Spring 3.2 with MVC, ContentNegotation, REST and PDF Generator

Question

Let's say, I have a REST styled controller mapping

@RequestMapping(value="users", produces = {MediaType.APPLICATION_JSON_VALUE})
public List<User> listUsers(@ReqestParams Integer offset, @ReqestParams Integer limit, @ReqestParams String query) {
    return service.loadUsers(query, offset, limit);
}

Serving JSON (or even XML) is not an issue, this is easy using ContentNegotation and MessageConverters

<bean id="contentNegotiationManager" class="org.springframework.web.accept.ContentNegotiationManagerFactoryBean">
    <property name="favorPathExtension" value="true" />
    <property name="favorParameter" value="false" />
    <property name="ignoreAcceptHeader" value="false" />
    <property name="mediaTypes" >
        <value>
            html=text/html
            json=application/json
            xml=application/xml
        </value>
    </property>
</bean>

Now, I need to add support for PDF. Naturally, I want to use (Spring) MVC + REST as much as possible. Most examples I have found implement this with an explicit definition not using REST style, e.g.

@RequestMapping(value="users", produces = {"application/pdf"})
public ModelAndView listUsersAsPdf(@ReqestParams Integer offset, @ReqestParams Integer limit, @ReqestParams String query) {
    List<User> users = listUsers(offset, limit, query); // delegated
    return new ModelAndView("pdfView", users);
}

That works, but is not very comfortable because for every alternate output (PDF, Excel, ...) I would add a request mapping.

I have already added application/pdf to the content negotation resolver; unfortunately any request with a suffix .pdf or the Accept-Header application/pdf were be responded with 406.

What is the ideal setup for a REST/MVC style pattern to integrate alternate output like PDF?

Answer 1

You can create a WEB-INF/spring/pdf-beans.xml like below.

 <bean id="listofusers" class="YourPDFBasedView"/>

And your controller method will return view name as listofusers.

@RequestMapping(value="users")
public ModelAndView listUsersAsPdf(@ReqestParams Integer offset, @ReqestParams Integer limit, @ReqestParams String query) {
    List<User> users = listUsers(offset, limit, query); // delegated
    return new ModelAndView("listofusers", users);
}

And you can use contentNegotiationViewResolver in this way:

 <bean class="org.springframework.web.servlet.view.XmlViewResolver">
            <property name="order" value="1"/>
            <property name="location" value="WEB-INF/spring/pdf-views.xml"/>
        </bean>

<!--
        View resolver that delegates to other view resolvers based on the content type
    -->
    <bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver">
       <!-- All configuration is now done by the manager - since Spring V3.2 -->
       <property name="contentNegotiationManager" ref="cnManager"/>
    </bean>

    <!--
        Setup a simple strategy:
           1. Only path extension is taken into account, Accept headers are ignored.
           2. Return HTML by default when not sure.
     -->
    <bean id="cnManager" class="org.springframework.web.accept.ContentNegotiationManagerFactoryBean">
        <property name="ignoreAcceptHeader" value="true"/>        
        <property name="defaultContentType" value="text/html" />
    </bean>

For JSON: Create a generic JSON view resolver like below and register it as bean in context file.

public class JsonViewResolver implements ViewResolver {
    /**
      * Get the view to use.
      *
      * @return Always returns an instance of {@link MappingJacksonJsonView}.
     */
    @Override
    public View resolveViewName(String viewName, Locale locale) throws Exception {
        MappingJacksonJsonView view = new MappingJacksonJsonView();
        view.setPrettyPrint(true);      // Lay the JSON out to be nicely readable 
        return view;
    }
}

Same for XML:

public class MarshallingXmlViewResolver implements ViewResolver {

    private Marshaller marshaller;

    @Autowired
    public MarshallingXmlViewResolver(Marshaller marshaller) {
        this.marshaller = marshaller;
    }

    /**
     * Get the view to use.
     * 
     * @return Always returns an instance of {@link MappingJacksonJsonView}.
     */
    @Override
    public View resolveViewName(String viewName, Locale locale)
            throws Exception {
        MarshallingView view = new MarshallingView();
        view.setMarshaller(marshaller);
        return view;
    }
}

and register above xml view resolver in context file like this:

