Package org.apache.struts.action

Class ActionServlet

java.lang.Object
jakarta.servlet.GenericServlet
jakarta.servlet.http.HttpServlet
org.apache.struts.action.ActionServlet
All Implemented Interfaces:
Servlet, ServletConfig, Serializable
Direct Known Subclasses:
RedeployableActionServlet
public class ActionServlet extends HttpServlet

ActionServlet provides the "controller" in the Model-View-Controller (MVC) design pattern for web applications that is commonly known as "Model 2". This nomenclature originated with a description in the JavaServerPages Specification, version 0.92, and has persisted ever since (in the absence of a better name).

Generally, a "Model 2" application is architected as follows:

  • The user interface will generally be created with server pages, which will not themselves contain any business logic. These pages represent the "view" component of an MVC architecture.
  • Forms and hyperlinks in the user interface that require business logic to be executed will be submitted to a request URI that is mapped to this servlet.
  • There can be one instance of this servlet class, which receives and processes all requests that change the state of a user's interaction with the application. The servlet delegates the handling of a request to a RequestProcessor object. This component represents the "controller" component of an MVC architecture.
  • The RequestProcessor selects and invokes an Action class to perform the requested business logic, or delegates the response to another resource.
  • The Action classes can manipulate the state of the application's interaction with the user, typically by creating or modifying JavaBeans that are stored as request or session attributes (depending on how long they need to be available). Such JavaBeans represent the "model" component of an MVC architecture.
  • Instead of producing the next page of the user interface directly, Action classes generally return an ActionForward to indicate which resource should handle the response. If the Action does not return null, the RequestProcessor forwards or redirects to the specified resource (by utilizing RequestDispatcher.forward or Response.sendRedirect) so as to produce the next page of the user interface.

The standard version of RequestsProcessor implements the following logic for each incoming HTTP request. You can override some or all of this functionality by subclassing this object and implementing your own version of the processing.

  • Identify, from the incoming request URI, the substring that will be used to select an action procedure.
  • Use this substring to map to the Java class name of the corresponding action class (an implementation of the Action interface).
  • If this is the first request for a particular Action class, instantiate an instance of that class and cache it for future use.
  • Optionally populate the properties of an ActionForm bean associated with this mapping.
  • Call the execute method of this Action class, passing on a reference to the mapping that was used, the relevant form-bean (if any), and the request and the response that were passed to the controller by the servlet container (thereby providing access to any specialized properties of the mapping itself as well as to the ServletContext).

The standard version of ActionServlet is configured based on the following servlet initialization parameters, which you will specify in the web application deployment descriptor (/WEB-INF/web.xml) for your application. Subclasses that specialize this servlet are free to define additional initialization parameters.

  • config - Comma-separated list of context-relative path(s) to the XML resource(s) containing the configuration information for the default module. (Multiple files support since Struts 1.1) [/WEB-INF/struts-config.xml].
  • config/${module} - Comma-separated list of Context-relative path(s) to the XML resource(s) containing the configuration information for the module that will use the specified prefix (/${module}). This can be repeated as many times as required for multiple modules. (Since Struts 1.1)
  • configFactory - The Java class name of the ModuleConfigFactory used to create the implementation of the ModuleConfig interface.
  • convertNull - Force simulation of the Struts 1.0 behavior when populating forms. If set to true, the numeric Java wrapper class types (like java.lang.Integer) will default to null (rather than 0). (Since Struts 1.1) [false]
  • rulesets - Comma-delimited list of fully qualified classnames of additional org.apache.commons.digester3.RuleSet instances that should be added to the Digester that will be processing struts-config.xml files. By default, only the RuleSet for the standard configuration elements is loaded. (Since Struts 1.1)
  • validating - Should we use a validating XML parser to process the configuration file (strongly recommended)? [true]
  • chainConfig - Comma-separated list of either context-relative or classloader path(s) to load commons-chain catalog definitions from. If none specified, the default Struts catalog that is provided with Struts will be used.
Version:
$Rev$ $Date: 2005-10-14 19:54:16 -0400 (Fri, 14 Oct 2005) $
See Also:

  • Field Details

    • config

      protected String config

      Comma-separated list of context-relative path(s) to our configuration resource(s) for the default module.

    • chainConfig

      protected String chainConfig

      Comma-separated list of context or classloader-relative path(s) that contain the configuration for the default commons-chain catalog(s).

    • configDigester

      protected org.apache.commons.digester.Digester configDigester

      The Digester used to produce ModuleConfig objects from a Struts configuration file.

