最近,在我对Servlets
中的异步处理的研究中,我遇到了至少三种实现方式
使用这种方法的一些功能。
问题是:
找到方法:
使用AsyncContext.start(Runnable)
。
这种方法非常简单明了。但是许多服务器在为HTTP
请求创建的线程池中执行这样的工作
(更多关于它http://www.nurkiewicz.com/2012/05/javaxservletservletrequeststartasync.html)
使用在Servlet上下文初始化期间创建的自定义线程池
(示例:http://www.journaldev.com/2008/async-servlet-feature-of-servlet-3)。
但我可以在Servlet容器中创建自己的线程吗? EJB
(JavaEE7
之前)不推荐(甚至禁止)。
我可以使用JavaSE
执行人员,还是应该使用ManagedExecutors
中的JavaEE7
(假设我使用JavaEE7
)?
使用EJB
和@Asynchronious
注释
(例如:https://github.com/wildfly/quickstart/tree/master/servlet-async/src/main/java/org/jboss/as/quickstarts/servlet/async)。 但是在这里我无法控制执行我的任务的线程(即应该创建多少线程等)。
我很高兴听到您对此问题的看法以及您对AsyncContext
的体验。
答案 0 :(得分:2)
全部将具有相同的性能,在后端,所有线程都将请求处理线程替换为另一个线程,以便可以处理更多请求。
下面您将找到一个简单的实现:
@WebServlet(urlPatterns = "/AsyncLongRunningServlet", asyncSupported = true)
public class AsyncLongRunningServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
System.out.println("Request Processing Thread "+Thread.currentThread().getName());
request.setAttribute("org.apache.catalina.ASYNC_SUPPORTED", true);
response.setContentType("text/html");
PrintWriter printWriter=response.getWriter();
printWriter.println("<html><head><title>Asynchronous servlet</title></head><body>");
printWriter.println("Request Processing Thread "+Thread.currentThread().getName());
printWriter.println("<br>");
printWriter.println("<progress id='progress' max='100')></progress>");
printWriter.println("<br>");
AsyncContext asyncCtx = request.startAsync();
asyncCtx.addListener(new AppAsyncListener());
asyncCtx.setTimeout(12000);
//release of request processing thread
asyncCtx.start(() ->{
printWriter.println("<br>");
printWriter.println("Async thread Name "+Thread.currentThread().getName());
printWriter.println("<br>");
int i=0;
while(i<100)
{
printWriter.println("<script>document.getElementById('progress').value=\""+i+"\";</script>");
printWriter.flush();
try {
Thread.sleep(100);
} catch (Exception e) {
}
i++;
}
printWriter.println("</body></html>");
asyncCtx.complete();
}
);
printWriter.println("<br>");
printWriter.println("End of response");
}
}
package com.journaldev.servlet.async;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.AsyncEvent;
import javax.servlet.AsyncListener;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebListener;
@WebListener
public class AppAsyncListener implements AsyncListener {
@Override
public void onComplete(AsyncEvent asyncEvent) throws IOException {
System.out.println("AppAsyncListener onComplete");
// we can do resource cleanup activity here
}
@Override
public void onError(AsyncEvent asyncEvent) throws IOException {
System.out.println("AppAsyncListener onError");
//we can return error response to client
}
@Override
public void onStartAsync(AsyncEvent asyncEvent) throws IOException {
System.out.println("AppAsyncListener onStartAsync");
//we can log the event here
}
@Override
public void onTimeout(AsyncEvent asyncEvent) throws IOException {
System.out.println("AppAsyncListener onTimeout");
//we can send appropriate response to client
ServletResponse response = asyncEvent.getAsyncContext().getResponse();
PrintWriter out = response.getWriter();
out.write("TimeOut Error in Processing");
}
}