Spring data and hibernate error with mysql in java

Question

I have been using Spring data and Hibernate to make query to mySql database. I Have an error

[http-nio-8086-exec-3] ERROR com.controller.ErrorController - org.springframework.http.converter.HttpMessageNotWritableException: Could not write content: could not initialize proxy - no Session (through reference chain: com.model.Response["body"]->java.util.ArrayList[0]->com.domain.Car["carType"]->com.domain.CarType_$$_jvste93_e["note"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: could not initialize proxy - no Session (through reference chain: com.model.Response["body"]->java.util.ArrayList[0]->com.domain.Car["carType"]->com.domain.CarType_$$_jvste93_e["note"]) 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)

and I would like to undestand why, if the problem is into my entity or in my code. I made entity through Hibernate tools Plugin, and this is part of car entity:

@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;
    private Set<Acquisition> acquisitions = new HashSet<Acquisition>(0);

carType:

    @Entity
@Table(name = "carType", catalog = "ATS")
public class CarType implements java.io.Serializable {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private String idCarType;
    private String note;
    //private Set<Car> cars = new HashSet<Car>(0);

    public CarType() {
    }

    public CarType(String idCarType) {
        this.idCarType = idCarType;
    }

    public CarType(String idCarType, String note, Set<Car> cars) {
        this.idCarType = idCarType;
        this.note = note;
//      this.cars = cars;
    }

    @Id

    @Column(name = "id_carType", unique = true, nullable = false, length = 5)
    public String getIdCarType() {
        return this.idCarType;
    }

    public void setIdCarType(String idCarType) {
        this.idCarType = idCarType;
    }

    @Column(name = "note", length = 100)
    public String getNote() {
        return this.note;
    }

    public void setNote(String note) {
        this.note = note;
    }

//  @OneToMany(fetch = FetchType.LAZY, mappedBy = "carType")
//  public Set<Car> getCars() {
//      return this.cars;
//  }
//
//  public void setCars(Set<Car> cars) {
//      this.cars = cars;
//  }

}

and this is part of my database ER shema:

In my Spring controller:

@Override
@RequestMapping(value = { "/cars/{idFleet}"}, method = RequestMethod.GET)
public @ResponseBody Response<List<Car>> getCars(@PathVariable int idFleet) throws QueryException{
    Response<List<Car>> cars=fleetAndCarService.findCarsByIdFleet(idFleet);
    return cars;

}

The query is so defined:

public interface CarRepository extends JpaRepository<Car, Integer> {

    //Query method of spring 
    List<Car> findByFleetIdFleet(int idFleet);
}

Service method:

@Override
    public Response<List<Car>> findCarsByIdFleet(int idFleet) throws QueryException {
        try{
            List<Car> cars=databaseFleetsAndCarsServices.findCarsByIdFleet(idFleet);
            System.out.println("Number of acquisition: "+cars.get(0).getAcquisitions().size());
            return new Response<List<Car>>(HttpStatus.OK.value(),databaseFleetsAndCarsServices.findCarsByIdFleet(idFleet));
        } catch (Exception e) {
            throw new QueryException(e);
        }
    }

return:

Caused by: org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.domain.Car.acquisitions, could not initialize proxy - no Session

What do you think?Thanks,regards

UPDATE with my configuration class

@EnableWebMvc
@Configuration
@PropertySource(value = { "classpath:application.properties" })
@ComponentScan({ "com.*" })
@EnableTransactionManagement
@Import({ SpringMvcInitializer.class })
@EnableJpaRepositories("com.repository")
public class AppConfig extends WebMvcConfigurerAdapter{
    @Autowired
    private Environment env;

    private static final String PROPERTY_NAME_DATABASE_DRIVER = "db.driver";
    private static final String PROPERTY_NAME_DATABASE_PASSWORD = "db.password";
    private static final String PROPERTY_NAME_DATABASE_URL = "db.url";
    private static final String PROPERTY_NAME_DATABASE_USERNAME = "db.username";

    private static final String PROPERTY_NAME_HIBERNATE_DIALECT = "hibernate.dialect";
    private static final String PROPERTY_NAME_HIBERNATE_SHOW_SQL = "hibernate.show_sql";
    private static final String PROPERTY_NAME_ENTITYMANAGER_PACKAGES_TO_SCAN = "entitymanager.packages.to.scan";
    private static final String PROPERTY_NAME_HIBERNATE_FORMAT_SQL = "hibernate.format_sql";

    private Properties getHibernateProperties() {
        Properties properties = new Properties();
        properties.put(PROPERTY_NAME_HIBERNATE_DIALECT, env.getRequiredProperty(PROPERTY_NAME_HIBERNATE_DIALECT));
        properties.put(PROPERTY_NAME_HIBERNATE_SHOW_SQL, env.getRequiredProperty(PROPERTY_NAME_HIBERNATE_SHOW_SQL));
        properties.put(PROPERTY_NAME_HIBERNATE_FORMAT_SQL, env.getRequiredProperty(PROPERTY_NAME_HIBERNATE_FORMAT_SQL));
        return properties;
    }

