Hibernate Interview Questions and Answers1. What is Hibernate
Framework?Object-relational mapping or ORM s the programmng
technque to map appcaton doman mode ob|ects to the reatona database
tabes. Hbernate s |ava based ORM too that provdes framework for
mappng appcaton doman ob|ects to the reatona database tabes and vce
versa.Hbernate provdes reference mpementaton of |ava Persstence
API, that makes t a great choce as ORM too wth benets of oose
coupng. We can use Hbernate persstence API for CRUD operatons.
Hbernate framework provde opton to map pan od |ava ob|ects to
tradtona database tabes wth the use of |PA annotatons as we as XML
based conguraton.Smary hbernate conguratons are exbe and can be
done from XML conguraton e as we as programmatcay. For a quck
overvew of hbernate framework usage, you can go through Hbernate
Begnners Tutora.2. What is Java Persistence API (JPA)?|ava
Persstence API (|PA) provdes speccaton for managng the reatona data
n appcatons. Current |PA verson 2.1 was started n |uy 2011 as |SR
338. |PA 2.1 was approved as na on 22 May 2013.|PA speccatons s
dened wth annotatons n |avax.persstence package. Usng |PA annotaton
heps us n wrtng mpementaton ndependent code.3. What are the
important beneits o !sin" Hibernate Framework?Some of the mportant
benets of usng hbernate framework are:A. Hbernate emnates a the
boer-pate code that comes wth |DBC and takes care of managng
resources, so we can focus on busness ogc.B. Hbernate framework
provdes support for XML as we as |PA annotatons, that makes our
code mpementaton ndependent.C. Hbernate provdes a powerfu query
anguage (HOL) that s smar to SOL. However, HOL s fuy ob|ect-orented
and understands concepts ke nhertance, poymorphsm and assocaton.D.
Hbernate s an open source pro|ect from Red Hat Communty and used
wordwde. Ths makes t a better choce than others because earnng
curve s sma and there are tons of onne documentatons and hep s easy
avaabe n forums.E. Hbernate s easy to ntegrate wth other |ava EE
frameworks, ts sopopuar that Sprng Framework provdes but-n support
for ntegratng hbernate wth Sprng appcatons.F. Hbernate supports azy
ntazaton usng proxy ob|ects and perform actua database queres ony
when ts requred.G. Hbernate cache heps us n gettng better
performance.H. For database vendor specc feature, hbernate s sutabe
because we can aso execute natve sq queres.Overa hbernate s the
best choce n current market for ORM too, t contans a the features
that you w ever need n an ORM too.#. What are the a$vanta"es o
Hibernate over J%&'?Some of the mportant advantages of Hbernate
framework over |DBC are:A. Hbernate removes a ot of boer-pate code
that comes wth |DBC API, the code ooks more ceaner and readabe.B.
Hbernate supports nhertance, assocatons and coectons. These
features are not present wth |DBC API.C. Hbernate mpcty provdes
transacton management, n fact most of the queres cant be executed
outsde transacton. In |DBC API, we need to wrte code for transacton
management usng commt and roback. Read more at |DBC Transacton
Management.D. |DBC API throws SOLExcepton that s a checked
excepton, so we needto wrte a ot of try-catch bock code. Most of
the tmes ts redundant n every |DBC ca and used for transacton
management. Hbernate wraps |DBC exceptons and throw |DBCExcepton or
HbernateExcepton un-checked excepton, so we dont need to wrte code
to hande t. Hbernate but-n transacton management removes the usage
of try-catch bocks.E. Hbernate Ouery Language (HOL) s more ob|ect
orented and cose to |ava programmng anguage. For |DBC, we need to
wrte natve sq queres.F. Hbernate supports cachng that s better for
performance, |DBC queres are not cached hence performance s ow.G.
Hbernate provde opton through whch we can create database tabes
too, for |DBC tabes must exst n the database.H. Hbernate conguraton
heps us n usng |DBC ke connecton as we as |NDI DataSource for
connecton poo. Ths s very mportant feature n enterprse appcaton and
competey mssng n |DBC API.I. Hbernate supports |PA annotatons, so
code s ndependent of mpementaton and easy repaceabe wth other ORM
toos. |DBC code s very tghty couped wth the appcaton.(. )ame some
important interaces o Hibernate ramework?Some of the mportant
nterfaces of Hbernate framework are:A. SessionFactory
(org.hibernate.SessionFactory): SessonFactory s an mmutabe
thread-safe cache of comped mappngsfor a snge database. We need to
ntaze SessonFactory once and thenwe can cache and reuse t.
SessonFactory nstance s used to get the Sesson ob|ects for database
operatons.B. Session (org.hibernate.Session): Sesson s a
snge-threaded, short-ved ob|ect representng a conversaton between
the appcaton and the persstent store. It wraps |DBC
|ava.sq.Connectonand works as a factory for
org.hbernate.Transacton. We shoud open sesson ony when ts requred
and cose t as soon as we are done usng t. Sesson ob|ect s the
nterface between |ava appcaton code and hbernate framework and
provde methods for CRUD operatons.C. Transaction
(org.hibernate.Transaction): Transacton s a snge-threaded,
short-ved ob|ect used by the appcaton to specfy atomc unts of work.
It abstracts the appcaton from the underyng |DBC or |TA transacton.
