Java Reference
In-Depth Information
•
GET
•
POST
•
HEAD
•
PUT
•
DELETE
•
OPTIONS
•
TRACE
If it's some other method, then a
java.net.ProtocolException
, a subclass of
IOException
, is thrown. However, it's generally not enough to simply set the request
method. Depending on what you're trying to do, you may need to adjust the HTTP
header and provide a message body as well. For instance,
POST
ing a form requires you
to provide a Content-length header. We've already explored the
GET
and
POST
methods.
Let's look at the other five possibilities.
Some web servers support additional, nonstandard request methods.
For instance, WebDAV requires servers to support
PROPFIND
,
PROP
PATCH
,
MKCOL
,
COPY
,
MOVE
,
LOCK
, and
UNLOCK
. However, Java doesn't
support any of these.
HEAD
The
HEAD
function is possibly the simplest of all the request methods. It behaves much
like
GET
. However, it tells the server only to return the HTTP header, not to actually
send the file. The most common use of this method is to check whether a file has been
modified since the last time it was cached.
Example 7-15
is a simple program that uses
the
HEAD
request method and prints the last time a file on a server was modified.
Example 7-15. Get the time when a URL was last changed
import
java.io.*
;
import
java.net.*
;
import
java.util.*
;
public
class
LastModified
{
public
static
void
main
(
String
[]
args
)
{
for
(
int
i
=
0
;
i
<
args
.
length
;
i
++)
{
try
{
URL
u
=
new
URL
(
args
[
i
]);
HttpURLConnection
http
=
(
HttpURLConnection
)
u
.
openConnection
();
http
.
setRequestMethod
(
"HEAD"
);
System
.
out
.
println
(
u
+
" was last modified at "
