The default handler is still a very simple Controller interface, offering just two methods:

The framework also includes most of the same controller implementation hierarchy, such as AbstractController, SimpleFormController, and so on. Data binding, command object usage, model handling, and view resolution are all the same as in the servlet framework.

All the view rendering capabilities of the servlet framework are used directly via a special bridge servlet named ViewRendererServlet. By using this servlet, the portlet request is converted into a servlet request and the view can be rendered using the entire normal servlet infrastructure. This means all the existing renderers, such as JSP, Velocity, etc., can still be used within the portlet.

Spring Portlet MVC supports beans whose lifecycle is scoped to the current HTTP request or HTTP Session (both normal and global). This is not a specific feature of Spring Portlet MVC itself, but rather of the WebApplicationContext container(s) that Spring Portlet MVC uses. These bean scopes are described in detail in the section entitled Section 3.4.4, “The other scopes”

Of course, just a Controller interface isn't enough. To provide a basic infrastructure, all of Spring Portlet MVC's Controllers inherit from AbstractController, a class offering access to Spring's ApplicationContext and control over caching.

The requireSession and cacheSeconds properties are declared on the PortletContentGenerator class, which is the superclass of AbstractController) but are included here for completeness.

When using the AbstractController as a baseclass for your controllers (which is not recommended since there are a lot of other controllers that might already do the job for you) you only have to override either the handleActionRequestInternal(ActionRequest, ActionResponse) method or the handleRenderRequestInternal(RenderRequest, RenderResponse) method (or both), implement your logic, and return a ModelAndView object (in the case of handleRenderRequestInternal).

The default implementations of both handleActionRequestInternal(..) and handleRenderRequestInternal(..) throw a PortletException. This is consistent with the behavior of GenericPortlet from the JSR- 168 Specification API. So you only need to override the method that your controller is intended to handle.

Here is short example consisting of a class and a declaration in the web application context.

package samples;

import javax.portlet.RenderRequest;
import javax.portlet.RenderResponse;

import org.springframework.web.portlet.mvc.AbstractController;
import org.springframework.web.portlet.ModelAndView;

public class SampleController extends AbstractController {

    public ModelAndView handleRenderRequestInternal(RenderRequest request, RenderResponse response) {
        ModelAndView mav = new ModelAndView("foo");
        mav.addObject("message", "Hello World!");
        return mav;
    }
}

<bean id="sampleController" class="samples.SampleController">
    <property name="cacheSeconds" value="120"/>
</bean>

The class above and the declaration in the web application context is all you need besides setting up a handler mapping (see Section 16.5, “Handler mappings”) to get this very simple controller working.

Although you can extend AbstractController, Spring Portlet MVC provides a number of concrete implementations which offer functionality that is commonly used in simple MVC applications.

The ParameterizableViewController is basically the same as the example above, except for the fact that you can specify the view name that it will return in the web application context (no need to hard-code the view name).

The PortletModeNameViewController uses the current mode of the portlet as the view name. So, if your portlet is in View mode (i.e. PortletMode.VIEW) then it uses "view" as the view name.

Spring Portlet MVC has the exact same hierarchy of command controllers as Spring Web MVC. They provide a way to interact with data objects and dynamically bind parameters from the PortletRequest to the data object specified. Your data objects don't have to implement a framework-specific interface, so you can directly manipulate your persistent objects if you desire. Let's examine what command controllers are available, to get an overview of what you can do with them:

These command controllers are quite powerful, but they do require a detailed understanding of how they operate in order to use them efficiently. Carefully review the Javadocs for this entire hierarchy and then look at some sample implementations before you start using them.

Instead of developing new controllers, it is possible to use existing portlets and map requests to them from a DispatcherPortlet. Using the PortletWrappingController, you can instantiate an existing Portlet as a Controller as follows:

<bean id="myPortlet" class="org.springframework.web.portlet.mvc.PortletWrappingController">
    <property name="portletClass" value="sample.MyPortlet"/>
    <property name="portletName" value="my-portlet"/>
    <property name="initParameters">
        <value>config=/WEB-INF/my-portlet-config.xml</value>
    </property>
</bean>

This can be very valuable since you can then use interceptors to pre-process and post-process requests going to these portlets. Since JSR-168 does not support any kind of filter mechanism, this is quite handy. For example, this can be used to wrap the Hibernate OpenSessionInViewInterceptor around a MyFaces JSF Portlet.