A org.hbernate.Sesson mght span mutpe org.hbernate.Transacton n
some cases.*. What is hibernate coni"!ration i+e?Hbernate
conguraton e contans database specc conguratons and used to ntaze
SessonFactory. We provde database credentas or |NDI resource
nformaton n the hbernate conguraton xm e. Some other mportant parts
of hbernate conguraton e s Daect nformaton, so that hbernate knows
the database type and mappng e or cass detas.,. What is hibernate
mappin" i+e?Hbernate mappng e s used to dene the entty bean eds and
database tabe coumn mappngs. We know that |PA annotatons can be
used for mappng but sometmes XML mappng e comes handy when we are
usng thrd party casses and we cant use annotatons.-. )ame some
important annotations !se$ or Hibernate mappin"?Hbernate supports
|PA annotatons and t has some other annotatons n
org.hbernate.annotatonspackage. Some of the mportant |PA and
hbernate annotatons used are:A. javax.persistence.Entity: Used wth
mode casses to specfy thatthey are entty beans.B.
javax.persistence.Table: Used wth entty beans to dene the
correspondng tabe name n database.C. javax.persistence.Access: Used
to dene the access type, ether ed or property. Defaut vaue s ed and
f you want hbernate to use getter/setter methods then you need to
set t to property.D. javax.persistence.I: Used to dene the prmary
key n the entty bean.E. javax.persistence.EmbeeI: Used to dene
composte prmary key n the entty bean.F. javax.persistence.!ol"mn:
Used to dene the coumn name n database tabe.G.
javax.persistence.#enerate$al"e: Used to dene the strategy to be
used for generaton of prmary key. Used n con|uncton wth
|avax.persstence.GeneratonType enum.H. javax.persistence.OneToOne:
Used to dene the one-to-one mappng between two entty beans. We have
other smar annotatons as OneToMany, ManyToOne and ManyToManyI.
org.hibernate.annotations.!ascae: Used to dene the cascadng between
two entty beans, used wth mappngs. It works n con|uncton wth
org.hbernate.annotatons.CascadeType|.
javax.persistence.%rimary&ey'oin!ol"mn: Used to dene the
property for foregn key. Used
wthorg.hbernate.annotatons.GenercGenerator and
org.hbernate.annotatons.ParameterHere are two casses showng usage
of these annotatons.Empoyee.|ava123456789101package
com.journaldev.hibernate.model; import
javax.persistence.Access;import javax.persistence.AccessType;import
javax.persistence.Column;import javax.persistence.Entity;import
javax.persistence.GeneratedValue;import
javax.persistence.GenerationType;import javax.persistence.Id;import
javax.persistence.neTone;import javax.persistence.Table;
11213141516171819202122232425262import
org.hibernate.annotations.Cascade; !Entity!Table"name $
%E&'()EE%*!Access"value$AccessType.+IE(,*public class Employee
- !Id!GeneratedValue"strategy $
GenerationType.I,E.TIT)*!Column"name $ %emp/id%*private long id;
!Column"name $ %emp/name%*private 0tring name; !neTone"mapped1y $
%employee%*!Cascade"value $
org.hibernate.annotations.CascadeType.A((*private Address address;
22getter setter
methods37282930313233Address.|ava1234567891011121package
com.journaldev.hibernate.model; import
javax.persistence.Access;import javax.persistence.AccessType;import
javax.persistence.Column;import javax.persistence.Entity;import
javax.persistence.GeneratedValue;import javax.persistence.Id;import
javax.persistence.neTone;import
javax.persistence.'rimary4ey5oinColumn;import
javax.persistence.Table; import
org.hibernate.annotations.GenericGenerator;import
org.hibernate.annotations.'arameter;
31415161718192021222324252627282!Entity!Table"name $
%A,,6E00%*!Access"value$AccessType.+IE(,*public class Address -
!Id!Column"name $ %emp/id%7 uni8ue $ true7 nullable $
9alse*!GeneratedValue"generator $ %gen%*!GenericGenerator"name $
%gen%7 strategy $ %9oreign%7 parameters $ - !'arameter"name $
%property%7 value $ %employee%* 3*private long id; !Column"name $
%address/line:%*private 0tring address(ine:;
!neTone!'rimary4ey5oinColumnprivate Employee employee; 22getter
setter methods39303132333435.. What is Hibernate /essionFactor0 an$
how to coni"!re it?SessonFactory s the factory cass used to get the
Sesson ob|ects. SessonFactory s responsbe to read the hbernate
conguraton parametersand connect to the database and provde Sesson
ob|ects. Usuay an appcaton has a snge SessonFactory nstance and
threads servcng cent requests obtan Sesson nstances from ths
factory.The nterna state of a SessonFactory s mmutabe. Once t s
created ths nterna state s set. Ths nterna state ncudes a of the
metadata about Ob|ect/Reatona Mappng.SessonFactory aso provde
methods to get the Cass metadata and Statstcs nstance to get the
stats of query executons, second eve cache detas etc.11. Hibernate
/essionFactor0 is threa$ sae?Interna state of SessonFactory s
mmutabe, so ts thread safe. Mutpe threads can access t smutaneousy
to get Sesson nstances.11. What is Hibernate /ession an$ how to "et
it?Hbernate Sesson s the nterface between |ava appcaton ayer and
hbernate. Ths s the core nterface used to perform database
operatons. Lfecyce of a sesson s bound by the begnnng and end of a
transacton.Sesson provde methods to perform create, read, update
and deete operatons for a persstent ob|ect. We can execute HOL
queres, SOL natve queres and create crtera usng Sesson ob|ect.12.