      Since:
      Struts 1.1

    • convertNull

      protected boolean convertNull

      The flag to request backwards-compatible conversions for form bean properties of the Java wrapper class types.

      Since:
      Struts 1.1

    • internal

      protected MessageResources internal

      The resources object for our internal resources.

    • internalName

      protected String internalName

      The Java base name of our internal resources.

      Since:
      Struts 1.1

    • registrations

      protected String[] registrations

      The set of public identifiers, and corresponding resource names, for the versions of the configuration file DTDs that we know about. There MUST be an even number of Strings in this list!

    • servletMapping

      protected String servletMapping

      The URL pattern to which we are mapped in our web application deployment descriptor.

    • servletName

      protected String servletName

      The servlet name under which we are registered in our web application deployment descriptor.

  • Constructor Details

    • ActionServlet

      public ActionServlet()

  • Method Details

    • destroy

      public void destroy()

      Gracefully shut down this controller servlet, releasing any resources that were allocated at initialization.

      Specified by:
      destroy in interface Servlet
      Overrides:
      destroy in class GenericServlet

    • init

      public void init() throws ServletException

      Initialize this servlet. Most of the processing has been factored into support methods so that you can override particular functionality at a fairly granular level.

      Overrides:
      init in class GenericServlet
      Throws:
      ServletException - if we cannot configure ourselves correctly

    • initModulePrefixes

      protected void initModulePrefixes(ServletContext context)

      Saves a String[] of module prefixes in the ServletContext under Globals.MODULE_PREFIXES_KEY. NOTE - the "" prefix for the default module is not included in this list.

      Parameters:
      context - The servlet context.
      Since:
      Struts 1.2

    • doGet

      public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException

      Process an HTTP "GET" request.

      Overrides:
      doGet in class HttpServlet
      Parameters:
      request - The servlet request we are processing
      response - The servlet response we are creating
      Throws:
      IOException - if an input/output error occurs
      ServletException - if a servlet exception occurs

    • doPost

      public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException

      Process an HTTP "POST" request.

      Overrides:
      doPost in class HttpServlet
      Parameters:
      request - The servlet request we are processing
      response - The servlet response we are creating
      Throws:
      IOException - if an input/output error occurs
      ServletException - if a servlet exception occurs

    • addServletMapping

      public void addServletMapping(String servletName, String urlPattern)

      Remember a servlet mapping from our web application deployment descriptor, if it is for this servlet.

      Parameters:
      servletName - The name of the servlet being mapped
      urlPattern - The URL pattern to which this servlet is mapped

    • getInternal

      public MessageResources getInternal()

      Return the MessageResources instance containing our internal message strings.

      Returns:
      the MessageResources instance containing our internal message strings.
      Since:
      Struts 1.1

    • destroyModules

      protected void destroyModules()

      Gracefully terminate use of any modules associated with this application (if any).

      Since:
      Struts 1.1

    • destroyConfigDigester

      protected void destroyConfigDigester()

      Gracefully release any configDigester instance that we have created.

      Since:
      Struts 1.1

    • destroyInternal

      protected void destroyInternal()

      Gracefully terminate use of the internal MessageResources.

    • getModuleConfig

      protected ModuleConfig getModuleConfig(HttpServletRequest request)

      Return the module configuration object for the currently selected module.

      Parameters:
      request - The servlet request we are processing
      Returns:
      The module configuration object for the currently selected module.
      Since:
      Struts 1.1

    • getRequestProcessor

      protected RequestProcessor getRequestProcessor(ModuleConfig config) throws ServletException

      Look up and return the RequestProcessor responsible for the specified module, creating a new one if necessary.

      Parameters:
      config - The module configuration for which to acquire and return a RequestProcessor.
      Returns:
      The RequestProcessor responsible for the specified module,
      Throws:
      ServletException - If we cannot instantiate a RequestProcessor instance a UnavailableException is thrown, meaning your application is not loaded and will not be available.
      Since:
      Struts 1.1

    • initModuleConfigFactory

      protected void initModuleConfigFactory()

      Initialize the factory used to create the module configuration.

      Since:
      Struts 1.2

    • initModuleConfig

      protected ModuleConfig initModuleConfig(String prefix, String paths) throws ServletException

      Initialize the module configuration information for the specified module.

      Parameters:
      prefix - Module prefix for this module
      paths - Comma-separated list of context-relative resource path(s) for this modules's configuration resource(s)
      Returns:
      The new module configuration instance.
      Throws:
      ServletException - if initialization cannot be performed
      Since:
      Struts 1.1

    • parseModuleConfigFile

      @Deprecated protected void parseModuleConfigFile(org.apache.commons.digester.Digester digester, String path) throws UnavailableException
      Deprecated.
      use parseModuleConfigFile(Digester digester, URL url) instead

      Parses one module config file.

