SSH2项目报空指针异常

大家帮我看看这个项目，怎么会出现空指针异常
action：

public class UserAction extends ActionSupport {
	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;
	private List<Item> items=null;
    private ItemDAO itemDAO ;
    public void setItemDAO(ItemDAO itemDAO){
    	this.itemDAO=itemDAO;
    }
	@SuppressWarnings("unchecked")
	@Override
	public String execute() throws Exception {
		// TODO Auto-generated method stub
		items = itemDAO.findAll();
		return SUCCESS;
	}
	public static void main(String[] args) {
        // TODO Auto-generated method stub

    }

	public List<Item> getItems() {
		return items;
	}
	public void setItems(List<Item> items) {
		this.items = items;
	}



}

DAO：

package com.lee.dao;

import java.util.List;
import org.hibernate.LockMode;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.orm.hibernate3.support.HibernateDaoSupport;

import com.lee.model.Item;

/**
 * A data access object (DAO) providing persistence and search support for Item
 * entities. Transaction control of the save(), update() and delete() operations
 * can directly support Spring container-managed transactions or they can be
 * augmented to handle user-managed Spring transactions. Each of these methods
 * provides additional information for how to configure it for the desired type
 * of transaction control.
 * 
 * @see com.lee.model.Item
 * @author MyEclipse Persistence Tools
 */
public class ItemDAO extends HibernateDaoSupport {
	private static final Logger log = LoggerFactory.getLogger(ItemDAO.class);
	// property constants
	public static final String ITEM_NAME = "itemName";
	public static final String SOURCE = "source";
	public static final String YEAR = "year";
	public static final String FUND = "fund";
	public static final String LEADER = "leader";

	protected void initDao() {
		// do nothing
	}

	public void save(Item transientInstance) {
		log.debug("saving Item instance");
		try {
			getHibernateTemplate().save(transientInstance);
			log.debug("save successful");
		} catch (RuntimeException re) {
			log.error("save failed", re);
			throw re;
		}
	}

	public void delete(Item persistentInstance) {
		log.debug("deleting Item instance");
		try {
			getHibernateTemplate().delete(persistentInstance);
			log.debug("delete successful");
		} catch (RuntimeException re) {
			log.error("delete failed", re);
			throw re;
		}
	}

	public Item findById(java.lang.Integer id) {
		log.debug("getting Item instance with id: " + id);
		try {
			Item instance = (Item) getHibernateTemplate().get(
					"com.lee.model.Item", id);
			return instance;
		} catch (RuntimeException re) {
			log.error("get failed", re);
			throw re;
		}
	}

	public List findByExample(Item instance) {
		log.debug("finding Item instance by example");
		try {
			List results = getHibernateTemplate().findByExample(instance);
			log.debug("find by example successful, result size: "
					+ results.size());
			return results;
		} catch (RuntimeException re) {
			log.error("find by example failed", re);
			throw re;
		}
	}

	public List findByProperty(String propertyName, Object value) {
		log.debug("finding Item instance with property: " + propertyName
				+ ", value: " + value);
		try {
			String queryString = "from Item as model where model."
					+ propertyName + "= ?";
			return getHibernateTemplate().find(queryString, value);
		} catch (RuntimeException re) {
			log.error("find by property name failed", re);
			throw re;
		}
	}

	public List findByItemName(Object itemName) {
		return findByProperty(ITEM_NAME, itemName);
	}

	public List findBySource(Object source) {
		return findByProperty(SOURCE, source);
	}

	public List findByYear(Object year) {
		return findByProperty(YEAR, year);
	}

	public List findByFund(Object fund) {
		return findByProperty(FUND, fund);
	}

	public List findByLeader(Object leader) {
		return findByProperty(LEADER, leader);
	}

	public List findAll() {
		log.debug("finding all Item instances");
		try {
			String queryString = "from Item";
			return getHibernateTemplate().find(queryString);
		} catch (RuntimeException re) {
			log.error("find all failed", re);
			throw re;
		}
	}

	public Item merge(Item detachedInstance) {
		log.debug("merging Item instance");
		try {
			Item result = (Item) getHibernateTemplate().merge(detachedInstance);
			log.debug("merge successful");
			return result;
		} catch (RuntimeException re) {
			log.error("merge failed", re);
			throw re;
		}
	}