Hibernate /ession is threa$ sae?Hbernate Sesson ob|ect s not thread
safe, every thread shoud get ts own sesson nstance and cose t after
ts work s nshed.13. What is $ierence between open/ession an$
"et'!rrent/ession?Hbernate SessonFactory getCurrentSesson() method
returns the sesson bound to the context. But for ths to work, we
need to congure t n hbernate conguraton e. Snce ths sesson ob|ect
beongs to the hbernate context, we dont need to cose t. Once the
sesson factory s cosed, ths sesson ob|ect gets cosed.1;property
name$%hibernate.current/session/context/class%;2versionbehind?Hibernate
uses a so"histicated algorithm to determine an efficient ordering
that avoids database foreign key constraint violations but is still
sufficiently "redictable to the user. This feature is called
transactional write5behind.$".What are Callback interfaces?,allback
interfaces allow the a""lication to receive a notification when
something interesting ha""ens to an ob)ectIfor e$am"le, when an
ob)ect is loaded, saved, or deleted. Hibernate a""lications dont
need to im"lement these callbacks, but theyre useful for
im"lementing certain kinds of generic functionality.$#.What are the
types of Hibernate instance states ?Three ty"es of instance states+
Transient 5The instance is not associated with any "ersistence
conte$t Persistent 5The instance is associated with a "ersistence
conte$t .etached 5The instance was associated with a "ersistence
conte$t which has been closed J currently not associated$$.What are
the differences between E46 #./ D HibernateHibernate Gs E&4 K.L
+5Hibernate-+, ./0 )essionJ,ache or collection of loaded ob)ects
relating to a single unit of work Aersistence Conte+t5#et of
entities that can be managed by a given Entity(anager is defined by
a "ersistence unitPeop+e who rea$ this5 a+so rea$H95451
&nterview 3uestions4)0 Butorial!y0aces E+amplesHibernate Es
i6atisBibco &nterview 3uestions1(oclet 5nnotations used to
su""ort Attribute 'riented Programming 4ava %./ 5nnotations used to
su""ort Attribute 'riented Programming (efines H32 for e$"ressing
/ueries to the database(efines E46 32 for e$"ressing /ueries
)upports Entity elationships through ma""ing files and annotations
in &ava.oc )upport Entity elationships through &ava M.L
annotationsArovides a Aersistence !anager 5A& e$"osed via the
#ession, 7uery, ,riteria, and Transaction API Arovides and Entity
!anager &nterface for managing ,R-. o"erations for an Entity
Arovides callback support through lifecycle, interce"tor, and
validatable interfaces Arovides callback support through Entity
3istener and ,allback methods Entity elationships are
unidirectional. 4idirectional relationshi"s are im"lemented by two
unidirectional relationshi"s Entity elationships are bidirectional
or unidirectional$%.What are the types of inheritance models in
Hibernate?There are three ty"es of inheritance models in Hibernate+
Table "er class hierarchy Table "er subclass Table "er concrete
class1/ What is benefit of using O23 tools??he main a$vanta"e o 6AB
+ike hibernate is that it shie+$s $eve+opers rom mess0 /;4. Apart
romthis5 6AB provi$es o++owin" beneitsH Improve$ pro$!ctivit0
Hi"h9+eve+ ob>ect9oriente$ API 4ess Java co$e to write )o /;4 to
write Improve$ perormance /ophisticate$ cachin" 4a=0 +oa$in"P 2a"er
+oa$in" Improve$ maintainabi+it0 A +ot +ess co$e to write Improve$
portabi+it0 6AB ramework "enerates $atabase9speciic /;4 or 0o!.4/
What are the most common methods of Hibernate configuration??he
most common metho$s o Hibernate coni"!ration areHPro"rammatic
coni"!rationCB4 coni"!ration (hibernate.c".3m+)./ What are the
&ore interfaces are of Hibernate framewor(??he ive core
interaces are !se$ in >!st abo!t ever0 Hibernate app+ication.
7sin" these interaces50o! can store an$ retrieve persistent
ob>ects an$ contro+ transactions. /ession interace
/essionFactor0 interace 'oni"!ration interace ?ransaction interace
;!er0 an$ 'riteria interace5/ What role does the ession interface
pla# in Hibernate??he /ession interace is the primar0 interace !se$
b0 Hibernate app+ications. It is a
sin"+e9threa$e$5short9+ive$ob>ect
representin"aconversationbetweentheapp+icationan$thepersistent
store./ession isnot threadsafe sowesho!+$not
sharesamesessionbetweenm!+tip+ethrea$s. Ita++ows 0o! to create ects
to retrieve persistent ob>ects. /ession session L
sessionFactor0.open/ession()S /ession interace ro+eH Wraps a
J%&' connection Factor0 or ?ransactionHo+$s a man$ator0
(irst9+eve+) cache o persistent ob>ects5 !se$ when navi"atin"
theob>ect "raph or +ookin" !p ob>ects b0 i$entiier6/ What
role does the ession$actor# interface pla# in Hibernate?App+ication
obtains /ession instances rom a /essionFactor0. ?here is t0pica++0
a singleession$actor# or the who+e app+ication create$ $!rin"
app+ication initia+i=ation. ?he/essionFactor0 caches "enerate /;4
statements an$ other mappin" meta$ata that Hibernate !sesat
r!ntime. It a+so ho+$s cache$ $ata that has been rea$ in one !nit o
work an$ ma0 be re!se$ in a!t!re !nit o work /essionFactor0
sessionFactor0 L coni"!ration.b!i+$/essionFactor0()S7/ What is the
general flow of Hibernate communication with 2D,3??he "enera+ +ow o
Hibernate comm!nication with A%&B/ is H4oa$the Hibernate
coni"!ration i+e an$ createconi"!rationob>ect.Itwi++
a!tomatica++0+oa$ a++ hbm mappin" i+es 'reate session actor0 rom
coni"!ration ob>ect:et one session rom this session actor0'reate
H;4 ;!er023ec!te ects8/ What is Hibernate Quer# !anguage
)HQ!*?Hibernate oers a ects rom a $atabase. ?his +an"!a"e5 the
Hibernate ect9oriente$ e3tension to /;4.9/ What:s the difference
between load)* and get)*?+oa$() vs. "et() H9load)* 6n+0 !se the
+oa$() metho$ i 0o! are s!re that the ob>ect e3ists. +oa$()
metho$ wi++ throw an e3ception i the !ni!st ret!rns a pro30 b0
$ea!+t an$ $atabase won8t be hit !nti+ the pro30 is irst invoke$.
get)* I 0o! are not s!re that the ob>ect e3ists5 then !se one o
the "et() metho$s. "et() metho$ wi++ ret!rn n!++ i the !niects.