This is a simple handler mapping that maps incoming requests based on the current mode of the portlet (e.g. ‘view’, ‘edit’, ‘help’). An example:

<bean class="org.springframework.web.portlet.handler.PortletModeHandlerMapping">
    <property name="portletModeMap">
        <map>
            <entry key="view" value-ref="viewHandler"/>
            <entry key="edit" value-ref="editHandler"/>
            <entry key="help" value-ref="helpHandler"/>
        </map>
    </property>
</bean>

If we need to navigate around to multiple controllers without changing portlet mode, the simplest way to do this is with a request parameter that is used as the key to control the mapping.

ParameterHandlerMapping uses the value of a specific request parameter to control the mapping. The default name of the parameter is 'action', but can be changed using the 'parameterName' property.

The bean configuration for this mapping will look something like this:

<bean class="org.springframework.web.portlet.handler.ParameterHandlerMapping”>
    <property name="parameterMap">
        <map>
            <entry key="add" value-ref="addItemHandler"/>
            <entry key="edit" value-ref="editItemHandler"/>
            <entry key="delete" value-ref="deleteItemHandler"/>
        </map>
    </property>
</bean>

The most powerful built-in handler mapping, PortletModeParameterHandlerMapping combines the capabilities of the two previous ones to allow different navigation within each portlet mode.

Again the default name of the parameter is "action", but can be changed using the parameterName property.

By default, the same parameter value may not be used in two different portlet modes. This is so that if the portal itself changes the portlet mode, the request will no longer be valid in the mapping. This behavior can be changed by setting the allowDupParameters property to true. However, this is not recommended.

The bean configuration for this mapping will look something like this:

<bean class="org.springframework.web.portlet.handler.PortletModeParameterHandlerMapping">
    <property name="portletModeParameterMap">
        <map>
            <entry key="view"> <!-- 'view' portlet mode -->
                <map>
                    <entry key="add" value-ref="addItemHandler"/>
                    <entry key="edit" value-ref="editItemHandler"/>
                    <entry key="delete" value-ref="deleteItemHandler"/>
                </map>
            </entry>
            <entry key="edit"> <!-- 'edit' portlet mode -->
                <map>
                    <entry key="prefs" value-ref="prefsHandler"/>
                    <entry key="resetPrefs" value-ref="resetPrefsHandler"/>
                </map>
            </entry>
        </map>
    </property>
</bean>

This mapping can be chained ahead of a PortletModeHandlerMapping, which can then provide defaults for each mode and an overall default as well.

Spring's handler mapping mechanism has a notion of handler interceptors, which can be extremely useful when you want to apply specific functionality to certain requests, for example, checking for a principal. Again Spring Portlet MVC implements these concepts in the same way as Web MVC.

Interceptors located in the handler mapping must implement HandlerInterceptor from the org.springframework.web.portlet package. Just like the servlet version, this interface defines three methods: one that will be called before the actual handler will be executed (preHandle), one that will be called after the handler is executed (postHandle), and one that is called after the complete request has finished (afterCompletion). These three methods should provide enough flexibility to do all kinds of pre- and post- processing.

The preHandle method returns a boolean value. You can use this method to break or continue the processing of the execution chain. When this method returns true, the handler execution chain will continue. When it returns false, the DispatcherPortlet assumes the interceptor itself has taken care of requests (and, for example, rendered an appropriate view) and does not continue executing the other interceptors and the actual handler in the execution chain.

The postHandle method is only called on a RenderRequest. The preHandle and afterCompletion methods are called on both an ActionRequest and a RenderRequest. If you need to execute logic in these methods for just one type of request, be sure to check what kind of request it is before processing it.

As with the servlet package, the portlet package has a concrete implementation of HandlerInterceptor called HandlerInterceptorAdapter. This class has empty versions of all the methods so that you can inherit from this class and implement just one or two methods when that is all you need.

The portlet package also has a concrete interceptor named ParameterMappingInterceptor that is meant to be used directly with ParameterHandlerMapping and PortletModeParameterHandlerMapping. This interceptor will cause the parameter that is being used to control the mapping to be forwarded from an ActionRequest to the subsequent RenderRequest. This will help ensure that the RenderRequest is mapped to the same Handler as the ActionRequest. This is done in the preHandle method of the interceptor, so you can still modify the parameter value in your handler to change where the RenderRequest will be mapped.

Be aware that this interceptor is calling setRenderParameter on the ActionResponse, which means that you cannot call sendRedirect in your handler when using this interceptor. If you need to do external redirects then you will either need to forward the mapping parameter manually or write a different interceptor to handle this for you.

