为什么我的简单Jetty服务器一次只处理一个请求?

我的服务器设置:

server = new Server(port);
ContextHandler testContext = new ContextHandler();
testContext.setContextPath("/test");
testContext.setHandler(new TestServlet());

ContextHandlerCollection contexts = new ContextHandlerCollection();
contexts.setHandlers(new Handler[]{ testContext});

HandlerCollection handlers = new HandlerCollection();
handlers.setHandlers(new Handler[]{ contexts, new DefaultHandler() });

server.setHandler(handlers);
server.setStopAtShutdown(true);
server.start();

测试代码:

public class TestServlet extends AbstractHandler
{
    @Override
    public void handle(String target, Request baseRequest, HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException
    {
        System.out.println("a");
        try {
            Thread.sleep(2500);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("b");
        try {
            Thread.sleep(2500);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("c");
        try {
            Thread.sleep(2500);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        baseRequest.setHandled(true);
    }
}

如果我访问 localhost/test

a
b
c
a
b
c

为什么这些请求没有并行处理?