?his is a ver0 convenient approach or !nctiona+it0 +ike YsearchY
screens where there is a variab+e n!mber o con$itions to be p+ace$
!pon the res!+t set.23amp+e H4ist emp+o0ees L
session.create'riteria(2mp+o0ee.c+ass).a$$(Aestrictions.+ike(YnameY5
Ya[Y) ).a$$(Aestrictions.+ike(Ya$$ressY5
Y&ostonY)).a$$6r$er(6r$er.asc(YnameY) ).+ist()S16/ What are the
benefits does HibernateAemplate
provide?or".sprin"ramework.orm.hibernate.Hibernate?emp+ate is a
he+per c+ass which provi$es $ierent metho$s or vm memor05 it can
throw 6!t o Bemor0 error. Order collection 6r$er co++ection is
sortin" a co++ection b0 speci0in" the order%b# clause in ect to an0
other session b0 ca++in" either update"* or saverDpdate"* metho$ on
that session.4./ What is automatic dirt# chec(ing?A!tomatic $irt0
checkin" is a eat!re that saves !s the eort o e3p+icit+0 askin"
Hibernate to !p$ate the $atabase when we mo$i0 the state o an
ob>ect insi$e a transaction.45/ ample of Hibernate transaction
management?A or".hibernate./ession is $esi"ne$ to represent a
sin"+e !nit o work (a sin"+e atmoic piece o work to be
perorme$./amp+e co$e o han$+in" transaction rom hibernate
session./ession session L
Hibernate7ti+."et/essionFactor0()."et'!rrent/ession()Ssession/beginAransaction)*F2vent
the2vent L new
2vent()Sthe2vent.set?it+e(tit+e)Sthe2vent.set%ate(the%ate)Ssession.save(the2vent)Ssession/getAransaction)*/commit)*F46/
How to implement Optimistic loc(ing in Database?Wo! can imp+ement
optimistic +ocks in 0o!r %& tab+e in this wa0 (?his is how
optimistic +ockin" is $one in Hibernate)H9 A$$ inte"er YversionY
co+!mn to 0o!r tab+e.9 Increase va+!e o this co+!mn with each
!p$ate o correspon$in" row.9 ?o obtain +ock5 >!st rea$ YversionY
va+!e o row.9 A$$ Yversion L obtaine$OversionY con$ition to where
c+a!se o 0o!r !p$ate statement.9 @eri0 n!mber o aecte$ rows ater
!p$ate. I no rows were aecte$ 9 someone has a+rea$0 mo$iie$ 0o!r
entr0.Wo!r !p$ate sho!+$ +ook +ike UPDATE mytable SET name'Andy'!
"ersion# $%E&E id' and "ersion()26. What is Second level Cache
and QueryCache in Hibernate?Second level Cache is maintained at
SessionFactory level and It improves performance by saving few
databaseround trip. Another worth noting point is that second level
cache is available to whole application rather than any particular
session. QueryCache actually stores result of sql query for future
calls. Query cache can be used along with second level cache for
improved performance. Hibernate support various open source caching
solution to implement Query cache e.g.
hCache.http://|avadecodedquestons.bogspot.n/2011/12/hbernate-ntervew-questons.htm1)
What is Hibernate?Hibernate is a power!+5 hi"h perormance
ob>ectPre+ationa+ persistence an$ ectPre+ationa+ persistence it
even re$!ces the46'. ?erformance > Han$9co$e$ persistence
provi$e$ "reater perormance than a!tomate$ one. &!t this is not
tr!e a++ the times. &!t in hibernate5 it provi$es more
optimi=ation that works a++ the time there b0 increasin" the
perormance. I it is a!tomate$ persistence then it sti++ increases
the perormance. Gendor independence > Irrespective o the $ierent
t0pes o $atabases that are there5 hibernateprovi$es a m!ch easier
wa0 to $eve+op a cross p+atorm app+ication.11) How $oes hibernate
co$e +ooks +ike?: 0ession session $
get0ession+actory"*.open0ession"*;H Transaction tx $
session.beginTransaction"*;? &y'ersistanceClass mpc $ neG
&y'ersistanceClass "%0ample App%*;> session.save"mpc*;@
tx.commit"*;T session.close"*;?he /ession an$ ?ransaction are the
interaces provi$e$ b0 hibernate. ?here are man0 other interaces
besi$es this.11) What is a hibernate 3m+ mappin" $oc!ment an$ how
$oes it +ook +ike?In or$er to make most o the thin"s work in
hibernate5 !s!a++0 the inormation is provi$e$ in an 3m+ $oc!ment.
?his $oc!ment is ca++e$ as 3m+ mappin" $oc!ment. ?he $oc!ment
$eines5 amon" other thin"s5 how properties o the !ser $eine$
persistence c+asses8 map to the co+!mns o the re+ative tab+es in
$atabase.: ;Bxml version$%:.C%Bect5 which compares ob>ect
i$entit0.3. Database identit# > 6b>ects store$ in a
re+ationa+ $atabase are i$entica+ i the0 represent the samerow or5
eoin etchin"5 &atch etchin"What is hibernate session and
session factory? How do you configure sessionfactory in spring
configuration file?Hibernate /ession is the main r!ntime interace
between a Java app+ication an$ Hibernate. /essionFactor0 a++ows
app+ications to create hibernate session b0 rea$in" hibernate
coni"!rations i+e hibernate.c".3m+.Con9iguration c9g $ neG
Con9iguration"*.con9igure"*; 22 InitialiKe the Jibernate
environment0ession+actory 9actory $ c9g.build0ession+actory"*; 22
Create the session 9actory0ession session $ 9actory.open0ession"*;
22 btain the neG session object ?he ca++ to
'oni"!ration().coni"!re() +oa$s the hibernate.c".3m+ coni"!ration
i+e an$ initia+i=es the Hibernate environment. 6nce the
coni"!ration is initia+i=e$5 0o! can make an0 a$$itiona+
mo$iications 0o! $esire pro"rammatica++0. However5 0o! m!st make
these mo$iications prior to creatin" the /essionFactor0 instance.
