What exactly is Apache Camel

Question

I don t understand what exactly Camel does   If you could give in 101 words an introduction to Camel    What exactly is it   How does it interact with an application written in Java   Is it something that goes together with the server   Is it an independent program     Please explain what Camel is

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There are lot of frameworks that facilitates us for messaging and solving problems in messaging. One such product is Apache Camel.

Most of the common problems have proven solutions called as design patterns. The design pattern for messaging is Enterprise Integration patterns(EIPs) which are well explained here. Apache camel help us to implement our solution using the EIPs.

The strength of an integration framework is its ability to facilitate us through EIPs or other patterns,number of transports and components and ease of development on which Apache camel stands on the top of the list

Each of the Frameworks has its own advantages Some of the special features of Apache camel are the following.

It provides the coding to be in many DSLs namely Java DSL and Spring xml based DSL , which are popular.
Easy use and simple to use.
Fuse IDE is a product that helps you to code through UI

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A diagram is better than thousands of description  This Diagram illustrates the architecture of Camel

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Here is another attempt at it   You know how there are were things like Webmethods  ICAN Seebeyond  Tibco BW  IBM Broker  They all did help with integration solutions in the enterprise  These tools are commonly known by the name Enterprise Application Integration  EAI  tools   There were mostly drag drop tools built around these technologies and in parts you would have to write adapters in Java  These adapter code were either untested or had poor tooling automation around testing   Just like with design patterns in programming  you have Enterprise Integration patterns for common integration solutions  They were made famous by a book of the same name by Gregor Hohpe and Bobby Woolf   Although it is quite possible to implement integration solutions which use one or many EIP  Camel is an attempt at doing this within your code base using one of XML  Java  Groovy or Scala   Camel supports all Enterprise Integration Patterns listed in the book via its rich DSL and routing mechanism   So Camel is a competing technoloy to other EAI tools with better support for testing your integration code  The code is concise because of the Domain Specific Languages  DSLs   It is readable by even business users and it is free and makes you productive

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Camel helps in routing  transformation  monitoring    It uses Routes  which can be described as    When service bus receives particular message  it will route it through no of services broker destinations such as queue topics  This path is known as route   Example  your stock application has got some input by analyst  it will be processed through the application web component and then result will be published to all the interested registered members for particular stock update

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Assume you create an ecommerce company like Amazon  and you want to only focus on strategy choice of products to sell  unlike amazon delivery fleet  instead of yourself handling moving of goods from sellers to warehouse  making changes to it in warehouse like packaging and sending it out to other city and customers  You hire a company that does all this and just give them info of all your warehouse locations  vehicle types  delivery locations and a list of when to do what  Then they handle that by themselves  that would be Apache Camel  They take care of moving things from one end to other  once you handover stuff to them  so that you are free to focus on other things

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What exactly is it   Apache Camel is a lightweight integration framework which implements many Enterprise Integration patterns You can easily integrate different applications using the required patterns  You can use Java  Spring XML  Scala or Groovy  Almost every technology you can imagine is available  for example HTTP  FTP  JMS  EJB  JPA  RMI  JMS  JMX  LDAP  Netty etc  Have a look at this article and EIP pattern article  How does it interact with an application written in Java   Camel uses a Java Domain Specific Language or DSL for creating Enterprise Integration Patterns or Routes in a variety of domain-specific languages  DSL  as listed below  Java DSL - A Java based DSL using the fluent builder style  The story of Enterprise Integration Pattern resolves around these concepts   Message  End Point  Producer  Consumer  Routing  Bus  Transform and Process  Have a look at this article By Anirban Konar  for one of real time use cases   Is it something that goes together with the server   It acts as a bridge across multiple enterprise sub systems   Is it an independent program   Apache Camel  an integration framework  integrates different independent applications  The major advantage of Camel   You can integrate different applications with different technologies  and different protocols  by using same same concepts for every integration

