Java tutorial
/********************************************************************************************** * Copyright 2009 Amazon.com, Inc. or its affiliates. All Rights Reserved. * * Licensed under the Apache License, Version 2.0 (the "License"). You may not use this file * except in compliance with the License. A copy of the License is located at * * http://aws.amazon.com/apache2.0/ * * or in the "LICENSE.txt" file accompanying this file. This file 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. * * ******************************************************************************************** * * Amazon Product Advertising API * Signed Requests Sample Code * * API Version: 2009-03-31 * */ package apaapi4j; import java.io.UnsupportedEncodingException; import java.net.URLDecoder; import java.net.URLEncoder; 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; /** * This class contains all the logic for signing requests * to the Amazon Product Advertising API. */ public class SignedRequestsHelper { private static final String UTF8_CHARSET = "UTF-8"; private static final String HMAC_SHA256_ALGORITHM = "HmacSHA256"; private static final String REQUEST_URI = "/onca/xml"; private static final String REQUEST_METHOD = "GET"; private final String endpoint; private final String awsAccessKeyId; private final SecretKeySpec secretKeySpec; private final Mac mac; /** * 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 */ public static SignedRequestsHelper getInstance(String endpoint, String awsAccessKeyId, String awsSecretKey) { if (null == endpoint || endpoint.length() == 0) throw new IllegalArgumentException("endpoint is null or empty"); 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"); return new SignedRequestsHelper(endpoint, awsAccessKeyId, awsSecretKey); } private SignedRequestsHelper(String endpoint, String awsAccessKeyId, String awsSecretKey) { try { this.endpoint = endpoint.toLowerCase(); this.awsAccessKeyId = awsAccessKeyId; byte[] secretyKeyBytes = awsSecretKey.getBytes(UTF8_CHARSET); this.secretKeySpec = new SecretKeySpec(secretyKeyBytes, HMAC_SHA256_ALGORITHM); this.mac = Mac.getInstance(HMAC_SHA256_ALGORITHM); this.mac.init(this.secretKeySpec); } catch (Exception e) { throw new RuntimeException(e); } } /** * 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 { out = URLEncoder.encode(s, UTF8_CHARSET).replace("+", "%20").replace("*", "%2A").replace("%7E", "~"); } 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; } }