An instance o /essionFactor0 is t0pica++0 create$ once an$ !se$ to
create a++ sessions re+ate$ to a "iven conte3t. ?he main !nction o
the /ession is to oer create5 rea$ an$ $e+ete operations or
instances o mappe$ entit0 c+asses. Instances ma0 e3ist in one o
three statesH transientH never persistent5 not associate$ with an0
/ession persistentH associate$ with a !niect represents a sin"+e
!nit9o9work or a "iven $ata store an$ is opene$ b0 a /essionFactor0
instance. Wo! m!st c+ose /essions when a++ work or a transaction is
comp+ete$. ?he o++owin" i++!strates a t0pica+ Hibernate sessionH
0ession session $ null; DserIn9o user $ null; Transaction tx $
null;try - session $ 9actory.open0ession"*; tx $
session.beginTransaction"*; user $
"DserIn9o*session.load"DserIn9o.class7 id*; tx.commit"*;3
catch"Exception e* - i9 "tx A$ null* -try - tx.rollback"*;3 catch
"JibernateException e:* - throG neG ,AException"e:.to0tring"**; 3 3
throG neG ,AException"e.to0tring"**;3 9inally - i9 "session A$
null* -try - session.close"*;3 catch "JibernateException e* - 3
33What is the difference between hibernate get and load methods??he
o++owin" Hibernate co$e snippet retrieves a 7ser ob>ect rom the
$atabaseH Dser user $ "Dser* session.get"Dser.class7 userI,*; ?he
"et() metho$ is specia+ beca!se the i$entiier !niect5 avoi$in" a
$atabase hit i the ob>ect is a+rea$0 cache$. ?he "et() metho$
ret!rns n!++ i the ob>ect can8t be o!n$.Hibernate a+so provi$es
a +oa$() metho$HDser user $ "Dser* session.load"Dser.class7
userI,*; I +oa$() can8t in$ the ob>ect in the cache or $atabase5
an e3ception is thrown. ?he +oa$() metho$ never ret!rns n!++.?he
+oa$() metho$ ma0 ret!rn a pro30 instea$ o a rea+ persistent
instance. A pro30 is a p+aceho+$er instance o a r!ntime9"enerate$
s!bc+ass (thro!"h c"+ib or Javassist) o a mappe$ persistent c+ass5
it can initia+i=e itse+ i an0 metho$ is ca++e$ that is not the
mappe$ $atabase i$entiier "etter9metho$. 6n the other han$5 "et()
never ret!rns a pro30. 'hoosin" between "et() an$ +oa$() is eas0H I
0o!8re certain the persistent ob>ect e3ists5 an$ none3istence
wo!+$ be consi$ere$ e3ceptiona+5 +oa$() is a "oo$ option. I 0o!
aren8t certain there is a persistent instance with the "iven
i$entiier5 !se "et() an$ test the ret!rn va+!e to see i it8s n!++.
7sin" +oa$() has a !rther imp+icationH ?he app+ication ma0 retrieve
a va+i$ reerence (a pro30) to a persistent instance witho!t hittin"
the $atabase toretrieve its persistent state. /o +oa$() mi"ht not
throw an e3ception when it $oesn8t in$ the persistent ob>ect in
the cache or $atabaseS the e3ception wo!+$ be thrown +ater5 when
the pro30 is accesse$.What type of transaction management is
supported in hibernate? Hibernate comm!nicates with the $atabase
via a J%&' 'onnectionS hence it m!st s!pport both mana"e$an$
non9mana"e$ transactions.non9mana"e$ in web containersH;bean
id$%transaction&anager%
class$%org.spring9rameGork.orm.hibernate.JibernateTransaction&anager%ects.
?he !nctionwith the secon$9+eve+ cache. Hibernate s!pports the
o++owin" open9so!rce cache imp+ementations o!t9o9the9bo3H o 2H'ache
is a ast5 +i"htwei"ht5 an$ eas09to9!se in9process cache. It
s!pports rea$9on+0 an$ rea$Pwrite cachin"5 an$ memor09 an$
$isk9base$ cachin". However5 it $oes not s!pport c+!sterin".o
6/'ache is another open9so!rce cachin" so+!tion. It is part o a
+ar"er packa"e5 which a+so provi$es cachin" !nctiona+ities or J/P
pa"es or arbitrar0 ob>ects. It is a power!+ an$ +e3ib+e packa"e5
which5 +ike 2H'ache5 s!pports rea$9on+0 an$ rea$Pwrite cachin"5 an$
memor09 an$ $isk9base$ cachin". It a+so provi$es basic s!pport or
c+!sterin" via either Java:ro!ps or JB/.o /warm'ache is a simp+e
c+!ster9base$ cachin" so+!tion base$ on Java:ro!ps. It s!pports
rea$9on+0 or nonstrict rea$Pwrite cachin" (the ne3t section
e3p+ains this term). ?his t0pe o cache is appropriate or
app+ications that t0pica++0 have man0 more rea$ operations than
write operations.o J&oss ?ree'ache is a power!+ rep+icate$
(s0nchrono!s or as0nchrono!s) an$ transactiona+ cache. 7se this
so+!tion i 0o! rea++0 nee$ a tr!e transaction9capab+e cachin"
architect!re.o 'ommercia+ ?an"oso+ 'oherence cache.What are the
different caching strategies? Aea$9on+0H ?his strate"0 is !se!+ or
$ata that is rea$ reava comparator5 whi+e or$er co++ection is
or$ere$ at the $atabase +eve+ !sin" or$er b0 c+a!se.What are the
types of inheritence models and describe how they work like
vertical inheritence andhorizontal??here are three t0pes o
inheritance mappin" in hibernate H23amp+eH 4et !s take the simp+e
e3amp+e o 3 >ava c+asses. '+ass Bana"er an$ Worker are inherite$
rom2mp+o0ee Abstract c+ass.1. ?ab+e per concrete c+ass with !nions
H In this case there wi++ be 2 tab+es. ?ab+esH Bana"er5 WorkerIa++
common attrib!tes wi++ be $!p+icate$J2. ?ab+e per c+ass hierarch0H
/in"+e ?ab+e can be mappe$ to a c+ass hierarch0. ?here wi++ be on+0
one tab+e in $atabase ca++e$ X2mp+o0eeX that wi++ represent a++ the
attrib!tes reect b0 +oa$in" the reect rom the $atabase. &!t i
there was not s!ch ob>ect in the $atabase then the metho$
session.+oa$(..) throws an e3ception whereas session."et(V) ret!rns
n!++. What is the difference between the session.update() method
and the session.lock() method? &oth o these metho$s an$
save6r7p$ate() metho$ are inten$e$ or reattachin" a $etache$
ob>ect. ?he session.+ock() metho$ simp+0 reattaches the
ob>ect to the session witho!t checkin" or !p$atin" the $atabase
on the ass!mption that the $atabase in s0nc with the $etache$
ob>ect. It is the best practice to !se either session.!p$ate(..)
