尝试在google app engine for java中实现异步http时遇到奇怪的exception
我正在尝试在java中实现async http。 这是代码的重要部分：
for (String urlString : urls) { // TODO: try and get rid of these two heap allocations url = new URL(urlString); request = new HTTPRequest(url); request.addHeader(userAgentHeader); request.addHeader(authorizationHeader); request.addHeader(acceptEncodingHeader); request.addHeader(acceptCharsetHeader); responses.add(URLFetchServiceFactory.getURLFetchService().fetchAsync(reques t)); apiCallsMade++; } for (Future futureResponse : responses) { parseResponse(new String(futureResponse.get().getContent())); } 我一直收到这个错误：
com.google.apphosting.api.ApiProxy $ CallNotFoundException：找不到API包’urlfetch’或调用’Fetch（）’。
我环顾四周寻找类路径中缺少的任何jar子，但没有看到任何遗漏。 你知道代码是哪个jar吗？ 我搜索了这个错误并搜索了这个组，但什么也没找到。 谢谢，大卫
使用Google appengine，您无法在本地Java应用程序中使用这些api。 只有在使用google appengine sdk开发和部署Web应用程序时，这才有效。 这只是为了这种方式而设计的。
当您使用此API时，它将使用http客户端，并且在应用引擎环境的情况下，它将使用谷歌基础设施。 如果您仍想对为google appengine设计的应用程序进行unit testing，则可以考虑使用LocalURLServiceFactory。
这是我为博客创建的一个简单的工作示例：
package org.appEngineAsync.server; import java.io.ByteArrayInputStream; import java.io.ByteArrayOutputStream; import java.net.URL; import java.util.ArrayList; import java.util.List; import java.util.concurrent.CopyOnWriteArrayList; import java.util.concurrent.Future; import org.appEngineAsync.client.GreetingService; import com.google.appengine.api.urlfetch.HTTPHeader; import com.google.appengine.api.urlfetch.HTTPRequest; import com.google.appengine.api.urlfetch.HTTPResponse; import com.google.appengine.api.urlfetch.URLFetchServiceFactory; import com.google.gwt.user.server.rpc.RemoteServiceServlet; @SuppressWarnings("serial") public class GreetingServiceImpl extends RemoteServiceServlet implements GreetingService { private HTTPRequest request = null; HTTPHeader acceptCharsetHeader = new HTTPHeader("Accept-Charset", "utf-8"); // All three of these data types are synchronized for thread safety List> responses = new CopyOnWriteArrayList>(); protected List tempSingleUrl = new CopyOnWriteArrayList (); StringBuffer sb = new StringBuffer(); public String greetServer(String input) throws Exception { List urlsToFetchInParrallel = new ArrayList (); urlsToFetchInParrallel.add("http://gdata.youtube.com/feeds/api/channels?q=" + input + "&start-index=1&max-results=10&v=2"); urlsToFetchInParrallel.add("http://gdata.youtube.com/feeds/api/channels?q=" + input + "&start-index=11&max-results=10&v=2"); urlsToFetchInParrallel.add("http://gdata.youtube.com/feeds/api/channels?q=" + input + "&start-index=21&max-results=10&v=2"); urlsToFetchInParrallel.add("http://gdata.youtube.com/feeds/api/channels?q=" + input + "&start-index=31&max-results=10&v=2"); urlsToFetchInParrallel.add("http://gdata.youtube.com/feeds/api/channels?q=" + input + "&start-index=41&max-results=10&v=2"); urlsToFetchInParrallel.add("http://gdata.youtube.com/feeds/api/channels?q=" + input + "&start-index=51&max-results=10&v=2"); urlsToFetchInParrallel.add("http://gdata.youtube.com/feeds/api/channels?q=" + input + "&start-index=61&max-results=10&v=2"); urlsToFetchInParrallel.add("http://gdata.youtube.com/feeds/api/channels?q=" + input + "&start-index=71&max-results=10&v=2"); urlsToFetchInParrallel.add("http://gdata.youtube.com/feeds/api/channels?q=" + input + "&start-index=81&max-results=10&v=2"); urlsToFetchInParrallel.add("http://gdata.youtube.com/feeds/api/channels?q=" + input + "&start-index=91&max-results=10&v=2"); return performHttpRequest(urlsToFetchInParrallel); } // pass in 10 urls at a time private final String performHttpRequest(List urls) throws NumberFormatException, Exception { URL url = null; request = null; byte[] tempBuffer = null; byte[] buffer = null; ByteArrayInputStream memoryStream = null; ByteArrayOutputStream baos = null; final int buffSize = 8192; int size = 0; sb.setLength(0); responses.clear(); try { for (String urlString : urls) { url = new URL(urlString); request = new HTTPRequest(url); request.addHeader(acceptCharsetHeader); responses.add(URLFetchServiceFactory.getURLFetchService().fetchAsync(request)); } for (Future futureResponse : responses) { try { memoryStream = new ByteArrayInputStream(futureResponse.get().getContent()); tempBuffer = new byte[buffSize]; baos = new ByteArrayOutputStream(); while ((size = memoryStream.read(tempBuffer, 0, buffSize)) != -1) { baos.write(tempBuffer, 0, size); } buffer = baos.toByteArray(); } catch (Exception ex) { // TODO: log or take other action return null; } finally { try { baos.close(); } catch (Exception ex) { // TODO: log } } // TODO: put this on one line when done debugging String responseString = new String(buffer, "UTF-8"); sb.append(responseString); } // TODO: put this on one line when done debugging String allResponsesString = sb.toString(); return allResponsesString; } catch (Exception ex) { // TODO: log return null; } finally { try { request = null; url = null; memoryStream = null; tempBuffer = null; baos = null; } catch (Exception ex) { // TODO: log return null; } } } }
我唯一的猜测是，由于Future在尝试访问其响应之前没有完成。 但这是一个完整而彻底的猜测！
也许在访问其.get()之前检查每个futureResponses .isDone()和.isCancelled() .get() 。