Spring MVC 3.2和JSON ObjectMapper问题 [英] Spring MVC 3.2 and JSON ObjectMapper issue

问题描述

我最近将Spring版本从3.1.2升级到了3.2.0.我发现JSON属性(例如，包装根元素)可防止ObjectMapper中定义的null值不再起作用.

I have recently upgraded my Spring version to 3.2.0 from 3.1.2. I find that that JSON properties like wrap root element, prevent null values that are defined in ObjectMapper are not working anymore.

这是代码段

<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.

What could be the issue? Any pointers are appreciated.

推荐答案

免责声明:我无法确定问题代码为何无法正常工作，但可以重现该问题.这个答案的确为我提供了另一种方法.

可能是一个错误，因为我可以使用显式配置重现这两个问题:

It could be a bug, as I can reproduce the problem with both with explicit config:

<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>

在使用示例类时，两者都给我{"foo":null,"bar":"bar"}

where both give me {"foo":null,"bar":"bar"} when using the example class

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，我本以为 mvc:message-converter 方法会起作用，只是因为我看到了覆盖<mvc:annotation-driven/>执行的默认bean注册的问题(请参见

However, I would have thought the mvc:message-converter method would work, only because I have seen issues overriding the default bean registration that <mvc:annotation-driven/> performs (see Web MVC Framework) and using the nested configuration is preferred(?).

也许

Maybe the Jackson 2 support has caused some backwards compatibility issues with Jackson 1?

但是，切换到 MappingJackson2HttpMessageConverter (在Spring 3.1.2和Spring 3.2中受支持)，我 am 能够更改ObjectMapper配置以不写入空值并包装JSON输出. .但是，仅当使用<mvc:message-converters/>！

However, switching to the MappingJackson2HttpMessageConverter (supported in Spring 3.1.2 and Spring 3.2), I am able to alter the ObjectMapper configuration to not write null values and wrap the JSON output... but only when using the config inside the <mvc:message-converters/>!

我得到{"Dummy":{"bar":"bar"}}并进行了以下更改:

I get {"Dummy":{"bar":"bar"}} with the following changes:

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的新程序包结构

Demo.java switch to new package structure for Jackson 2

import com.fasterxml.jackson.annotation.JsonProperty;

demo-servlet.xml

<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，根据存在于您的代码中的原因.在Jackson> = v2.0中，已将其删除，因此 CustomJacksonObjectMapper.java 示例中的代码更改.

Lastly, according to the SerializationConfig.Feature documentation, WRITE_NULL_PROPERTIES feature is deprecated < v2.0 and you should be using SerializationConfig.setSerializationInclusion() anyway. I assume this is why the @SuppressWarnings("deprecation") exists in your code. In Jackson >= v2.0, it has been removed, hence the code change in the CustomJacksonObjectMapper.java example.

在Spring中配置ObjectMapper 提出了另一种解决方案.

Configuring ObjectMapper in Spring proposes an alternate solution.

希望有帮助！

这篇关于Spring MVC 3.2和JSON ObjectMapper问题的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！