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Improve  your  legacy  application   with  Spring Marten  Deinum   @mdeinum

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Improve  your  monolithic  legacy  application   with  some  redesign,  refactoring  and  Spring Marten  Deinum   @mdeinum

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A  Little  History 6

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Legacy  Software  /  Code “In  computing  a  legacy  system  is  an  old  method,  technology,   computer  system,  or  application  program,"of,  relating  to,  or   being  a  previous  or  outdated  computer  system."  Often  a   pejorative  term,  referencing  a  system  as  "legacy"  often  implies   that  the  system  is  out  of  date  or  in  need  of  replacement.” -­‐  Wikipedia

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“organiza@ons  which  design  systems  ...  are  constrained  to   produce  designs  which  are  copies  of  the  communica@on   structures  of  these  organiza@ons Legacy  Software  /  Code -­‐  Melvin  E.  Conway  (April  1968)

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DEMO

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„I  think  there  has  been  a  general  abandonment  of  good   design  and  development  prac@ces  in  the  Java   community.” Legacy  Software  -­‐  Design -­‐  Vaughn  Vernon

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„Architecture  is  like  weather:  you  can’t  have  none” Legacy  Software  -­‐  Design -­‐  Oliver  Gierke

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Legacy  Software  -­‐  Design 13 Domain Presentation Service Data Access Presentation Service Data Access Domain DTO

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Legacy  Software • Has  proven  to  work  (kind  of)   • Has  proven  business  value   • It  exists  (in  various  degrees  and  languages)   • Have  to  deal  with  it

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Dealing  With  Legacy  Software • Ignore   • Hide   • Full  Rebuild   • Gradual  Redesign

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“Monolithic  gravity:  large  system  will  aNract  new  features   and  changes.  In  the  process  it  will  become  larger  and   eventually  collapse.”   Legacy  Software  /  Code -­‐  Eberhard  Wolff  (@ewolff)  on  27  April  2015

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Dealing  With  Legacy  Software • Ignore   • Hide   • Full  Rebuild   • Gradual  Redesign

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Dealing  With  Legacy  Software   • Spring  Remoting   • HttpInvoker,  RMI,  Hessian   • JMS,  AMQP,  …   • Spring  WS     • Spring  MVC  Rest  Service   • Spring  Integration   • Anti-­‐Corruption  layer

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Dealing  With  Legacy  Software • Ignore   • Hide   • Full  Rebuild   • Gradual  Redesign

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Dealing  With  Legacy  Software   • Starts  of  nice  greenfield   • Hidden  features  in  legacy  software   • Sparse  documentation,     • Knowledge  of  legacy  system   • We  don’t  know  how  to  estimate   • Generally  Big  Bang

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Dealing  With  Legacy  Software • Ignore   • Hide   • Full  Rebuild   • Gradual  Redesign

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„If  you  can't  build  a  structured  monolith,  what  makes  you   think  microservices  are  the  answer?” Dealing  With  Legacy  Software -­‐  Simon  Brown

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DEMO

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Recap • Legacy  systems  are  here  and  they  probably  will   stay   • Refactoring  can  make  your  life,  and  the  ops   teams,  easier

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Learn  More.    Stay  Connected. 25 Twitter: twitter.com/mdeinum YouTube: spring.io/video LinkedIn: nl.linkedin.com/in/mdeinum GitHub: github.com/mdeinum

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Reading  List 26