or session.save6r7p$ate(). 7se session.+ock() on+0 i 0o! are
abso+!te+0 s!re that the $etache$ ob>ect is in s0nc with 0o!r
$etache$ ob>ect or i it $oes not matter beca!se 0o! wi++ be
overwritin" a++ the co+!mns that wo!+$ have chan"e$ +ater on within
the same transaction. )oteH When 0o! reattach $etache$ ob>ects
0o! nee$ to make s!re that the $epen$ent ob>ects are reatche$ as
we++. How would you reatach detached obects to a session when the
same obect has already been loaded into the session? Wo! can !se
the session.mer"e() metho$ ca++. What are the general
considerations or best practices for defining your Hibernate
persistent classes? 1. Wo! m!st have a $ea!+t no9ar"!ment
constr!ctor or 0o!r persistent c+asses an$ there sho!+$ be "etCCC()
(i.e accessorP"etter) an$ setCCC( i.e. m!tatorPsetter) metho$s or
a++ 0o!r persistab+e instance variab+es. 2. Wo! sho!+$ imp+ement
the eect. 3. It is recommen$e$ to imp+ement the /eria+i=ab+e
interace. ?his is potentia++0 !se!+ i 0o! want to mi"rate aro!n$ a
m!+ti9processor c+!ster. #. ?he persistent c+ass sho!+$ not be ina+
beca!se i it is ina+ then +a=0 +oa$in" cannot be !se$ b0 creatin"
pro30 ob>ects. (. 7se C%oc+et ta"s or "eneratin" 0o!r \.hbm.3m+
i+es or Annotations (J%F 1.( onwar$s)5 which are +ess verbose than
\.hbm.3m+ i+es. 1. What is Hibernate?Hibernate is a pure Java
object-relational mapping (ORM) and persistence framework that
allows ou to map plain old Java objects to relational database
tables using (!M") configuration files# $ts purpose is to relieve
the developer from a significant amount of relational data
persistence-related programming tasks#Hibernate simplifies%
&aving and retrieving our domain objects Making database column
and table name changes 'entrali(ing pre save and post retrieve
logic 'omple) joins for retrieving related items &chema
creation from object model#2. Benefits of hibernate over JDBC?
Hibernate is database independent while in case of J*+', developer
has to write database specific -ueries# $n case of Hibernate
developer doesn.t need to be an e)pert of writing comple) -ueries
as H/" simplifies -uer writing process while in case of J*+', its
job of developer to write and tune -ueries# $n Hibernate, 'riteria
/uer takes care of /uer 0uning# $n case of J*+' ou need to tune our
-ueries# 1o need to create an connection pool in case of Hibernate#
2ou can use c3p4# $n case of J*+' ou need to write our own
connection pool# 5utomatic primar ke generation# 6erformance
benefits like "a( initiali(ation, Outer join fetching, +atch
fetching3. Difference between different saving methods in
Hibernate?saveOrUdate! +ased on some checks it will calls either
save or update# 7#g# if no identifier e)ists, save is called#
Otherwise update is called#save $t will 6ersists an entit and will
assign an identifier if one doesn.t e)ist# $f one does, it.s
essentiall doing an update# 5nd returns the generated $* of the
entit#"date%$t will persist the entit using an e)isting identifier#
$f no identifier e)ists, $ believe an e)ception is thrown#merge
Hibernate has following three Object states#ransient$ Detached and
%ersistant.Object states, with save 8 update, ou are dealing with
persistant objects# 0he are linked to a &ession so Hibernate
knows what has changed# +ut when ou have a transient object, there
is no session involved# $n these cases ou need to use merge for
updates and persist for saviing#ersist! 5s mentioned above, this is
used on transient objects# $t does not return the generated
$*#9#What are the Core interfaces of Hibernate framewor&?0he
five core interfaces are used in just about ever Hibernate
application# :sing these interfaces, ou an store and retrieve
persistent objects and control transactions# &ession interface
&ession;actor interface 0ransaction interface /uer and 'riteria
interfacesfrom &tudent where student1ame A Esuresh. >)B14.
What is %OJO?%OJO56lain Old Java Object)is a javabean that have
defined setter and getter methods for all properties# *ecoupling
the application code from the infrastructure frameworks isone of
the man benefits of using 6OJOs# 0he also simplif development
because rather than being forced to think about everthing =
business logic, persistence, transactions, etc#16#What the fo"r O78
+eve+s are in hibernate?;ollowing are the four ORM levels in
hibernate%a# 6ure Relationalb# "ight Object Mappingc# Medium Object
Mappingd# ;ull Object Mapping1*. How to reattach detached ob(ects
in hibernate? *etached objects can be reattached b calling
session#merge() method of session class#1-#Difference between
+oad59 and get59 method in hibernate? $f ou are sure that the
object e)ists then use load() else use get() methods# load() method
will throw an e)ception if the uni-ue id is not found in the
database but get() method will return null if the uni-ue id is not
found in the database#1.. Difference between detached state and
transient state Ob(ects?0ransient objects do not have association
with the databases and session objects but detached objects have
corresponding entries in the database# 0hese are persistent and not
connected to the &ession object# 0hese objects have the
snchroni(ed data with the database when the session was
closed#Fersion propert is used in hibernate to know whether an
object is in transient state or in detached state#1/. Difference
between the session."date59 method and the session.+oc&59
method?0he session#lock() method simpl reattaches the object to the
session without checking or updating the database on the assumption
that the database in snc with the detached object#:se
session#lock() onl if ou are absolutel sure that the detached
object is in snc with our detached object otherwise
usesession."date59.C4# Different fetching strateg' in Hibernate?
