Java tutorial
/* * Copyright 2011 Revelytix Inc. * * 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 spark.protocol; import static org.apache.http.protocol.HTTP.UTF_8; import java.io.ByteArrayOutputStream; import java.io.IOException; import java.io.UnsupportedEncodingException; import java.net.URISyntaxException; import java.net.URL; import java.net.URLEncoder; import org.apache.http.Header; import org.apache.http.HttpEntity; import org.apache.http.HttpResponse; import org.apache.http.StatusLine; import org.apache.http.client.ClientProtocolException; import org.apache.http.client.HttpClient; import org.apache.http.client.methods.HttpGet; import org.apache.http.client.methods.HttpPost; import org.apache.http.client.methods.HttpUriRequest; import org.apache.http.entity.StringEntity; import org.apache.http.params.BasicHttpParams; import org.apache.http.params.HttpConnectionParams; import org.apache.http.params.HttpParams; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import spark.api.Command; import spark.api.exception.SparqlException; /** * This class provides a single method for executing a SPARQL HTTP query request and returning the * server response. It is called by ProtocolCommand, and the primary purpose for having this as a * separate class is to isolate the code which uses the Apache HTTP client in one place. */ public class SparqlCall { private static final Logger logger = LoggerFactory.getLogger(SparqlCall.class); // HTTP response codes. private static final int SUCCESS_MIN = 200; private static final int SUCCESS_MAX = 299; @SuppressWarnings("unused") private static final int REDIRECT_MIN = 300; @SuppressWarnings("unused") private static final int REDIRECT_MAX = 399; /** The maximum length of a GET request */ private static final int QUERY_LIMIT = 1024; /** Method name for HTTP POST. */ private static final String POST = "POST"; /** Accept header for content negotiation. */ private static final String ACCEPT = "Accept"; /** Content-Type header for content negotiation. */ private static final String CONTENT_TYPE = "Content-Type"; /** Content-Type value to use for URL-encoded query params included in the POST request body. */ private static final String FORM_ENCODED = "application/x-www-form-urlencoded"; /** URL-encode a string as UTF-8, catching any thrown UnsupportedEncodingException. */ private static final String encode(String s) { try { return URLEncoder.encode(s, UTF_8); } catch (UnsupportedEncodingException e) { throw new Error("JVM unable to handle UTF-8"); } } /** Logs a request, executes it, and dumps the response to the logger. For development use only. */ @SuppressWarnings("unused") private static final void dump(HttpClient client, HttpUriRequest req) { if (logger.isTraceEnabled()) { StringBuilder sb = new StringBuilder("\n=== Request ==="); sb.append("\n").append(req.getRequestLine()); for (Header h : req.getAllHeaders()) { sb.append("\n").append(h.getName()).append(": ").append(h.getValue()); } logger.trace(sb.toString()); HttpResponse resp = null; try { resp = client.execute(req); } catch (Exception e) { logger.trace("Error executing request", e); return; } sb = new StringBuilder("\n=== Response ==="); sb.append("\n").append(resp.getStatusLine()); for (Header h : resp.getAllHeaders()) { sb.append("\n").append(h.getName()).append(": ").append(h.getValue()); } logger.trace(sb.toString()); HttpEntity entity = resp.getEntity(); if (entity != null) { sb = new StringBuilder("\n=== Content ==="); try { int len = (int) entity.getContentLength(); if (len < 0) len = 100; ByteArrayOutputStream baos = new ByteArrayOutputStream(len); entity.writeTo(baos); sb.append("\n").append(baos.toString("UTF-8")); logger.trace(sb.toString()); } catch (IOException e) { logger.trace("Error reading content", e); } } } } /** * Executes a SPARQL HTTP protocol request for the given command, and returns the response. * @param command The SPARQL protocol command. * @return The HTTP response. */ static HttpResponse executeRequest(ProtocolCommand command, String mimeType) { HttpClient client = ((ProtocolConnection) command.getConnection()).getHttpClient(); URL url = ((ProtocolDataSource) command.getConnection().getDataSource()).getUrl(); HttpUriRequest req; try { String params = "query=" + encode(command.getCommand()); String u = url.toString() + "?" + params; if (u.length() > QUERY_LIMIT) { // POST connection try { req = new HttpPost(url.toURI()); } catch (URISyntaxException e) { throw new SparqlException("Endpoint <" + url + "> not in an acceptable format", e); } ((HttpPost) req).setEntity((HttpEntity) new StringEntity(params)); } else { // GET connection req = new HttpGet(u); } if (command.getTimeout() != Command.NO_TIMEOUT) { HttpParams reqParams = new BasicHttpParams(); HttpConnectionParams.setSoTimeout(reqParams, (int) (command.getTimeout() * 1000)); req.setParams(reqParams); } // Add Accept and Content-Type (for POST'ed queries) headers to the request. addHeaders(req, mimeType); // There's a small chance the request could be aborted before it's even executed, we'll have to live with that. command.setRequest(req); //dump(client, req); HttpResponse response = client.execute(req); StatusLine status = response.getStatusLine(); int code = status.getStatusCode(); // TODO the client doesn't handle redirects for posts; should we do that here? if (code >= SUCCESS_MIN && code <= SUCCESS_MAX) { return response; } else { throw new SparqlException("Unexpected status code in server response: " + status.getReasonPhrase() + "(" + code + ")"); } } catch (UnsupportedEncodingException e) { throw new SparqlException("Unabled to encode data", e); } catch (ClientProtocolException cpe) { throw new SparqlException("Error in protocol", cpe); } catch (IOException e) { throw new SparqlException(e); } } /** * Add headers to a request. * @param req The request to set the headers on. */ static void addHeaders(HttpUriRequest req, String mimeType) { if (POST.equalsIgnoreCase(req.getMethod())) { req.addHeader(CONTENT_TYPE, FORM_ENCODED); } if (mimeType != null) req.setHeader(ACCEPT, mimeType); } }