空下例外从下拉列表中节省价值

Question

我正在将一个产品对象保存到数据库中，当我对字段使用输入时一切正常但是我的下拉列表有问题我收到以下错误，因为idcategory返回Null：

org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [paxtecum] in context with path [/paxtecum] threw exception [Request processing failed; nested exception is org.hibernate.exception.ConstraintViolationException: could not execute statement] with root cause
com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Column 'idcategory' cannot be null
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
    at java.lang.reflect.Constructor.newInstance(Unknown Source)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:408)
    at com.mysql.jdbc.Util.getInstance(Util.java:383)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1049)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4226)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4158)
    at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2615)
    at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2776)
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2840)
    at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2082)
    at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2334)
    at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2262)
    at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2246)
    at org.apache.tomcat.dbcp.dbcp2.DelegatingPreparedStatement.executeUpdate(DelegatingPreparedStatement.java:97)
    at org.apache.tomcat.dbcp.dbcp2.DelegatingPreparedStatement.executeUpdate(DelegatingPreparedStatement.java:97)
    at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:208)
    at org.hibernate.id.IdentityGenerator$GetGeneratedKeysDelegate.executeAndExtract(IdentityGenerator.java:96)
    at org.hibernate.id.insert.AbstractReturningDelegate.performInsert(AbstractReturningDelegate.java:58)
    at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:3032)
    at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:3558)
    at org.hibernate.action.internal.EntityIdentityInsertAction.execute(EntityIdentityInsertAction.java:98)
    at org.hibernate.engine.spi.ActionQueue.execute(ActionQueue.java:490)
    at org.hibernate.engine.spi.ActionQueue.addResolvedEntityInsertAction(ActionQueue.java:195)
    at org.hibernate.engine.spi.ActionQueue.addInsertAction(ActionQueue.java:179)
    at org.hibernate.engine.spi.ActionQueue.addAction(ActionQueue.java:214)
    at org.hibernate.event.internal.AbstractSaveEventListener.addInsertAction(AbstractSaveEventListener.java:324)
    at org.hibernate.event.internal.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:288)
    at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:194)
    at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:125)
    at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:209)
    at org.hibernate.event.internal.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:55)
    at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:194)
    at org.hibernate.event.internal.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:49)
    at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:90)
    at org.hibernate.internal.SessionImpl.fireSave(SessionImpl.java:715)
    at org.hibernate.internal.SessionImpl.save(SessionImpl.java:707)
    at org.hibernate.internal.SessionImpl.save(SessionImpl.java:702)
    at com.wizardofoz.paxtecum.web.dao.ProductDao.create(ProductDao.java:28)
    at com.wizardofoz.paxtecum.web.dao.ProductDao$$FastClassBySpringCGLIB$$8c448070.invoke(<generated>)
    at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
    at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:717)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
    at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:98)
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:266)
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:95)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:653)
    at com.wizardofoz.paxtecum.web.dao.ProductDao$$EnhancerBySpringCGLIB$$c35808a4.create(<generated>)
    at com.wizardofoz.paxtecum.web.service.ProductService.create(ProductService.java:19)
    at com.wizardofoz.paxtecum.web.controllers.ProductController.createProduct(ProductController.java:38)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:215)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:781)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:721)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:83)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:943)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:877)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:863)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:644)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:118)
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:84)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:113)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:103)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:113)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:154)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:45)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:199)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:110)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:50)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:87)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:192)
    at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:160)
    at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:344)
    at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:261)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:503)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:136)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:526)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1078)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:655)
    at org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:222)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1566)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1523)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Unknown Source)**


product DAO class:


            ProductDao.java
            import java.util.Date;
            import java.util.List;

            import org.hibernate.Session;
            import org.hibernate.SessionFactory;
            import org.springframework.beans.factory.annotation.Autowired;
            import org.springframework.stereotype.Component;
            import org.springframework.stereotype.Repository;
            import org.springframework.transaction.annotation.Transactional;

            @Repository
            @Transactional
            @Component
            public class ProductDao {

                @Autowired
                private SessionFactory sessionFactory;

                public Session session() {
                    return sessionFactory.getCurrentSession();
                }   
                public void create(Product product) {

                    product.setCreatedate(new Date());          
                    session().save(product);
                }

                public List<Product> getProducts() {

                    return session().createQuery("from Product").list();
                }

            }

newproduct.jsp


        <%@ page language="java" contentType="text/html; charset=ISO-8859-1"
            pageEncoding="ISO-8859-1"%>
        <%@ taglib prefix="sf" uri="http://www.springframework.org/tags/form"%>

        <form method="post"
            action="${pageContext.request.contextPath}/createproduct">

            <table>
                <tr>
                    <td>Product</td>
                    <td><input name="name" type="text" /></td>
                </tr>

