Introduction to Spring Integration

Katowice, 04.02.2016Dominik Strzyżewski

Logistics

• Around 2-2.5 hours• On site presentation & webinar• Questions at the end

Agenda

• High-level view • Anatomy of an message and types of channels• Endpoints• Basic enterprise integration patterns• Adapters• Errors handling• Extras *

High-level view

Main concepts• Components can communicate using in-memory messaging• Adapters to integrate with external systems• Use of Spring framework programming model• Based on Enterprise Integration Patterns book• http://projects.spring.io/spring-integration

Sample workflow

http://docs.spring.io/autorepo/docs/spring-integration/2.0.x/reference/htmlsingle/images/cafe-eip.png

Adapters

• Application components are separated from integration details

• External systems (file system, JMS) can produce new message

• Implementation details not important for components

• Payload is important! (and metadata)

• Spring Integration message can create an external event (SOAP, JDBC)http://www.javacodegeeks.com/2015/09/spring-integration-fundamentals.html

Hello World demo

Benefits• Loose coupling• Separation of concerns• EDA

Competitors• Apache Camel• ESB:

• Mule ESB• Apache ServiceMix• Red Hat Fuse ESB• IBM WebSphere ESB• Oracle Enterprise

Service Bus• TIBCO ESB

http://www.infoq.com/articles/ESB-Integration

Anatomy of an message and types of channels

Basic interaction• An endpoint sends a message• Endpoints are connected using MessageChannels• Endpoints can receive messages from channels by:

• Subscribing (passive)• Polling (active)

Message

• Messages are immutable• GenericMessage• MessageBuilder

• Payload is a Java object• Headers:

• Predefined – always present

• Predefined – specific for each component/adapter

• Custom• From Spring 4: spring-

messaging module

Message channel• Connects endpoints• No persistence (in-memory)• Can be backed by messages store:

• JDBC• MongoDB• Redis• Gemfire

• JMS (special channels defined in JMS namespace)

Types of message channels• Pollable channels

• Buffer messages• Poller is necessary

• Subscribable channels• Call message handlers

Lubos Krnac „Pivotal Certified Spring Enterprise Integration Specialist Exam A Study Guide”, Apress, p. 350

Point-to-point channels• Only one receiver• DirectChannel

• Default• Use sender’s thread• Blocking• Dispatcher can be configured

• QueueChannel• Internal queue for messages• Different threads (no transaction and

security context propagation)• Not blocking

<int:channel id="directChannel"/>

<int:channel id="queueChannel"> <int:queue capacity="20"/></int:channel>

Point-to-point channels• PriorityChannel

• Priority queue• Use priority header• Or custom comparator

• RendezvousChannel• Use SynchronousQueue• Sender knows that some receiver has accepted the message• Request-reply operations

• ExecutorChannel• Like DirectChannel• Use TaskExecutor to dispatch – different thread

• NullChannel (disarded messages)

<int:channel id="rendezvousChannel"> <int:rendezvous-queue/></int:channel>

<int:channel id="priorityChannel"> <int:priority-queue capacity="10"/></int:channel>

<int:channel id="executorChannel"> <int:dispatcher task-executor="taskExecutor"/></int:channel>

Publish-subscribe• Multiple receivers• PublishSubscribeChannel – synchronous, using sender’s thread,

default• Parallel using TaskExecutor – different threads

<int:publish-subscribe-channel id="synchronousChannel"/>

<int:publish-subscribe-channel id="asynchronousChannel" task-executor="taskExecutor"/><task:executor id="taskExecutor" pool-size="10"/>

Publish-subscribe demo

Channel interceptors• ChannelInterceptor interface• Defined per channel

• Global

<int:channel id="testChannel"> <int:interceptors> <ref bean="someCustomInterceptor"/> </int:interceptors></int:channel>

<int:channel-interceptor ref="someCustomInterceptor" pattern="test*"/>

Wire tap• Special type of interceptor• Sends a message to another channel without affecting original

flow• Useful for monitoring and debugging• Often combined with logging channel adapter

<int:channel id="testChannel"> <int:interceptors> <int:wire-tap channel="logChannel"/> </int:interceptors></int:channel>

<int:channel id="logChannel"/>

<int:logging-channel-adapter channel="logChannel" level="INFO" />

<int:wire-tap channel="logChannel" pattern="*"/>

Endpoints

Types of endpoints• Messaging components

• Adapters (inbound and outbound) – covered in more detail later• Gateways (inbound and outbound)• Service Activator

• Message routing (filter, router, splitter, agregator, resequencer…)

• Message transformation (content enricher, claim check…)• And much more…

Adapters• One way integration• Inbound

• Used to generate new messages with a poller (file system, Spring bean)• Accept external input (JMS, HTTP)

• Outbound – send an event to an external system

<int:inbound-channel-adapter id="generator" channel="numbers" ref="numberGenerator" method="getRandomNumber"> <int:poller fixed-rate="1000"/></int:inbound-channel-adapter>

<int-jms:inbound-channel-adapter id="jmsIn" destination="queue" channel="testChannel"> <int:poller fixed-rate="1000"/></int-jms:inbound-channel-adapter>

Gateways• Two way integration

• Inbound Gateway - deliver message into application and waits for a response

• Outbound Gateway - invokes external system and gets a response• Categories

• Generic messaging gateway – proxy between Java code and Spring Integration infrastructure

• Technology-specific messaging gateways – handle communication with external systems (JDBS, JMS, SOAP, HTTP)

Messaging gateway• Proxy for sending messages from Java code• Temporary reply channel created automatically• Converts a parameter to a message payload• May return Future (asynchronous) or void

public interface HRService {

Status doubleSalary(Person person);

