空指针异常

Question

java.lang.NullPointerException
at com.esoft.wuliu.web.action.system.VehicleMgrAction.showUpdate(VehicleMgrAction.java:121)
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:613)
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)
at com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:163)
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
at com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:249)
at org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:68)
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
at com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:122)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:195)
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:195)
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
at com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:148)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
at org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:93)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
at org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:235)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
at com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:89)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
at com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:128)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
at org.apache.struts2.interceptor.ProfilingActivationInterceptor.intercept(ProfilingActivationInterceptor.java:104)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
at org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:267)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
at com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:126)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
at com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:138)
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
at com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:148)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
at org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
at com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:128)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
at com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:176)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
at org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:52)
at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:468)
at org.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:395)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:845)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Thread.java:717)
vehicle=vehicleManager.get(vid);这条鱼局没有获取到直。我也有封装，怎么还是没有获取到呢？

Answer 1

com.esoft.wuliu.web.action.system.VehicleMgrAction的showUpdate方法出现空指针，鉴定完毕。
不要忘了结贴

Answer 2

vehicleManager为空，还是把代码贴多点吧。

Answer 3

package com.esoft.wuliu.web.action.system;import java.io.InputStream;
import java.io.StringBufferInputStream;
import java.util.List;import com.esoft.wuliu.model.system.Vehicle;
import com.esoft.wuliu.service.system.VehicleManager;
import com.opensymphony.xwork2.ActionContext;
import com.opensymphony.xwork2.ActionSupport;public class VehicleMgrAction extends ActionSupport { private VehicleManager vehicleManager;

private Vehicle vehicle;

private Integer vid;

private InputStream inputStream;

private int id;

private List<Integer> ids;

private int currentPage=1;

/**
 * 显示所有车辆
 * @return
 */
public String list(){
ActionContext ctx=ActionContext.getContext();
int pageCount=5;
int totalPage = 0;
int totalCount = 0;
int pageStartRow = 0; // 计算总记录数
totalCount = vehicleManager.showList().size(); // 计算总页数
if (totalCount % pageCount == 0) {
totalPage = totalCount / pageCount;
} else {
totalPage = totalCount / pageCount + 1;
} // 修改currentPage，保证1<=currentPage<=totalPage
if (currentPage < 1) {
currentPage = 1;
} else if (currentPage > totalPage) {
currentPage = totalPage;
} // 计算当前页第一条记录的索引号
pageStartRow = (currentPage - 1) * pageCount;
List<Vehicle> list = vehicleManager.showPage(pageStartRow, pageCount); ctx.put("pageCount", pageCount);
ctx.put("totalCount", totalCount);
ctx.put("totalPage", totalPage);
ctx.put("list", list);
return SUCCESS;
}
/**
 * 显示添加页面
 * @return
 */
public String showAdd(){
return SUCCESS;
}
/**
 * 添加车辆
 * @return
 */
public String add(){
if(vehicleManager.save(vehicle)){
return SUCCESS;
}else{
ActionContext.getContext().put("error","添加车辆失败");
return ERROR;
}
}
/**
 * 判断车辆是否存在
 * @return
 */
public String check(){
try{
if(vid!=null&&!"".equals(vid)){
if(vehicleManager.ckVehiclevid(vid)){
inputStream = new StringBufferInputStream("valid");
} else {
inputStream = new StringBufferInputStream("invalid");
}
}
}catch(Exception e){
e.printStackTrace();
}
return SUCCESS;
}
/**
 * 删除车辆
 * @return
 */
public String delete(){
try{
vehicleManager.delete(id);
}catch(Exception e){
e.printStackTrace();
}
return SUCCESS;
}
/**
 * 显示修改页面
 * @return
 */
public String showUpdate(){
try{
vehicle=vehicleManager.get(vid);

}catch(Exception e){
e.printStackTrace();
}
return SUCCESS;
}
/**
 * 修改
 * @return
 */
public String update(){
try{
vehicleManager.update(vehicle);
}catch(Exception e){
e.printStackTrace();
}
return SUCCESS;
}
public List<Integer> getIds(){
return this.ids=ids;
} public void setIds(List<Integer> ids) {
this.ids = ids;
} public int getCurrentPage() {
return currentPage;
} public void setCurrentPage(int currentPage) {
this.currentPage = currentPage;
} public Integer getVid() {
return vid;
} public void setVid(Integer vid) {
this.vid = vid;
} public Vehicle getVehicle() {
return vehicle;
} public void setVehicle(Vehicle vehicle) {
this.vehicle = vehicle;
} public VehicleManager getVehicleManager() {
return vehicleManager;
} public void setVehicleManager(VehicleManager vehicleManager) {
this.vehicleManager = vehicleManager;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}


