Java tutorial
/* * Copyright 2011 Mind Ltd. * * 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. * * This file incorporates work covered by the following copyright and permission * notice: * * Copyright 2008 Google 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 com.google.gwt.http.client; import com.google.gwt.user.client.Timer; import com.google.gwt.xhr.client.XMLHttpRequest; /** * An HTTP request that is waiting for a response. Requests can be queried for * their pending status or they can be canceled. * * <h3>Required Module</h3> Modules that use this class should inherit * <code>com.google.gwt.http.HTTP</code>. * * {@gwt.include * com/google/gwt/examples/http/InheritsExample.gwt.xml} * */ public class Request { /** * Creates a {@link Response} instance for the given JavaScript XmlHttpRequest * object. * * @param xmlHttpRequest xmlHttpRequest object for which we need a response * @return a {@link Response} object instance */ private static Response createResponse(final XMLHttpRequest xmlHttpRequest) { assert (isResponseReady(xmlHttpRequest)); Response response = new Response() { @Override public String getHeader(String header) { StringValidator.throwIfEmptyOrNull("header", header); return xmlHttpRequest.getResponseHeader(header); } @Override public Header[] getHeaders() { return Request.getHeaders(xmlHttpRequest); } @Override public String getHeadersAsString() { return xmlHttpRequest.getAllResponseHeaders(); } @Override public int getStatusCode() { return xmlHttpRequest.getStatus(); } @Override public String getStatusText() { return xmlHttpRequest.getStatusText(); } @Override public String getText() { return xmlHttpRequest.getResponseText(); } }; return response; } /** * Returns an array of headers built by parsing the string of headers returned * by the JavaScript <code>XmlHttpRequest</code> object. * * @param xmlHttpRequest * @return array of Header items */ private static Header[] getHeaders(XMLHttpRequest xmlHttp) { String allHeaders = xmlHttp.getAllResponseHeaders(); String[] unparsedHeaders = allHeaders.split("\n"); Header[] parsedHeaders = new Header[unparsedHeaders.length]; for (int i = 0, n = unparsedHeaders.length; i < n; ++i) { String unparsedHeader = unparsedHeaders[i]; if (unparsedHeader.length() == 0) { continue; } int endOfNameIdx = unparsedHeader.indexOf(':'); if (endOfNameIdx < 0) { continue; } final String name = unparsedHeader.substring(0, endOfNameIdx).trim(); final String value = unparsedHeader.substring(endOfNameIdx + 1).trim(); Header header = new Header() { @Override public String getName() { return name; } @Override public String getValue() { return value; } @Override public String toString() { return name + " : " + value; } }; parsedHeaders[i] = header; } return parsedHeaders; } private static boolean isResponseReady(XMLHttpRequest xhr) { return xhr.getReadyState() == XMLHttpRequest.DONE; } /** * The number of milliseconds to wait for this HTTP request to complete. */ private final int timeoutMillis; /* * Timer used to force HTTPRequest timeouts. If the user has not requested a * timeout then this field is null. */ private final Timer timer; /* * JavaScript XmlHttpRequest object that this Java class wraps. This field is * not final because we transfer ownership of it to the HTTPResponse object * and set this field to null. */ private XMLHttpRequest xmlHttpRequest; /** * Only used for building a * {@link com.google.gwt.user.client.rpc.impl.FailedRequest}. */ protected Request() { timeoutMillis = 0; xmlHttpRequest = null; timer = null; } /** * Constructs an instance of the Request object. * * @param xmlHttpRequest JavaScript XmlHttpRequest object instance * @param timeoutMillis number of milliseconds to wait for a response * @param callback callback interface to use for notification * * @throws IllegalArgumentException if timeoutMillis < 0 * @throws NullPointerException if xmlHttpRequest, or callback are null */ Request(XMLHttpRequest xmlHttpRequest, int timeoutMillis, final RequestCallback callback) { if (xmlHttpRequest == null) { throw new NullPointerException(); } if (callback == null) { throw new NullPointerException(); } if (timeoutMillis < 0) { throw