677fca51a9
Complete: -------- - src/* documentation resources moved to 'docs' subproject - docbook sources upgraded to Docbook 5 - formatted all docbook sources to strip tab characters and eliminate trailing whitespace - all projects compile and test successfully - all artifacts upload successfully to s3, static.sf.org, etc. Remaining: --------- - documentation L&F needs work. CSS, images, and highlighting aren't hooked up properly - spring-integration-jdbc codegen bits in Maven POM need to be transcribed into gradle - dependencies that were optional or provided scope in maven are currently 'compile' scope in Gradle. Need to figure out support in Gradle to fix this. - run through Eclipse classpath and project generation scenarios - delete all Maven artifacts
92 lines
4.8 KiB
XML
92 lines
4.8 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<chapter xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="stream"
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xmlns:xlink="http://www.w3.org/1999/xlink">
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<title>Stream Support</title>
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<section id="stream-intro">
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<title>Introduction</title>
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<para>
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In many cases application data is obtained from a stream. It is <emphasis>not</emphasis> 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.
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</para>
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</section>
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<section id="stream-reading">
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<title>Reading from streams</title>
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<para>
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Spring Integration provides two adapters for streams. Both <classname>ByteStreamReadingMessageSource</classname> and
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<classname>CharacterStreamReadingMessageSource</classname> implement <interfacename>MessageSource</interfacename>.
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By configuring one of these within a channel-adapter element, the polling period can be configured,
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and the Message Bus can automatically detect and schedule them. The byte stream version requires an
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<classname>InputStream</classname>, and the character stream version requires a <classname>Reader</classname> as
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the single constructor argument. The <classname>ByteStreamReadingMessageSource</classname> also accepts the 'bytesPerMessage'
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property to determine how many bytes it will attempt to read into each <interfacename>Message</interfacename>. The
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default value is 1024
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<programlisting language="xml"><![CDATA[<bean class="org.springframework.integration.stream.ByteStreamReadingMessageSource">
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<constructor-arg ref="someInputStream"/>
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<property name="bytesPerMessage" value="2048"/>
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</bean>
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<bean class="org.springframework.integration.stream.CharacterStreamReadingMessageSource">
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<constructor-arg ref="someReader"/>
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</bean>]]>
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</programlisting>
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</para>
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</section>
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<section id="stream-writing">
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<title>Writing to streams</title>
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<para>
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For target streams, there are also two implementations: <classname>ByteStreamWritingMessageHandler</classname> and
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<classname>CharacterStreamWritingMessageHandler</classname>. Each requires a single constructor argument -
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<classname>OutputStream</classname> for byte streams or <classname>Writer</classname> for character streams,
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and each provides a second constructor that adds the optional 'bufferSize'. Since both of these
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ultimately implement the <interfacename>MessageHandler</interfacename> interface, they can be referenced from a
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<emphasis>channel-adapter</emphasis> configuration as described in more detail in
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<xref linkend="channel-adapter"/>.
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<programlisting language="xml"><![CDATA[<bean class="org.springframework.integration.stream.ByteStreamWritingMessageHandler">
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<constructor-arg ref="someOutputStream"/>
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<constructor-arg value="1024"/>
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</bean>
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<bean class="org.springframework.integration.stream.CharacterStreamWritingMessageHandler">
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<constructor-arg ref="someWriter"/>
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</bean>]]>
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</programlisting>
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</para>
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</section>
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<section id="stream-namespace">
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<title>Stream namespace support</title>
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<para>
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To reduce the configuration needed for stream related channel adapters there is a namespace defined. The following schema locations are needed to use it.
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<programlisting language="xml"><![CDATA[<?xml version="1.0" encoding="UTF-8"?>
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<beans:beans xmlns="http://www.springframework.org/schema/integration/stream"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xmlns:beans="http://www.springframework.org/schema/beans"
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xsi:schemaLocation="http://www.springframework.org/schema/beans
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http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
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http://www.springframework.org/schema/integration/stream
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http://www.springframework.org/schema/integration/stream/spring-integration-stream-2.0.xsd">]]></programlisting>
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</para>
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<para>
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To configure the inbound channel adapter the following code snippet shows the different configuration options that are supported.
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<programlisting language="xml"><![CDATA[<stdin-channel-adapter id="adapterWithDefaultCharset"/>
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<stdin-channel-adapter id="adapterWithProvidedCharset" charset="UTF-8"/>]]></programlisting>
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</para>
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<para>
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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.
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<programlisting language="xml"><![CDATA[<stdout-channel-adapter id="stdoutAdapterWithDefaultCharset" channel="testChannel"/>
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<stdout-channel-adapter id="stdoutAdapterWithProvidedCharset" charset="UTF-8" channel="testChannel"/>
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<stderr-channel-adapter id="stderrAdapter" channel="testChannel"/>
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<stdout-channel-adapter id="newlineAdapter" append-newline="true" channel="testChannel"/>
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]]></programlisting>
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</para>
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</section>
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</chapter>
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