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Its like a pipeline connecting   From---- gt To   In between u can add as many channels and pipes  The faucet can be of any type  automatic or manual for flow of data and a route to channelize the flow   It supports and have implementation for all types and kinds of processing  And for same processing many approaches because it has many components and each component can also provide the desired output using different methods under it   For instance   File transfer can be done in camel with types file moved or copied and also from folder  server or queue    -from-- gt To    - from-- gt process-- gt to    - from-- gt bean-- gt to    - from-- gt process-- gt bean-- gt to    -from-- gt marshal-- gt process-- gt unmarshal-- gt to   From to----folder  direct  seda  vm can be anything

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One of the things you need to understand  before you try to understand Apache Camel  are Enterprise Integration Patterns  Not everyone in the field is actually aware of them  While you can certainly read the Enterprise Integration Patterns book  a quicker way to get up to speed on them would be to read something like the Wikipedia article on Enterprise Application Integration    One you have read and understood the subject area  you would be much more likely to understand the purpose of Apache Camel  HTH

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My take to describe this in a more accessible way     In order to understand what Apache Camel is  you need to understand what Enterprise Integration Patterns are   Let s start with what we presumably already know  The Singleton pattern  the Factory pattern  etc  They are merely ways of organizing your solution to the problem  but they are not solutions themselves  These patterns were analyzed and extracted for the rest of us by the Gang of Four  when they published their book  Design Patterns  They saved some of us tremendous effort in thinking of how to best structure our code   Much like the Gang of Four  Gregor Hohpe and Bobby Woolf authored the book Enterprise Integration Patterns  EIP  in which they propose and document a set of new patterns and blueprints for how we could best design large component-based systems  where components can be running on the same process or in a different machine   They basically propose that we structure our system to be message oriented -- where components communicate with each others using messages as inputs and outputs and absolutely nothing else  They show us a complete set of patterns that we may choose from and implement in our different components that will together form the whole system   So what is Apache Camel   Apache Camel offers you the interfaces for the EIPs  the base objects  commonly needed implementations  debugging tools  a configuration system  and many other helpers which will save you a ton of time when you want to implement your solution to follow the EIPs   Take MVC  MVC is pretty simple in theory and we could implement it without any framework help  But good MVC frameworks provide us with the structure ready-to-use and have gone the extra mile and thought out all the other  side  things you need when you create a large MVC project and that s why we use them most of the time   That s exactly what Apache Camel is for EIPs  It s a complete production-ready framework for people who want to implement their solution to follow the EIPs

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101 Word Intro  Camel is a framework with a consistent API and programming model for integrating applications together   The API is based on theories in Enterprise Integration Patterns - i e   bunch of design patterns that tend to use messaging   It provides out of the box implementations of most of these patterns  and additionally ships with over 200 different components you can use to easily talk to all kinds of other systems   To use Camel  first write your business logic in POJOs and implement simple interfaces centered around messages   Then use Camel   s DSL to create  Routes  which are sets of rules for gluing your application together   Extended Intro  On the surface  Camel s functionality rivals traditional Enterprise Service Bus products   We typically think of a Camel Route being a  mediation   aka orchestration  component that lives on the server side  but because it s a Java library it   s easy to embed and it can live on a client side app just as well and help you integrate it with point to point services  aka choreography    You can even take your POJOs that process the messages inside the Camel route and easily spin them off into their own remote consumer processes  e g  if you needed to scale just one piece independently   You can use Camel to connect routes or processors through any number of different remote transport protocols depending on your needs   Do you need an extremely efficient and fast binary protocol  or one that is more human readable and easy to debug   What if you wanted to switch   With Camel this is usually as easy as changing a line or two in your route and not changing any business logic at all   Or you could support both - you   re free to run many Routes at once in a Camel Context   You don t really need to use Camel for simple applications that are going to live in a single process or JVM - it would be overkill   But it s not conceptually any more difficult than code you may write yourself   And if your requirements change  the separation of business logic and glue code makes it easier to maintain over time   Once you learn the Camel API  it is easy to use it like a Swiss-Army knife and apply it quickly in many different contexts to cut down on the amount of custom code you   d otherwise have to write   You can learn one flavor - the Java DSL  for example  a fluent API that s easy to chain together - and pick up the other flavors easily   Overall Camel is a great fit if you are trying to do microservices   I have found it invaluable for evolutionary architecture  because you can put off a lot of the difficult   easy-to-get-wrong  decisions about protocols  transports and other system integration problems until you know more about your problem domain   Just focus on your EIPs and core business logic and switch to new Routes with the  right  components as you learn more