The following example shows how to use the CommonsPortletMultipartResolver:

<bean id="portletMultipartResolver"
        class="org.springframework.web.portlet.multipart.CommonsPortletMultipartResolver">

    <!-- one of the properties available; the maximum file size in bytes -->
    <property name="maxUploadSize" value="100000"/>
</bean>

Of course you also need to put the appropriate jars in your classpath for the multipart resolver to work. In the case of the CommonsMultipartResolver, you need to use commons-fileupload.jar. Be sure to use at least version 1.1 of Commons FileUpload as previous versions do not support JSR-168 Portlet applications.

Now that you have seen how to set Portlet MVC up to handle multipart requests, let's talk about how to actually use it. When DispatcherPortlet detects a multipart request, it activates the resolver that has been declared in your context and hands over the request. What the resolver then does is wrap the current ActionRequest into a MultipartActionRequest that has support for multipart file uploads. Using the MultipartActionRequest you can get information about the multiparts contained by this request and actually get access to the multipart files themselves in your controllers.

Note that you can only receive multipart file uploads as part of an ActionRequest, not as part of a RenderRequest.

After the PortletMultipartResolver has finished doing its job, the request will be processed like any other. To use it, you create a form with an upload field (see immediately below), then let Spring bind the file onto your form (backing object). To actually let the user upload a file, we have to create a (JSP/HTML) form:

<h1>Please upload a file</h1>
<form method="post" action="<portlet:actionURL/>" enctype="multipart/form-data">
    <input type="file" name="file"/>
    <input type="submit"/>
</form>

As you can see, we've created a field named “file” after the property of the bean that holds the byte[]. Furthermore we've added the encoding attribute (enctype="multipart/form-data"), which is necessary to let the browser know how to encode the multipart fields (do not forget this!).

Just as with any other property that's not automagically convertible to a string or primitive type, to be able to put binary data in your objects you have to register a custom editor with the PortletRequestDataBinder. There are a couple of editors available for handling files and setting the results on an object. There's a StringMultipartFileEditor capable of converting files to Strings (using a user-defined character set) and there is a ByteArrayMultipartFileEditor which converts files to byte arrays. They function just as the CustomDateEditor does.

So, to be able to upload files using a form, declare the resolver, a mapping to a controller that will process the bean, and the controller itself.

<bean id="portletMultipartResolver"
        class="org.springframework.web.portlet.multipart.CommonsPortletMultipartResolver"/>

<bean class="org.springframework.web.portlet.handler.PortletModeHandlerMapping">
    <property name="portletModeMap">
        <map>
            <entry key="view" value-ref="fileUploadController"/>
        </map>
    </property>
</bean>

<bean id="fileUploadController" class="examples.FileUploadController">
    <property name="commandClass" value="examples.FileUploadBean"/>
    <property name="formView" value="fileuploadform"/>
    <property name="successView" value="confirmation"/>
</bean>

After that, create the controller and the actual class to hold the file property.

public class FileUploadController extends SimpleFormController {

    public void onSubmitAction(ActionRequest request, ActionResponse response,
            Object command, BindException errors) throws Exception {

        // cast the bean
        FileUploadBean bean = (FileUploadBean) command;

        // let's see if there's content there
        byte[] file = bean.getFile();
        if (file == null) {
            // hmm, that's strange, the user did not upload anything
        }

        // do something with the file here
    }

    protected void initBinder(
            PortletRequest request, PortletRequestDataBinder binder) throws Exception {
        // to actually be able to convert Multipart instance to byte[]
        // we have to register a custom editor
        binder.registerCustomEditor(byte[].class, new ByteArrayMultipartFileEditor());
        // now Spring knows how to handle multipart object and convert
    }
}

public class FileUploadBean {

    private byte[] file;

    public void setFile(byte[] file) {
        this.file = file;
    }

    public byte[] getFile() {
        return file;
    }
}

As you can see, the FileUploadBean has a property typed byte[] that holds the file. The controller registers a custom editor to let Spring know how to actually convert the multipart objects the resolver has found to properties specified by the bean. In this example, nothing is done with the byte[] property of the bean itself, but in practice you can do whatever you want (save it in a database, mail it to somebody, etc).