    @Bean(name = "dataSource")
    public BasicDataSource dataSource() {
        BasicDataSource ds = new BasicDataSource();
        ds.setDriverClassName(env.getRequiredProperty(PROPERTY_NAME_DATABASE_DRIVER));
        ds.setUrl(env.getRequiredProperty(PROPERTY_NAME_DATABASE_URL));
        ds.setUsername(env.getRequiredProperty(PROPERTY_NAME_DATABASE_USERNAME));
        ds.setPassword(env.getRequiredProperty(PROPERTY_NAME_DATABASE_PASSWORD));
        return ds;
    }

    @Bean
    public ServletContextTemplateResolver TemplateResolver(){
        ServletContextTemplateResolver resolver = new ServletContextTemplateResolver();
        resolver.setPrefix("/WEB-INF/templates/pages/");
        resolver.setSuffix(".html");
        resolver.setTemplateMode("LEGACYHTML5");
        resolver.setCacheable(false);
        return resolver;
        /*ServletContextTemplateResolver resolver = new ServletContextTemplateResolver();
        resolver.setPrefix("/WEB-INF/pages/");
        resolver.setSuffix(".html");
        resolver.setTemplateMode("HTML5");
        return resolver;*/
    }

    @Bean
    public SpringTemplateEngine templateEngine(){
        SpringTemplateEngine templateEngine = new SpringTemplateEngine();
        templateEngine.setTemplateResolver(TemplateResolver());
        return templateEngine;
    }


    @Bean
    public ThymeleafViewResolver viewResolver() {
        ThymeleafViewResolver resolver = new ThymeleafViewResolver();
        resolver.setTemplateEngine(templateEngine());
        resolver.setOrder(1);
        resolver.setViewNames(new String[]{"*", "js/*", "template/*"});
        return resolver;
    }

    /**
     * Register multipartResolver for file upload
     * @return
     */
    @Bean
    public CommonsMultipartResolver multipartResolver() {
        CommonsMultipartResolver resolver=new CommonsMultipartResolver();
        resolver.setDefaultEncoding("utf-8");
        return resolver;    
    }

    /**
     * Allow use of bootstrap
     */
    @Override
    public void addResourceHandlers(ResourceHandlerRegistry registry) {
            registry.addResourceHandler("/static/**")
                    .addResourceLocations("/static/");
    }

    /**
     * Allow use of JPA
     */
    @Bean
    public JpaTransactionManager transactionManager() {
        JpaTransactionManager transactionManager = new JpaTransactionManager();
        transactionManager.setEntityManagerFactory(entityManagerFactory().getObject());
        return transactionManager;
    }
    @Bean
    public LocalContainerEntityManagerFactoryBean entityManagerFactory() {
        LocalContainerEntityManagerFactoryBean entityManagerFactoryBean = new LocalContainerEntityManagerFactoryBean();
        entityManagerFactoryBean.setDataSource(dataSource());
        entityManagerFactoryBean.setPersistenceProviderClass(HibernatePersistenceProvider.class);
        entityManagerFactoryBean.setPackagesToScan(env.
        getRequiredProperty(PROPERTY_NAME_ENTITYMANAGER_PACKAGES_TO_SCAN));
        entityManagerFactoryBean.setJpaProperties(getHibernateProperties());
        return entityManagerFactoryBean;

    }

Answer 1

Add this property to your EntityManager configuration

<prop key="hibernate.enable_lazy_load_no_trans">true</prop>

Example:

<bean id="entityManagerFactory"
  class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
<property name="dataSource" ref="myDataSource"/>
<property name="packagesToScan" value="com.mycompany.somepackage"/>
<property name="jpaVendorAdapter" ref="hibernateVendorAdapter"/>
<property name="jpaDialect" ref="jpaDialect"/>
<property name="jpaProperties">
    <props>
        <prop key="hibernate.enable_lazy_load_no_trans">true</prop>
    </props>
</property>

Java Config:

@Bean
    public LocalContainerEntityManagerFactoryBean entityManagerFactory(){
        LocalContainerEntityManagerFactoryBean entityManager = new LocalContainerEntityManagerFactoryBean();
        //..
        entityManager.setJpaProperties(additionalProperties());
        //..
        return entityManager;
    }


  public Properties additionalProperties(){
        Properties properties = new Properties();

        // Etc
        properties.setProperty("hibernate.enable_lazy_load_no_trans",true));
     // Etc
    return properties;
  }