Java 使用具有延迟获取类型的检索外部对象的正确方法
我正在使用Spring、Hibernate和MySql,我将fetchType设置为LAZY以提高软件的性能,因为使用Earge时速度非常慢。 现在我需要检索链接到我的类的外部对象的信息,例如我有Java 使用具有延迟获取类型的检索外部对象的正确方法,java,mysql,spring,hibernate,lazy-loading,Java,Mysql,Spring,Hibernate,Lazy Loading,我正在使用Spring、Hibernate和MySql,我将fetchType设置为LAZY以提高软件的性能,因为使用Earge时速度非常慢。 现在我需要检索链接到我的类的外部对象的信息,例如我有Carclass: /** * Car generated by hbm2java */ @Entity @Table(name = "car", catalog = "ats") public class Car implements java.io.Serializable { /** *
Car
class:
/**
* Car generated by hbm2java
*/
@Entity
@Table(name = "car", catalog = "ats")
public class Car implements java.io.Serializable {
/**
*
*/
private static final long serialVersionUID = 1L;
private Integer idCar;
private CarType carType;
private Fleet fleet;
private String id;
private int initialKm;
private String carChassis;
private String note;
@JsonIgnore
private Set<Acquisition> acquisitions = new HashSet<Acquisition>(0);
我检索到一个异常,因为我将结果放在另一个我的类TableUi中(用于允许从表中调用ajax):
我的控制器返回@ResponseBody TableUI
。显然,Jackson无法映射对象,因为其字段fleet和carType只是代理。
这是一个例外:
ERROR com.controller.ErrorController - org.springframework.http.converter.HttpMessageNotWritableException: Could not write content: No serializer found for class org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) ) (through reference chain: com.model.tablesField.TableUI["data"]->java.util.ArrayList[0]->com.domain.Car["carType"]->com.domain.CarType_$$_jvst4de_f["handler"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: No serializer found for class org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) ) (through reference chain: com.model.tablesField.TableUI["data"]->java.util.ArrayList[0]->com.domain.Car["carType"]->com.domain.CarType_$$_jvst4de_f["handler"])
at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:271)
at org.springframework.http.converter.AbstractGenericHttpMessageConverter.write(AbstractGenericHttpMessageConverter.java:100)
at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:167)
at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:100)
at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.handleReturnValue(RequestResponseBodyMethodProcessor.java:166)
at org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:80)
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:127)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:806)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:729)
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:959)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
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.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:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:673)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1526)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1482)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
Caused by: com.fasterxml.jackson.databind.JsonMappingException: No serializer found for class org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) ) (through reference chain: com.model.tablesField.TableUI["data"]->java.util.ArrayList[0]->com.domain.Car["carType"]->com.domain.CarType_$$_jvst4de_f["handler"])
at com.fasterxml.jackson.databind.ser.impl.UnknownSerializer.failForEmpty(UnknownSerializer.java:59)
at com.fasterxml.jackson.databind.ser.impl.UnknownSerializer.serialize(UnknownSerializer.java:26)
at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:505)
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:639)
at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:152)
at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:505)
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:639)
at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:152)
at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serializeContents(IndexedListSerializer.java:100)
at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serializeContents(IndexedListSerializer.java:21)
at com.fasterxml.jackson.databind.ser.std.AsArraySerializerBase.serialize(AsArraySerializerBase.java:183)
at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:505)
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:639)
at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:152)
at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:128)
at com.fasterxml.jackson.databind.ObjectWriter.writeValue(ObjectWriter.java:602)
at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:264)
... 37 more
.11:24:38.387 [http-nio-8086-exec-4] WARN o.s.w.s.m.m.a.ExceptionHandlerExceptionResolver - Handler execution resulted in exception: Could not write content: No serializer found for class org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) ) (through reference chain: com.model.tablesField.TableUI["data"]->java.util.ArrayList[0]->com.domain.Car["carType"]->com.domain.CarType_$$_jvst4de_f["handler"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: No serializer found for class org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) ) (through reference chain: com.model.tablesField.TableUI["data"]->java.util.ArrayList[0]->com.domain.Car["carType"]->com.domain.CarType_$$_jvst4de_f["handler"])
相反,如果我在model.addAttribute
中使用findbyFleetFleet
,它会起作用
因此,我需要另一个方法,该方法返回Car对象的carType,我只在需要更多信息时使用它(如果我需要所有对象,JOIN-FETCH可以处理一个对象?)。
我发现的唯一工作方式是:
@SuppressWarnings("unchecked")
@Override
public List<CarWithCarType> findByFleetIdFleetFetch(int idFleet) {
String jpql = "select f from Fleet f where f.idFleet = :idFleet";
Query query = entityManager.createQuery(jpql);
query.setParameter("idFleet", idFleet);
Fleet fleet=(Fleet) query.getSingleResult();
String jpql2 = "select c from Car c JOIN FETCH c.carType where c.fleet = :fleet";
Query query2 = entityManager.createQuery(jpql2);
query2.setParameter("fleet", fleet);
List<Car> cars= query2.getResultList();
List<CarWithCarType> carsList = new ArrayList<CarWithCarType>();
for (Car car: cars){
CarWithCarType newCar = new CarWithCarType();
newCar.setId(car.getId());
newCar.setCarChassis(car.getCarChassis());
newCar.setCarType(car.getCarType());
newCar.setIdCar(car.getIdCar());
newCar.setInitialKm(car.getInitialKm());
newCar.setNote(car.getNote());
carsList.add(newCar);
}
return carsList;