                <tr>
                    <td>Category</td>
                    <td><sf:select path="categories" >
                           <sf:option value="-" label="Select a Category"></sf:option>
                            <sf:options items="${categories}" itemValue="idcategory" 
                            itemLabel="name" />
                        </sf:select></td>
                </tr>

                <tr>            
                    <td><input value="Save" type="submit" /></td>
                </tr>

            </table>

        </form>


ProductController.java


    import java.util.List;

    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.stereotype.Controller;
    import org.springframework.ui.Model;
    import org.springframework.validation.BindingResult;
    import org.springframework.web.bind.annotation.RequestMapping;
    import org.springframework.web.bind.annotation.RequestMethod;

    import com.wizardofoz.paxtecum.web.dao.Category;
    import com.wizardofoz.paxtecum.web.dao.Product;
    import com.wizardofoz.paxtecum.web.service.CategoryService;
    import com.wizardofoz.paxtecum.web.service.ProductService;

    @Controller
    public class ProductController {

        @Autowired
        private CategoryService categoryService;

        @Autowired
        private ProductService productService;

        @RequestMapping("/newproduct")
        public String newcategory(Model model) {

            List<Category> categories = categoryService.getAllCategories();

            model.addAttribute("categories",categories);
            return "newproduct";
        }

        @RequestMapping(value="/createproduct", method=RequestMethod.POST)
        public String createProduct(Product product, BindingResult result){

            productService.create(product);

            return "productcreated";
        }

        @RequestMapping(value="/products")
        public String getProducts(Model model) { 

            List<Product> products = productService.getProducts();
            model.addAttribute("products", products);

            return "products";
        }

    }
Product.java
import java.util.Date;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

@Entity
@Table(name="products")
public class Product  {
    @Id
    @Column(name="idproducts")
    @GeneratedValue
    private int id;

    @ManyToOne
    @JoinColumn(name="idcategory")
    private Category category;
    private String name;
    private Date createdate;


    @Override
    public String toString() {
        return "Product [id=" + id + ", category=" + category + ", name="
                + name + ", createdate=" + createdate + "]";
    }

    public Product(){

    }

    public Product(Category category, String name, Date createdate) {
        super();
        this.category = category;
        this.name = name;
        this.createdate = createdate;
    }

    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public Category getCategory() {
        return category;
    }
    public void setCategory(Category category) {
        this.category = category;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Date getCreatedate() {
        return createdate;
    }
    public void setCreatedate(Date createdate) {
        this.createdate = createdate;
    }


}

Category.java
import java.util.Date;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name="category")
public class Category {

    @Id
    @GeneratedValue
    private int idcategory;
    private String name;
    private Date createdate;


    @Override
    public String toString() {
        return "Category [idcategory=" + idcategory + ", name=" + name
                + ", createdate=" + createdate + "]";
    }


    public int getIdcategory() {
        return idcategory;
    }


    public void setIdcategory(int idcategory) {
        this.idcategory = idcategory;
    }


    public Category(String name, Date createdate) {
        super();
        this.name = name;
        this.createdate = createdate;
    }


    public Category() {
    }


    public String getName() {
        return name;
    }


    public void setName(String name) {
        this.name = name;
    }


    public Date getCreatedate() {
        return createdate;
    }


    public void setCreatedate(Date createdate) {
        this.createdate = createdate;
    }

}

会出现什么问题？

Answer 1

将控制器处理程序方法更改为：

//Here, add a Product instance to model as you have done for categories, for binding product information from JSP.
@RequestMapping("/newproduct")
public String newcategory(Model model) {

   List<Category> categories = categoryService.getAllCategories();
   model.addAttribute("categories",categories);
   model.addAttribute("newProduct",new Product()); //missing
   return "newproduct";
}

然后在你的POST处理程序中从模型中获取Product实例。

@RequestMapping(value="/createproduct", method=RequestMethod.POST)
public String createProduct(@ModelAttribute("newProduct")Product product, BindingResult result){

   //Here, validate product instance
   //Here, set product/category relationships
   Category category = productService.findOne(product.getCategory().getIdcategory()); //validate for null
   product.setCategory(category);

   productService.create(product);

   return "productcreated";
}

最后，在JSP中指定modelAttribute名称和操作URL：

<sf:form method="post"
    action="${pageContext.request.contextPath}/createproduct" modelAttribute="newProduct">

 Product
    <sf:input path="name"/>
 Category
    <sf:select path="category.idcategory">
      <sf:option value="0" label="Select a Category"></sf:option>
      <sf:options items="${categories}" itemValue="idcategory" 
                    itemLabel="name" />
    </sf:select>
      <input value="Save" type="submit" />
</sf:form> 

Answer 2

在尝试在数据库中插入int之前，尝试对idcategory变量执行system.out.println（）。我怀疑idcategory值不是从下拉列表中正确读取的。