}
这是action的代码

Answer 4

function showAdd() {
location.href = "${path}/system/vehicle/showAdd.action";
}// 全选
function checkAll() {
var ids = document.getElementsByName("ids");
for ( var i = 0; i < ids.length; i++) {
ids[i].checked = document.getElementById("checkList").checked;
}
}function deleteCheck() {
var ids = document.getElementsByName("ids");
var flag = false;
for ( var i = 0; i < ids.length; i++) {
if ( ids[i].checked==true ) {
flag = true;
break;
}
}
if(!flag) {
alert("请选择要删除的数据！");
return false;
}
if(confirm("确认删除这些数据吗？")) {
var f = document.getElementById("fList");
var url = "${path}/system/emp/deleteCheck.action";
f.action = url;
f.submit();
}
}function go() {
var cp = document.getElementById("cp").value;
location.href = "${path}/system/emp/list.action?currentPage=" + cp;
}//仅允许输入数字
function checkNumber() {
    //判断输入字符的keyCode，数字在48到57之间，超出部分返回false
    if ((event.keyCode >= 48) && (event.keyCode <= 57)) {
        event.returnValue = true;
    } else {
        event.returnValue = false;
    }
}
</script>
</head><body>
<form id="fList">
<table width="100%" border="0" cellspacing="0" cellpadding="0">
  <tr>
    <td height="30" background="${path}/images/tab_05.gif"><table width="100%" border="0" cellspacing="0" cellpadding="0">
      <tr>
        <td width="12" height="30"><img src="${path}/images/tab_03.gif" width="12" height="30" /></td>
        <td><table width="100%" border="0" cellspacing="0" cellpadding="0">
          <tr>
            <td width="46%" valign="middle"><table width="100%" border="0" cellspacing="0" cellpadding="0">
            <tr>
            </tr>
              <tr>
                <td width="5%"><div align="center"><img src="${path}/images/tb.gif" width="16" height="16" /></div></td>
                <td width="95%" class="STYLE1"><span class="STYLE3">您当前的位置</span>：[车辆管理]-[车辆信息管理]</td>
              </tr>
            </table></td>
            <td width="54%"><table border="0" align="right" cellpadding="0" cellspacing="0">
              <tr>
                <td width="60"><table width="90%" border="0" cellpadding="0" cellspacing="0">
                  <tr onclick="showAdd()" style="cursor:hand">
                    <td class="STYLE1"><div align="center"><img src="${path}/images/22.gif" width="14" height="14" /></div></td>
                    <td class="STYLE1"><div align="center">新增</div></td>
                  </tr>
                </table></td>
                <td width="100"><table width="88%" border="0" cellpadding="0" cellspacing="0">
                  <tr onclick="return deleteCheck()" style="cursor:hand">
                    <td class="STYLE1"><div align="center"><img src="${path}/images/11.gif" width="14" height="14" /></div></td>
                    <td class="STYLE1"><div align="center">删除选中</div></td>
                  </tr>
                </table></td>
              </tr>
            </table></td>
          </tr>
        </table></td>
        <td width="16"><img src="${path}/images/tab_07.gif" width="16" height="30" /></td>
      </tr>
    </table></td>
  </tr>
  <tr>
    <td><table width="100%" border="0" cellspacing="0" cellpadding="0">
      <tr>
        <td width="" background="${path}/images/tab_12.gif">&nbsp;</td>
        <td><table width="100%" border="0" cellpadding="0" cellspacing="1" bgcolor="b5d6e6" onmouseover="changeto()"  onmouseout="changeback()">
          <tr>
            <td width="3%" height="15" background="${path}/images/bg1.gif" bgcolor="#FFFFFF"><div align="center">
              <input type="checkbox" id="checkList" onclick="checkAll()" />
            </div></td>
            <td width="4%" height="10" background="${path}/images/bg1.gif" bgcolor="#FFFFFF"><div align="center"><span class="STYLE1">车辆编号</span></div></td>
            <td width="6%" height="10" background="${path}/images/bg1.gif" bgcolor="#FFFFFF"><div align="center"><span class="STYLE1">所属车队</span></div></td>
            <td width="6%" height="10" background="${path}/images/bg1.gif" bgcolor="#FFFFFF"><div align="center"><span class="STYLE1">车牌号码</span></div></td>
            <td width="6%" background="${path}/images/bg1.gif" bgcolor="#FFFFFF"><div align="center"><span class="STYLE1">车辆类型</span></div></td>
            
            <td width="6%" height="10" background="${path}/images/bg1.gif" bgcolor="#FFFFFF"><div align="center"><span class="STYLE1">车辆载重</span></div></td>
            <td width="5%" height="15" background="${path}/images/bg1.gif" bgcolor="#FFFFFF"><div align="center"><span class="STYLE1">车辆状态</span></div></td>
            
             <td width="5%" height="10" background="${path}/images/bg1.gif" bgcolor="#FFFFFF"><div align="center"><span class="STYLE1">备注</span></div></td>
             
                    
                     <td width="10%" height="15" background="${path}/images/bg1.gif" bgcolor="#FFFFFF"><div align="center"><span class="STYLE1">操作</span></div></td>
          </tr>
          
