How to use lazy loading in Spring MVC

问题:

How to use lazy loading in Spring MVC? I'm using eager at this moment, but this makes my app works slowler. This is part of my domain:

@ManyToMany(fetch = FetchType.EAGER)
@JoinTable(name = "NEWS_TAG", joinColumns = @JoinColumn(name = "NEWS_ID"), inverseJoinColumns = @JoinColumn(name = "TAG_ID"))
private List<Tags> tags = new ArrayList<Tags>();

public List<Tags> getTags() {
    return this.tags;
}

And dao:

public List<News> getSomeNews(long b, long hm) {

    List<News> news = (List<News>) sessionFactory
            .getCurrentSession()
            .createQuery(
                    "from News WHERE title!='About' ORDER BY publish_time")
            .setMaxResults((int) hm).setFirstResult((int) b).list();
    return news;
}

Servlet-context:

    <context:annotation-config />

    <context:component-scan base-package="net.babobka.blog" />



    <import resource="../../db/db-config.xml" />

    <bean id="urlForwardController"
        class="org.springframework.web.servlet.mvc.UrlFilenameViewController" />

    <bean id="tilesConfigurer"
        class="org.springframework.web.servlet.view.tiles2.TilesConfigurer">
        <property name="definitions">
            <list>
                <value>/WEB-INF/tiles.xml</value>
            </list>
        </property>
    </bean>

    <bean id="viewResolver"
        class="org.springframework.web.servlet.view.UrlBasedViewResolver">
        <property name="viewClass"
            value="org.springframework.web.servlet.view.tiles2.TilesView" />
    </bean>

</beans>

Db-config:

<bean id="propertyConfigurer"
        class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"
        p:location="/WEB-INF/db/jdbc.properties" />

    <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"
        destroy-method="close" p:driverClassName="${jdbc.driverClassName}"
        p:url="${jdbc.databaseurl}" p:username="${jdbc.username}" p:password="${jdbc.password}" />

    <bean id="sessionFactory"
        class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">
        <property name="dataSource" ref="dataSource" />
        <property name="configLocation">
            <value>/WEB-INF/db/hibernate.cfg.xml</value>
        </property>
        <property name="configurationClass">
            <value>org.hibernate.cfg.AnnotationConfiguration</value>
        </property>
        <property name="hibernateProperties">
            <props>
                <prop key="hibernate.dialect">${jdbc.dialect}</prop>
                <prop key="hibernate.show_sql">${jdbc.show_sql}</prop>
            </props>
        </property>
    </bean>

    <bean id="transactionManager"
        class="org.springframework.orm.hibernate3.HibernateTransactionManager">
        <property name="sessionFactory" ref="sessionFactory" />
    </bean>

    <tx:annotation-driven />

</beans>

Web.xml:

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">

    <!-- The definition of the Root Spring Container shared by all Servlets 
        and Filters -->
    <context-param>
        <param-name>contextConfigLocation</param-name>

        <param-value>
        /WEB-INF/spring/root-context.xml
        /WEB-INF/spring/application-security.xml
        </param-value>
    </context-param>



    <!-- Creates the Spring Container shared by all Servlets and Filters -->
    <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>



    <!-- Processes application requests -->
    <servlet>
        <servlet-name>appServlet</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>/WEB-INF/spring/appServlet/servlet-context.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>appServlet</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

    <servlet-mapping>
        <servlet-name>appServlet</servlet-name>
        <url-pattern>*.gif</url-pattern>
    </servlet-mapping>
    <filter>
        <filter-name>springSecurityFilterChain</filter-name>
        <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
    </filter>

    <filter-mapping>
        <filter-name>springSecurityFilterChain</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

    <filter>
        <filter-name>hibernateFilterChain</filter-name>
        <filter-class>org.springframework.orm.hibernate3.support.OpenSessionInViewFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>hibernateFilterChain</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>




</web-app>

What I have to do to solve my problem?

回答1:

You can use OpenSessionInViewFilter to prevent hibernate session get closed. Add this to web.xml:

  <filter>
    <filter-name>hibernateFilterChain</filter-name>
    <filter-class>org.springframework.orm.hibernate4.support.OpenSessionInViewFilter</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>hibernateFilterChain</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>

@see read more here: OpenSessionInViewFilter

And remove fetch = FetchType.EAGER. @ManyToMany is LAZY by default.

回答2:

Change your annotation to (fetch = FetchType.LAZY). Be aware that if you're passing the result to some code outside the transaction (such as a view template), you might encounter errors if associated objects needed by the external code haven't already been loaded.