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.

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>

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

The CharacterStreamReadingMessageSource wraps the reader in a BufferedReader (if it’s not one already). You can set the buffer size used by the buffered reader in the second constructor argument. Starting with version 5.0, a third constructor argument (blockToDetectEOF) controls the behavior of the CharacterStreamReadingMessageSource. When false (default), the receive() method checks if the reader is ready() and returns null if not. EOF is not detected in this case. When true, the receive() method blocks until data is available, or EOF is detected on the underlying stream. When EOF is detected, a StreamClosedEvent (application event) is published; you can consume this event with a bean implementing ApplicationListener<StreamClosedEvent>.

This facilitates "piping" or redirecting data to stdin, such as…​

cat foo.txt | java -jar my.jar

or

java -jar my.jar < foo.txt

allowing the application to terminate when the pipe is closed.

Four convenient factory methods are available:

public static final CharacterStreamReadingMessageSource stdin() { ... }

public static final CharacterStreamReadingMessageSource stdin(String charsetName) { ... }

public static final CharacterStreamReadingMessageSource stdinPipe() { ... }

public static final CharacterStreamReadingMessageSource stdinPipe(String charsetName) { ... }

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 4.3, “Channel Adapter”.

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

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

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:int-stream="http://www.springframework.org/schema/integration/stream"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:beans="http://www.springframework.org/schema/beans"
  xsi:schemaLocation="http://www.springframework.org/schema/beans
      http://www.springframework.org/schema/beans/spring-beans.xsd
      http://www.springframework.org/schema/integration/stream
      http://www.springframework.org/schema/integration/stream/spring-integration-stream.xsd">

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

<int-stream:stdin-channel-adapter id="adapterWithDefaultCharset"/>

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

Starting with version 5.0 you can set the detect-eof attribute which sets the blockToDetectEOF property - see Section 30.2, “Reading from streams” for more information.

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.

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

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

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

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