Question

当我想将数据保存到数据库时，它会抛出异常。

我的Jsp如下：

的List.jsp

<body>
    <s:form action="userActionForm">
        <s:submit value="Add"/>
    </s:form>        

        <div class="content">
            <table class="userTable" cellpadding="5px">
                <tr class="even">
                    <th>First Name</th>
                    <th>Last Name</th>
                    <th>Contact</th>                        
                    <th>Edit</th>
                    <th>Delete</th>
                </tr>
                <s:iterator value="userList" status="userStatus">
                    <tr
                        class="<s:if test="#userStatus.odd == true ">odd</s:if>   <s:else>even</s:else>">
                        <td><s:property value="fName" /></td>
                        <td><s:property value="lName" /></td>
                        <td><s:property value="contact" /></td>                            
                        <td><s:url id="editURL" action="editUser">
                                <s:param name="id" value="%{id}"></s:param>
                            </s:url> <s:a href="%{editURL}">Edit</s:a></td>
                        <td><s:url id="deleteURL" action="deleteUser">
                                <s:param name="id" value="%{id}"></s:param>
                            </s:url> <s:a href="%{deleteURL}">Delete</s:a></td>
                        </tr>
                </s:iterator>
            </table>
        </div>
 <s:a href="logOut">LogOut</s:a>
</body>

register.jsp

<body>         
    <s:form action="saveOrUpdateUser" method="post">
        <s:push value="userdata">
            <s:hidden name="id" />                
            <s:textfield name="First name" label="Enter Name"/>
            <s:textfield name="Lst Name" label="Enter Lst Name"/>
            <s:textfield name="Contact" label="Enter Contact"/>
            <s:submit />
        </s:push>
    </s:form>       
</body>

UserAction.java

public class UserAction extends ActionSupport implements ModelDriven<UserData> {
private UserData userdata = new UserData();    
private UserDAO userDAO = new UserDAOImpl();
setters & getters
@Override
public UserData getModel() {

    System.out.println("userdata = ==" + userdata.getName());
    return userdata;
}
public String saveOrUpdate() {
    System.out.println("user data" + userdata);
    userDAO.saveOrUpdateUser(userdata);
    return SUCCESS;
}
}

UserDAO的

public interface UserDAO
{
public void saveOrUpdateUser(UserData userData);
}

在UserDAOImpl

public class UserDAOImpl implements UserDAO 
{
@SessionTarget
private Session session;
@TransactionTarget
Transaction transaction;
 public void saveOrUpdateUser(UserData userdata) {
    try {           
        session.saveOrUpdate(userdata);
    } catch (Exception e) {
        transaction.rollback();
        e.printStackTrace();
    }

}

struts.xml中

<struts>
<constant name="struts.devMode" value="true" />
<package name="helloworld" extends="hibernate-default">
    <interceptors>
        <interceptor name="mylogging" class="Demo.AuthenticationInterceptor">  </interceptor>
        <interceptor-stack name="loggingStack">
            <interceptor-ref name="mylogging" />
            <interceptor-ref name="defaultStack" />
        </interceptor-stack>
    </interceptors>
    <default-interceptor-ref name="loggingStack"></default-interceptor-ref>
 <action name="saveOrUpdateUser" method="saveOrUpdate" class="Demo.UserAction">            
        <result name="success" type="redirect" >list.jsp</result>
        <result name="login">/login.jsp</result>
    </action>
</package>
</struts>

当我运行应用程序时，我得到了像NullPointer Exception

这样的异常

java.lang.NullPointerException
at Demo.UserDAOImpl.saveOrUpdateUser(UserDAOImpl.java:36)
at Demo.UserAction.saveOrUpdate(UserAction.java:44)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:440)
at com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:279)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:242)

AuthenticationInterceptor：

public class AuthenticationInterceptor implements Interceptor
{
public String intercept(ActionInvocation ai) throws Exception 
{       
System.out.println("inside the interceptor()......new");
Map session = ai.getInvocationContext().getSession();
String name = (String) session.get("name");
System.out.println("inside the session or loginaction=" + name);
if ((session.get("name") != null) || ((session.get("name") == null))) {
    System.out.println("inside the session or loginaction ");
    return ai.invoke();
} else {
    return "login";
}
}
}

这个例外我得到了如何克服我不知道

Answer 1

您有逻辑错误。我注意到你有一个无意义的if语句似乎总是会返回true。

if ((session.get("name") != null) || ((session.get("name") == null)))

您正在检查或声明此处（|| = OR）如果该声明为空，则该声明将为真。

你可能想要更多的内容：

if (session.get("name") != null)
{
    do the is NOT null actions
}else if(session.get("name") == null)
{
    do the IS null actions
    (probably put a warning message here to help you better diagnose null problems with your session)
}

这可能是您当前nullPointerException的原因，或者它可能不是，但无论哪种方式，这将解决将来涉及该语句的可能问题。

我怎样才能克服java.lang.NullPointerException？

1 个答案: