Java tutorial
/** * * BibSonomy-Scraper - Web page scrapers returning BibTeX for BibSonomy. * * Copyright (C) 2006 - 2011 Knowledge & Data Engineering Group, * University of Kassel, Germany * http://www.kde.cs.uni-kassel.de/ * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License * as published by the Free Software Foundation; either version 2 * of the License, or (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ package org.bibsonomy.scraper.util; import java.io.UnsupportedEncodingException; import java.net.URL; import java.net.URLDecoder; import java.net.URLEncoder; import java.security.InvalidKeyException; import java.security.NoSuchAlgorithmException; import java.text.DateFormat; import java.text.SimpleDateFormat; import java.util.Calendar; import java.util.HashMap; import java.util.Iterator; import java.util.Map; import java.util.SortedMap; import java.util.TimeZone; import java.util.TreeMap; import javax.crypto.Mac; import javax.crypto.spec.SecretKeySpec; import org.apache.commons.codec.binary.Base64; import org.bibsonomy.scraper.exceptions.ScrapingException; /** * This class contains all the logic for signing requests * to the Amazon Product Advertising API. */ public class SignedRequestsHelper { /** * All strings are handled as UTF-8 */ private static final String UTF8_CHARSET = "UTF-8"; /** * The HMAC algorithm required by Amazon */ private static final String HMAC_SHA256_ALGORITHM = "HmacSHA256"; /** * This is the URI for the service, don't change unless you really know * what you're doing. */ private static final String REQUEST_URI = "/onca/xml"; /** * The sample uses HTTP GET to fetch the response. If you changed the sample * to use HTTP POST instead, change the value below to POST. */ private static final String REQUEST_METHOD = "GET"; /** * Supported AMAZON Hosts */ private static final String AMAZON_HOST_COM = "amazon.com"; private static final String AMAZON_HOST_DE = "amazon.de"; private static final String AMAZON_HOST_CA = "amazon.ca"; private static final String AMAZON_HOST_FR = "amazon.fr"; private static final String AMAZON_HOST_CO_JP = "amazon.co.jp"; private static final String AMAZON_HOST_JP = "amazon.jp"; private static final String AMAZON_HOST_CO_UK = "amazon.co.uk"; private static final String ECS_AMAZON_HOST_COM = "ecs.amazonaws.com"; private static final String ECS_AMAZON_HOST_DE = "ecs.amazonaws.de"; private static final String ECS_AMAZON_HOST_CA = "ecs.amazonaws.ca"; private static final String ECS_AMAZON_HOST_FR = "ecs.amazonaws.fr"; private static final String ECS_AMAZON_HOST_JP = "ecs.amazonaws.jp"; private static final String ECS_AMAZON_HOST_CO_UK = "ecs.amazonaws.co.uk"; private String endpoint = null; private String awsAccessKeyId = null; private String awsSecretKey = null; private SecretKeySpec secretKeySpec = null; private Mac mac = null; /** * You must provide the three values below to initialize the helper. * * @param endpoint Destination for the requests. * @param awsAccessKeyId Your AWS Access Key ID * @param awsSecretKey Your AWS Secret Key * @throws ScrapingException */ public static SignedRequestsHelper getInstance(URL url, String awsAccessKeyId, String awsSecretKey) throws IllegalArgumentException, UnsupportedEncodingException, NoSuchAlgorithmException, InvalidKeyException, ScrapingException { if (null == url) { throw new IllegalArgumentException("endpoint is null"); } if (null == awsAccessKeyId || awsAccessKeyId.length() == 0) { throw new IllegalArgumentException("awsAccessKeyId is null or empty"); } if (null == awsSecretKey || awsSecretKey.length() == 0) { throw new IllegalArgumentException("awsSecretKey is null or empty"); } SignedRequestsHelper instance = new SignedRequestsHelper(); instance.endpoint = getEndpointForLocale(url); instance.awsAccessKeyId = awsAccessKeyId; instance.awsSecretKey = awsSecretKey; byte[] secretyKeyBytes = instance.awsSecretKey.getBytes(UTF8_CHARSET); instance.secretKeySpec = new SecretKeySpec(secretyKeyBytes, HMAC_SHA256_ALGORITHM); instance.mac = Mac.getInstance(HMAC_SHA256_ALGORITHM); instance.mac.init(instance.secretKeySpec); return instance; } /** * returns ecs endpoint for specific locales * * @param url * @return * @throws ScrapingException */ private static String getEndpointForLocale(URL url) throws ScrapingException { final String host = url.getHost(); if (host.contains(AMAZON_HOST_COM)) return ECS_AMAZON_HOST_COM; else if (host.contains(AMAZON_HOST_DE)) return ECS_AMAZON_HOST_DE; else if (host.contains(AMAZON_HOST_CA)) return ECS_AMAZON_HOST_CA; else if (host.contains(AMAZON_HOST_FR)) return ECS_AMAZON_HOST_FR; else if (host.contains(AMAZON_HOST_CO_JP) || host.contains(AMAZON_HOST_JP)) return ECS_AMAZON_HOST_JP; else if (host.contains(AMAZON_HOST_CO_UK)) return ECS_AMAZON_HOST_CO_UK; else { throw new ScrapingException("The Amazon service for " + host + " is currently not supported."); } } /** * The construct is private since we'd rather use getInstance() */ private SignedRequestsHelper() { } /** * This method signs requests in hashmap form. It returns a URL that should * be used to fetch the response. The URL returned should not be modified in * any way, doing so will invalidate the signature and Amazon will reject * the request. */ public String sign(Map<String, String> params) { // Let's add the AWSAccessKeyId and Timestamp parameters to the request. params.put("AWSAccessKeyId", this.awsAccessKeyId); params.put("Timestamp", this.timestamp()); // The parameters need to be processed in lexicographical order, so we'll // use a TreeMap implementation for that. SortedMap<String, String> sortedParamMap = new TreeMap<String, String>(params); // get the canonical form the query string String canonicalQS = this.canonicalize(sortedParamMap); // create the string upon which the signature is calculated String toSign = REQUEST_METHOD + "\n" + this.endpoint + "\n" + REQUEST_URI + "\n" + canonicalQS; // get the signature String hmac = this.hmac(toSign); String sig = this.percentEncodeRfc3986(hmac); // construct the URL String url = "http://" + this.endpoint + REQUEST_URI + "?" + canonicalQS + "&Signature=" + sig; return url; } /** * This method signs requests in query-string form. It returns a URL that * should be used to fetch the response. The URL returned should not be * modified in any way, doing so will invalidate the signature and Amazon * will reject the request. */ public String sign(String queryString) { // let's break the query string into it's constituent name-value pairs Map<String, String> params = this.createParameterMap(queryString); // then we can sign the request as before return this.sign(params); } /** * Compute the HMAC. * * @param stringToSign String to compute the HMAC over. * @return base64-encoded hmac value. */ private String hmac(String stringToSign) { String signature = null; byte[] data; byte[] rawHmac; try { data = stringToSign.getBytes(UTF8_CHARSET); rawHmac = mac.doFinal(data); Base64 encoder = new Base64(); signature = new String(encoder.encode(rawHmac)); } catch (UnsupportedEncodingException e) { throw new RuntimeException(UTF8_CHARSET + " is unsupported!", e); } return signature; } /** * Generate a ISO-8601 format timestamp as required by Amazon. * * @return ISO-8601 format timestamp. */ private String timestamp() { String timestamp = null; Calendar cal = Calendar.getInstance(); DateFormat dfm = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'"); dfm.setTimeZone(TimeZone.getTimeZone("GMT")); timestamp = dfm.format(cal.getTime()); return timestamp; } /** * Canonicalize the query string as required by Amazon. * * @param sortedParamMap Parameter name-value pairs in lexicographical order. * @return Canonical form of query string. */ private String canonicalize(SortedMap<String, String> sortedParamMap) { if (sortedParamMap.isEmpty()) { return ""; } StringBuffer buffer = new StringBuffer(); Iterator<Map.Entry<String, String>> iter = sortedParamMap.entrySet().iterator(); while (iter.hasNext()) { Map.Entry<String, String> kvpair = iter.next(); buffer.append(percentEncodeRfc3986(kvpair.getKey())); buffer.append("="); buffer.append(percentEncodeRfc3986(kvpair.getValue())); if (iter.hasNext()) { buffer.append("&"); } } String cannoical = buffer.toString(); return cannoical; } /** * Percent-encode values according the RFC 3986. The built-in Java * URLEncoder does not encode according to the RFC, so we make the * extra replacements. * * @param s decoded string * @return encoded string per RFC 3986 */ private String percentEncodeRfc3986(String s) { String out; try { /* * Somehow the encode() Method appends a carriage return and new line char to the string. * Therefore this signature does not match the Amazon signature. * * This is not the most elegant way to fix, but replacing the "chars" is working for now. */ out = URLEncoder.encode(s, UTF8_CHARSET).replace("+", "%20").replace("*", "%2A").replace("%7E", "~") .replace("%0D%0A", ""); } catch (UnsupportedEncodingException e) { out = s; } return out; } /** * Takes a query string, separates the constituent name-value pairs * and stores them in a hashmap. * * @param queryString * @return */ private Map<String, String> createParameterMap(String queryString) { Map<String, String> map = new HashMap<String, String>(); String[] pairs = queryString.split("&"); for (String pair : pairs) { if (pair.length() < 1) { continue; } String[] tokens = pair.split("=", 2); for (int j = 0; j < tokens.length; j++) { try { tokens[j] = URLDecoder.decode(tokens[j], UTF8_CHARSET); } catch (UnsupportedEncodingException e) { } } switch (tokens.length) { case 1: { if (pair.charAt(0) == '=') { map.put("", tokens[0]); } else { map.put(tokens[0], ""); } break; } case 2: { map.put(tokens[0], tokens[1]); break; } } } return map; } }