Common Router Parameters

本节描述了所有路由器参数通用的参数（即本章前面显示的两个表格中全部选中框的参数）。

Inside and Outside a Chain

以下参数对链路内外的所有路由器有效。

apply-sequence

This attribute specifies whether sequence number and size headers should be added to each message. This optional attribute defaults to false.

default-output-channel

If set, this attribute provides a reference to the channel where messages should be sent if channel resolution fails to return any channels. If no default output channel is provided, the router throws an exception. If you would like to silently drop those messages instead, set the default output channel attribute value to nullChannel.

从 6.0 版本开始，设置默认输出通道也会将 channelKeyFallback 选项重置为 false。因此，不会尝试从其名称解析通道，但会退回到此默认输出通道 - 类似于 Java switch 语句。如果 channelKeyFallback 显式设置为 true，进一步的逻辑将取决于 resolutionRequired 选项：仅当 resolutionRequired 为 false 时，该消息才能从键到未解析通道到达 defaultOutputChannel。因此，AbstractMappingMessageRouter 初始化阶段会拒绝提供 defaultOutputChannel 并且将 channelKeyFallback 和 resolutionRequired 都设置为 true 的配置。

resolution-required

This attribute specifies whether channel names must always be successfully resolved to channel instances that exist. If set to true, a MessagingException is raised when the channel cannot be resolved. Setting this attribute to false causes any unresolvable channels to be ignored. This optional attribute defaults to true.

仅当指定了 resolution-required 为 false 且未解析通道时，才会向 default-output-channel 发送消息。

ignore-send-failures

If set to true, failures to send to a message channel is ignored. If set to false, a MessageDeliveryException is thrown instead, and, if the router resolves more than one channel, any subsequent channels do not receive the message.

此属性的确切行为取决于发送消息到的 Channel 的类型。例如，当使用直接通道（单线程）时，组件抛出的异常可能会导致发送失败。但是，当将消息发送到简单队列通道（异步）时，抛出异常的可能性比较小。

虽然大多数路由器会路由到一个通道，但它们可以返回多个通道名称。例如，recipient-list-router 执行的操作就是这样的。如果您在一个仅路由到单个通道的路由器上将此属性设置为 true，将忽略任何造成的异常，这通常毫无意义。在这种情况中，最好在流程入口处的错误流程中捕获异常。因此，当路由器实施返回多个通道名称时，将 ignore-send-failures 属性设置为 true 通常更有意义，因为失败通道后的其他通道仍然会收到消息。

此属性默认为 false。

timeout: The timeout attribute specifies the maximum amount of time in milliseconds to wait when sending messages to the target Message Channels.

Top-Level (Outside a Chain)

以下参数仅对链路外部的所有顶级路由器有效。

id: Identifies the underlying Spring bean definition, which, in the case of routers, is an instance of EventDrivenConsumer or PollingConsumer, depending on whether the router’s input-channel is a SubscribableChannel or a PollableChannel, respectively. This is an optional attribute.
auto-startup: This “lifecycle” attribute signaled whether this component should be started during startup of the application context. This optional attribute defaults to true.
input-channel: The receiving message channel of this endpoint.
order: This attribute defines the order for invocation when this endpoint is connected as a subscriber to a channel. This is particularly relevant when that channel uses a failover dispatching strategy. It has no effect when this endpoint itself is a polling consumer for a channel with a queue.