EDIT

# cdmlib-remote-webapp configuration and bootstrapping

{{>toc}}

This page describes how spring mvc in `cdmlib-remote-webapp` is configured and whow the application is being bootstrapped based on this configuration.  

## Bootstrap

The bootstraping startst with the [[Cdmlib-remote-webappConfigurationAndBootstrapping#webxml|web.xml]] file in which the _main application context_ and the _DispatcherServlet context_ configured to be picked up by the application container.

In a Spring MVC web application you will typically have a **root WebApplicationContext** loaded via Spring's **ContextLoaderListener** and a **child WebApplicationContext** loaded via Spring's **DispatcherServlet**. This results in a parent-child context hierarchy where shared components and infrastructure configuration are declared in the root context and consumed in the child context by web-specific components.

Spring has support for **hierarchical bean factories**, so in the case of the spring mvc, the dispatcher servlet context is a child of the main application context:

* Main application context (beans such as data sources, jpa configuration, business services) --> [[Cdmlib-remote-webappConfigurationAndBootstrapping#applicationContextxml|/WEB-INF/applicationContext.xml]]

  * -[has child context]-> dispatcher servlet context (MVC specific configuration, components, beans) --> [[Cdmlib-remote-webappConfigurationAndBootstrapping#cdmlib-remote-servletxml|/WEB-INF/cdmlib-remote-servlet.xml]]

If the servlet context was asked for a bean called "abc" it will look in the servlet context first, if it does not find it there it will look in the parent context, which is the application context.

For very detailed explanation on this topic, see http://stackoverflow.com/questions/15818047/spring-namespace-vs-contextconfiglocation-init-parameters-in-web-xml#answer-15825207

### DispatcherServlet context

The DispatcherServlet builds the MVC context, handles all HTTP requests and delegates them to other components of the MVC architecture.

The configuration file for this context is the [[Cdmlib-remote-webappConfigurationAndBootstrapping#cdmlib-remote-servletxml|/WEB-INF/cdmlib-remote-servlet.xml]]

### main application context

The _main application context_ the the context in which the core cdm application with model, persistence and services is initialized.  

The configuration file for this context is the [[Cdmlib-remote-webappConfigurationAndBootstrapping#applicationContextxml|/WEB-INF/applicationContext.xml]]

## Java Spring configuration classes & packages

The CDM-Library has a couple of packages in which Java Spring configuration classes are located:

###  eu.etaxonomy.cdm.api.config

The package eu.etaxonomy.cdm.api.config contains spring configurations 

which are loaded automatically into the root application context.

These classes are injected into the context via component scan.

Found in:

* cdmlib/cdmlib-services

### eu.etaxonomy.cdm.opt.config

The package eu.etaxonomy.cdm.opt.config contains spring configurations 

which can be loaded into the **root WebApplicationContext** loaded via 

*Spring's ContextLoaderListener*, but which are optional.

This package must not be covered by a component scan the bean in here should be **added 

individually to the context**. 

Found in:

* cdmlib/cdmlib-remote

### eu.etaxonomy.cdm.remote.config

The package eu.etaxonomy.cdm.remote.config contains spring configurations 

which are to be loaded into the **child WebApplicationContext** loaded via 

Spring's DispatcherServlet. These classes are injected into the context via **component scan**.

Found in:

* cdmlib/cdmlib-remote-webapp

* cdmlib-remote

### eu.etaxonomy.cdm.addon.config

The package eu.etaxonomy.cdm.addon.config is an **extension point** where

addon-modules can place their Spring configuration classes. 

A component scan defined in cdmlib-remote-webapp will find them:

~~~xml

  <context:component-scan base-package="eu/etaxonomy/cdm/addon/config" />

~~~

Found in:

* cdmlib/cdmlib-remote-webapp

* cdm-vaadin

## Participating classes and configuration files

### web.xml

The file `/cdmlib-remote-webapp/src/main/webapp/WEB-INF/web.xml` contains an listener entry and the configuration of the Spring dispatcher servlet:

 **ContextLoaderListener:** 

~~~

<!-- Creates the Spring Container shared by all Servlets and Filters -->

<context-param>

  <param-name>contextConfigLocation</param-name>

  <param-value>/WEB-INF/applicationContext.xml</param-value>

</context-param>

<listener>

    <!-- loads by default /WEB-INF/applicationContext.xml but this can be overridden above -->

    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>

</listener>

