title: Tomcat HTTP Status 500 - could not initialize proxy - no Session
body: <p>I have an error when I run as Server my application, and I know why. This is my error:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>HTTP Status 500 - could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]-&gt;it.jack.fdd.model.Staff["staffType"]-&gt;it.jack.fdd.model.StaffType_$$_jvstbaa_15["type"])
  
  
  type Exception report
  
  message could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]-&gt;it.jack.fdd.model.Staff["staffType"]-&gt;it.jack.fdd.model.StaffType_$$_jvstbaa_15["type"])
  
  description The server encountered an internal error that prevented it from fulfilling this request.
  
  exception
  org.codehaus.jackson.map.JsonMappingException: could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]-&gt;it.jack.fdd.model.Staff["staffType"]-&gt;it.jack.fdd.model.StaffType_$$_jvstbaa_15["type"])
   org.codehaus.jackson.map.JsonMappingException.wrapWithPath(JsonMappingException.java:218)
   org.codehaus.jackson.map.JsonMappingException.wrapWithPath(JsonMappingException.java:183)
   org.codehaus.jackson.map.ser.std.SerializerBase.wrapAndThrow(SerializerBase.java:140)
   org.codehaus.jackson.map.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:158)
   org.codehaus.jackson.map.ser.BeanSerializer.serialize(BeanSerializer.java:112)
   org.codehaus.jackson.map.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:446)
   org.codehaus.jackson.map.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:150)
   org.codehaus.jackson.map.ser.BeanSerializer.serialize(BeanSerializer.java:112)
   org.codehaus.jackson.map.ser.std.CollectionSerializer.serializeContents(CollectionSerializer.java:72)
   org.codehaus.jackson.map.ser.std.CollectionSerializer.serializeContents(CollectionSerializer.java:23)
   org.codehaus.jackson.map.ser.std.AsArraySerializerBase.serialize(AsArraySerializerBase.java:86)
   org.codehaus.jackson.map.ser.StdSerializerProvider._serializeValue(StdSerializerProvider.java:659)
   org.codehaus.jackson.map.ser.StdSerializerProvider.serializeValue(StdSerializerProvider.java:271)
   org.codehaus.jackson.map.ObjectWriter.writeValue(ObjectWriter.java:325)
   org.codehaus.jackson.jaxrs.JacksonJsonProvider.writeTo(JacksonJsonProvider.java:556)
   com.sun.jersey.json.impl.provider.entity.JacksonProviderProxy.writeTo(JacksonProviderProxy.java:160)
   com.sun.jersey.spi.container.ContainerResponse.write(ContainerResponse.java:302)
   com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1510)
   com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1419)
   com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1409)
   com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:409)
   com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:558)
   com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:733)
   javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
   org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
  
  
  root cause
  org.hibernate.LazyInitializationException: could not initialize proxy - no Session
   org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:165)
   org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:286)
   org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:185)
   it.jack.fdd.model.StaffType_$$_jvstbaa_15.getType(StaffType_$$_jvstbaa_15.java)
   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:497)
   org.codehaus.jackson.map.ser.BeanPropertyWriter.get(BeanPropertyWriter.java:483)
   org.codehaus.jackson.map.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:418)
   org.codehaus.jackson.map.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:150)
   org.codehaus.jackson.map.ser.BeanSerializer.serialize(BeanSerializer.java:112)
   org.codehaus.jackson.map.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:446)
   org.codehaus.jackson.map.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:150)
   org.codehaus.jackson.map.ser.BeanSerializer.serialize(BeanSerializer.java:112)
   org.codehaus.jackson.map.ser.std.CollectionSerializer.serializeContents(CollectionSerializer.java:72)
   org.codehaus.jackson.map.ser.std.CollectionSerializer.serializeContents(CollectionSerializer.java:23)
   org.codehaus.jackson.map.ser.std.AsArraySerializerBase.serialize(AsArraySerializerBase.java:86)
   org.codehaus.jackson.map.ser.StdSerializerProvider._serializeValue(StdSerializerProvider.java:659)
   org.codehaus.jackson.map.ser.StdSerializerProvider.serializeValue(StdSerializerProvider.java:271)
   org.codehaus.jackson.map.ObjectWriter.writeValue(ObjectWriter.java:325)
   org.codehaus.jackson.jaxrs.JacksonJsonProvider.writeTo(JacksonJsonProvider.java:556)
   com.sun.jersey.json.impl.provider.entity.JacksonProviderProxy.writeTo(JacksonProviderProxy.java:160)
   com.sun.jersey.spi.container.ContainerResponse.write(ContainerResponse.java:302)
   com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1510)
   com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1419)
   com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1409)
   com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:409)
   com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:558)
   com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:733)
   javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
   org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)</code></pre>
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  </div>
  </p>
  
