Java 为什么代码在Spring验证之前插入数据

我这里有代码：

@Controller
@RequestMapping(value="/guestbook")
public class GuestBookController {


     @Autowired
     GuestBookServiceIF guestBookServiceIF; 



     @ModelAttribute("messagesModel")
     public List<UserMessage> getMessagesModel() {
          return guestBookServiceIF.fetchAllService();
        }


     @RequestMapping(method = RequestMethod.GET)
     public String renderGuestBook(Model model) {
         GuestBookBackObject guestBookBackObject = new GuestBookBackObject();
         model.addAttribute("guestBookBackObject", guestBookBackObject);
         return "book";
        }



        @RequestMapping(method=RequestMethod.POST)
        public String saveGuestBookMessage(@ModelAttribute(value="guestBookBackObject") GuestBookBackObject guestBookBackObject, 
                                                                                                    BindingResult buindingResult) {


            guestBookBackObject.setIsNameExist(guestBookServiceIF.isUserInDBService(guestBookBackObject.getUser().getUserName()));

            GuestBookValidation validator = new GuestBookValidation();
            validator.validate(guestBookBackObject, buindingResult);
            if(buindingResult.hasErrors()) {    
                return "book";      
            } else {

            guestBookBackObject.getUserMessage().setTheUser(guestBookBackObject.getUser());
            guestBookServiceIF.saveMessageService(guestBookBackObject.getUserMessage());

            return "redirect:/guestbook";

            }
     }

基本上，它应该可以正常工作，但会产生错误：

Hibernate: insert into USER_DESC (USER_NAME) values (?)
WARN : org.hibernate.engine.jdbc.spi.SqlExceptionHelper - SQL Error: 1062, SQLState: 23000
ERROR: org.hibernate.engine.jdbc.spi.SqlExceptionHelper - Duplicate entry 'we' for key 'UK_ok6uvp3eyniad0xua3xdt5icw'
Oct 01, 2013 9:27:04 AM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [appServlet] in context with path [/web] 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: Duplicate entry 'we' for key 'UK_ok6uvp3eyniad0xua3xdt5icw'
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
    at com.mysql.jdbc.Util.getInstance(Util.java:386)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1041)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4190)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4122)
    at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2570)
    at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2731)
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2818)
    at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2157)
    at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2460)
    at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2377)
    at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2361)
    at com.mchange.v2.c3p0.impl.NewProxyPreparedStatement.executeUpdate(NewProxyPreparedStatement.java:105)
    at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:133)
    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:2975)
    at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:3487)
    at org.hibernate.action.internal.EntityIdentityInsertAction.execute(EntityIdentityInsertAction.java:81)
    at org.hibernate.engine.spi.ActionQueue.execute(ActionQueue.java:377)
    at org.hibernate.engine.spi.ActionQueue.addResolvedEntityInsertAction(ActionQueue.java:214)
    at org.hibernate.engine.spi.ActionQueue.addInsertAction(ActionQueue.java:194)
    at org.hibernate.engine.spi.ActionQueue.addAction(ActionQueue.java:178)
    at org.hibernate.event.internal.AbstractSaveEventListener.addInsertAction(AbstractSaveEventListener.java:321)
    at org.hibernate.event.internal.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:286)
    at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:192)
    at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:125)
    at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:206)
    at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:191)
    at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.performSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:114)
    at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:90)
    at org.hibernate.internal.SessionImpl.fireSaveOrUpdate(SessionImpl.java:735)
    at org.hibernate.internal.SessionImpl.saveOrUpdate(SessionImpl.java:727)
    at org.hibernate.engine.spi.CascadingAction$5.cascade(CascadingAction.java:258)
    at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:388)
    at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:331)
    at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:209)
    at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:166)
    at org.hibernate.event.internal.AbstractSaveEventListener.cascadeBeforeSave(AbstractSaveEventListener.java:424)
    at org.hibernate.event.internal.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:263)
    at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:192)
    at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:125)
    at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:206)
    at org.hibernate.event.internal.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:55)
    at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:191)
    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:764)
    at org.hibernate.internal.SessionImpl.save(SessionImpl.java:756)
    at org.hibernate.internal.SessionImpl.save(SessionImpl.java:752)
    at demidov.pkg.persistence.GuestBookDAOImpl.saveMessage(GuestBookDAOImpl.java:30)
    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:606)
    at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:317)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:183)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
    at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:96)
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:260)
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:94)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)
    at com.sun.proxy.$Proxy8.saveMessage(Unknown Source)
    at demidov.pkg.service.GuestBookServiceImpl.saveMessageService(GuestBookServiceImpl.java:27)
    at demidov.pkg.web.GuestBookController.saveGuestBookMessage(GuestBookController.java:60)
    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:606)
    at org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:219)
    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:745)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:686)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:925)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:856)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:936)
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:838)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:812)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:240)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:164)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:462)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:562)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:395)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:250)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:188)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:302)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:724)

这说明数据库中存在值，并且该值应该是唯一的。好啊但是为什么验证器允许先插入值而不检查它们呢

我的背对象（GuestBookBackObject）：

---

谢谢。

缺少更多信息，如

GuestBookBackObject的实现。但是基于你所付出的

只是抛出了您得到的异常，因为您从未在数据库中检查要插入的值是否存在于称为唯一的列中

在保存之前，您应该在验证器内或任何地方实现这一点。比如说

boolean exists = guestBookServiceIF.isMessageExists(guestBookBackObject);

只有在执行该语句时，才能通过数据库发现您违反了a约束。
要存储验证消息，您调用了错误的方法

if(guestBookBackObject.getIsNameExist()== null) {
    ValidationUtils.rejectIfEmpty(error, "user.userName", "", "Please choose different user name");
}

如果设置了属性，但用户名不是空的，则不会设置任何内容。您只需在
Errors
对象上调用
reject
方法即可

if(guestBookBackObject.getIsNameExist()== null) {
    errrors.reject("username.not.unique", "Please choose different user name");
}

接下来，您应该在
验证器中进行检查，而不是在控制器中进行检查。这样你就可以让Spring帮你完成所有的重担
 先生，这里是代码的和平guestBookBackObject.setIsNameExist（GuestBookService.isUserInDBService（guestBookBackObject.getUser（）.getUserName（））；我确实将isUserInDBService（）方法返回的值注入back对象（Spring支持backing对象进行验证等）。在我用以下代码对它们进行验证之后：GuestBookValidation validator=newGuestbookValidation（）；validator.validate（guestBookBackObject、BudingResult）；if（buindingResult.hasErrors（））{return“book”}else{…我提供的问题中的back对象是guestBookBackObject。getIsNameExist（）在具有该名称的用户已经存在时返回null？
if(guestBookBackObject.getIsNameExist()== null) {
    ValidationUtils.rejectIfEmpty(error, "user.userName", "", "Please choose different user name");
}

if(guestBookBackObject.getIsNameExist()== null) {
    errrors.reject("username.not.unique", "Please choose different user name");
}