【发布时间】：2015-07-12 21:13:57
【问题描述】：
我想知道是否有人可以解释为什么 DAO 和 Spring 和 Hibernate 网络应用程序中的以下代码：
@Override
public Book get(Integer bookId) {
logger.info(BookDAOImpl.class.getName() + ".get() method called.");
Session session = sessionFactory.openSession();
try {
System.out.println("Book : " + bookId);
Book book = (Book) session.get(Book.class, bookId);
return book;
}
finally {
session.close();
}
}
在其父 Web 应用程序中可以很好地工作，但是当通过 controller 和 service 类通过 REST 调用时：
// Gets a Book via REST.
@RequestMapping(value="/book/{bookId}", method=RequestMethod.GET)
public @ResponseBody Object getBook(@PathVariable("bookId") String bookId) {
logger.info(RestController.class.getName() + ".getBook() method called.");
if (bookIdValid(bookId)) {
Book book = bookService.get(Integer.parseInt(bookId));
System.out.println("ABook " + book.toString());
return book;
}
else {
Messages messages = new Messages();
messages.addMessage(messageSource.getMessage("bookId.required", null, null));
return messages;
}
}
Book book = (Book) session.get(Book.class, bookId); 行返回 null。
BookDAOImpl 的第 53 行是下面方法中的return bookId == book.getBookId().intValue(); 行：
@Override
public boolean check(Integer bookId) {
logger.info(BookDAOImpl.class.getName() + ".check() method called.");
try {
Book book = this.get(bookId);
return bookId == book.getBookId().intValue();
}
catch(IndexOutOfBoundsException e) {
return false;
}
}
堆栈跟踪是：
Book : 78
INFO|12 07 2015|22 07 16|http-apr-8080-exec-123|library.controller.PersonController| - library.controller.ExceptionController.exception() method called.
null
library.dao.BookDAOImpl.check(BookDAOImpl.java:53)
library.service.BookServiceImpl.check(BookServiceImpl.java:32)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:483)
org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:317)
org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:201)
com.sun.proxy.$Proxy571.check(Unknown Source)
library.controller.RestController.bookIdValid(RestController.java:127)
library.controller.RestController.getBook(RestController.java:102)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:483)
org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:215)
org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)
org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104)
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:749)
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:690)
org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:83)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:945)
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:876)
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
javax.servlet.http.HttpServlet.service(HttpServlet.java:618)
org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:301)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:503)
org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:136)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:74)
org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610)
org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:516)
org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1015)
org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:652)
org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:277)
org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.doRun(AprEndpoint.java:2451)
org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:2440)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
java.lang.Thread.run(Thread.java:744)
library.interceptor.ClientInterceptor.afterCompletion() method completed: GET: /Library/rest/book/78?null at 12 07 2015 @ 22 07 ended with HTTP code: 500.
【问题讨论】：
-
你确定第 78 本书在场吗？如果 >= Java 8，我也会得到 return
Optional<Book>并使用“try-with-resources”来关闭，而不是“finally”，这可能会引发 NPE。 -
我不返回空值。它在 BookDAOImpl.java 的第 53 行抛出异常，可能是 NullPointerException。那条线是什么？向我们展示服务和 DAO 的完整相关代码。尤其是字段的声明和初始化方式。
-
这是一个
Java 1.7项目。填充了 get 方法的bookId参数，并将check方法（在某些情况下调用get）附加到问题中。
标签： java spring hibernate spring-mvc dao