{"id":333,"date":"2009-03-18T20:13:19","date_gmt":"2009-03-18T23:13:19","guid":{"rendered":"https:\/\/devkico.itexto.com.br\/?p=333"},"modified":"2009-03-29T11:57:55","modified_gmt":"2009-03-29T14:57:55","slug":"grails-and-legacy-code-making-old-code-groovy-again","status":"publish","type":"post","link":"https:\/\/devkico.itexto.com.br\/?p=333","title":{"rendered":"Grails and legacy code: making old code groovy again!"},"content":{"rendered":"

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Code reuse with Grails is amazingly easy. When working with this framework, it’s really cool to see the huge improvement in productivity that we can achieve. But if you have a large legacy code behind you, this productivity will simply disappear. And this is where Grails really shines and become a real choice for a Java developer.<\/p>\n

This week I needed to start a new project which<\/span> in reality was just a web interface for one of our legacy projects. So, I had some options in front of me: I could start with Struts, JSF or even plain servlets (I was out of my mind to just cogitate this third option!). At\u00a0 first, I choosed JSF to interact with our legacy code. After all, it was plain Java to deal with Java code, right?<\/p>\n

Then I started a new JSF project using Netbeans, added the jars which<\/span> contained my legacy code + all the other jars which<\/span> it depends on (basically all the Spring + Hibernate dependencies). Some time after that, I started to face some problems with Tomcat, which<\/span> was having problems reading my faces configuration file (again). At this moment something hit me: a Grails application doesn’t need domain classes!<\/strong><\/span><\/p>\n

In this moment I started my experiment: what if this web interface I needed was entirely wrote in Grails interacting with my legacy code? <\/strong>So I started a new Grails project and used only controllers (just ignored GORM entirely) and my legacy code. And it worked pretty well!<\/p>\n

Here is the procedure I took:<\/p>\n

1. Start a new Grails project that only uses controller classes
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In this state, the only thing I needed to do was to change my DataSource.groovy file to look like the one below:<\/p>\n

\r\n\r\ndataSource {\r\n\r\n}\r\nhibernate {\r\n\r\n}\r\n\/\/ environment specific settings\r\nenvironments {\r\ndevelopment {\r\ndataSource {\r\n}\r\n}\r\ntest {\r\ndataSource {\r\n}\r\n}\r\nproduction {\r\ndataSource {\r\n}\r\n}\r\n}\r\n\r\n<\/pre>\n
This step is optional, but is a good move to do so. After all, it’s not a good idea to have a instance of HSQLDB floating around without any use, right?<\/p>\n
2. Copy all your jar files to the lib directory of your Grails application
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In this case, you only need to copy those jar files which<\/span> contain your legacy code. And here things get really exciting: as Grails already comes with a full stack, basically you’ll only need to copy your legacy code and few libraries your application relies on.<\/p>\n
If your code already uses some of the libraries above, you don’t need to copy their jars to your application. Grails will add them for you: after all, they are the basic components of Grails!. Well, here is the list: Sitemesh, Hibernate, Sprng, Log4J, JUnit, Ant, Commons (several Apache Commons are used by Grails), Xalan, Xerces, Hsqldb.<\/p>\n
As you can see, in many cases the only library you’ll need is your JDBC driver. In my case, I only needed to copy the MySQL Connector and JExcel! Neat!<\/p>\n
Tip: in your Grails installation directory, browse the contents of the lib folder. Maybe you’ll find some library I just forget to mention.<\/p>\n
3. There’s no step 3!!!<\/strong><\/p>\n
At the end of this process, all you have to do consist in work only with controllers classes and it’s respective views. And believe-me: it’s far more productive than using JSF managed beans or actions of Struts!<\/p>\n
Notice: in this case, the best thing to do is: forget about GORM!<\/strong><\/p>\n
Main advantages of this approach compared to the use of “traditional” frameworks<\/h2>\n
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