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In short    When there is a requirement to connect   integrate systems  you will probably need to connect to some data source and then process this data to match your business requirements   In order to do that   1  You could develop custom program that would do it  might be time consuming and hard to understand  maintain for other developer    2  Alternatively  you could use Apache Camel to do it in standardised way  it has most of the connectors already developed for you  you just need to set it up and plug your logic - called Process    Camel will help you to    Consume data from any source format Process this data Output data to any source format   By using Apache Camel you will make it easy to understand   maintain   extend your system to another developer   Apache Camel is developed with Enterprise Integration Patterns  The patterns help you to integrate systems in a good way  -

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In plain English  camel gets  many  things done without much of boiler plate code   Just to give you a perspective  the Java DSL given below will create a REST endpoint which will be able to accept an XML consisting of List of Products and splits it into multiple products and invoke Process method of BrandProcessor with it   And just by adding  parallelProcessing  note the commented out part  it will parallel process all the Product Objects   Product class is JAXB XJC generated Java stub from the XSD which the input xml is confined to   This much code  along with few Camel dependencies  will get the job done which used to take 100s of lines of Java code   from  servlet item-delta matchOnUriPrefix true amp httpMethodRestrict POST    split stax Product class      parallelProcessing      process itemDeltaProcessor     After adding the route ID and logging statement  from  servlet item-delta matchOnUriPrefix true amp httpMethodRestrict POST    routeId  Item-DeltaRESTRoute    log LoggingLevel INFO   Item Delta received on Item-DeltaRESTRoute    split stax Product class    parallelProcessing    process itemDeltaProcessor     This is just a sample  Camel is much more than just REST end point  Just take a look the pluggable component list http   camel apache org components html

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If you are aware of Enterprise Integration Patterns  Apache Camel is one integration framework which implements all EIPs   And you can deploy Camel as a standalone application in a web-container   Basically  if you have to integrate several applications with different protocols and technologies  you can use Camel

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Apache Camel is a lightweight integration framework that implements all Enterprise Integration patterns  You can easily integrate different applications using the required patterns  You can use Java  Spring XML  Scala or Groovy   Apache Camel runs on the Java Virtual Machine  JVM       The core functionality of Apache Camel is its routing engine  It allocates messages based on the related routes  A route contains flow and integration logic  It is implemented using EIPs and a specific DSL

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Another point of view  based on more fundamental mathematical topics  The most general computing platform is a Turing Machine  There is a problem with the Turing machine  All the input output data stays inside the turing machine  In the real world there are input sources and output sinks external to our Turing machine  and in general governed by systems outside of our control  That is  those external system will send receive data at will in any format with any desired data-scheduler  Question  How do we manage to make independent turing-machines speak to each other in the most-general way so that each turing-machine sees their peers as either a source of input-data or sink of output-data  Answer  Using something like camel  mule  BizTalk or any other ESB that abstract away the data handling between completing distinct  quot physical quot   or virtual software  turing machines

