Using `MessageSessionCallback`

从 Spring Integration 4.2 开始，可以使用 MessageSessionCallback<F, T> 实现和 <int-ftp:outbound-gateway/> (Java 中的 FtpOutboundGateway) 对 Session<FTPFile> 使用 requestMessage 上下文执行任何操作。它可用于任何非标准或低级 FTP 操作，并允许从集成流定义和函数接口（Lambda）实现注入访问，如下例所示：

Starting with Spring Integration 4.2, you can use a MessageSessionCallback<F, T> implementation with the <int-ftp:outbound-gateway/> (FtpOutboundGateway in Java) to perform any operations on the Session<FTPFile> with the requestMessage context. It can be used for any non-standard or low-level FTP operations and allows access from an integration flow definition and functional interface (Lambda) implementation injection, as the following example shows:

@Bean
@ServiceActivator(inputChannel = "ftpChannel")
public MessageHandler ftpOutboundGateway(SessionFactory<FTPFile> sessionFactory) {
    return new FtpOutboundGateway(sessionFactory,
         (session, requestMessage) -> session.list(requestMessage.getPayload()));
}

另一个示例可能是预处理或后处理正在发送或检索的文件数据。

Another example might be to pre- or post-process the file data being sent or retrieved.

使用 XML 配置时，<int-ftp:outbound-gateway/> 提供 session-callback 属性，可用于指定 MessageSessionCallback bean 名称。

When using XML configuration, the <int-ftp:outbound-gateway/> provides a session-callback attribute to let you specify the MessageSessionCallback bean name.

session-callback 互斥地与 command 和 expression 属性。在使用 Java 配置时， FtpOutboundGateway 类中提供了不同的构造函数。

The session-callback is mutually exclusive with the command and expression attributes. When configuring with Java, different constructors are available in the FtpOutboundGateway class.

Using MessageSessionCallback

Using `MessageSessionCallback`