Question

我尝试使用spring和JackSon JSON创建REST服务。

我的DAOImpl：

    @Override
    @SuppressWarnings("unchecked")
    public Users findByUserName(String username) {

        Users user = new Users();
        session = getSessionFactory().openSession();
        try {
            transaction = session.beginTransaction();
            if (!username.isEmpty() && username != null) {
                List<Users> users = new ArrayList<Users>();
                users = session.createQuery("from Users where username=?")
                        .setParameter(0, username)
                        .list();

                if (!users.isEmpty()) {
                    user = users.get(0);
                }

                transaction.commit();
            }
        } catch (HibernateException e) {

            if (transaction != null) {
                transaction.rollback();
            }

            e.printStackTrace();
        } finally {
            session.close();
        }

        return user;
    }

我的控制器类：

    @RequestMapping(value = "/rest/userbyname/{username}",
            method = RequestMethod.GET,
            headers = "Accept=application/json")
    public Users findByUserName(@PathVariable("username") String username) {

        return userDao.findByUserName(username);
    }

我收到了这个错误：

HTTP状态500 - 无法写入JSON：无法初始化代理 - 没有会话（通过参考链： com.spring.example.entities.Users [＆＃34;作用＆＃34;] - ＆GT; com.enclaveit.brea.entities.Roles _ _ $$ jvstd4_2 [＆＃34;作用＆＃34;]）; 嵌套异常是 com.fasterxml.jackson.databind.JsonMappingException：不能初始化代理 - 没有会话（通过参考链： com.enclaveit.brea.entities.Users [＆＃34;作用＆＃34;] - ＆GT; com.enclaveit.brea.entities.Roles _ _ $$ jvstd4_2 [＆＃34;作用＆＃34;]）

据我所知，因为会话在DAOImpl类中关闭所以在控制器中会话不再存在，是否正确？当我尝试评论代码行session.close();然后网络工作正常，我可以收到Json。但是当会话无法结束时会很危险，对吧？

寻找最佳解决方案。

注意：如果您需要更多信息，请告诉我。

谢谢。

更新：

Hibernate配置文件：

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:aop="http://www.springframework.org/schema/aop"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd 
    http://www.springframework.org/schema/aop 
    http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
    http://www.springframework.org/schema/tx
    http://www.springframework.org/schema/tx/spring-tx-3.0.xsd">

    <!-- MySQL data source -->
    <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"
        destroy-method="close">
        <property name="driverClassName" value="com.mysql.jdbc.Driver" />
        <property name="url" value="jdbc:mysql://192.168.10.116:3306/brea" />
        <property name="username" value="root" />
        <property name="password" value="brea@123" />
        <property name="maxActive" value="-1"/>
    </bean>
    <!-- If request parameter "targetUrl" is existed, then forward to this url --> 
    <!-- For update login form -->
    <bean id="savedRequestAwareAuthenticationSuccessHandler"
        class="org.springframework.security.web.authentication.SavedRequestAwareAuthenticationSuccessHandler">
        <property name="targetUrlParameter" value="targetUrl" />
     </bean>
    <!-- Hibernate session factory -->
    <bean id="sessionFactory"
        class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">
        <property name="dataSource" ref="dataSource" />
        <property name="mappingResources">
            <list>
                <value>orm/Roles.hbm.xml</value>
                <value>orm/Users.hbm.xml</value>
                <value>orm/UsersInfo.hbm.xml</value>
            </list>
        </property>
        <property name="hibernateProperties">
            <props>
            <prop key="hibernate.dialect">
                           org.hibernate.dialect.MySQL5Dialect
                        </prop>
            <prop key="hibernate.format_sql">true</prop>
            <prop key="hibernate.show_sql">true</prop>
            </props>
        </property>
    </bean>

    <bean id="userDao" class="com.enclaveit.brea.dao.UserDaoImpl">
        <property name="sessionFactory" ref="sessionFactory" />
    </bean>

    <bean id="myUserDetailsService" 
                class="com.enclaveit.brea.services.MyUserDetailsService">
        <property name="userDao" ref="userDao" />
    </bean>

    <tx:annotation-driven />

    <!-- MUST have transaction manager, using aop and aspects  -->
    <bean id="transactionManager"
        class="org.springframework.orm.hibernate4.HibernateTransactionManager">
        <property name="dataSource" ref="dataSource" />
        <property name="sessionFactory" ref="sessionFactory"></property>
    </bean>

    <tx:advice id="txAdvice" transaction-manager="transactionManager">
        <tx:attributes>
        <tx:method name="get*" read-only="true" />
        <tx:method name="find*" read-only="true" />
        <tx:method name="*" />
        </tx:attributes>
    </tx:advice>

    <aop:config>
        <aop:pointcut id="userServicePointCut"
        expression="execution(* com.enclaveit.brea.services.*Service.*(..))" />
        <aop:advisor advice-ref="txAdvice" pointcut-ref="userServicePointCut" />
    </aop:config>
</beans>

