Create an instance of HttpClient and use it to execute a GetMethod object. Once the method has been executed, the response
body can be accessed as an InputStream, byte[], or String. The following example gets the
contents of http://www.discursive.com/jccook/
and retrieves the response body as a string:
import org.apache.commons.httpclient.HttpClient;
import org.apache.commons.httpclient.HttpException;
import org.apache.commons.httpclient.HttpMethod;
import org.apache.commons.httpclient.methods.GetMethod;
HttpClient client = new HttpClient( );
String url = "http://www.discursive.com/jccook/";
HttpMethod method = new GetMethod( url );
try {
client.executeMethod( method );
if( method.getStatusCode( ) == HttpStatus.SC_OK ) {
String response = method.getResponseBodyAsString( );
System.out.println( response );
}
} catch( HttpException he ) {
System.out.println( "HTTP Problem: " + he.getMessage( ) );
} catch( IOException ioe ) {
System.out.println( "IO Exeception: " + ioe.getMessage( ) );
} finally {
method.releaseConnection( );
method.recycle( );
}This code retrieves the content of http://www.discursive.com/jccook
using the HTTP GET method. If the response code is HttpStatus.SC_OK or 200, the response is printed to the
console:
<html> <head> <title>JCCook Example</title> </head> <body> <h1>Hello World!</h1> </body> </html>
Note the exception handling involved in this example. Performing a
simple HTTP GET called for two catch blocks: HttpException and IOException. An HttpException is thrown if there is a problem
relating to the HTTP protocol, and an IOException is thrown if there is a problem
with the network. Examples in this chapter omit the rigorous exception
handling from the previous example; you can assume that every call to
execute() is surrounded by the
appropriate try/catch block.
GetMethod is an implementation
of the HttpMethod interface, which is
executed by HttpClient. The lifecycle
of any HttpMethod implementation is
straightforward; an HttpMethod is
created, executed by an instance of HttpClient, and, once the response has been
examined, the connection is released and the method is recycled. When an
HttpMethod object is recycled by a
call to recycle( ), it is a signal to
the system that this specific HttpMethod instance can be used again.
releaseConnection( ) instructs
HttpClient to release the connection
that is associated with an HttpMethod
instance. No matter what happens during the execution of a method, the
releaseConnection( ) must be called
to free network resources.
Once a method has been executed, you can get the response status
code from method.getStatusCode( ).
This method returns an int, which
will correspond to one of the public static
final variables on HttpStatus. Some of the more common status
codes on HttpStatus are SC_OK (200), SC_NOT_FOUND (404), SC_INTERNAL_SERVER_ERROR (500), SC_MOVED_TEMPORARILY (302), and SC_UNAUTHORIZED (401). For a full list of HTTP
status codes, see the Javadoc for HttpStatus. When a server sends back a bad
HTTP status, it is sometimes accompanied by a short message. This
message can be read by calling method.getStatusText( ).
For a formal definition of the HTTP GET method, see Section 9.3 of RFC 2616 at http://www.zvon.org/tmRFC/RFC2616/Output/index.html.
For a full list of HTTP status codes, see the HttpStatus Javadoc at http://hc.apache.org/httpclient-3.x/apidocs/index.html.
Common Java Cookbook by Tim O'Brien is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 United States License.
Permissions beyond the scope of this license may be available at http://www.discursive.com/books/cjcook/reference/jakartackbk-PREFACE-1.html. Copyright 2009. Common Java Cookbook Chunked HTML Output. Some Rights Reserved.