          <c:forEach items="${list}" var="item">
          <tr>
            <td height="8" bgcolor="#FFFFFF"><div align="center">
              <input type="checkbox" name="ids" value="${item.vid }" />
            </div></td>
            <td height="8" bgcolor="#FFFFFF"><div align="center" class="STYLE1">
              <div align="center">${item.vid }</div>
            </div></td>
         
   
             <td height="5" bgcolor="#FFFFFF" ><div align="center"><span class="STYLE1">${item.motorcade.mid }</span></div></td>
            <td height="5" bgcolor="#FFFFFF"><div align="center"><span class="STYLE1">${item.vname}</span></div></td>
            
            <td height="15" bgcolor="#FFFFFF"><div align="center"><span class="STYLE1">${item.vtype}</span></div></td>
            <td height="15" bgcolor="#FFFFFF"><div align="center"><span class="STYLE1">${item.vweight}</span></div></td>
            <td height="15" bgcolor="#FFFFFF"><div align="center"><span class="STYLE1">${item.vstatution}</span></div></td>
            <td height="15" bgcolor="#FFFFFF"><div align="center"><span class="STYLE1">${item.re}</span></div></td>
            
            
           
            <td height="15" bgcolor="#FFFFFF"><div align="center"><span class="STYLE4"><a href="${path}/system/vehicle/showUpdate.action?id=${item.vid }"><img src="${path}/images/reply.gif" width="16" height="16" />编辑</a><a href="${path}/system/vehicle/delete.action?id=${item.vid }" onclick="return confirm('确认删除该数据吗？')"><img src="${path}/images/del.gif" width="16" height="16" />删除</a></span></div></td>
          </tr>
          </c:forEach>
          
        </table></td>
        <td width="8" background="${path}/images/tab_15.gif">&nbsp;</td>
      </tr>
    </table></td>
  </tr>
  <tr>
    <td height="35" background="${path}/images/tab_19.gif"><table width="100%" border="0" cellspacing="0" cellpadding="0">
      <tr>
        <td width="12" height="35"><img src="${path}/images/tab_18.gif" width="12" height="35" /></td>
        <td><table width="100%" border="0" cellspacing="0" cellpadding="0">
          <tr>
            <td class="STYLE4">&nbsp;&nbsp;共有 ${requestScope.totalCount } 条记录，当前第 ${requestScope.currentPage }/${requestScope.totalPage } 页</td>
            <td><table border="0" align="right" cellpadding="0" cellspacing="0">
                <tr>
                  <td width="40"><a href="${path}/system/manager/list.action?currentPage=1"><img src="${path}/images/first.gif" width="37" height="15" /></a></td>
                  <td width="45"><a href="${path}/system/manager/list.action?currentPage=${requestScope.currentPage-1 }"><img src="${path}/images/back.gif" width="43" height="15" /></a></td>
                  <td width="45"><a href="${path}/system/manager/list.action?currentPage=${requestScope.currentPage+1 }"><img src="${path}/images/next.gif" width="43" height="15" /></a></td>
                  <td width="40"><a href="${path}/system/manager/list.action?currentPage=${requestScope.totalPage }"><img src="${path}/images/last.gif" width="37" height="15" /></a></td>
                  <td width="100"><div align="center"><span class="STYLE1">转到第
                    <input id="cp" onkeypress="checkNumber()" type="text" size="4" style="height:12px; width:20px; border:1px solid #999999;" /> 
                    页 </span></div></td>
                  <td width="40"><img src="${path}/images/go.gif" width="37" height="15" onclick="go()"  style="cursor:hand"/></td>
                </tr>
            </table></td>
          </tr>
        </table></td>
        <td width="16"><img src="${path}/images/tab_20.gif" width="16" height="35" /></td>
      </tr>
    </table></td>
  </tr>
</table>
</form>
</body>
</html>
这是list.jsp部分代码

Answer 5

vehicleManager 有值么
判断下vehicleManager==null

Answer 6

vehicle=vehicleManager.get(vid);只有一种可能，就是 vehicleManager是null.

Answer 7

private VehicleManager vehicleManager;lz看下，是否注入成功

Answer 8

和vid没关系吧，你看看7楼说的， VehicleManager vehicleManager是否注入成功

Answer 9

vehicle=vehicleManager.get(vid);这句里的vehicle始终是获取不到得

Answer 10

空指针这样异常应该是很好解决的啊：
vehicle=vehicleManager.get(vid);
vehicle如果为空，那么肯定就是vehicleManager.get(vid);
返回值为空,原因呢,要门vid根本就没有获取到，要么get(vid)没有查询到,再要么vehicleManager实例为空,你只要挨着排查这三个就可以了

Answer 11

vid的值没有，当然那个会引起空指针异常了，可以进行判断
if(vid==null){
   如何如何
}
else{
   如何如何
}
你这个vid是否是从jsp页面传入的值？？

Answer 12

又看了一下楼主的jsp代码，觉得存在问题。就是你action里的vid在jsp里没有对应项，还有代码太乱，不容易让人理解，楼主应该整理思路重新设计