  <p>check it out: <code>java.util.ArrayList[0]-&gt;it.jack.fdd.model.Staff["staffType"]-&gt;it.jack.fdd.model.StaffType_$$_jvstbaa_15["type"])</code></p>
  
  <p>This is because I have two model classes, join on two tables of my database, this two classes are:</p>
  
  <p>Staff.java:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>package it.jack.fdd.model;
  // Generated 30-nov-2016 0.17.09 by Hibernate Tools 4.3.1.Final
  
  import java.util.Date;
  import java.util.HashSet;
  import java.util.Set;
  import javax.persistence.Column;
  import javax.persistence.Entity;
  import javax.persistence.FetchType;
  import javax.persistence.GeneratedValue;
  import static javax.persistence.GenerationType.IDENTITY;
  import javax.persistence.Id;
  import javax.persistence.JoinColumn;
  import javax.persistence.ManyToOne;
  import javax.persistence.OneToMany;
  import javax.persistence.OneToOne;
  import javax.persistence.Table;
  import javax.persistence.Temporal;
  import javax.persistence.TemporalType;
  import javax.xml.bind.annotation.XmlRootElement;
  
  import org.codehaus.jackson.annotate.JsonIgnore;
  
  /**
   * Staff generated by hbm2java
   */
  @XmlRootElement
  @Entity
  @Table(name = "staff", catalog = "fdd_dbproducts")
  public class Staff implements java.io.Serializable {
  
   private Integer idstaff;
   private StaffType staffType;
   private String name;
   private String surname;
   private Date birthDate;
   private String phone;
   private boolean gender;
   private StaffLogin staffLogin;
   private Set&lt;RtStaffDispenser&gt; rtStaffDispensers = new HashSet&lt;RtStaffDispenser&gt;(0);
  
   public Staff() {
   }
  
   public Staff(StaffType staffType, String name, String surname, Date birthDate, String phone, boolean gender) {
    this.staffType = staffType;
    this.name = name;
    this.surname = surname;
    this.birthDate = birthDate;
    this.phone = phone;
    this.gender = gender;
   }
  
   public Staff(StaffType staffType, String name, String surname, Date birthDate, String phone, boolean gender,
     StaffLogin staffLogin, Set&lt;RtStaffDispenser&gt; rtStaffDispensers) {
    this.staffType = staffType;
    this.name = name;
    this.surname = surname;
    this.birthDate = birthDate;
    this.phone = phone;
    this.gender = gender;
    this.staffLogin = staffLogin;
    this.rtStaffDispensers = rtStaffDispensers;
   }
  
   @Id
   @GeneratedValue(strategy = IDENTITY)
  
   @Column(name = "idstaff", unique = true, nullable = false)
   public Integer getIdstaff() {
    return this.idstaff;
   }
  
   public void setIdstaff(Integer idstaff) {
    this.idstaff = idstaff;
   }
  
   @ManyToOne(fetch = FetchType.LAZY)
   @JoinColumn(name = "fkstaff_type_staff", nullable = false)
   @JsonIgnore
   public StaffType getStaffType() {
    return this.staffType;
   }
  
   public void setStaffType(StaffType staffType) {
    this.staffType = staffType;
   }
  