      Parameters:
      digester - Digester instance that does the parsing
      path - The path to the config file to parse.
      Throws:
      UnavailableException - if file cannot be read or parsed
      Since:
      Struts 1.2

    • parseModuleConfigFile

      protected void parseModuleConfigFile(org.apache.commons.digester.Digester digester, URL url) throws UnavailableException

      Parses one module config file.

      Parameters:
      digester - Digester instance that does the parsing
      url - The url to the config file to parse.
      Throws:
      UnavailableException - if file cannot be read or parsed
      Since:
      Struts 1.3

    • initModulePlugIns

      protected void initModulePlugIns(ModuleConfig config) throws ServletException

      Initialize the plug ins for the specified module.

      Parameters:
      config - ModuleConfig information for this module
      Throws:
      ServletException - if initialization cannot be performed
      Since:
      Struts 1.1

    • initModuleFormBeans

      protected void initModuleFormBeans(ModuleConfig config) throws ServletException

      Initialize the form beans for the specified module.

      Parameters:
      config - ModuleConfig information for this module
      Throws:
      ServletException - if initialization cannot be performed
      Since:
      Struts 1.3

    • processFormBeanExtension

      protected void processFormBeanExtension(FormBeanConfig beanConfig, ModuleConfig moduleConfig) throws ServletException

      Extend the form bean's configuration as necessary.

      Parameters:
      beanConfig - the configuration to process.
      moduleConfig - the module configuration for this module.
      Throws:
      ServletException - if initialization cannot be performed.

    • processFormBeanConfigClass

      protected FormBeanConfig processFormBeanConfigClass(FormBeanConfig beanConfig, ModuleConfig moduleConfig) throws ServletException

      Checks if the current beanConfig is using the correct class based on the class of its ancestor form bean config.

      Parameters:
      beanConfig - The form bean to check.
      moduleConfig - The config for the current module.
      Returns:
      The form bean config using the correct class as determined by the config's ancestor and its own overridden value.
      Throws:
      UnavailableException - if an instance of the form bean config class cannot be created.
      ServletException - on class creation error

    • initModuleForwards

      protected void initModuleForwards(ModuleConfig config) throws ServletException

      Initialize the forwards for the specified module.

      Parameters:
      config - ModuleConfig information for this module
      Throws:
      ServletException - if initialization cannot be performed

    • processForwardExtension

      protected void processForwardExtension(ForwardConfig forwardConfig, ModuleConfig moduleConfig, ActionConfig actionConfig) throws ServletException

      Extend the forward's configuration as necessary. If actionConfig is provided, then this method will process the forwardConfig as part of that actionConfig. If actionConfig is null, the forwardConfig will be processed as a global forward.

      Parameters:
      forwardConfig - the configuration to process.
      moduleConfig - the module configuration for this module.
      actionConfig - If applicable, the config for the current action.
      Throws:
      ServletException - if initialization cannot be performed.

    • processForwardConfigClass

      protected ForwardConfig processForwardConfigClass(ForwardConfig forwardConfig, ModuleConfig moduleConfig, ActionConfig actionConfig) throws ServletException

      Checks if the current forwardConfig is using the correct class based on the class of its configuration ancestor. If actionConfig is provided, then this method will process the forwardConfig as part of that actionConfig. If actionConfig is null, the forwardConfig will be processed as a global forward.

      Parameters:
      forwardConfig - The forward to check.
      moduleConfig - The config for the current module.
      actionConfig - If applicable, the config for the current action.
      Returns:
      The forward config using the correct class as determined by the config's ancestor and its own overridden value.
      Throws:
      UnavailableException - if an instance of the forward config class cannot be created.
      ServletException - on class creation error

    • initModuleExceptionConfigs

      protected void initModuleExceptionConfigs(ModuleConfig config) throws ServletException

      Initialize the exception handlers for the specified module.

      Parameters:
      config - ModuleConfig information for this module
      Throws:
      ServletException - if initialization cannot be performed
      Since:
      Struts 1.3

    • processExceptionExtension

      protected void processExceptionExtension(ExceptionConfig exceptionConfig, ModuleConfig moduleConfig, ActionConfig actionConfig) throws ServletException

      Extend the exception's configuration as necessary. If actionConfig is provided, then this method will process the exceptionConfig as part of that actionConfig. If actionConfig is null, the exceptionConfig will be processed as a global forward.

