = this.selector.keys()

        val selectionKeysIterator = selectedKeys.iterator()

        while (selectionKeysIterator.hasNext && this.isRunning) {

          val selectionKey = selectionKeysIterator.next()

          selectionKeysIterator.remove()

          if (!selectionKey.isAcceptable)
            throw new IllegalStateException("The SelectionKey is not on the valid state [Acceptable].")

          this.accept(selectionKey)
        }
      }
    }

    this.selector.close()
  }

Answer 1

选择键集由selector.selectedKey返回（你有select.keys，指定为不可修改）