Join fetching%:sing an O:07R JO$1 hibernate retrieves the
associated instance or collection in the same &7"7'0# Select
fetching% a second &7"7'0 is used to retrieve the associated
entit or collection# :nless ou e)plicitl disable la( fetching b
specifing la(A?false?, this second select will onl be e)ecuted when
ou access the association# Subselect fetching% a second &7"7'0
is used to retrieve the associated collections for all entities
retrieved in a previous -uer or fetch# :nless ou e)plicitl disable
la( fetching b specifingla(A?false?, this second select will onl be
e)ecuted when ou access the association# Batch fetching! $t is an
optimi(ation strateg for select fetching#:sing primar or foreign
kes hibernate retrieves a batch of entit instances or collections
in a single &7"7'0# ;ind the more info about ;etching
strategies here# 7hcache = Hibernate &econd "evel 'ache with
&pring 7)ample GH@4I@C4G3 b admin 5nother must know concept in
Hibernate#Here we are going to see about Hibernate &econd "evel
'ache#Wh' we need caching? $t is mainl about application
performance optimi(ation and it will happen between our application
and the database to avoid the number of database hits as man as
possible to give a better performance for critical
applications#:sing ;ollowing 7)ample we will see how to reduce
database hits#Je know Hibernate handles 1irst:+eve+ cache b default
and it is associates with the )ession ob(ect# What is )econd 3eve+
Cache and How it wor&s? 0his cache is associated with )ession
1actor' Ob(ect so itdon.t bounds to single user#Jhile running the
transactions, in between it loads the objects at the )ession
1actor' +evel, so that those objects will available to the entire
application# &ince the objects are alread loaded in the cache,
whenever an object is returned b the -uer, at that time no need to
go for a database transaction# "et.s see simple e)ample program
about ;etching all :sers with the help of Hibernate )econd 3eve+
Cache5;hCache9 "sing )ring.< have "sed Hibernate 4 and )ring
1ramewor& 3.2 version. $ have created following class files# 1.
User8anager.(ava 2.;+ements?>TC:U@H:::XX(; !Id
!GeneratedValue"strategy $ GenerationType.I,E.TIT)* 22 Generator
user/se8 !Column"name $ %user/id%* private int userId; !Column"name
$ %username%7 nullable $ 9alse* private 0tring username;
!Column"name $ %passGord%7 nullable $ 9alse* 22
!Type"type$%encrypted0tring%* private 0tring passGord; !Column"name
$ %9irstname%7 nullable $ 9alse* private 0tring 9irst.ame;
!Column"name $ %lastname%7 nullable $ 9alse* private 0tring
last.ame; !Column"name $ %email%7 nullable $ 9alse* private 0tring
email; !Column"name $ %role%7 nullable $ 9alse*$'$($)$*%!%"%#%$%%
private 0tring role $ %D0E6%; 22 Generate getters and setters 9or
above 9ields. parent reatonshp woud be created.In Hbernate, ony the
"reatonshp owner" shoud mantan the reatonshp, and the "nverse"
keyword s created to denes whch sde s the owner to mantan the
reatonshp. However the "nverse" keyword tsef s not verbose enough,
I woud suggest change the keyword to "reatonshp_owner".In short,
nverse="true" means ths s the reatonshp owner, and nverse="fase"
(defaut) means ts not.Suppose Stock s parent and StockDayRecords s
Chd ob|ect.Inverse keyword s apped n one to many reatonshp. Heres
the queston, f save or update operaton perform n "Stock" ob|ect,
shoud t update the "stockDayRecords" reatonshp?1. nverse="true"If
nverse="true" n the set varabe, t means "stock_day_record" s the
reatonshp owner,so Stock w NOT UPDATE the reatonshp.2.
nverse="fase"If nverse="fase" (defaut) n the set varabe, t means
"stock" s the reatonshp owner, and Stock w UPDATE the reatonshp.If
keyword "nverse" s not dene, the nverse = "fase" w be used, whch
sHow do you nvoke Stored Procedures?Ans. { ? = ca seectAEmpoyees()
}
Expan Crtera API?Ans. Crtera s a smped API for retrevng enttes
by composng Crteron ob|ects. Ths s a very convenent approach for
functonaty ke "search" screens where there s a varabe number of
condtons to be paced upon the resut set. Exampe : Lst empoyees =
sesson.createCrtera(Empoyee.cass) .add(Restrctons.ke("name", "a%")
) .add(Restrctons.ke("address", "Boston"))
.addOrder(Order.asc("name") ) .st();s 34. What are the benets does
HbernateTempate provde?Ans. The benets of HbernateTempate are : *
HbernateTempate, a Sprng Tempate cass smpes nteractons wth Hbernate
Sesson. * Common functons are smped to snge method cas. * Sessons
are automatcay cosed. * Exceptons are automatcay caught and
converted to runtme exceptons. How w you congure Hbernate?Ans. The
conguraton es hbernate.cfg.xm (or hbernate.propertes) and mappng es
*.hbm.xm are used by the Conguraton cass to create (.e. congure and
bootstrap hbernate) the SessonFactory, whch n turn creates the
Sesson nstances. Sesson nstancesare the prmary nterface for the
persstence servce. " hbernate.cfg.xm (aternatvey can use
hbernate.propertes): These two es are used to congure the hbernate
sevce (connecton drver cass, connecton URL, connecton username,
connecton password, daect etc). If both es are present n the
casspath then hbernate.cfg.xm e overrdes the settngs found n the
hbernate.propertes e. " Mappng es (*.hbm.xm): These es are used to
map persstent ob|ects to a reatona database. It s the best practce
to store each ob|ect n an ndvdua mappng e (.e mappng e per cass)
because storng arge number of persstent casses nto one mappng e can
be dmcut to manage and mantan. The namng conventon s to use the
same name as the persstent (PO|O) cass name. For exampe
Account.cass w have a mappng e named Account.hbm.xm. Aternatvey
hbernate annotatons can be used as part of your persstent cass code
nstead of the *.hbm.xm es.What s a SessonFactory? Is t a
thread-safe ob|ect?Ans. SessonFactory s Hbernates concept of a snge
datastore and s threadsafe so that many threads can access t
concurrenty and request for sessons and mmutabe cache of comped
mappngs for a snge database. A SessonFactory s usuay ony but once
at startup. SessonFactory shoud be wrapped n some knd of sngeton so
that t can be easy accessed n an appcaton code.What s a Sesson? Can
you share a sesson ob|ect between dherent threads?Ans. Sesson s a
ght weght and a non-threadsafe ob|ect (No, you cannot share t
between threads) that represents a snge unt-of-work wth the
database. Sessons are opened by a SessonFactory and then are cosed
when a work s compete. Sesson s the prmary nterface for the
persstence servce. A sesson obtans a database connecton azy (.e.