      Parameters:
      exceptionConfig - the configuration to process.
      moduleConfig - the module configuration for this module.
      actionConfig - If applicable, the config for the current action.
      Throws:
      ServletException - if initialization cannot be performed.

    • processExceptionConfigClass

      protected ExceptionConfig processExceptionConfigClass(ExceptionConfig exceptionConfig, ModuleConfig moduleConfig, ActionConfig actionConfig) throws ServletException

      Checks if the current exceptionConfig is using the correct class based on the class of its configuration ancestor. If actionConfig is provided, then this method will process the exceptionConfig as part of that actionConfig. If actionConfig is null, the exceptionConfig will be processed as a global forward.

      Parameters:
      exceptionConfig - The config to check.
      moduleConfig - The config for the current module.
      actionConfig - If applicable, the config for the current action.
      Returns:
      The exception config using the correct class as determined by the config's ancestor and its own overridden value.
      Throws:
      ServletException - if an instance of the exception config class cannot be created.

    • initModuleActions

      protected void initModuleActions(ModuleConfig config) throws ServletException

      Initialize the action configs for the specified module.

      Parameters:
      config - ModuleConfig information for this module
      Throws:
      ServletException - if initialization cannot be performed
      Since:
      Struts 1.3

    • processActionConfigExtension

      protected void processActionConfigExtension(ActionConfig actionConfig, ModuleConfig moduleConfig) throws ServletException

      Extend the action's configuration as necessary.

      Parameters:
      actionConfig - the configuration to process.
      moduleConfig - the module configuration for this module.
      Throws:
      ServletException - if initialization cannot be performed.

    • processActionConfigClass

      protected ActionConfig processActionConfigClass(ActionConfig actionConfig, ModuleConfig moduleConfig) throws ServletException

      Checks if the current actionConfig is using the correct class based on the class of its ancestor ActionConfig.

      Parameters:
      actionConfig - The action config to check.
      moduleConfig - The config for the current module.
      Returns:
      The config object using the correct class as determined by the config's ancestor and its own overridden value.
      Throws:
      ServletException - if an instance of the action config class cannot be created.

    • initModuleMessageResources

      protected void initModuleMessageResources(ModuleConfig config) throws ServletException

      Initialize the application MessageResources for the specified module.

      Parameters:
      config - ModuleConfig information for this module
      Throws:
      ServletException - if initialization cannot be performed
      Since:
      Struts 1.1

    • initConfigDigester

      protected org.apache.commons.digester.Digester initConfigDigester() throws ServletException

      Create (if needed) and return a new Digester instance that has been initialized to process Struts module configuration files and configure a corresponding ModuleConfig object (which must be pushed on to the evaluation stack before parsing begins).

      Returns:
      A new configured Digester instance.
      Throws:
      ServletException - if a Digester cannot be configured
      Since:
      Struts 1.1

    • initInternal

      protected void initInternal() throws ServletException

      Initialize our internal MessageResources bundle.

      Throws:
      ServletException - if we cannot initialize these resources
      UnavailableException - if we cannot load resources

    • initChain

      protected void initChain() throws ServletException

      Parse the configuration documents specified by the chainConfig init-param to configure the default Catalog that is registered in the CatalogFactory instance for this application.

      Throws:
      ServletException - if an error occurs.

    • initOther

      protected void initOther() throws ServletException

      Initialize other global characteristics of the controller servlet.

      Throws:
      ServletException - if we cannot initialize these resources

    • initServlet

      protected void initServlet() throws ServletException

      Initialize the servlet mapping under which our controller servlet is being accessed. This will be used in the <html:form> tag to generate correct destination URLs for form submissions.

      Throws:
      ServletException - if error happens while scanning web.xml

    • splitAndResolvePaths

      protected List<URL> splitAndResolvePaths(String paths) throws ServletException

      Takes a comma-delimited string and splits it into paths, then resolves those paths using the ServletContext and appropriate ClassLoader. When loading from the classloader, multiple resources per path are supported to support, for example, multiple jars containing the same named config file.

      Parameters:
      paths - A comma-delimited string of paths
      Returns:
      A list of resolved URL's for all found resources
      Throws:
      ServletException - if a servlet exception is thrown

    • process

      protected void process(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException

      Perform the standard request processing for this request, and create the corresponding response.

      Parameters:
      request - The servlet request we are processing
      response - The servlet response we are creating
      Throws:
      IOException - if an input/output error occurs
      ServletException - if a servlet exception is thrown