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Scala Scala Servlets

A nice example of how familiar Java programming "feels" in Scala are Servlets :

 package com.muchsoft.scala.servlets 
 
 import javax.servlet.http.HttpServlet import javax.servlet.http 
 . HttpServletRequest {=> Request, HttpServletResponse 
 => Response} 
 
 MeinErstesScalaServlet class extends HttpServlet {override def 
 
 doGet (request: Request, response: response) {
 
 val output = 
 \u0026lt;html> 
 \u0026lt; head> Scala \u0026lt;title> Hello \u0026lt;/ title> \u0026lt;/ head> 
 \u0026lt;body> 
 \u0026lt;h1> Scala Hello World \u0026lt;/ h1> 
 \u0026lt;/ body> 
 \u0026lt;/ html> 
 
 response.getWriter (). Print (output) 
}} 
 

The looks around as Java, right? Not quite: When importing we can make Redefinitions that override before the method definition is mandatory, also a key word and no annotation. The return type of method doGet () is not specified and thus corresponds to the Java void. For Scala we had before the opening curly Clamp methods : Unit = can write. doGet

Within () we put the issue on XML literal (as non-modifiable value val; with var scale variables, one tries to avoid in functional languages). This XML literal, we write as usual in the output stream of the Response object. The type of output is scala.xml.Elem .

The structure of the web application corresponding to the JavaEE standard:


of the Scala compiler produces Java byte code ends up in WEB-INF/classes . The Scala standard library scala-library.jar be delivered (from the Scala installation directory) must be in WEB-INF/lib with. In WEB-INF/web.xml we map the class com.muchsoft.scala.servlets.MeinErstesScalaServlet to the URL "hallo.scala. After you deploy (deployment), for example in Tomcat or GlassFish the servlet in the Web browser will be invoked with the URL http://localhost:8080/halloscala/hallo.scala .

To compile the servlet class must have the servlet API on the build path (class path) are located. This can be done servlet example from the Tomcat installation directory -api.jar or from the GlassFish directory javaee.jar embed as an external library.

Now we improve the first Scala Servlet and separate display and control each other a little better:

 MeinZweitesScalaServlet class extends HttpServlet {
 
 def output = 
 \u0026lt;html> 
 \u0026lt;head> \u0026lt;title> Scala Hello \u0026lt;/ title> !; \u0026lt;/ head> 
 \u0026lt;body> 
 \u0026lt;h1> Scala Hello World \u0026lt;/ h1> 
 \u0026lt;p> time on the server: {now} \u0026lt;/ p> 
 \u0026lt;/ body> 
 \u0026lt;/ html> 
 
 def now = new java.util.Date 
 
 override def doGet (request: Request, response: response) {. 
 response.getWriter () print (output) 
}} 
 

output is now a function outside of doGet () , which relies on the function now to output a current time stamp. Both functions are defined without parameters brackets and must be called without parentheses. If we had defined the parameters of functions with empty parentheses, we could have chosen it when you call us not if we write down the brackets or. It has been the convention developed to omit the brackets in the definition, if a function, no side effects (side effects) has.

for a "full" web application is missing a form. Here we go:

 MeinDrittesScalaServlet class extends HttpServlet {
 
 def output (username: String) = 
 \u0026lt;html> 
 \u0026lt;head> \u0026lt;title> Scala Hello World \u0026lt;/ title> \u0026lt;/ head> 
 \u0026lt;body> ; 
 \u0026lt;h1> Hello {username} \u0026lt;/ h1> 
 \u0026lt;p> time on the Server: {now} \u0026lt;/ p> 
 \u0026lt;form method="get" action="hallo3.scala"> 
 \u0026lt;p> What's your name? 
 \u0026lt;input name="benutzer" 
 /> \u0026lt;input type="submit" value="Submit" 
 /> \u0026lt;/ p> 
 \u0026lt;/ form> 
 \u0026lt;/ body> 
 \u0026lt; / html> 
 
 def now = new java.util.Date 
 
 override def doGet (request: Request, response: response) {val 
 
 param = getParameter request "user" 
 
 val = username 
 if ((param == null)  is mapped in web.xml 
 
 to the URL "hallo3.scala" may be the call in the local application server with 
 http://localhost:8080/halloscala/hallo3.scala?benutzer=Thomas 
. 
 
 In practice, you probably do not servlets programming more direct, but a framework like Struts 
 
, 
 

JSF, Wicket etc. . Insert We see here but well, how easy it into existing Java-Scala (web) applications can integrate. And if you want to develop web applications really functional, you can use the Scala Lift framework.