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Most  new  things in computing aren t really new at all  they re just a mystifying wrapper around something that already well-understood   When they re hard to understand  it s usually because someone decided to invent new language terms or colonise existing terms for a different purpose  a good example of that is the X developers  reversal of what  client  and  server  mean    Camel is a Java-based wrapper API for inter-application middleware     Middleware is a general term for software that provides interpretation services between entities that don t share a common language or data types   That s what Camel is  at bottom   We can flesh out the description by noting that it provides for EIP-type middleware   It doesn t provide the middleware itself  since it can t know the details of what the applications need to communicate   But it provides the API for creating the invariant parts of that middleware  create a start point  create an end point  create conditions for starting and ending  etc   Hope that helps

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Yes  this is probably a bit late  But one thing to add to everyone else s comments is that  Camel is actually a toolbox rather than a complete set of features  You should bear this in mind when developing and need to do various transformations and protocol conversions    Camel itself relies on other frameworks and therefore sometimes you need to understand those as well in order to understand which is best suited for your needs  There are for example multiple ways to handle REST  This can get a bit confusing at first  but once you starting using and testing you will feel at ease and your knowledge of the different concepts will increase

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A definition from another perspective    Apache Camel is an integration framework  It consists of some Java libraries  which helps you implementing integration problems on the Java platform  What this means and how it differs from APIs on the one side and an Enterprise Service Bus  ESB  on the other side is described in my article  When to use Apache Camel

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If you have 5 to 10 minutes  I generally recommend people to read this Integration with Apache Camel by Jonathan Anstey  It s a well written piece which gives a brief introduction to and overview of some of Camel s concepts  and it implements a use case with code samples  In it  Jonathan writes   Apache Camel is an open source Java framework that focuses on making integration easier and more accessible to developers  It does this by providing   concrete implementations of all the widely used Enterprise Integration Patterns  EIPs  connectivity to a great variety of transports and APIs easy to use Domain Specific Languages  DSLs  to wire EIPs and transports together   There is also a free chapter of Camel in Action  Camel in Action  2nd ed  is here  which introduces Camel in the first chapter  Jonathan is a co-author on that book with me

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Camel sends messages from A to B     Why a whole framework for this  Well  what if you have    many senders and many receivers a dozen of protocols  ftp  http  jms  etc   many complex rules    Send a message A to Receivers A and B only Send a message B to Receiver C as XML  but partly translate it  enrich it  add metadata  and IF condition X  then send it to Receiver D too  but as CSV     So now you need    translate between protocols glue components together define routes - what goes where filter some things in some cases   Camel gives you the above  and more  out of the box     with a cool DSL language for you to define the what and how     new DefaultCamelContext   addRoutes new RouteBuilder             public void configure                 from  jms incomingMessages                        choice      start router rules                      when header  CamelFileName                                endsWith   xml                         to  jms xmlMessages                        when header  CamelFileName                                endsWith   csv                         to  ftp csvMessages        See also this and this and Camel in Action  as others have said  an excellent book

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Apache Camel is a Java framework for Enterprise integration  Eg - if you are building a web application which interacts with many vendor API s we can use the camel as the External integration tool  We can do more with it based on the use case  Camel in Action from Manning publications is a great book for learning Camel  The integrations can be defined as below   Java DSL  from  jetty   0 0 0 0 8080 searchProduct   routeId  searchProduct products   threads        log LoggingLevel INFO   searchProducts request Received with body    body         bean Processor class   createSearchProductsRequest   removeHeaders  CamelHttp         setHeader Exchange HTTP METHOD  constant org apache camel component http4 HttpMethods POST        to  http4       preLiveBaseAPI   searchProductsUrl     apiKey     ApiKey                         amp bridgeEndpoint true        bean Processor class   buildResponse   log LoggingLevel INFO   Search products finished      This is to just create a REST API endpoint which in turn calls an external API and sends the request back  Spring DSL   lt route id  GROUPS-SHOW  gt       lt from uri  jetty   0 0 0 0 8080 showGroups    gt       lt log loggingLevel  INFO  message  Reqeust receviced service to fetch groups - gt    body     gt       lt to uri  direct auditLog    gt       lt process ref  TestProcessor    gt   lt  route gt    Coming to your questions   What exactly is it  Ans - It is a framework which implements Enterprise integration patterns How does it interact with an application written in Java  Ans - it can interact with any available protocols like http  ftp  amqp etc Is it something that goes together with the server  Ans - It can be deployed in a container like tomcat or can be deployed independently as a java process Is it an independent program  Ans - It can be    Hope it helps

