Spring MVC 3.2和JSON ObjectMapper问题

Question

我最近将我的Spring版本从3.1.2升级到3.2.0.我发现像包装根元素这样的JSON属性,防止在ObjectMapper中定义的空值不再起作用.

这是代码片段

<mvc:annotation-driven content-negotiation-manager="contentNegotiationManager" /> 
    <bean id="contentNegotiationManager" class="org.springframework.web.accept.ContentNegotiationManagerFactoryBean">
    <property name="favorPathExtension" value="true" />
    <property name="ignoreAcceptHeader" value="false" /> 
    <property name="mediaTypes" >
        <value>
            json=application/json
            xml=application/xml
        </value>
    </property>
</bean>

和JSON转换器

<bean class="org.springframework.http.converter.json.MappingJacksonHttpMessageConverter">
   <property name="objectMapper" ref="customJacksonObjectMapper"/>  
   <property name="supportedMediaTypes" value="application/json"/>
</bean>

对象映射器代码

public class CustomJacksonObjectMapper extends ObjectMapper {

@SuppressWarnings("deprecation")
public CustomJacksonObjectMapper() {
    super();
    final AnnotationIntrospector introspector = new JaxbAnnotationIntrospector();

    this.configure(org.codehaus.jackson.map.DeserializationConfig.Feature.UNWRAP_ROOT_VALUE, true);
    this.configure(org.codehaus.jackson.map.SerializationConfig.Feature.WRAP_ROOT_VALUE, true);

    this.configure(org.codehaus.jackson.map.SerializationConfig.Feature.WRITE_NULL_PROPERTIES, false);

    this.setDeserializationConfig(this.getDeserializationConfig().withAnnotationIntrospector(introspector));
    this.setSerializationConfig(this.getSerializationConfig().withAnnotationIntrospector(introspector));

   }
}

杰克逊版

<dependency>
        <groupId>org.codehaus.jackson</groupId>
        <artifactId>jackson-xc</artifactId>
        <version>1.9.7</version>
    </dependency>

可能是什么问题？任何指针都表示赞赏.

Answer 1

免责声明:我无法确定为什么有问题的代码不起作用,但我可以重现这个问题.这个答案确实提供了一种适合我的替代方法.

它可能是一个错误,因为我可以使用显式配置重现问题:

<bean id="jacksonObjectMapper" class="com.demo.CustomJacksonObjectMapper"/>

<bean class="org.springframework.http.converter.json.MappingJacksonHttpMessageConverter">
   <property name="objectMapper" ref="jacksonObjectMapper"/>
   <property name="supportedMediaTypes" value="application/json"/>
</bean>

并通过mvc:message-converter:

<mvc:annotation-driven content-negotiation-manager="contentNegotiationManager">
    <mvc:message-converters>
        <bean class="org.springframework.http.converter.json.MappingJacksonHttpMessageConverter">
            <property name="objectMapper" ref="jacksonObjectMapper" />
        </bean>
   </mvc:message-converters>
</mvc:annotation-driven>

在{"foo":null,"bar":"bar"}使用示例类时,两者都给了我

Demo.java

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.*;
import org.codehaus.jackson.annotate.JsonProperty;

@Controller
@RequestMapping("/data")
public class Data {
    @RequestMapping
    @ResponseBody
    public Dummy dataIndex() {
        return new Dummy();
    }

    public class Dummy {
        String foo = null;
        @JsonProperty
        public String foo() {
            return foo;
        }
        String bar = "bar";
        @JsonProperty
        public String bar() {
            return bar;
        }
    }
}

但是,我原本认为mvc:message-converter方法可行,只是因为我看到了覆盖<mvc:annotation-driven/>执行的默认bean注册的问题(请参阅Web MVC框架),并且首选使用嵌套配置(？).

也许杰克逊2的支持导致杰克逊1的一些向后兼容性问题？

然而,切换到MappingJackson2HttpMessageConverter(在Spring 3.1.2和Spring 3.2的支持),我是能够改变ObjectMapper配置不写空值,敷JSON输出... 但使用内部的配置,只有当<mvc:message-converters/>!

我得到{"Dummy":{"bar":"bar"}}以下更改:

的pom.xml

<dependency>
   <groupId>com.fasterxml.jackson.core</groupId>
   <artifactId>jackson-core</artifactId>
   <version>2.1.0</version>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.1.0</version>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-annotations</artifactId>
    <version>2.1.0</version>
</dependency>

CustomJacksonObjectMapper.java

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.SerializationFeature;
import static com.fasterxml.jackson.annotation.JsonInclude.*;

public class CustomJacksonObjectMapper extends ObjectMapper {

public CustomJacksonObjectMapper() {
    super();
    this.configure(DeserializationFeature.UNWRAP_ROOT_VALUE, true);
    this.configure(SerializationFeature.WRAP_ROOT_VALUE, true);
    this.setSerializationInclusion(Include.NON_NULL);
   }
}

Demo.java切换到Jackson 2的新包结构

import com.fasterxml.jackson.annotation.JsonProperty;

演示servlet.xml中

<mvc:annotation-driven content-negotiation-manager="contentNegotiationManager">
    <mvc:message-converters>
        <bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
            <property name="objectMapper" ref="jacksonObjectMapper" />
        </bean>
    </mvc:message-converters>
</mvc:annotation-driven>

最后,根据SerializationConfig.Feature文档,WRITE_NULL_PROPERTIES功能已弃用<v2.0,SerializationConfig.setSerializationInclusion()无论如何您应该使用.我假设这就是@SuppressWarnings("deprecation")你的代码中存在的原因.在Jackson> = v2.0中,它已被删除,因此CustomJacksonObjectMapper.java示例中的代码更改.

在Spring中配置ObjectMapper提出了另一种解决方案.

希望能帮助到你!