[Spring] 15 - Spring MVC Handler Mapping

TOPIC

• Available HandlerMapping Strategories
• Chaining HandlerMappings
• Handler Method Mapping Techniques
• Resolving Handler Exceptions
• Attaching Handle Interceptors
  

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• Available Handler Mapping Strategies

• BeanNameUrlHandlerMapping

• SimpleUrlHandlerMapping

* Notes:

• Single component that has all of our mapping explicitly declared
• Mapping table to map all mapping cases.

• Controller-ClassNameHandlerMapping

• You can also define your own

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• Chaining HandlerMappings
• Multiple HandlerMapping strategies can be configured
• For example, Simple, ControllerClass, BeanName
• The DispatcherServlet will iterate (~iterate: looping to run) through them until a handler is found for the request
• The iteration order can be configured

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• Handler Method Mapping Technique
• Best practice often makes a single handler responsible for several related actions.
• Especially for create-read-update-delete(CRUD) action
• For example
• A RewardController might create, show, update, and delete rewards.
• Such multi-action handlers are typically mapped using wildcards
• /reward/* or /reward/**
• A common URL form is ${handler}/${action} like 
• /reward/new
• /reward/show
• /reward/update
• /reward/delete
• The handler typically maps the requested ${action} to a method on itself

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• Multi Action Handlers with Spring MVC
• To implement a multi-action handler in Spring MVC
• Subclass MultiActionController
• Configure the action method mapping strategy if desired
• Implement your action methods
• Register the Controller with the DispatcherServlet

* Notes:
MultiActionController is a standard MVC controller, and the RewardController is a subclass which extends the superclass MultiActionController
All of these methods are exactly the same as what you think inside of them, and they serve a certain set of URLs

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• MethodNameResolver Strategies
• InternalPathMethodNameResolver(default)
• As shown in previous example
• Also provides configurable prefix and suffix
• ParameterMethodNameResolver
• Resolves parameter value (or name) to method
• PropertiesMethodNameResolver
• Allows for externalized mappings
• Supports wildcards
• or implement your own custom strategy

• Custom Action Method Mapping Example
• Suppose the following action method mappings are desired
• GET /controller/new --> newForm
• POST / controller/new -->create
• GET / contorller/show/{id} --> show
• To apply custom method mappings, configure a custom MethodNameResolver on your MultiActionController

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• Resolving Handler Exceptions
• By default exceptions thrown by handlers propagate
• The user will see a stack trace in their browser
• Resolve exceptions to error views by registering a HandlerExceptonResolver with the DispatchServlet

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• Attaching Handler Interceptors
• Specific groups of handlers can have their execution intercepted
• Allows for applying pre and post-processing aspects
• Especially useful for
• Authorization checks
• Centralized handling of application exceptions
• Factoring out common handler code

• Implementing a HandlerInterceptor
• Implement the HandlerInterceptor interface
• Consider extending from HandlerInteceptorAdapter and overriding the callbacks you need
• Register your interceptor with the HandlerMapping for the handlers you wish to intercept

• HandlerInterceptor vs. Filters
• Both are "interceptors"
• Handler Interceptors are finer-grained
• Filters intercept Servlets
• Handler Interceptors are best suited for factoring out common handler code
• Filters are best suited for more general processing
• Handler Interceptors are managed by Spring
• Filters are managed by the Servlet container

• DelegatingFilterProxy
• DelegatingFilterProxy is a Servlet Filter which delegates to a Filter managed by Spring
• Allows a Filter to benefit from dependency injection
• How to use
• Define the "real" Filter as a Spring bean
• Define Spring's DelegatingFilterProxy in web.xml
• Have it reference your Filter bean by its name

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• Summary

• Spring MVC supports several ways to map requests to Handlers
• Bean Name, Explicit (Simple), Convention-based
• Use MultiActionController to have a single handler centralize several related actions
• An AccountController to create, edit, delete and sow accounts
• Use a HandlerExceptionResolver to map application exceptions to error views
• Use HandlerInterceptors and Filters to intercept request processing and factor out common handler code