onywhen requred). To avod creatng too many sessons ThreadLoca cass
can be used as shown beow to get the current sesson no matter how
many tmes you make ca to the currentSesson() method.What are the
pros and cons of detached ob|ects?Ans. Pros: " When ong transactons
are requred due to user thnk-tme, t s the best practce to break the
ong transacton up nto two or more transactons. You can use detached
ob|ects from the rst transacton to carry data a the way up to the
presentaton ayer. These detached ob|ects get moded outsde a
transacton and ater on re-attached to a new transacton va another
sesson. Cons " In genera, workng wth detached ob|ects s qute
cumbersome, and better to not cutter up the sesson wth them f
possbe. It s better to dscard them and re-fetch them on subsequent
requests. Ths approach s not ony more portabe but aso more emcent
because - the ob|ects hang around n Hbernate's cache anyway. " Aso
from pure rch doman drven desgn perspectve t s recommended to use
DTOs (DataTransferOb|ects) and DOs (DomanOb|ects) to mantan the
separaton between Servceand UI ters.What s the dherence between the
sesson.update() method and the sesson.ock() method?Ans. Both of
these methods and saveOrUpdate() method are ntended for reattachng
a detached ob|ect. The sesson.ock() method smpy reattaches the
ob|ect to the sesson wthout checkng or updatng the database on the
assumpton that the database n sync wththe detached ob|ect. It s the
best practce to use ether sesson.update(..) or
sesson.saveOrUpdate(). Use sesson.ock() ony f you are absoutey sure
that the detached ob|ect s n sync wth your detached ob|ect or f t
does not matter because you w be overwrtng a the coumns that woud
have changed ater on wthn the same transacton. Note: When you
reattach detached ob|ects you need to make sure that the dependent
ob|ects are reatched as we.How woud you reatach detached ob|ects to
a sesson when the same ob|ect has areadybeen oaded nto the
sesson?Ans. You can use the sesson.merge() method ca.What are the
genera consderatons or best practces for denng your Hbernate
persstent casses?Ans. 1.You must have a defaut no-argument
constructor for your persstent casses and there shoud be getXXX()
(.e accessor/getter) and setXXX( .e. mutator/setter) methods for a
your persstabe nstance varabes. 2.You shoud mpement the equas() and
hashCode() methods based on your busness key and t s mportant not
to use the d ed n your equas() and hashCode() denton f the d ed s a
surrogate key (.e. Hbernate managed denter). Ths s because the
Hbernate ony generates and sets the ed when savng the ob|ect. 3. It
s recommended to mpement the Serazabe nterface. Ths s potentay
usefu f you want to mgrate around a mut-processor custer. 4.The
persstent cass shoud not be na because f t s na then azy oadng
cannot be used by creatng proxy ob|ects. 5.Use XDocet tags for
generatng your *.hbm.xm es or Annotatons (|DK 1.5 onwards), whch
are ess verbose than *.hbm.xm es.What s CRUD?Ans. A CRUD operaton
deas wth creatng , retrvng , updatng and deetng from the tabe.We
have aready descrbed prevousy how to persst "Empoyee" Cass to
database. Here weare addng more operaton on thatEmpoyee Cass.1.
Creatng/Persstng the cass to databae2. Retrvng records from
database3. Updatng decord(Condton : Where sa s 8000 ,update sa to
11000)4. Deetng decord (condton: where deptno s 30)Expan the fe
cyce method of E|B?1. Ans. Lfe Cyce of Entty Bean:Frst stage s Does
Not Exst Stage then Contaner creates the nstance of E|B and
caSetEnttyContext() method whch w set a entty context to bean and
now t w become avaabe on poo ,to get a partcuar dentty of an E|B
ob|ect t has to move from Pooed stage to ready stage whch s done by
cang the create () method whch n turns ca e|bCreate() and
e|bPostCreate() method .There s another way by whch drecty entty
bean can move to pooed stage to ready stage thats s ca e|bActvate()
method.now we are ready to nvoke the busness method of entty bean
.After competon of busness method f we want to move agan n pooed
stage from ready stage we can ca remove() method whch n turns ca
e|bRemove() or drecty ca e|bPassvate () method.At the end contaner
remove the nstance of E|Bfrom poo and ca unSetEnttyContext().Lfe
Cyce of Statefu Sesson Bean :Statefu sesson beans fe cyce starts
when cent ca create() method.The contanercreate the nstance of
sesson bean and ca setSessonContext() and e|bCreate() methodNow the
statefu sesson bean s ready to serve the cent request after servng
the request f t s not used after a ong tme contaner can move ths
bean to passve stage by cang the e|bPassvate() method.smary when
bean s n passve stage and cent nvoke the busness method the
contaner ca e|bActvate() method to move bean from passve stage to
actve or ready stage.At the end of fe cyce cent ca remove() method
and contaner w ca e|bRemove() method and bean s ready for garbage
coecton.Lfe Cyce of Stateess sesson bean :Staes sesson bean has
short fe cyce t can have two stage does not exst and ready stage.
e|b contaner create the nstance of stateess sesson bean and ca
setSessonContext () and e|bCreate() method.Now the bean s ready to
nvoke busness method on ths.t w not mantan the state so remove ()
method s been caed after competon of busness method whch n turns ca
e|bRemove () and now ts ready for garbage coecton.Lfe cyce of
Message Drven bean:MDBs have same fe cyce ke stateess sesson bean.
setMessageDrvenContext() method and e|bCreate() method s caed by
contaner to create the nstance of MDB.now ts ready to receve
message .and at the end of fecyce cent w ca remove () methodwhch n
turns ca e|bRemove () and now ts ready for garbage
coecton.Difference between session/save)* , session/saveOrUpdate)*
and session/persist)*? session/save)* < ave does an insert and
will fail if the primar# (e# is alread# persistent/
session/saveOrUpdate)* < saveOrUpdate does a select first to
determine if it needs to do an insert or an update/ Insert data if
primar# (e# not e@ist otherwise update data/ session/persist)* <
Does the same li(e session/save)*/ ,ut session/save)* return
erialiCable ob'ect but session/persist)* return void/
session/save)* returns the generated identifier )erialiCable
ob'ect* and session/persist)* doesnIt/ $or -@ample < if #ou
do
