项目记事【SpringMVC-2】：将后台的对象，转成JSON报文

Spring版本：3.2.7

Jackson版本：

<!--Jackson -->
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.1.3</version>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-core</artifactId>
    <version>2.1.3</version>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-annotations</artifactId>
    <version>2.1.2</version>
</dependency>

背景：

需要将后端的一个对象，通过SPringMVC框架，传递到前端时，自动转换成对应的JSON格式报文。

堆栈信息：

org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: No serializer found for class 

org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer and no properties discovered to create BeanSerializer (to avoid exception, disable 

SerializationConfig.SerializationFeature.FAIL_ON_EMPTY_BEANS) ) (through reference chain: com.siebre.pms.common.model.ResponseVO["data"]-

>com.siebre.pms.template.model.LiabilityTemplateDO["propertyAssignments"]->org.hibernate.collection.PersistentBag[0]-

>com.siebre.pms.template.model.PropertyAssignmentTemplateDO["propertyTemplate"]->com.siebre.pms.template.model.PropertyTemplateDO_$

$_javassist_187["handler"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: No serializer found for class 

org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer and no properties discovered to create BeanSerializer (to avoid exception, disable 

SerializationConfig.SerializationFeature.FAIL_ON_EMPTY_BEANS) ) (through reference chain: com.siebre.pms.common.model.ResponseVO["data"]-

>com.siebre.pms.template.model.LiabilityTemplateDO["propertyAssignments"]->org.hibernate.collection.PersistentBag[0]-

>com.siebre.pms.template.model.PropertyAssignmentTemplateDO["propertyTemplate"]->com.siebre.pms.template.model.PropertyTemplateDO_$

$_javassist_187["handler"])
    at org.springframework.http.converter.json.MappingJackson2HttpMessageConverter.writeInternal

(MappingJackson2HttpMessageConverter.java:207)
    at org.springframework.http.converter.AbstractHttpMessageConverter.write(AbstractHttpMessageConverter.java:179)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter

$ServletHandlerMethodInvoker.writeWithMessageConverters(AnnotationMethodHandlerAdapter.java:1037)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter$ServletHandlerMethodInvoker.handleResponseBody

(AnnotationMethodHandlerAdapter.java:995)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter$ServletHandlerMethodInvoker.getModelAndView

(AnnotationMethodHandlerAdapter.java:944)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod

(AnnotationMethodHandlerAdapter.java:441)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:428)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:925)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:856)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:953)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:844)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:627)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:829)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
    at com.siebre.web.servlet.filter.CorsFilter.doFilter(CorsFilter.java:53)
    at com.siebre.web.servlet.filter.CorsFilter.doFilter(CorsFilter.java:34)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:215)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
    at com.siebre.webapp.filter.WindowContextFilter.doFilterInternal(WindowContextFilter.java:274)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:215)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
    at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:378)
    at org.springframework.security.intercept.web.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:109)
    at org.springframework.security.intercept.web.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:83)
    at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:390)
    at org.springframework.security.ui.SessionFixationProtectionFilter.doFilterHttp(SessionFixationProtectionFilter.java:67)
    at org.springframework.security.ui.SpringSecurityFilter.doFilter(SpringSecurityFilter.java:53)
    at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:390)
    at org.springframework.security.ui.ExceptionTranslationFilter.doFilterHttp(ExceptionTranslationFilter.java:101)
    at org.springframework.security.ui.SpringSecurityFilter.doFilter(SpringSecurityFilter.java:53)
    at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:390)
    at org.springframework.security.providers.anonymous.AnonymousProcessingFilter.doFilterHttp(AnonymousProcessingFilter.java:105)
    at org.springframework.security.ui.SpringSecurityFilter.doFilter(SpringSecurityFilter.java:53)
    at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:390)
    at org.springframework.security.ui.rememberme.RememberMeProcessingFilter.doFilterHttp(RememberMeProcessingFilter.java:116)
    at org.springframework.security.ui.SpringSecurityFilter.doFilter(SpringSecurityFilter.java:53)
    at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:390)
    at org.springframework.security.wrapper.SecurityContextHolderAwareRequestFilter.doFilterHttp

