Sunday, January 12, 2020

GitLab migration

Beginning today (January 12, 2020) OOP University will be migrating all version control activity to GitLab.  All new or updated code samples will be found at https://gitlab.com/oop-university.

I am thinking of doing some tutorials on some more peripheral topics such as continuous integration pipelines.  While not directly related to OOP, we need to have a grasp on these topics as software developers.

Tuesday, March 20, 2018

Lets give Spring the Boot

Hi folks.  It's been a while since I've posted anything here.  Let's just say that life is complicated.

I was inspired to write this based on some recent experiences with Spring Boot.  This is a very powerful technology that relies on Spring and takes it to new and interesting places.  The bottom line is that while there are many ways to structure a system, if we pick one and stick with it we see some real benefits.  Productivity improves, communication between developers is facilitated, and some really cool automation can be brought to bear on the task of building a system.

So what IS Spring Boot?  It's really a few classes and conventions wrapped around Spring that frees the developer from a lot of the grunt work that used to be required.  For instance, the need for xml configuration files has been essentially eliminated.  Can I get an amen?  There is a lot more to it, but why don't we just dig in and create a simple application?

package com.oopuniversity.hellospringboot;
import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplicationpublic class App  {
    public static void main(String args[]) {
        SpringApplication.run(App.class, args);    }
}

There you have it.  A complete application which does nearly nothing...  And yet it's really got a lot going on inside of it.  This will actually create an application server listening (by default) on port 8080.

If we run this program we will see output like this:

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.0.0.RELEASE)

2018-03-19 20:08:06.184  INFO 248504 --- [           main] com.oopuniversity.hellospringboot.App    : Starting App on Razer-Laptop with PID 248504 (C:\Users\jd\workspace\basics\hello-spring-boot\build\classes\java\main started by jd in C:\Users\jd\workspace\basics)
2018-03-19 20:08:06.186  INFO 248504 --- [           main] com.oopuniversity.hellospringboot.App    : The following profiles are active: development
2018-03-19 20:08:06.225  INFO 248504 --- [           main] ConfigServletWebServerApplicationContext : Refreshing org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@6a01e23: startup date [Mon Mar 19 20:08:06 EDT 2018]; root of context hierarchy
2018-03-19 20:08:07.349  INFO 248504 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2018-03-19 20:08:07.386  INFO 248504 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2018-03-19 20:08:07.386  INFO 248504 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/8.5.28
2018-03-19 20:08:07.398  INFO 248504 --- [ost-startStop-1] o.a.catalina.core.AprLifecycleListener   : The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path: [C:\Program Files\Java\jdk1.8.0_152\bin;C:\WINDOWS\Sun\Java\bin;C:\WINDOWS\system32;C:\WINDOWS;C:\ProgramData\Oracle\Java\javapath;C:\Program Files (x86)\Razer Chroma SDK\bin;C:\Program Files\Razer Chroma SDK\bin;C:\Program Files (x86)\Intel\iCLS Client\;C:\Program Files\Intel\iCLS Client\;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;C:\Program Files (x86)\Intel\Intel(R) Management Engine Components\DAL;C:\Program Files\Intel\Intel(R) Management Engine Components\DAL;C:\Program Files (x86)\Intel\Intel(R) Management Engine Components\IPT;C:\Program Files\Intel\Intel(R) Management Engine Components\IPT;C:\Program Files (x86)\NVIDIA Corporation\PhysX\Common;C:\Users\Administrator\AppData\Local\Microsoft\WindowsApps;C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem;C:\WINDOWS\System32\WindowsPowerShell\v1.0\;C:\Program Files\PuTTY\;C:\ProgramData\chocolatey\bin;c:\bin;c:\bin\flyway-5.0.6;C:\Program Files\MySQL\MYSQL Server 5.7\bin;C:\Program Files\MySQL\MySQL Utilities 1.6\;C:\Program Files\Git\cmd;C:\Program Files\Git\mingw64\bin;C:\Program Files\Git\usr\bin;C:\Program Files\Amazon\AWSCLI\;C:\Program Files (x86)\Graphviz2.38\bin;C:\Ruby24-x64\bin;C:\Users\jd\AppData\Local\Microsoft\WindowsApps;C:\Users\jd\apache-maven-3.5.2\bin;;.]
2018-03-19 20:08:07.500  INFO 248504 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2018-03-19 20:08:07.500  INFO 248504 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1277 ms
2018-03-19 20:08:07.606  INFO 248504 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean  : Servlet dispatcherServlet mapped to [/]
2018-03-19 20:08:07.609  INFO 248504 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'characterEncodingFilter' to: [/*]
2018-03-19 20:08:07.609  INFO 248504 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
2018-03-19 20:08:07.610  INFO 248504 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'httpPutFormContentFilter' to: [/*]
2018-03-19 20:08:07.610  INFO 248504 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'requestContextFilter' to: [/*]
2018-03-19 20:08:07.898  INFO 248504 --- [           main] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@6a01e23: startup date [Mon Mar 19 20:08:06 EDT 2018]; root of context hierarchy
2018-03-19 20:08:07.967  INFO 248504 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error]}" onto public org.springframework.http.ResponseEntity<java.util.Map<java.lang.String, java.lang.Object>> org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.error(javax.servlet.http.HttpServletRequest)
2018-03-19 20:08:07.969  INFO 248504 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error],produces=[text/html]}" onto public org.springframework.web.servlet.ModelAndView org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.errorHtml(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse)
2018-03-19 20:08:07.993  INFO 248504 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2018-03-19 20:08:07.993  INFO 248504 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2018-03-19 20:08:08.024  INFO 248504 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**/favicon.ico] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2018-03-19 20:08:08.131  INFO 248504 --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
2018-03-19 20:08:08.162  INFO 248504 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2018-03-19 20:08:08.164  INFO 248504 --- [           main] com.oopuniversity.hellospringboot.App    : Started App in 2.244 seconds (JVM running for 2.621)