}
所以我使用了Hibernate.initialize(car.getCarType())并且它可以工作。正确吗 我认为解决方案是(使用其中一种):
hbm.enable(Hibernate4Module.Feature.FORCE\u LAZY\u加载)代码>
当然,您可以手动初始化,但此解决方案要简单得多。您收到LazyInitializationException了吗?没有,我使用StackTrace更新了我相信代理对象带有id(proxy.getId()
),因此,您可以进行另一个DB调用,传递id并获得完整的对象1)Earge有什么区别?它总是序列化所有对象吗?2) 它是另一个bean中的副本,但查询必须以任何方式进行1)在检索Car后立即向db进行查询。2) 我不明白。。。你有杰克逊的例外。您是否正确配置了它?如果你想解决这个问题,你应该这样做。使用它有什么障碍吗?强制加载将填充所有外部对象?它不是比使用另一个只包含所需对象的类并在需要时调用它更重吗?更重-它可能会加载您不需要的字段。您可以使用此问题
ERROR com.controller.ErrorController - org.springframework.http.converter.HttpMessageNotWritableException: Could not write content: No serializer found for class org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) ) (through reference chain: com.model.tablesField.TableUI["data"]->java.util.ArrayList[0]->com.domain.Car["carType"]->com.domain.CarType_$$_jvst4de_f["handler"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: No serializer found for class org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) ) (through reference chain: com.model.tablesField.TableUI["data"]->java.util.ArrayList[0]->com.domain.Car["carType"]->com.domain.CarType_$$_jvst4de_f["handler"])
at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:271)
at org.springframework.http.converter.AbstractGenericHttpMessageConverter.write(AbstractGenericHttpMessageConverter.java:100)
at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:167)
at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:100)
at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.handleReturnValue(RequestResponseBodyMethodProcessor.java:166)
at org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:80)
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:127)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:806)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:729)
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:959)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
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.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:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:673)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1526)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1482)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
Caused by: com.fasterxml.jackson.databind.JsonMappingException: No serializer found for class org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) ) (through reference chain: com.model.tablesField.TableUI["data"]->java.util.ArrayList[0]->com.domain.Car["carType"]->com.domain.CarType_$$_jvst4de_f["handler"])
at com.fasterxml.jackson.databind.ser.impl.UnknownSerializer.failForEmpty(UnknownSerializer.java:59)
at com.fasterxml.jackson.databind.ser.impl.UnknownSerializer.serialize(UnknownSerializer.java:26)
at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:505)
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:639)
at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:152)
at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:505)
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:639)
at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:152)
at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serializeContents(IndexedListSerializer.java:100)
at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serializeContents(IndexedListSerializer.java:21)
at com.fasterxml.jackson.databind.ser.std.AsArraySerializerBase.serialize(AsArraySerializerBase.java:183)
at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:505)
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:639)
at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:152)
at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:128)
at com.fasterxml.jackson.databind.ObjectWriter.writeValue(ObjectWriter.java:602)
at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:264)
... 37 more
.11:24:38.387 [http-nio-8086-exec-4] WARN o.s.w.s.m.m.a.ExceptionHandlerExceptionResolver - Handler execution resulted in exception: Could not write content: No serializer found for class org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) ) (through reference chain: com.model.tablesField.TableUI["data"]->java.util.ArrayList[0]->com.domain.Car["carType"]->com.domain.CarType_$$_jvst4de_f["handler"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: No serializer found for class org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) ) (through reference chain: com.model.tablesField.TableUI["data"]->java.util.ArrayList[0]->com.domain.Car["carType"]->com.domain.CarType_$$_jvst4de_f["handler"])
@SuppressWarnings("unchecked")
@Override
public List<CarWithCarType> findByFleetIdFleetFetch(int idFleet) {
String jpql = "select f from Fleet f where f.idFleet = :idFleet";
Query query = entityManager.createQuery(jpql);
query.setParameter("idFleet", idFleet);
Fleet fleet=(Fleet) query.getSingleResult();
String jpql2 = "select c from Car c JOIN FETCH c.carType where c.fleet = :fleet";
Query query2 = entityManager.createQuery(jpql2);
query2.setParameter("fleet", fleet);
List<Car> cars= query2.getResultList();
List<CarWithCarType> carsList = new ArrayList<CarWithCarType>();
for (Car car: cars){
CarWithCarType newCar = new CarWithCarType();
newCar.setId(car.getId());
newCar.setCarChassis(car.getCarChassis());
newCar.setCarType(car.getCarType());
newCar.setIdCar(car.getIdCar());
newCar.setInitialKm(car.getInitialKm());
newCar.setNote(car.getNote());
carsList.add(newCar);
}
return carsList;
}
public MappingJackson2HttpMessageConverter jacksonMessageConverter(){
MappingJackson2HttpMessageConverter messageConverter = new MappingJackson2HttpMessageConverter();
ObjectMapper mapper = new ObjectMapper();
//Registering Hibernate4Module to support lazy objects
mapper.registerModule(new Hibernate4Module());
messageConverter.setObjectMapper(mapper);
return messageConverter;
}
@Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
//Here we add our custom-configured HttpMessageConverter
converters.add(jacksonMessageConverter());
super.configureMessageConverters(converters);
}
{
"data": [
{
"idCar": 4,
"carType": null,
"fleet": null,
"id": "06",
"initialKm": 1000,
"carChassis": "VPNEWCAR",
"note": ""
}
]
}