	public void attachDirty(Item instance) {
		log.debug("attaching dirty Item instance");
		try {
			getHibernateTemplate().saveOrUpdate(instance);
			log.debug("attach successful");
		} catch (RuntimeException re) {
			log.error("attach failed", re);
			throw re;
		}
	}

	public void attachClean(Item instance) {
		log.debug("attaching clean Item instance");
		try {
			getHibernateTemplate().lock(instance, LockMode.NONE);
			log.debug("attach successful");
		} catch (RuntimeException re) {
			log.error("attach failed", re);
			throw re;
		}
	}

	public static ItemDAO getFromApplicationContext(ApplicationContext ctx) {
		return (ItemDAO) ctx.getBean("ItemDAO");
	}
}

xml：

<?xml version="1.0" encoding="UTF-8"?>
<beans
	xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:p="http://www.springframework.org/schema/p"
	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">


	<bean id="dataSource"
		class="org.apache.commons.dbcp.BasicDataSource">
		<property name="driverClassName"
			value="com.mysql.jdbc.Driver">
		</property>
		<property name="url" value="jdbc:mysql://localhost:3306/data"></property>
		<property name="username" value="root"></property>
		<property name="password" value="madge881227"></property>
	</bean>
	<bean id="sessionFactory"
		class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">
		<property name="dataSource">
			<ref bean="dataSource" />
		</property>
		<property name="hibernateProperties">
			<props>
				<prop key="hibernate.dialect">
					org.hibernate.dialect.MySQLDialect
				</prop>
			</props>
		</property>
		<property name="mappingResources">
			<list>
				<value>com/lee/model/Item.hbm.xml</value></list>
		</property></bean>
		<bean id="transactionManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager">
           <property name="sessionFactory"><ref local="sessionFactory"/></property>
      </bean>	
	<bean id="ItemDAO" class="com.lee.dao.ItemDAO">
		<property name="sessionFactory">
			<ref bean="sessionFactory" />
		</property>
	</bean>
	 <bean id="hibernateTemplate" class="org.springframework.orm.hibernate3.HibernateTemplate">
              <property name="sessionFactory" ref="sessionFactory"></property>
     </bean>
      <bean id="UserAction" class="com.lee.action.UserAction">
              <property name="itemDAO" ref="ItemDAO"></property>
     </bean>
	</beans>

6 个解决方案

#1

HTTP Status 500 - 

--------------------------------------------------------------------------------

type Exception report

message 

description The server encountered an internal error () that prevented it from fulfilling this request.

exception 

java.lang.NullPointerException
com.lee.action.UserAction.execute(UserAction.java:23)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
java.lang.reflect.Method.invoke(Method.java:597)
com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:452)
com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:291)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:254)
com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:176)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:263)
org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:68)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:133)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:207)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:207)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:190)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:75)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:94)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:243)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:100)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:141)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:267)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:142)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:166)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:176)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:190)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:187)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:52)
org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:485)
org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)
org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:91)


note The full stack trace of the root cause is available in the Apache Tomcat/6.0.29 logs.


--------------------------------------------------------------------------------

Apache Tomcat/6.0.29

#2

你struts.xml  有没有 <constant name="struts.objectFactory" value="spring" />    ItemDAO 没有注入到UserAction里面

#3

你没有service层吗》？？

#4

像你这种情况，报空指针的可能原因
1.缺少set/get方法
2.spring注入有问题，我觉得你的原因应该是第二种，
<bean id="ItemDAO" class="com.lee.dao.ItemDAO">
        <property name="sessionFactory">
            <ref bean="sessionFactory" />
        </property>
    </bean>
与
private ItemDAO itemDAO ;
最好包id改成itemDAO ，保持一致。。。。
检查上面两步之后，还是有空指针的话，设断点，慢慢找

#5

你的DAO有没有定义接口，在spring配置中没有发现service层。

#6

报的空指针异常指的是没找到UserAction类里的itemDAO。
原因：
1、是否把struts交给spring管理<constant name="struts.objectFactory" value="spring" />
2、把spring配置文件里的ItemDAO改成itemDAO
建议：
你可以学习下注解，使用注解会方便不少