}

<int:gateway id="hrService" service-interface="com.hr.HRService" default-request-channel="people" />

Service Activator• Invoke bean method• Return value becomes a message• method attribute (or @ServiceActivator) if there are more

methods

public class MessageProcessor { Status process(Data data) { … } }

<int:service-activator ref="messageProcessor" input-channel="input" output-channel="output"/><bean id="messageProcessor" class="test.MessageProcessor">

Demo: rest controller + gateway + JMS

Basic enterprise integration patterns

Bridge• Connects two channels (pollable to subscribable channel)• Connects two channel adapters

<int:bridge input-channel="inputChannel" output-channel="outputChannel"> <int:poller fixed-delay="1000"/></int:bridge>

Message transformer• Payload conversion• Header enriching• Generic transformer• Support for maps, XML, JSON…

<int:transformer input-channel="inputChannel" output-channel="outputChannel" expression="payload.toUpperCase()"/>

Filter• Decides to allow message processing• Default: drop message

• Exception on rejection• Discard channel

<int:filter input-channel="inputChannel" output-channel="outputChannel" ref="filterBean" method="filter" discard-channel="invalidData"/>

Router• Choose next channel• Calls bean’s method and treats return value as channel name,

other options available• List of names• Channel or list of channels

• Additional routers based on• Payload type• Header value• Exception type• SpEL• Recipients list• XPath<int:router input-channel="inputChannel" ref="router" method="route"/>

Splitter• Input – one message• Output – many messages

<int:splitter input-channel="orders" output-channel="items" ref="orderSplitter" method="split"/>

List<LineItem> split(Order order) { return order.getItems();}

Adapters

Plenty of them…• Files/FTP/FTPS/SFTP• JDBC/JPA• MongoDB• Redis• JMS/AMQP• RSS• HTTP/WebSockets/SOAP/RMI• Mails• MQTT• Twitter• That’s not all!

JDBC• Could be used to retrieve or write data• Backing Message Channels

<int-jdbc:inbound-channel-adapter query="select * from item where status=2" channel="dataChannel" data-source="dataSource" update="update item set status=10 where id in (:id)"> <int:poller fixed-rate="1000"> <int:transactional/> </int:poller></int-jdbc:inbound-channel-adapter>

Files support • AcceptOnceFileListFilter – default, in memory• FileSystemPersistentAcceptOnceFileListFilter – use of

MetadataStore<int-file:inbound-channel-adapter id="filesIn1" directory="file:${input.directory}" prevent-duplicates="true"/>

<int-file:inbound-channel-adapter id="filesIn2" directory="file:${input.directory}" filter="customFilterBean" />

<int-file:inbound-channel-adapter id="filesIn3" directory="file:${input.directory}" filename-pattern="test*" />

<int-file:inbound-channel-adapter id="filesIn4" directory="file:${input.directory}" filename-regex="test[0-9]+\.txt" />

JMS• Inbound/Outbound Channel Adapter• Message-Driven Channel Adapter (uses MessageListener

container)• Inbound/Outbound Gateway• JMS Backed Message Channels

Demo: JDBC in + JMS channel +splitter + MongoDB out

Errors handling

Synchronous call (sender’s thread)• Sender receives a MessageHandlingException• It wraps original exception• Exception is also returned for a bidirectionl asynchronous call

Unidirectional asynchronous call• Message is sent to error channel

• Use of error channel header• Use global channel named „errorChannel”

• errorChannel• publish-subscribe• Could be overriden

• exception-type-router<int:exception-type-router input-channel="inputChannel" default-output-channel="defaultChannel"> <int:mapping exception-type="java.lang.IllegalArgumentException" channel="illegalChannel"/> <int:mapping exception-type="java.lang.NullPointerException" channel="npeChannel"/></int:exception-type-router>

Extras

Chaining endpoints• Only last element can define output channel• Intermediates steps have to return a message (or null)• If last endpoint returns sth, output channel or replyChannel in a

message have to be defined• Implicit use of direct channels - elements in a chain can’t be

active<int:chain input-channel="input" output-channel="output"> <int:filter ref="someSelector" throw-exception-on-rejection="true"/> <int:header-enricher error-channel="customErrorChannel"> <header name="foo" value="bar"/> </int:header-enricher> <int:service-activator ref="someService" method="someMethod"/></int:chain>

Java Configuration/Annotations• @Bean annotation do declare i.e. channels• Component scanning: @MessageEndpoint, @ServiceActivator,

@Filter, @Router etc.@Beanpublic MessageChannel channel() { List<ChannelInterceptor> interceptors = /* ... */ final PublishSubscribeChannel channel = new PublishSubscribeChannel(executor()); channel.setInterceptors(interceptors); return channel;}

@Filter(inputChannel = "input", outputChannel = "output", discardChannel = "dropped")public boolean filter(final String message) { return message.startsWith("prefix");}

Java DSL• https://github.com/spring-projects/spring-integration-java-dsl

@Beanpublic IntegrationFlow myFlow() { return IntegrationFlows.from(this.integerMessageSource(), c -> c.poller(Pollers.fixedRate(100))) .channel(this.inputChannel()) .filter((Integer p) -> p > 0) .transform(Object::toString) .channel(MessageChannels.queue()) .get();}

Testing• Unit testing – nothing special• Use of standard Spring support for integration testing• MessagingTemplate to interact with SI

Demo: simple testing example

Questions?

Thanks for listening

Dominik Strzyżewskidominik.strzyzewski@gmail.com

Examples: https://github.com/krzyzol/spring-integration-presentation/