HTTP Status 500 - failed to lazily initialize a collection of role: ..., could not initialize proxy - no Session

Question

I try query customer list as json from spring controller. when i access url i can get list no error.

-CustomerController

@RequestMapping("getCustomerListRB")
public @ResponseBody List<Customer> getCustomerListsRB() {
    List<Customer> cusList = new ArrayList<Customer>();
    cusList = cusService.getList();
    return cusList;
}

but when i try join table in customer model -Customer.java

   @OneToMany(mappedBy = "Customer", cascade = CascadeType.ALL)
    private List<MainOrder> MainOrder;

    public List<MainOrder> getMainOrder() {
        return MainOrder;
    }
    public void setMainOrder(List<MainOrder> mainOrder) {
        MainOrder = mainOrder;
    }

run server again it have error like bellow:

org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: failed to lazily initialize a collection of role: com.mdr.model.Customer.mainOrders, could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]->com.mdr.model.Customer["mainOrders"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: failed to lazily initialize a collection of role: com.mdr.model.Customer.mainOrders, could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]->com.mdr.model.Customer["mainOrders"])
    org.springframework.http.converter.json.MappingJackson2HttpMessageConverter.writeInternal(MappingJackson2HttpMessageConverter.java:256)
    org.springframework.http.converter.AbstractHttpMessageConverter.write(AbstractHttpMessageConverter.java:208)
    org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:143)
    org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:89)
    org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.handleReturnValue(RequestResponseBodyMethodProcessor.java:193)
    org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:71)
    org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:122)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:749)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:689)
    org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:83)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:938)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:870)
    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:622)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

After i add fetch = FetchType.EAGER like below

@OneToMany(mappedBy = "Customer", cascade = CascadeType.ALL,fetch = FetchType.EAGER)

I run server again it don't have error but can't get data. please help me !

Rafal G. · Answer 1 · 2015-08-31T07:47:02.483

1

First of all, you need a transaction that will last long enough for the Session to be available for lazy fetching of the related entities. In your example, you are returning list of entities with unfetched related entities outside of the Transaction scope (Spring internals will transform List to JSON after the transaction has ended - that is why it fails).

You can do one of the following:

Skip lazyness in your relation since all related entities have to be fetched anyway to prerpare a full JSON response.
Modify your method to be: 'String getCustomerListsRB()' and use an ObjectMapper to serialize 'List' to JSON by yourself (you can autowire ObjectMapper to your controller).
Try to use Open Session In View filter, but I do strongly discourage you from using this approach as it affects performance because database connections are held longer than necessary.

edited Aug 31 '15 at 07:47

answered Aug 31 '15 at 05:29

Rafal G.

4,252
1
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41

I add @Transactional on 'List getCustomerListsRB' and change somethin same but it still error – Ma YongChhin Aug 31 '15 at 05:52
Post the stacktrace after adding @Transactional please. – Rafal G. Aug 31 '15 at 05:57
Sorry , what is stacktrace? – Ma YongChhin Aug 31 '15 at 06:03
http://stackoverflow.com/questions/3988788/what-is-a-stack-trace-and-how-can-i-use-it-to-debug-my-application-errors – Rafal G. Aug 31 '15 at 06:13
Alright. I see it now. Check edited answer for more details. – Rafal G. Aug 31 '15 at 07:43
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/88349/discussion-between-ma-yongchhin-and-r4j). – Ma YongChhin Aug 31 '15 at 07:46

tanson · Answer 2 · 2017-01-23T08:37:23.467

1

I got the same exception when using jackson with spring. Add @jsonignore to the field declared as lazy or creating circular dependancy in your entity class. Make sure you use same library's(codehaus/jackson/..) jsonignore in all layers of your application.

edited Jan 23 '17 at 08:37

answered Jan 23 '17 at 08:11

tanson

82
3

score 0 · Answer 3 · answered Jun 20 '17 at 16:14

Look at: Spring MVC :could not initialize proxy - no Session (through reference chain:

As a solution you could use addition entity annotation to prevent lazy init

@Entity @Table(name="Country") **@Proxy(lazy = false)** public class Country {}

or use @JsonBackReference in mapping

HTTP Status 500 - failed to lazily initialize a collection of role: ..., could not initialize proxy - no Session

3 Answers3