   @Column(name = "name", nullable = false, length = 45)
   public String getName() {
    return this.name;
   }
  
   public void setName(String name) {
    this.name = name;
   }
  
   @Column(name = "surname", nullable = false, length = 45)
   public String getSurname() {
    return this.surname;
   }
  
   public void setSurname(String surname) {
    this.surname = surname;
   }
  
   @Temporal(TemporalType.DATE)
   @Column(name = "birth_date", nullable = false, length = 10)
   public Date getBirthDate() {
    return this.birthDate;
   }
  
   public void setBirthDate(Date birthDate) {
    this.birthDate = birthDate;
   }
  
   @Column(name = "phone", nullable = false, length = 45)
   public String getPhone() {
    return this.phone;
   }
  
   public void setPhone(String phone) {
    this.phone = phone;
   }
  
   @Column(name = "gender", nullable = false)
   public boolean isGender() {
    return this.gender;
   }
  
   public void setGender(boolean gender) {
    this.gender = gender;
   }
  
   @OneToOne(fetch = FetchType.LAZY, mappedBy = "staff")
   @JsonIgnore
   public StaffLogin getStaffLogin() {
    return this.staffLogin;
   }
  
   public void setStaffLogin(StaffLogin staffLogin) {
    this.staffLogin = staffLogin;
   }
  
   @OneToMany(fetch = FetchType.LAZY, mappedBy = "staff")
   @JsonIgnore
   public Set&lt;RtStaffDispenser&gt; getRtStaffDispensers() {
    return this.rtStaffDispensers;
   }
  
   public void setRtStaffDispensers(Set&lt;RtStaffDispenser&gt; rtStaffDispensers) {
    this.rtStaffDispensers = rtStaffDispensers;
   }
  
  }</code></pre>
  </div>
  </div>
  </p>
  
  <p>and StaffType.java:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>package it.jack.fdd.model;
  // Generated 30-nov-2016 0.17.09 by Hibernate Tools 4.3.1.Final
  
  import java.util.HashSet;
  import java.util.Set;
  import javax.persistence.Column;
  import javax.persistence.Entity;
  import javax.persistence.FetchType;
  import javax.persistence.GeneratedValue;
  import static javax.persistence.GenerationType.IDENTITY;
  import javax.persistence.Id;
  import javax.persistence.OneToMany;
  import javax.persistence.Table;
  import javax.xml.bind.annotation.XmlRootElement;
  
  import org.codehaus.jackson.annotate.JsonIgnore;
  
  /**
   * StaffType generated by hbm2java
   */
  @XmlRootElement
  @Entity
  @Table(name = "staff_type", catalog = "fdd_dbproducts")
  public class StaffType implements java.io.Serializable {
  
   private Integer idstaffType;
   private String type;
   private Set&lt;Staff&gt; staffs = new HashSet&lt;Staff&gt;(0);
  
   public StaffType() {
   }
  
   public StaffType(String type) {
    this.type = type;
   }
  
   public StaffType(String type, Set&lt;Staff&gt; staffs) {
    this.type = type;
    this.staffs = staffs;
   }
  
   @Id
   @GeneratedValue(strategy = IDENTITY)
  
   @Column(name = "idstaff_type", unique = true, nullable = false)
   public Integer getIdstaffType() {
    return this.idstaffType;
   }
  
   public void setIdstaffType(Integer idstaffType) {
    this.idstaffType = idstaffType;
   }
  
   @Column(name = "type", nullable = false, length = 45)
   public String getType() {
    return this.type;
   }
  
   public void setType(String type) {
    this.type = type;
   }
  
   @OneToMany(fetch = FetchType.LAZY, mappedBy = "staffType")
   @JsonIgnore
   public Set&lt;Staff&gt; getStaffs() {
    return this.staffs;
   }
  
   public void setStaffs(Set&lt;Staff&gt; staffs) {
    this.staffs = staffs;
   }
  
  }</code></pre>
  </div>
  </div>
  </p>
  
  <p>And I have this error because I have a relation many to one between Staff and StaffType.
  This is the problem:</p>
  
  <pre><code>@OneToMany(fetch = FetchType.LAZY, mappedBy = "staffType")
  @JsonIgnore
  public Set&lt;Staff&gt; getStaffs() {
      return this.staffs;
  }
  </code></pre>
  
  <p>in fact, using @JsonIgnore it works! Now my question is: how can I fix it without @JsonIgnore? Because, if i use @JsonIgnore, my result json file doesn't contain the foreign key: fkstaff_type_staff. How I can fix it?
  Thanks.</p>
  
