java - Solution for JsonMappingException: lazily initialize a collection without using @Jsonignore -

i need response json output. shows exception

org.codehaus.jackson.map.jsonmappingexception: failed lazily initialize collection of role: com.sublime.np.entity.user.roles, not initialize proxy - no session (through reference chain: java.util.arraylist[0]->com.sublime.np.entity.question["user"]->com.sublime.np.entity.user["roles"])     @ 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.stdcontainerserializers$indexedlistserializer.serializecontents(stdcontainerserializers.java:122)     @ org.codehaus.jackson.map.ser.std.stdcontainerserializers$indexedlistserializer.serializecontents(stdcontainerserializers.java:71)     @ org.codehaus.jackson.map.ser.std.asarrayserializerbase.serialize(asarrayserializerbase.java:86)     @ org.codehaus.jackson.map.ser.stdserializerprovider._serializevalue(stdserializerprovider.java:610)     @ org.codehaus.jackson.map.ser.stdserializerprovider.serializevalue(stdserializerprovider.java:256)     @ org.codehaus.jackson.map.objectmapper.writevalue(objectmapper.java:1613)     @ org.springframework.http.converter.json.mappingjacksonhttpmessageconverter.writeinternal(mappingjacksonhttpmessageconverter.java:209)     @ 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) 

i used many relationship among entities. qustion entity looks like,

@entity public class question {      @id     @generatedvalue     private integer id;      @size(min=5, message = "title must @ least 5 characters !" )     private string title;      @size(min=20, message = "description must @ least 20 characters !" )     private string description;      private int upvote;      private int downvote;      @column(name = "published_date")     private date publisheddate;      @manytoone     @joincolumn(name="user_id")      private user user;      @onetomany(mappedby="question", cascade=cascadetype.remove)     private list<answer> answers;      @onetomany(mappedby="question", cascade=cascadetype.remove)      private list<comment> comments;      @manytoone     @joincolumn(name="tag_id")     private tag tag; 

when use @jsonignore annotation, works. json field in relationship disappear.

@onetomany(mappedby="question", cascade=cascadetype.remove)     @jsonignore       private list<answer> answers;      @onetomany(mappedby="question", cascade=cascadetype.remove)     @jsonignore       private list<comment> comments;      @manytoone     @joincolumn(name="tag_id")     @jsonignore       private tag tag; 

json after using @jsonignore,

[   {     "id": 1,     "title": "abc",     "description": "abc",     "upvote": 0,     "downvote": 0,     "publisheddate": 1433436068000   },   {     "id": 2,     "title": "sql exception",     "description": "abc",     "upvote": 0,     "downvote": 0,     "publisheddate": 1433436068000   } ] 

my controller,

@requestmapping(value = "getquestion", method = requestmethod.get)     public @responsebody list<question> getquestion() {         list<question> questions = questionservice.getall();         return questions; } 

so, need json fields of entity. how can ? idea ?

if you're using spring, opensessioninviewfilter http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/orm/hibernate3/support/opensessioninviewfilter.html or can make @onetomany fetch eager https://docs.oracle.com/javaee/6/api/javax/persistence/onetomany.html

more reading: http://howtodoinjava.com/2014/09/26/lazy-loading-in-hibernate/