~~~

Which creates the Spring Container shared by all Servlets and Filters. The ContextLoaderListener will load the main [[Cdmlib-remote-webappConfigurationAndBootstrapping#applicationContextxml|applicationContext configuration file]] `/WEB-INF/applicationContext.xml` 

 **DispatcherServlet:** 

~~~

<servlet>

    <description>CDM Remote API</description>

    <servlet-name>cdmlib-remote</servlet-name>

    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>

    <load-on-startup>1</load-on-startup>

    <!-- loads by default policy /WEB-INF/cdmlib-remote-servlet.xml  -->

</servlet>

~~~

### applicationContext.xml

The `cdmlib-remote-webapp` is configured using the [MVC Java Config](http://docs.spring.io/spring/docs/current/spring-framework-reference/htmlsingle/#mvc-config-enable) therefore the `applicationContext.xml` does not contain `<mvc:annotation-driven/>` but a `<context:annotation-config />` entry:

* **`<context:annotation-config />`** activates the annotations only on beans which have already been discovered and registered, see http://howtodoinjava.com/2014/07/19/spring-mvc-difference-between-contextannotation-config-vs-contextcomponent-scan/ for detailed explanations.

 `/WEB-INF/applicationContext.xml` 

~~~

<context:annotation-config />

~~~

### cdmlib-remote-servlet.xml

This is the configuration  of the MVC context of the cdmlib-remote servlet. It contains two parts, of which the first one lets spring find the [[Cdmlib-remote-webappConfigurationAndBootstrapping#CdmSpringMVCConfig|CdmSpringMVCConfig]] class which is the main configuration bean for the MVC context. This class defines a couple of component scans to expose further beans to the context:

~~~

<!-- 

  Initialize SpringMVCConfig and its dependency SpringSwaggerConfig.

  All further component scans are defined in this mvc configuration class 

-->

<context:component-scan base-package="eu/etaxonomy/cdm/remote/config" />

~~~

In addition to the CdmSpringMVCConfig class this component scan also covers the 

The second part in this file is a conditional entry is an import directive which is only evaluated when the JVM option `-Dspring.profiles.active=remoting` is supplied. This import causes the initialization of the HTTP Invoker based remoting services needed by the Taxonomic Editor to be able to connect to the CDM Server:

~~~

<!-- FIXME:Remoting Expose remoting services currently only for testing -->

<!-- Using Spring Beans Profile (>3.1) http://spring.io/blog/2011/02/11/spring-framework-3-1-m1-released/ 

  only valid if it is at the end of the xml file activated by the vmarg -Dspring.profiles.active=remoting -->

<beans profile="remoting">

  <import resource="classpath:/eu/etaxonomy/cdm/remoting-services.xml" />

</beans>

~~~

### CdmSpringMVCConfig

The Java configuration bean for the spring MVC context, that is it is annotated with `@Configuration` but it has not the `@EnableWebMvc` annotation, since it directly subclasses @WebMvcConfigurationSupport@. _"... An alternative more advanced option is to extend directly from this class and override methods as necessary remembering to add @Configuration to the subclass and @Bean to overridden @Bean methods. For more details see the Javadoc of @EnableWebMvc. ..."_

The reason for this is that the method `WebMvcConfigurationSupport.requestMappingHandlerMapping()` needs to be overridden in the @CdmSpringMVCConfig@. We may be able go without this method override once we no longer need CdmAntPathMatcher. which is only needed  since the controllers need absolute method level RequestMapping values in some few cases. **TODO** 

It enables swagger by the type annotation:

~~~

@EnableSwagger

~~~

and defines a couple of component scans:

~~~

@ComponentScan(basePackages = {

        "eu.etaxonomy.cdm.remote.l10n",

        "eu.etaxonomy.cdm.remote.controller",

        "eu.etaxonomy.cdm.remote.service",

        "eu.etaxonomy.cdm.remote.config"

        }

)

~~~

### CdmSwaggerConfig

This is also a spring java configuration class and thus annotated with `@Configuration`.

It provides the cdmlib-remote-webapp specific configuration for swagger.