That's really am amazing amount of output for what appears to be a one-liner, isn't it?  One of the beautiful things about Spring Boot (and Spring in general) is that it is well documented internally and tells you what it's doing.  Perhaps more importantly it's really good about telling you what went wrong, which is pretty much an inevitability.

Since no URIs are defined, it won't actually serve up any pages as written, but you can tell it's doing at least something by hitting it with a browser.

Spring Boot is incredibly well suited to today's world of cloud-native applications built as micro-services.  An application such as this really doesn't need anything more than a functional JVM to be spun up as one instance or a hundred.  Everything it really requires to run can be bundled into a single .jar file and distributed where needed.  There's no more hassle with deploying application servers and the attendant configuration and devops challenges.

Let's add some functionality to this little program, so that it actually does a task for us.  We're going to build a RESTful calculator.  If you aren't familiar with RESTful services you can go look up what I'm talking about, but in short RESTful services are stateless web-based services that accept parameters in a URL and return usable responses to whoever calls them.  This allows for amazing levels of integration, and every task can be built using the technology best suited for it.

Since this is really just a technology demonstrator, I will not be building any of this using best practices for project layout and the like.  All of that is ultimately important but unnecessary for the purpose of this post.

Let's start with adding two numbers.  As this will be a RESTful service, everything needed to perform the math must be specified on the URL.  I will define it like this:

/add/number1/number2

That way, all I should really need to do to add 1 and 1 is call "http://localhost:8080/add/1/1"

Doing this is really very easy.  First, I need to inform Spring Boot that I want to serve up RESTful responses.  In the real world I'd create a new class (or several of them) for this purpose, but for now I'll just add it to the same little program.



That's straightforward enough.  Now we have to put in the code to do the math:

First we will need to add a couple of supporting imports:



And then we're ready to craft a working service:



The '@RequestMapping' annotation sets up a URI with embedded variables that will be used to invoke our new service.  The @PathVariable annotation ties the embedded variables to the parameter list for our method.

Believe it or not, that's all we need to get this working:



As you can imagine, it's as straightforward as can be to extend this to additional operations.

I will leave it as an exercise for the reader to add more operations to this.  It's very straightforward and you really shouldn't have any problems doing so.

That's about it for now.  Have fun!