new IllegalArgumentException(); } this.timeoutMillis = timeoutMillis; this.xmlHttpRequest = xmlHttpRequest; if (timeoutMillis > 0) { // create and start a Timer timer = new Timer() { @Override public void run() { fireOnTimeout(callback); } }; timer.schedule(timeoutMillis); } else { // no Timer required timer = null; } } /** * Cancels a pending request. If the request has already been canceled or if * it has timed out no action is taken. */ public void cancel() { /* * There is a strange race condition that occurs on Mozilla when you cancel * a request while the response is coming in. It appears that in some cases * the onreadystatechange handler is still called after the handler function * has been deleted and during the call to XmlHttpRequest.abort(). So we * null the xmlHttpRequest here and that will prevent the * fireOnResponseReceived method from calling the callback function. * * Setting the onreadystatechange handler to null gives us the correct * behavior in Mozilla but crashes IE. That is why we have chosen to fixed * this in Java by nulling out our reference to the XmlHttpRequest object. */ if (xmlHttpRequest != null) { XMLHttpRequest xmlHttp = xmlHttpRequest; xmlHttpRequest = null; xmlHttp.clearOnReadyStateChange(); xmlHttp.abort(); cancelTimer(); } } /** * Returns true if this request is waiting for a response. * * @return true if this request is waiting for a response */ public boolean isPending() { if (xmlHttpRequest == null) { return false; } int readyState = xmlHttpRequest.getReadyState(); /* * Because we are doing asynchronous requests it is possible that we can * call XmlHttpRequest.send and still have the XmlHttpRequest.getReadyState * method return the state as XmlHttpRequest.OPEN. That is why we include * open although it is nottechnically true since open implies that the * request has not been sent. */ switch (readyState) { case XMLHttpRequest.OPENED: case XMLHttpRequest.HEADERS_RECEIVED: case XMLHttpRequest.LOADING: return true; } return false; } /* * Method called when the JavaScript XmlHttpRequest object's readyState * reaches 4 (LOADED). */ void fireOnResponseReceived(RequestCallback callback) { if (xmlHttpRequest == null) { // the request has timed out at this point return; } cancelTimer(); /* * We cannot use cancel here because it would clear the contents of the * JavaScript XmlHttpRequest object so we manually null out our reference to * the JavaScriptObject */ final XMLHttpRequest xhr = xmlHttpRequest; xmlHttpRequest = null; String errorMsg = getBrowserSpecificFailure(xhr); if (errorMsg != null) { Throwable exception = new RuntimeException(errorMsg); callback.onError(this, exception); } else { Response response = createResponse(xhr); callback.onResponseReceived(this, response); } } /* * Stops the current HTTPRequest timer if there is one. */ private void cancelTimer() { if (timer != null) { timer.cancel(); } } /* * Method called when this request times out. * * NOTE: this method is called from JSNI */ private void fireOnTimeout(RequestCallback callback) { if (xmlHttpRequest == null) { // the request has been received at this point return; } cancel(); callback.onError(this, new RequestTimeoutException(this, timeoutMillis)); } /** * Tests if the JavaScript <code>XmlHttpRequest.status</code> property is * readable. This can return failure in two different known scenarios: * * <ol> * <li>On Mozilla, after a network error, attempting to read the status code * results in an exception being thrown. See <a * href="https://bugzilla.mozilla.org/show_bug.cgi?id=238559" * >https://bugzilla.mozilla.org/show_bug.cgi?id=238559</a>.</li> * <li>On Safari, if the HTTP response does not include any response text. See * <a * href="http://bugs.webkit.org/show_bug.cgi?id=3810">http://bugs.webkit.org * /show_bug.cgi?id=3810</a>.</li> * </ol> * * @param xhr the JavaScript <code>XmlHttpRequest</code> object to test * @return a String message containing an error message if the * <code>XmlHttpRequest.status</code> code is unreadable or null if * the status code could be successfully read. */ private String getBrowserSpecificFailure(XMLHttpRequest xhr) { return xhr.getFailureMessage(); } }