An equivalent example in which a file is bound straight to a String-typed property on a (form backing) object might look like this:

public class FileUploadController extends SimpleFormController {

    public void onSubmitAction(ActionRequest request, ActionResponse response,
            Object command, BindException errors) throws Exception {

        // cast the bean
        FileUploadBean bean = (FileUploadBean) command;

        // let's see if there's content there
        String file = bean.getFile();
        if (file == null) {
            // hmm, that's strange, the user did not upload anything
        }

        // do something with the file here
    }

    protected void initBinder(
        PortletRequest request, PortletRequestDataBinder binder) throws Exception {

        // to actually be able to convert Multipart instance to a String
        // we have to register a custom editor
        binder.registerCustomEditor(String.class,
            new StringMultipartFileEditor());
        // now Spring knows how to handle multipart objects and convert
    }
}

public class FileUploadBean {

    private String file;

    public void setFile(String file) {
        this.file = file;
    }

    public String getFile() {
        return file;
    }
}

Of course, this last example only makes (logical) sense in the context of uploading a plain text file (it wouldn't work so well in the case of uploading an image file).

The third (and final) option is where one binds directly to a MultipartFile property declared on the (form backing) object's class. In this case one does not need to register any custom property editor because there is no type conversion to be performed.

public class FileUploadController extends SimpleFormController {

    public void onSubmitAction(ActionRequest request, ActionResponse response,
            Object command, BindException errors) throws Exception {

        // cast the bean
        FileUploadBean bean = (FileUploadBean) command;

        // let's see if there's content there
        MultipartFile file = bean.getFile();
        if (file == null) {
            // hmm, that's strange, the user did not upload anything
        }

        // do something with the file here
    }
}

public class FileUploadBean {

    private MultipartFile file;

    public void setFile(MultipartFile file) {
        this.file = file;
    }

    public MultipartFile getFile() {
        return file;
    }
}

@RequestMapping will only be processed if a corresponding HandlerMapping (for type level annotations) and/or HandlerAdapter (for method level annotations) is present in the dispatcher. This is the case by default in both DispatcherServlet and DispatcherPortlet.

However, if you are defining custom HandlerMappings or HandlerAdapters, then you need to make sure that a corresponding custom DefaultAnnotationHandlerMapping and/or AnnotationMethodHandlerAdapter is defined as well - provided that you intend to use @RequestMapping.

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">

    <bean class="org.springframework.web.portlet.mvc.annotation.DefaultAnnotationHandlerMapping"/>

    <bean class="org.springframework.web.portlet.mvc.annotation.AnnotationMethodHandlerAdapter"/>

    // ... (controller bean definitions) ...

</beans>

Defining a DefaultAnnotationHandlerMapping and/or AnnotationMethodHandlerAdapter explicitly also makes sense if you would like to customize the mapping strategy, e.g. specifying a custom WebBindingInitializer (see below).

The @Controller annotation indicates that a particular class serves the role of a controller. There is no need to extend any controller base class or reference the Portlet API. You are of course still able to reference Portlet-specific features if you need to.

The basic purpose of the @Controller annotation is to act as a stereotype for the annotated class, indicating its role. The dispatcher will scan such annotated classes for mapped methods, detecting @RequestMapping annotations (see the next section).

Annotated controller beans may be defined explicitly, using a standard Spring bean definition in the dispatcher's context. However, the @Controller stereotype also allows for autodetection, aligned with Spring 2.5's general support for detecting component classes in the classpath and auto-registering bean definitions for them.

To enable autodetection of such annotated controllers, you have to add component scanning to your configuration. This is easily achieved by using the spring-context schema as shown in the following XML snippet:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:p="http://www.springframework.org/schema/p"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context-2.5.xsd">

    <context:component-scan base-package="org.springframework.samples.petportal.portlet"/>

    // ...

</beans>

The @RequestMapping annotation is used to map portlet modes like 'VIEW'/'EDIT' onto an entire class or a particular handler method. Typically the type-level annotation maps a specific mode (or mode plus parameter condition) onto a form controller, with additional method-level annotations 'narrowing' the primary mapping for specific portlet request parameters.

Tip

@RequestMapping at the type level may be used for plain implementations of the Controller interface as well. In this case, the request processing code would follow the traditional handle(Action|Render)Request signature, while the controller's mapping would be expressed through an @RequestMapping annotation. This works for pre-built Controller base classes, such as SimpleFormController, too. In the following discussion, we'll focus on controllers that are based on annotated handler methods.