<oxm:jaxb2-marshaller id="marshaller" >
        <oxm:class-to-be-bound name="some.package.Account"/>
        <oxm:class-to-be-bound name="some.package.Customer"/>
        <oxm:class-to-be-bound name="some.package.Transaction"/>
    </oxm:jaxb2-marshaller>

    <!-- View resolver that returns an XML Marshalling view. -->
    <bean class="some.package.MarshallingXmlViewResolver" >
        <constructor-arg ref="marshaller"/>
    </bean>

You can find more information at this link: http://spring.io/blog/2013/06/03/content-negotiation-using-views/

Using all view resolver techniques, you can avoid writing duplicate methods in controller, such as one for xml/json, other for excel, other for pdf, another for doc, rss and all.

Answer 2

Knalli, if you replace @ResponseBody with ModelAndView(), you can achieve both the features. Is there any reason you want to keep @ResponseBody ? I just want to know if I am missing anything, just want to learn.

Other option is to write HttpMessageConverters then: Some samples are here.

Custom HttpMessageConverter with @ResponseBody to do Json things

http://www.javacodegeeks.com/2013/07/spring-mvc-requestbody-and-responsebody-demystified.html

Answer 3

This is working sample. I have configured contentnegotiationviewresolver for this, and give highest order. After that I have ResourceBundleViewResolver for JSTL and Tiles View, then XmlViewResolver for excelResolver, pdfResolver, rtfResolver. excelResolver, pdfResolver, rtfResolver. XmlViewResolver and ResourceBundleViewResolver works only with MAV only, but MappingJacksonJsonView and MarshallingView takes care for both MAV and @ResponseBody return value.

<bean id="contentNegotiatingResolver" class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver">
<property name="order"
                  value="#{T(org.springframework.core.Ordered).HIGHEST_PRECEDENCE}" />
<property name="mediaTypes">
            <map>
                <entry key="json" value="application/json" />
                <entry key="xml" value="application/xml" />
                <entry key="pdf" value="application/pdf" />
                <entry key="xlsx" value="application/vnd.openxmlformats-officedocument.spreadsheetml.sheet" />
                <entry key="doc" value="application/msword" />
            </map>
        </property>

        <property name="defaultViews">
            <list>
                <!-- JSON View -->
                <bean class="org.springframework.web.servlet.view.json.MappingJacksonJsonView" />

                <!-- XML View -->
                <bean class="org.springframework.web.servlet.view.xml.MarshallingView">
                        <constructor-arg>
                            <bean id="jaxbMarshaller" class="org.springframework.oxm.jaxb.Jaxb2Marshaller">
                            <property name="classesToBeBound">
                            <list>
                                <value>Employee</value>
                                <value>EmployeeList</value>
                            </list>
                            </property>
                            </bean>
                        </constructor-arg>
            </bean>
            </list>
        </property>
        <property name="ignoreAcceptHeader" value="true" />
 </bean>
<bean class="org.springframework.web.servlet.view.ResourceBundleViewResolver"
        id="resourceBundleResolver">
        <property name="order" value="#{contentNegotiatingResolver.order+1}" />
    </bean>
<bean id="excelResolver" class="org.springframework.web.servlet.view.XmlViewResolver">
       <property name="location">
           <value>/WEB-INF/tiles/spring-excel-views.xml</value>
       </property>
       <property name="order" value="#{resourceBundleResolver.order+1}" />
    </bean>

    <bean id="pdfResolver" class="org.springframework.web.servlet.view.XmlViewResolver">
       <property name="location">
           <value>/WEB-INF/tiles/spring-pdf-views.xml</value>
       </property>
       <property name="order" value="#{excelResolver.order+1}" />
    </bean>

    <bean id="rtfResolver" class="org.springframework.web.servlet.view.XmlViewResolver">
       <property name="location">
           <value>/WEB-INF/tiles/spring-rtf-views.xml</value>
       </property>
       <property name="order" value="#{excelResolver.order+1}" />
    </bean>

And our XMLViewResolver spring-pdf-views.xml looks like this.

<bean id="employees"
        class="EmployeePDFView"/>

And EmployeePDFView will have code for generating pdf and writing pdf byte stream on Response object. This will resolve to rest url that will end with .pdf extension, and when you return MAV with "employees" id.