Java Reference
In-Depth Information
A
library
fielddeclarationfollowsthe
wsContext
declaration,where
library
isdeclaredtobeoftype
Map<String, Book>
.Thisvariablestoresbooksinamap,
whereabook'sISBNservesasamapentry'skey,andthebook'sinformationisrecorded
in a
Book
object that serves as the map entry's value.
Library
next declares a noargument constructor whose job is to initialize
lib-
rary
. The constructor first attempts to deserialize
library.ser
's contents to a
java.util.HashMap
instancebycallingthe
deserialize()
method(explained
later), and assign the instance's reference to
library
. If this file does not exist,
java.io.IOException
isthrownandanempty
HashMap
instanceiscreatedand
assigned to
library
—note the use of Java 7's diamond operator to avoid having to
respecify the map's
java.lang.String
and
Book
actual type arguments.
The
invoke()
method is now declared. Its first task is to verify that dependency
injection succeeded by testing
wsContext
to determine if it contains the null ref-
erence. If so, dependency injection failed and an instance of the
java.lang.RuntimeException
class is created with a suitable message and
thrown.
Continuing,
invoke()
calls
WebServiceContext
's
MessageContext
getMessageContext()
methodtoreturnaninstanceofaclassthatimplementsthe
javax.xml.ws.handler.MessageContext
interface. This instance abstracts
the message context for the request being served at the time this method is called.
MessageContext
extends
Map<String, Object>
, making
MessageCon-
text
a special kind of map. This interface declares various constants that are used
withtheinherited
Object get(String key)
methodtoobtaininformationabout
therequest.Forexample,
get(MessageContext.HTTP_REQUEST_METHOD)
re-
turns a
String
object identifying the HTTP operation that the RESTful client wants
performed; for example,
POST
.
At this point, you might want to convert the string's contents to uppercase and trim
offanyleadingortrailingwhitespace.Idon'tperformthesetasksbecausetheclientthat
IpresentlaterwillnotallowanHTTPverbtobespecifiedthatisn'tentirelyuppercase
and/or is preceded/followed by whitespace.
Java 7's switch-on-string language feature is used to simplify the logic for invoking
the method that corresponds to the HTTP verb. The first argument passed to each
of the
doDelete()
,
doGet()
,
doPost()
, and
doPut()
helper methods is the
MessageContext
instance (assigned to
msgContext
). Although not used by
doPost()
and
doPut()
,thisinstanceispassedtothesemethodsforconsistency—I
might want to access the message context from
doPost()
and
doPut()
in the fu-