  <p>ps: This is my BaseDaoImpl.java:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>package it.jack.fdd.dao.impl;
  
  import it.jack.fdd.dao.interfaces.BaseDao;
  import it.jack.fdd.model.Product;
  import it.jack.fdd.model.Staff;
  import it.jack.fdd.model.User;
  import it.jack.fdd.util.HibernateUtilLezione;
  
  import java.io.Serializable;
  import java.util.Calendar;
  import java.util.Date;
  import java.util.List;
  
  import org.hibernate.HibernateException;
  import org.hibernate.Query;
  import org.hibernate.Session;
  import org.hibernate.SessionFactory;
  import org.hibernate.Transaction;
  
  public class BaseDaoImpl&lt;T&gt; implements BaseDao&lt;T&gt; {
  
   public BaseDaoImpl() {
    super();
   }
  
   /* (non-Javadoc)
    * @see it.unisalento.se.dao.impl.BaseDao#save(T)
    */
   public int save(T entity) {
   
    int id = 0;
    
    try {
     
     
     /*
      *  DIFFERENZA TRA openSession() e getCurrentSession):
      *  
        When you create a hibernate session using any of the sessionFactory.openSession(...)
       methods the session factory will 'bind' the session to the current context.
        The default context is 'thread' which means the sesion factory will bind the session
        to the thread from which openSession(...) is called. 
  
      This is useful because you can later call sessionFactory.getCurrentSession() which will
      return the session that is bound to the currently running thread. 
  
      You can use other predefined current_session_context_class values such as 'jta' which will
      bind the session to the currently running JTA transaction (if you're running in an
      application server that supports JTA this is really useful). Or you can write your
      own implementation of org.hibernate.context.CurrentSessionContext and use that implementation
      to manage the current session context (not really advisable unless you absolutely need to). 
      * 
      */
     
     
     //Prep work
     //SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
     
     Session session = HibernateUtilLezione.openSession(); //dall'esempio mio fa getCurrentSession()
     Transaction tx = session.beginTransaction();
     
     id =  (Integer) session.save(entity);
     tx.commit();
     session.close();
    }catch(HibernateException e){
     e.printStackTrace();
    }
    return id;
   }
  
   /* (non-Javadoc)
    * @see it.unisalento.se.dao.impl.BaseDao#getAll(java.lang.Class)
    */
   public List&lt;T&gt; getAll(Class clazz) {
    
    Session session = HibernateUtilLezione.openSession();
    Transaction tx = session.beginTransaction();
    
    @SuppressWarnings("unchecked")
    List&lt;T&gt; list = session.createQuery("from "+clazz.getName()).list();
    tx.commit();
    session.close();
      
    return list; 
   }
  
   /* (non-Javadoc)
    * @see it.unisalento.se.dao.impl.BaseDao#getById(int, java.lang.Class)
    */
   public T getById(int id, Class clazz) {
    try{
    
     Session session = HibernateUtilLezione.openSession();
     Transaction tx = session.beginTransaction();
     
     @SuppressWarnings("unchecked")
     T returnObj = (T) session.get(clazz.getName(), id);
     /*
     System.out.println("vediamo "+session.getIdentifier(returnObj));
     System.out.println("vediamo2 "+session.getEntityName(returnObj));
     */
     tx.commit();
     session.close();
     
     return returnObj;
    }
    catch(HibernateException e){
     e.printStackTrace();
     return null;
    }
    
   }
   
   /* (non-Javadoc)
    * @see it.unisalento.se.dao.impl.BaseDao#delete(int, java.lang.Class)
    */
   public void delete (int id, Class clazz){
    
    Session session = HibernateUtilLezione.openSession();
    Transaction tx = session.beginTransaction();
    
    T t = (T) session.get(clazz, id);
    session.delete(t);
    tx.commit();
    session.close();
    
   }
  
  
  /*
   public Serializable getByUID(Staff stf) {
    // TODO Auto-generated method stub
    return null;
   }
   */
  
   public void update(T entity) {
    try {
     Session session = HibernateUtilLezione.openSession();
     Transaction tx = session.beginTransaction();
       
     session.update(entity);
     tx.commit();
     session.close();
    }
    catch(HibernateException e){
     e.printStackTrace();
    }
    
   }
   
  }</code></pre>
  </div>
  </div>
  </p>