您需要異步servlet，但您還需要對外部令牌生成器進行異步HTTP調用。如果您仍然在每個令牌請求的某個位置創建一個線程，您將無法通過將Servlet的請求傳遞給帶有線程池的ExecutorService來獲得任何收益。您必須從HTTP請求中分離線程，以便一個線程可以處理多個HTTP請求。這可以通過異步HTTP客戶端（如Apache Asynch HttpClient或Async Http Client）來實現。
首先，你必須創建一個異步的servlet這樣一個
public class ProxyService extends HttpServlet {
private CloseableHttpAsyncClient httpClient;
@Override
public void init() throws ServletException {
httpClient = HttpAsyncClients.custom().
setMaxConnTotal(Integer.parseInt(getInitParameter("maxtotalconnections"))).
setMaxConnPerRoute(Integer.parseInt(getInitParameter("maxconnectionsperroute"))).
build();
httpClient.start();
}
@Override
public void destroy() {
try {
httpClient.close();
} catch (IOException e) { }
}
@Override
public void doGet(HttpServletRequest request, HttpServletResponse response) {
AsyncContext asyncCtx = request.startAsync(request, response);
asyncCtx.setTimeout(ExternalServiceMock.TIMEOUT_SECONDS * ExternalServiceMock.K);
ResponseListener listener = new ResponseListener();
asyncCtx.addListener(listener);
Future<String> result = httpClient.execute(HttpAsyncMethods.createGet(getInitParameter("serviceurl")), new ResponseConsumer(asyncCtx), null);
}
}
這個servlet進行使用Apache HttpClient的非同步異步HTTP調用。請注意，您可能需要配置每個路由的最大連接數，因爲根據RFC 2616規範，默認情況下，HttpAsyncClient最多隻允許同一主機的兩個併發連接。還有很多其他選項可以配置，如HttpAsyncClient configuration中所示。 HttpAsyncClient創建起來非常昂貴，因此您不希望在每個GET操作中創建它的實例。
一個偵聽器掛鉤到AsyncContext，這個偵聽器僅用於上面的例子來處理超時。
public class ResponseListener implements AsyncListener {
@Override
public void onStartAsync(AsyncEvent event) throws IOException {
}
@Override
public void onComplete(AsyncEvent event) throws IOException {
}
@Override
public void onError(AsyncEvent event) throws IOException {
event.getAsyncContext().getResponse().getWriter().print("error:");
}
@Override
public void onTimeout(AsyncEvent event) throws IOException {
event.getAsyncContext().getResponse().getWriter().print("timeout:");
}
}
然後你需要一個消費者的HTTP客戶端。此消費者通過在buildResult()由HttpClient在內部執行時調用complete()來通知AsyncContext，作爲將Future<String>返回給調用者ProxyService servlet的步驟。
public class ResponseConsumer extends AsyncCharConsumer<String> {
private int responseCode;
private StringBuilder responseBuffer;
private AsyncContext asyncCtx;
public ResponseConsumer(AsyncContext asyncCtx) {
this.responseBuffer = new StringBuilder();
this.asyncCtx = asyncCtx;
}
@Override
protected void releaseResources() { }
@Override
protected String buildResult(final HttpContext context) {
try {
PrintWriter responseWriter = asyncCtx.getResponse().getWriter();
switch (responseCode) {
case javax.servlet.http.HttpServletResponse.SC_OK:
responseWriter.print("success:" + responseBuffer.toString());
break;
default:
responseWriter.print("error:" + responseBuffer.toString());
}
} catch (IOException e) { }
asyncCtx.complete();
return responseBuffer.toString();
}
@Override
protected void onCharReceived(CharBuffer buffer, IOControl ioc) throws IOException {
while (buffer.hasRemaining())
responseBuffer.append(buffer.get());
}
@Override
protected void onResponseReceived(HttpResponse response) throws HttpException, IOException {
responseCode = response.getStatusLine().getStatusCode();
}
}
爲ProxyService servlet的web.xml配置可以像
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
id="WebApp_ID" version="3.0" metadata-complete="true">
<display-name>asyncservlet-demo</display-name>
<servlet>
<servlet-name>External Service Mock</servlet-name>
<servlet-class>ExternalServiceMock</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet>
<servlet-name>Proxy Service</servlet-name>
<servlet-class>ProxyService</servlet-class>
<load-on-startup>1</load-on-startup>
<async-supported>true</async-supported>
<init-param>
<param-name>maxtotalconnections</param-name>
<param-value>200</param-value>
</init-param>
<init-param>
<param-name>maxconnectionsperroute</param-name>
<param-value>4</param-value>
</init-param>
<init-param>
<param-name>serviceurl</param-name>
<param-value>http://127.0.0.1:8080/asyncservlet/externalservicemock</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>External Service Mock</servlet-name>
<url-pattern>/externalservicemock</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>Proxy Service</servlet-name>
<url-pattern>/proxyservice</url-pattern>
</servlet-mapping>
</web-app>
並與在幾秒鐘的延遲令牌生成一個模擬的servlet可能是：
public class ExternalServiceMock extends HttpServlet{
public static final int TIMEOUT_SECONDS = 13;
public static final long K = 1000l;
public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
Random rnd = new Random();
try {
Thread.sleep(rnd.nextInt(TIMEOUT_SECONDS) * K);
} catch (InterruptedException e) { }
final byte[] token = String.format("%10d", Math.abs(rnd.nextLong())).getBytes(ISO_8859_1);
response.setContentType("text/plain");
response.setCharacterEncoding(ISO_8859_1.name());
response.setContentLength(token.length);
response.getOutputStream().write(token);
}
}
你可以獲得fully working example at GitHub。
你說：「在令牌生成過程中，每秒接近80％的傳入請求需要等待*」，對於每個人來說，這80％的傳入請求是傳入請求還是應用程序或請求您已發送至第三方系統以生成令牌。我認爲你需要在完整答案中澄清這一點，因爲當你談論哪件事情時，因爲就像我說過的那樣，對每個人都不明顯，請澄清一下，你可能有更大的機會獲得解決方案。 – hagrawal
@hagrawal 80％的傳入請求將等待第三方。 –