Question

我的问题是为什么我会收到NullPointerException，尤其是在可变会话中，控制台日志是：

Grave: java.lang.NullPointerException
at com.curso.struts2.dao.UserDAOImpl.listUser(UserDAOImpl.java:28)
at com.curso.struts2.UserAction.list(UserAction.java:39)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 ...

我的源代码是：

web.xml

<listener>
    <listener-class>org.apache.struts2.tiles.StrutsTilesListener</listener-class>
</listener>
<context-param>
    <param-name>tilesDefinitions</param-name>
    <param-value>/WEB-INF/tiles.xml</param-value>
</context-param>

struts.xml

<struts> 
<constant name="struts.devMode" value="false" />
<constant name="struts.custom.i18n.resources" value="ApplicationResources" />

<package name="default" extends="hibernate-default,struts-default" namespace="/">

    <result-types>
        <result-type name="tiles"
            class="org.apache.struts2.views.tiles.TilesResult" />
    </result-types>

    <action name="addUser" method="add" class="com.curso.struts2.UserAction">
        <result name="success" type="redirect">listUser</result>
    </action>

    <action name="listUser" method="list" class="com.curso.struts2.UserAction">
        <result name="success">register.tiles</result>
    </action>
</package>

UserDAOImpl.java

    @SuppressWarnings("unchecked")
@Override
public List<User> listUser() {  
    List<User> courses = null;
    try { 
        System.out.println("UserDAOImpl.listUser()_session:" + session);
        Query query = session.createQuery("from User");
        courses = query.list();
    } catch (Exception e) {
        e.printStackTrace();
    } 
    return courses;
}

在这种情况下， session 变量显示为空

tiles.xml

<definition name="/register.tiles" extends="baseLayout">
    <put-attribute name="title" value="Struts 2 Hibernate example"/>
    <put-attribute name="body" value="/jsp/register.jsp"></put-attribute>
</definition>

在我的register.jsp中，我发送一张表格

Struts 2：Grave：java.lang.NullPointerException，会话变量为null

0 个答案: