com.discursive.jccook.httpclient.ConditionalGetExample.java Source code

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Here is the source code for com.discursive.jccook.httpclient.ConditionalGetExample.java

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/* 
 * ========================================================================
 * 
 * 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;
    }
}