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Creating a project description should not be complicated   I say      Apache Camel is messaging technology glue with routing  It joins together messaging start and end points allowing the transference of messages from different sources to different destinations  For example  JMS -  JSON  HTTP -  JMS or funneling FTP -  JMS  HTTP -  JMS  JSON -  JMS   Wikipedia says      Apache Camel is a rule-based routing and mediation engine which provides a Java object based implementation of the Enterprise Integration Patterns using an API  or declarative Java Domain Specific Language  to configure routing and mediation rules  The domain specific language means that Apache Camel can support type-safe smart completion of routing rules in your IDE using regular Java code without huge amounts of XML configuration files  though XML configuration inside Spring is also supported    See  That wasn t hard was it

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BASED ON ANALOGY  Camel based routing can be understood much easily by putting yourself in the shoes of a Airline owner  eg   American Airlines  Jet Airways     Purpose of  your airline  is to  carry   passengers  from one  city  to another one in the world  You use aircrafts from different  aircraft companies  like Boeing  Airbus  HAL for carrying passengers   Your airline s boards passengers using  airports  of the from city and deboards them using the airport of the to city  A passenger may  travel  to multiple cities  but everywhere they have to go through the airport to travel between your airline s aircraft and the city   Note that a passenger  departing  from the city is essentially  arriving  into your airlines  aircraft  And a passeger   arriving  into the city  is essentially departing from the aircraft  Since we are in the shoes of airline owner  the term  arrival passenger  and  departing passenger  are reversed from our conventional notions which are based on cities perspective   Same  airport  infrastructure of each city is used by  departing  passengers and  arrival  passengers  An airport provides  departing infrastructure  for departing passengers  which is different from the  arrival infrastructure  provided for arriving passengers   Passengers can continue doing their day to their activities due to various  amenities  provided inside the aircraft by your airlines  while travelling   On top of that  your airline also provides lounge facilities for special treatments like  understanding local language  and or preparing you for the  travel    Lets replace few words phrases used above with following   your airline  Apache Camel  aircraft companies  Transport mechanisms  your airline s aircraft  Apache Camel s underlying transport mechanism  carry  route  passengers  message   city  system   airport  Camel Component   understanding local languages  Type Conversions   departing  producing  produced  arriving  consuming  consumed  travel  routed  amenities  provided  After replacing the words  here is what you get   Purpose of  Apache Camel  is to route  messages  from one  system  to another one in the world  Apache camel uses different transport mechanisms for message routing   Apache Camel picks up messages using  Camel based Component  of the  from  system and drops them using the  Camel based Component  of the  to  system  A message may route to multiple systems  but everywhere they have to go through  Camel based Components  to travel between  Apache Camel s underlying transport mechanism  and the system   Note that a message  produced  from the system is essentially  consumed  into Apache Camel s underlying transport mechanism   And a message consumed by a system  is essentially produced by the  Apache Camel s underlying transport mechanism    Since we are attempting to understand Camel  we must think from Camel s perspective here onwards  The meaning of the terms  consumer message  and  producer message  are  thus  reversed from our conventional notions which are based on a system s perspective   Same  Camel based Component s   coding infrastructure is used by  producer message  and  consumer message   A  Camel based Component  provides a  producer endpoint  for  producer message  and a  consumer endpoint  for  consumer message    Messages can be processed by Camel when they are being routed   On top of this routing  Camel provides special features like  Type Conversion  and many more

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