SSH2项目报空指针异常

lovecx24 2014-09-01 05:15:32
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>

...全文
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innight 2014-09-02
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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
搬砖的IT农民工 2014-09-02
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你的DAO有没有定义接口，在spring配置中没有发现service层。
w_l_o_v_e_c 2014-09-02
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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
LOVE-漂泊 2014-09-02
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你没有service层吗》？？
jinnykang900513 2014-09-02
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你struts.xml 有没有 <constant name="struts.objectFactory" value="spring" /> ItemDAO 没有注入到UserAction里面
lovecx24 2014-09-01
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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
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