21. Stream Support

21.1 Introduction

In many cases application data is obtained from a stream. It is not recommended to send a reference to a Stream as a message payload to a consumer. Instead messages are created from data that is read from an input stream and message payloads are written to an output stream one by one.

21.2 Reading from streams

Spring Integration provides two adapters for streams. Both ByteStreamReadingMessageSource and CharacterStreamReadingMessageSource implement MessageSource. By configuring one of these within a channel-adapter element, the polling period can be configured, and the Message Bus can automatically detect and schedule them. The byte stream version requires an InputStream, and the character stream version requires a Reader as the single constructor argument. The ByteStreamReadingMessageSource also accepts the 'bytesPerMessage' property to determine how many bytes it will attempt to read into each Message. The default value is 1024

<bean class="org.springframework.integration.stream.ByteStreamReadingMessageSource">
  <constructor-arg ref="someInputStream"/>
  <property name="bytesPerMessage" value="2048"/>

<bean class="org.springframework.integration.stream.CharacterStreamReadingMessageSource">
  <constructor-arg ref="someReader"/>

21.3 Writing to streams

For target streams, there are also two implementations: ByteStreamWritingMessageHandler and CharacterStreamWritingMessageHandler. Each requires a single constructor argument - OutputStream for byte streams or Writer for character streams, and each provides a second constructor that adds the optional 'bufferSize'. Since both of these ultimately implement the MessageHandler interface, they can be referenced from a channel-adapter configuration as described in more detail in Section 3.2, “Channel Adapter”.

<bean class="org.springframework.integration.stream.ByteStreamWritingMessageHandler">
  <constructor-arg ref="someOutputStream"/>
  <constructor-arg value="1024"/>

<bean class="org.springframework.integration.stream.CharacterStreamWritingMessageHandler">
  <constructor-arg ref="someWriter"/>

21.4 Stream namespace support

To reduce the configuration needed for stream related channel adapters there is a namespace defined. The following schema locations are needed to use it.

<?xml version="1.0" encoding="UTF-8"?>
<beans:beans xmlns="http://www.springframework.org/schema/integration/stream"

To configure the inbound channel adapter the following code snippet shows the different configuration options that are supported.

<stdin-channel-adapter id="adapterWithDefaultCharset"/>

<stdin-channel-adapter id="adapterWithProvidedCharset" charset="UTF-8"/>

To configure the outbound channel adapter you can use the namespace support as well. The following code snippet shows the different configuration for an outbound channel adapters.

<stdout-channel-adapter id="stdoutAdapterWithDefaultCharset" channel="testChannel"/>

<stdout-channel-adapter id="stdoutAdapterWithProvidedCharset" charset="UTF-8" channel="testChannel"/>

<stderr-channel-adapter id="stderrAdapter" channel="testChannel"/>

<stdout-channel-adapter id="newlineAdapter" append-newline="true" channel="testChannel"/>