错误日志：

com.fasterxml.jackson.databind.JsonMappingException: could not initialize proxy - no Session (through reference chain: com.spring.example.entities.Users["roles"]->com.spring.example.entities.Roles_$$_jvstdf1_2["role"])
    com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:232)
    com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:197)
    com.fasterxml.jackson.databind.ser.std.StdSerializer.wrapAndThrow(StdSerializer.java:184)
    com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:605)
    com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:142)
    com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:569)
    com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:597)
    com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:142)
    com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:118)
    com.fasterxml.jackson.databind.ObjectMapper.writeValue(ObjectMapper.java:1819)
    org.springframework.http.converter.json.MappingJackson2HttpMessageConverter.writeInternal(MappingJackson2HttpMessageConverter.java:241)
    org.springframework.http.converter.AbstractHttpMessageConverter.write(AbstractHttpMessageConverter.java:207)
    org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:148)
    org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:90)
    org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.handleReturnValue(RequestResponseBodyMethodProcessor.java:193)
    org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:71)
    org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:122)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:749)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:690)
    org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:83)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:945)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:876)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
    org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:118)
    org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:84)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:113)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:103)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:113)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.authentication.rememberme.RememberMeAuthenticationFilter.doFilter(RememberMeAuthenticationFilter.java:139)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:154)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:45)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.authentication.www.BasicAuthenticationFilter.doFilter(BasicAuthenticationFilter.java:150)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:199)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:110)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.csrf.CsrfFilter.doFilterInternal(CsrfFilter.java:85)
    org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:108)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:50)
    org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:108)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:87)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:192)
    org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:160)
    org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:344)
    org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:261)

org.hibernate.LazyInitializationException: could not initialize proxy - no Session
    org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:164)
    org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:285)
    org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:185)
    com.spring.example.entities.Roles_$$_jvstdf1_2.getRole(Roles_$$_jvstdf1_2.java)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    java.lang.reflect.Method.invoke(Method.java:606)
    com.fasterxml.jackson.databind.ser.BeanPropertyWriter.get(BeanPropertyWriter.java:679)
    com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:534)
    com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:597)
    com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:142)
    com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:569)
    com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:597)
    com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:142)
    com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:118)
    com.fasterxml.jackson.databind.ObjectMapper.writeValue(ObjectMapper.java:1819)
    org.springframework.http.converter.json.MappingJackson2HttpMessageConverter.writeInternal(MappingJackson2HttpMessageConverter.java:241)
    org.springframework.http.converter.AbstractHttpMessageConverter.write(AbstractHttpMessageConverter.java:207)
    org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:148)
    org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:90)
    org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.handleReturnValue(RequestResponseBodyMethodProcessor.java:193)
    org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:71)
    org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:122)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:749)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:690)
    org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:83)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:945)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:876)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
    org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:118)
    org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:84)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:113)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:103)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:113)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.authentication.rememberme.RememberMeAuthenticationFilter.doFilter(RememberMeAuthenticationFilter.java:139)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:154)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:45)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.authentication.www.BasicAuthenticationFilter.doFilter(BasicAuthenticationFilter.java:150)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:199)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:110)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.csrf.CsrfFilter.doFilterInternal(CsrfFilter.java:85)
    org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:108)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:50)
    org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:108)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:87)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:192)
    org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:160)
    org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:344)
    org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:261)

Answer 1

最快的解决方案是首先从您的服务中删除会话和交易处理代码，然后将其替换为代码中的@Transactional（以及配置中的<tx:annotation-driven />。

@Override
@SuppressWarnings("unchecked")
@Transactional(readOnly="true")
public Users findByUserName(String username) {
    Session session = getSessionFactory().getCurrentSession();      
    return (Users) session
                    .createQuery("from Users where username=?")
                    .setParameter(0, username)
                    .uniqueResult();
}

另请注意，session的范围应该是方法，永远不要将Session存储为实例变量。（想象一下，如果对findByUserName进行10次当前调用会对实例变量session产生什么影响，会发生什么。）

在您的配置中启用注释驱动的事务管理。（假设你已经定义了HibernateTransactionManager！）。

<tx:annotation-driven />

接下来将OpenSessionInViewFilter添加到您的请求处理链（即在使用java配置时在web.xml或初始化程序中注册过滤器）。

<filter>
    <filter-name>OpenSessionInViewFilter</filter-name>
    <filter-class>org.springframework.orm.hibernate4.support.OpenSessionInViewFilter</filter-class>
    <!-- Replace with hibernate3, hibernate4 or hibernate5 depending on the hibernate version one uses -->
</filter>

<filter-mapping>
    <filter-name>OpenSessionInViewFilter</filter-name>
    <servlet-name>dispatcher</servlet-name> <!-- name of your DispatcherServlet -->
</filter-mapping>

Answer 2

由于您正在使用Spring框架，请使用declarative transaction管理而不是programmatic transactions。

我相信您的Users实体具有延迟加载的role属性。您可以将此更改为急切加载（不是更可取），或者在DAO方法中，在会话结束前使用getter role加载user.getRole()信息。

Answer 3

将代理注释添加到Entity类可以完成这项工作。

@Entity @Table(name="Country") @Proxy(lazy = false) public class Country {}

无法写入JSON：无法初始化代理 - 没有会话错误

3 个答案: