/*
* ========================================================================
*
* Copyright 2005 Tim O'Brien.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* ========================================================================
*/
package com.discursive.jccook.httpclient;
import java.io.IOException;
import org.apache.commons.httpclient.Header;
import org.apache.commons.httpclient.HeaderElement;
import org.apache.commons.httpclient.HttpClient;
import org.apache.commons.httpclient.HttpException;
import org.apache.commons.httpclient.HttpMethod;
import org.apache.commons.httpclient.HttpStatus;
import org.apache.commons.httpclient.methods.GetMethod;
public class ConditionalGetExample {
public static void main(String[] args) throws HttpException, IOException {
// Configure Logging
System.setProperty("org.apache.commons.logging.Log",
"org.apache.commons.logging.impl.SimpleLog");
System.setProperty("org.apache.commons.logging.simplelog.showdatetime",
"true");
System.setProperty("org.apache.commons.logging.simplelog.log.httpclient.wire",
"debug");
System.setProperty("org.apache.commons.logging.simplelog.log.org.apache.commons.httpclient",
"debug");
ConditionalGetExample example = new ConditionalGetExample();
example.start();
}
String entityTag = "";
String lastModified = "";
public void start() throws HttpException, IOException {
HttpClient client = new HttpClient();
HttpMethod method = new GetMethod("http://www.apache.org");
for( int i = 0; i < 3; i++ ) {
setHeaders(method);
client.executeMethod(method);
processResults(method);
method.releaseConnection();
method.recycle();
}
}
private void setHeaders(HttpMethod method) {
method.setRequestHeader(new Header("If-None-Match", entityTag ) );
method.setRequestHeader(new Header("If-Modified-Since", lastModified ) );
}
private void processResults(HttpMethod method) throws HttpException {
if(method.getStatusCode() == HttpStatus.SC_NOT_MODIFIED ) {
System.out.println( "Content not modified since last request" );
} else {
System.out.println( "Get Method retrieved content." );
entityTag = retrieveHeader( method, "ETag" );
lastModified = retrieveHeader( method, "Last-Modified" );
System.out.println( "Entity Tag: " + entityTag );
System.out.println( "Last Modified: " + lastModified );
}
}
private String retrieveHeader( HttpMethod method, String name ) throws HttpException {
HeaderElement[] header = method.getResponseHeader(name).getElements();
String value = "";
if(header.length > 0) {
value = header[0].getName();
}
return value;
}
}
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