Spring Integration-3 :Filters

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Filters allow, on the basis of a message’s content or metadata (in the message header), a message to pass from one channel to the next or reject and discard the message from the system – that is, not allowing the rejected message into the next channel. The filter is a “yea or nay” component determining which messages flow through and which messages do not.

  • Filters are again endpoints that sit between channels that allows or rejects messages from one message channel to other.
  • Filters allows some messages to pass from one channels to another channel.
  • Messages not selected are discarded
  • Selection occur based on message payload or message metadata(header information)
  • As with Adapters, SI provides many filters out of the box
  • We can create out own filter with its own custom message selection criteria
filter-between-channels

SI Built-In Filters

  • Spring Integration provides several ready to use filters with the framework , you merely have to configure them to use
  • Built-In filters include Expression filter , Xpath filter and XML validation filter

Expression filter – A filter that uses SPEL against the message to select messages

Xpath filter – A filter that uses XPath against the XML payload to select messages

XML Validation filter – A filter that uses XML payload messages that validate against a given schema

Examples of Filters:

Here is a filter that accepts all messages that do not start with text “Hello”

<int:filter input-channel="inboundChannel" output-channel = "outboundChannel" expression="payload.startsWith('Hello')"/>

Optionally discard channel also can be defined so filtered messages can be route using this channel.

<int:filter input-channel="inboundChannel" output-channel = "outboundChannel" discard-channel="relookChannel" expression="payload.startsWith('Hello')"/>

Custom Filters:

public class MySelector implements MessageSelector{    public Boolean accept(Message<?> msg){      if(msg.getPayload() instanceof String &&            msg.getPayload().startsWith("Hello"))       return true;return false;    }}

Above class configuration:

<int:filter input-channel="inboundChannel" output-channel = "outboundChannel" discard-channel="relookChannel" ref="selector"/><bean id="selector" class="com.dpq.MySelector"/>

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