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问NullPointerException on ModelAttribute对象
EN

Stack Overflow用户
提问于 2016-10-29 15:16:52
回答 1查看 901关注 0票数 0

我正在为我的webservice编写控制器，在添加新方法时，旧方法开始抛出nullPointerException。我只是寻求一个答案或提示，可以指出什么可能是错误的这一点，我只是张贴代码和jsp，并解释是怎么回事。

控制器方法：

代码语言：javascript
复制
@RequestMapping(value={"/items"}, method = RequestMethod.GET)
public String listItems(ModelMap model) {
    model.addAttribute("item", new GenericItem());
    model.addAttribute("itemList", this.adminService.getAllGenericItems());
    model.addAttribute("itemTypes", ItemType.values());
    return "/admin/items";
}


@RequestMapping(value={"/items", "/edit-item-{id}"}, method = RequestMethod.POST)
public String addItem(@ModelAttribute("item") GenericItem item) {
    if(item.getId() == 0) { // THIS LINE CAUSE NULL POINTER EXCEPTION
        this.adminService.saveGenericItem(item);
    }
    else {
        this.adminService.updateGenericItem(item);
    }
    return "redirect:/admin/items";
}

用于填充"GenericItem“对象的Jsp表单：

代码语言：javascript
复制
<table>
<c:if test="${!empty item.name}">
<form:hidden path="id" />
</c:if>
<tr>
    <td colspan = "2">Item details
    </td>
</tr>
<tr>
    <td>Name:
    </td>
    <td>
        <form:input path="name" />
    </td> 
</tr>
<tr>
    <td>Weight:
    </td>
    <td>
        <form:input path="weight" />
    </td> 
</tr>
<tr>
    <td>Value:
    </td>
    <td>
        <form:input path="value" />
    </td> 
</tr>
<tr>
    <td>Item type:
    </td>
    <td>
        <form:select path="itemType">
            <form:option value="">---</form:option>
            <form:options items="${itemTypes}" />
        </form:select>
    </td> 
</tr>
<tr>
    <td>Detail:
    </td>
    <td>
        <form:input path="detail" />
    </td> 
</tr>
<tr>
    <td>Graphic:
    </td>
    <td>
        <form:input path="graphic" />
    </td> 
</tr>
<tr>
    <td colspan="2">
        <c:if test="${!empty item.name}">
            <input type="submit"
                value="Edit" />
        </c:if>
        <c:if test="${empty item.name}">
            <input type="submit"
                value="Add" />
        </c:if>
    </td>
</tr>

GenericItem的POJO：

代码语言：javascript
复制
public class GenericItem {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "generic_item_id")
private Long id;

@Column(name = "name")
private String name;

@Column(name = "weight")
private int weight;

@Column(name = "value")
private int value;

@Column(name = "item_type")
@Enumerated(EnumType.STRING)
private ItemType itemType;

@Column(name = "detail")
private String detail;

@Column(name = "graphic")
private String graphic;

//getter setters

}

因此，我刚刚开始在控制器方法上获得nullPointerExceptions，在该方法中，我希望读取POSTed值ModelAttribute项。奇怪的是，它以前起作用，现在停止了，我不知道从哪里开始寻找我的错误。

如果这是帮助，这是完全错误的。

代码语言：javascript
复制
org.springframework.web.util.NestedServletException: Request processing failed; nested exception is java.lang.NullPointerException
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:982)
org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872)
javax.servlet.http.HttpServlet.service(HttpServlet.java:648)
org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:316)
org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:126)
org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:90)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:114)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:122)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:111)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:168)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:48)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:205)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:120)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.csrf.CsrfFilter.doFilterInternal(CsrfFilter.java:120)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:64)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:91)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:53)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:213)
org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:176)
org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:346)
org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:262)

根本原因

代码语言：javascript
复制
java.lang.NullPointerException
eu.kerdev.webproject.controller.ApplicationController.addItem(ApplicationController.java:52)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:606)
org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221)
org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136)
org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:114)
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963)
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897)
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872)
javax.servlet.http.HttpServlet.service(HttpServlet.java:648)
org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:316)
org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:126)
org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:90)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:114)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:122)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:111)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:168)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:48)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:205)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:120)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.csrf.CsrfFilter.doFilterInternal(CsrfFilter.java:120)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:64)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:91)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:53)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:213)
org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:176)
org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:346)
org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:262)
java
nullpointerexception
EN

回答 1

Stack Overflow用户

回答已采纳

发布于 2016-10-29 15:46:38

项的id等于null，因此：

item.getId() == 0

会把NullPointerException扔出去。使用：

Long.valueOf(0L).equals(item.getId())

或者给你的Id设置一些值。

票数 2
EN
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：

https://stackoverflow.com/questions/40320556

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