The following is an example of a form controller from the PetPortal sample application using this annotation:

@Controller
@RequestMapping("EDIT")
@SessionAttributes("site")
public class PetSitesEditController {

    private Properties petSites;

    public void setPetSites(Properties petSites) {
        this.petSites = petSites;
    }

    @ModelAttribute("petSites")
    public Properties getPetSites() {
        return this.petSites;
    }

    @RequestMapping  // default (action=list)
    public String showPetSites() {
        return "petSitesEdit";
    }

    @RequestMapping(params = "action=add")  // render phase
    public String showSiteForm(Model model) {
        // Used for the initial form as well as for redisplaying with errors.
        if (!model.containsAttribute("site")) {
            model.addAttribute("site", new PetSite());
        }
        return "petSitesAdd";
    }

    @RequestMapping(params = "action=add")  // action phase
    public void populateSite(
            @ModelAttribute("site") PetSite petSite, BindingResult result,
            SessionStatus status, ActionResponse response) {

        new PetSiteValidator().validate(petSite, result);
        if (!result.hasErrors()) {
            this.petSites.put(petSite.getName(), petSite.getUrl());
            status.setComplete();
            response.setRenderParameter("action", "list");
        }
    }

    @RequestMapping(params = "action=delete")
    public void removeSite(@RequestParam("site") String site, ActionResponse response) {
        this.petSites.remove(site);
        response.setRenderParameter("action", "list");
    }
}

Handler methods which are annotated with @RequestMapping are allowed to have very flexible signatures. They may have arguments of the following types, in arbitrary order (except for validation results, which need to follow right after the corresponding command object, if desired):

The following return types are supported for handler methods:

The @RequestParam annotation is used to bind request parameters to a method parameter in your controller.

The following code snippet from the PetPortal sample application shows the usage:

@Controller
@RequestMapping("EDIT")
@SessionAttributes("site")
public class PetSitesEditController {

    // ...

    public void removeSite(@RequestParam("site") String site, ActionResponse response) {
        this.petSites.remove(site);
        response.setRenderParameter("action", "list");
    }

    // ...
}

Parameters using this annotation are required by default, but you can specify that a parameter is optional by setting @RequestParam's required attribute to false (e.g., @RequestParam(value="id", required="false")).

@ModelAttribute has two usage scenarios in controllers. When placed on a method parameter, @ModelAttribute is used to map a model attribute to the specific, annotated method parameter (see the processSubmit() method below). This is how the controller gets a reference to the object holding the data entered in the form. In addition, the parameter can be declared as the specific type of the form backing object rather than as a generic java.lang.Object, thus increasing type safety.

@ModelAttribute is also used at the method level to provide reference data for the model (see the populatePetTypes() method below). For this usage the method signature can contain the same types as documented above for the @RequestMapping annotation.

Note: @ModelAttribute annotated methods will be executed before the chosen @RequestMapping annotated handler method. They effectively pre-populate the implicit model with specific attributes, often loaded from a database. Such an attribute can then already be accessed through @ModelAttribute annotated handler method parameters in the chosen handler method, potentially with binding and validation applied to it.

The following code snippet shows these two usages of this annotation:

@Controller
@RequestMapping("EDIT")
@SessionAttributes("site")
public class PetSitesEditController {

    // ...

    @ModelAttribute("petSites")
    public Properties getPetSites() {
        return this.petSites;
    }

    @RequestMapping(params = "action=add")  // action phase
    public void populateSite(
            @ModelAttribute("site") PetSite petSite, BindingResult result,
            SessionStatus status, ActionResponse response) {

        new PetSiteValidator().validate(petSite, result);
        if (!result.hasErrors()) {
            this.petSites.put(petSite.getName(), petSite.getUrl());
            status.setComplete();
            response.setRenderParameter("action", "list");
        }
    }
}

The type-level @SessionAttributes annotation declares session attributes used by a specific handler. This will typically list the names of model attributes which should be transparently stored in the session or some conversational storage, serving as form-backing beans between subsequent requests.

The following code snippet shows the usage of this annotation:

@Controller
@RequestMapping("EDIT")
@SessionAttributes("site")
public class PetSitesEditController {
  // ...
}

To customize request parameter binding with PropertyEditors, etc. via Spring's WebDataBinder, you can either use @InitBinder-annotated methods within your controller or externalize your configuration by providing a custom WebBindingInitializer.

@Controller
public class MyFormController {

    @InitBinder
    public void initBinder(WebDataBinder binder) {
        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
        dateFormat.setLenient(false);
        binder.registerCustomEditor(Date.class, new CustomDateEditor(dateFormat, false));
    }

    // ...
}