(SecurityContextHolderAwareRequestFilter.java:91)
    at org.springframework.security.ui.SpringSecurityFilter.doFilter(SpringSecurityFilter.java:53)
    at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:390)
    at com.siebre.security.ui.ClientLoginProcessingFilter.doFilterHttp(ClientLoginProcessingFilter.java:147)
    at org.springframework.security.ui.SpringSecurityFilter.doFilter(SpringSecurityFilter.java:53)
    at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:390)
    at org.springframework.security.ui.basicauth.BasicProcessingFilter.doFilterHttp(BasicProcessingFilter.java:174)
    at org.springframework.security.ui.SpringSecurityFilter.doFilter(SpringSecurityFilter.java:53)
    at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:390)
    at org.springframework.security.ui.AbstractProcessingFilter.doFilterHttp(AbstractProcessingFilter.java:277)
    at org.springframework.security.ui.SpringSecurityFilter.doFilter(SpringSecurityFilter.java:53)
    at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:390)
    at org.springframework.security.ui.logout.LogoutFilter.doFilterHttp(LogoutFilter.java:89)
    at org.springframework.security.ui.SpringSecurityFilter.doFilter(SpringSecurityFilter.java:53)
    at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:390)
    at org.springframework.security.context.HttpSessionContextIntegrationFilter.doFilterHttp(HttpSessionContextIntegrationFilter.java:235)
    at org.springframework.security.ui.SpringSecurityFilter.doFilter(SpringSecurityFilter.java:53)
    at org.springframework.security.util.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:390)
    at org.springframework.security.util.FilterChainProxy.doFilter(FilterChainProxy.java:175)
    at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:343)
    at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:260)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:215)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
    at org.springframework.orm.hibernate3.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:230)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:215)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
    at com.siebre.webapp.filter.CacheControlFilter.doFilter(CacheControlFilter.java:34)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:215)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
    at com.siebre.webapp.filter.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:29)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:215)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:172)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:174)
    at org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:845)
    at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:688)
    at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1315)
    at java.lang.Thread.run(Thread.java:595)

错误原因分析：

后端对象中，有部分对象是以懒加载的形式初始化的，在ObjectMapper将对象转为JSON时，这部分对象尚未初始化，报错。

解决方案分析：

这种情况，在Jackson设计的时候，一定会考虑到。

通过堆栈信息，不难发现，这个转换工作，是由框架的 MappingJackson2HttpMessageConverter 这个类完成。

通过堆栈信息，还可以发现，问题主要由ObjectMapper的这个属性：SerializationFeature.FAIL_ON_EMPTY_BEANS，引发的。

由此，我们可以自定义一个 Mapper 继承 ObjectMapper，将以上属性转成我们所需要的即可。

解决方案：

public class CustomMapper extends ObjectMapper {

    public CustomMapper() {
        this.setSerializationInclusion(JsonInclude.Include.NON_NULL);
        // 设置 SerializationFeature.FAIL_ON_EMPTY_BEANS 为 false
        this.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
    }

}

<bean id="jacksonMessageConverter" class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
    <!-- 解决 HttpMediaTypeNotAcceptableException: Could not find acceptable representation -->
    <property name="supportedMediaTypes">
        <list>
            <value>text/html;charset=UTF-8</value>
            <value>application/x-www-form-urlencoded;charset=UTF-8</value>
            <value>application/json;charset=UTF-8</value>
        </list>
    </property>
    <!-- 解决懒加载问题 -->
    <property name="objectMapper">
        <bean class="com.siebre.pms.actual.service.util.CustomMapper">
        </bean>
    </property>
</bean>

Over，问题解决！