Spring 3.2 content negotiation class cast exception

问题

We develop a standard Java web application using Spring MVC, and have recently tried to upgrade from 3.0.6 to 3.2.0. Nearly of all our servlet responses are JSP or Json views, but there are some that are pdf requests, with extension 'pdf'.

In Spring 3.0.6 we had this set up, taken from the Spring MVC documentation.

<bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver">
<property name="mediaTypes">
<map>
  <entry key="pdf" value="application/pdf"/>
  <entry key="html" value="text/html"/>
  <entry key="json" value="application/json"/>
</map>

which worked fine, in combination with an XMLViewResolver.

After updating to 3.2.0, there is a failure :

Error creating bean with name' org.springframework.web.servlet.view.ContentNegotiatingViewResolver#0' defined in class path  resource [dispatcher-test-servlet.xml]: Invocation of init method failed; nested exception is 

java.lang.ClassCastException: java.lang.String cannot be cast to                   org.springframework.http.MediaType'

After investigating the docs and some blogs, this configuration seems to work:

<bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver">
   <property name="contentNegotiationManager">
<bean class="org.springframework.web.accept.ContentNegotiationManager">
<constructor-arg>
    <list>
    <!-- These are evaluated in order -->
    <!-- Is there a media type based on suffix? -->
<bean                  class="org.springframework.web.accept.PathExtensionContentNegotiationStrategy">
<constructor-arg>
    <map>
<entry key="html" value="text/html" />
<entry key="json" value="application/json" />
<entry key="pdf" value="application/pdf" />
</map>
</constructor-arg>
</bean>
<!-- Else use request header -->
<bean
            class="org.springframework.web.accept.HeaderContentNegotiationStrategy">

</bean>
</list>
</constructor-arg>
</bean>
</property>

But, we have tried running the new Spring MVC test framework using this configuration, and get the ClassCast exception again, so it seems the test framework is not initialising the beans in the same way as when the application runs... Does anyone have a clear explanation of how to configure the ContentNegotiatingViewResolver in Spring 3,2 in a robust fashion? Thanks

Richard

回答1:

With spring 3.2 it is better resolved using ContentNegotiationManager. It is working for me. You could use the static field like org.springframework.http.MediaType.APPLICATION_JSON_VALUE to mention the mediatype. check the following code:

<bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver">
        <property name="contentNegotiationManager">
            <bean class="org.springframework.web.accept.ContentNegotiationManager">
                <constructor-arg>
                    <bean class="org.springframework.web.accept.PathExtensionContentNegotiationStrategy">
                        <constructor-arg>
                            <map>
                                <entry key="json">
                                    <util:constant static-field="org.springframework.http.MediaType.APPLICATION_JSON_VALUE" />
                                </entry>
                                <entry key="xml">
                                    <util:constant static-field="org.springframework.http.MediaType.APPLICATION_XML_VALUE" />
                                </entry>
                            </map>
                        </constructor-arg>
                    </bean>
                </constructor-arg>
            </bean>
        </property>

        <property name="defaultViews">
            <list>
               <!-- default views -->
            </list>
        </property>

    </bean>

For this you have to use util schema in your dispatcher-servlet.xml file, i.e. xmlns:util="http://www.springframework.org/schema/util" and schema location http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.0.xsd

回答2:

I fixed the problem by removing duplicated <mvc:annotation-driven/> from xml-configuration or @EnableWebMVC annotation from the class because spring documentation warns about that and allowed only once by contract.

回答3:

I think you can achieve the same thing more easily using the ContentNegotiationManagerFactoryBean. By default it checks the URL path extension first, then a format property in the URL (such as ..../accounts?format=pdf) and then the standard HTTP Accept header property. The use of the format parameter is off by default.

<bean id="contentNegotiationManager"
      class="org.springframework.web.accept.ContentNegotiationManagerFactoryBean">
    <property name="defaultContentType" value="text/html" />

    <property name="mediaTypes">
        <map>
            <entry key="json" value="application/json" />
            <entry key="pdf" value="application/pdf" />
            <entry key="pdf" value="text/html" />
       </map>
    </property>
</bean>

<bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver">
        <property name="contentNegotiationManager" ref=""/>
</bean>

If you use the JavaBeans Activation Framework, JAF, you shouldn't need the mediaTypes section. Just put activation.jar on the classpath.

Did you try this and did you also get class-cast exceptions?

回答4:

Well, the error you posted is basically saying that Spring doesn't have a way to convert the string you provided, for example "application/pdf", to the MediaType objects. I am guessing the ContentNegotiatingViewResolver changed it's mediaTypes map to be a Map to a Map. You could try something like this:

<bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver">
<property name="mediaTypes">
<map>
  <entry key="pdf">
    <value>
      <bean class="org.springframework.http.MediaType">
        <constructor-arg value="application/pdf" />
      </bean>
    </value>
  </entry>
  <entry key="html">
    <value>
      <bean class="org.springframework.http.MediaType">
        <constructor-arg value="text/html" />
      </bean>
    </value>
  </entry>
  <entry key="json">
    <value>
      <bean class="org.springframework.http.MediaType">
        <constructor-arg value="application/json" />
      </bean>
    </value>
  </entry>
</map>
</bean>

Note: I did this from memory, so I may have typo'd this. Basically, you need the entry values to be MediaTypes, not strings.

来源：https://stackoverflow.com/questions/14631992/spring-3-2-content-negotiation-class-cast-exception

标签

Spring

spring-mvc

content-negotiation