用Jetty和redis实现接入服务器adapter
传统的服务器端为若干个客户端提供服务，一般需要开启多个服务器端进程。为了进一步提升服务器端的处理能力，可以如下图所示将服务解耦为两部分（adapter与workers），它们之间通过消息队列传输数据，其中workers处理具体业务，adapter负责接入请求以及反馈结果，具体包含下面两个工作。1，将所有客户端的请求发送到消息队列（进而传给后台处理）
2，后台处理完毕后将结果返回响应队列，client adapter获取到结果后返回给相应客户端。
流程图如下：
我们选择用Jetty（8），redis以及php简单实现这个场景，主要用到Jetty的continuation机制和redis的list先进先出数据结构
接入服务器：
A.1，先配置一个服务器如下，同时开启一个守护线程阻塞监听response queue（用到json lib库以及jedis库）（使用专用线程处理响应可以避免“惊群”现象，不影响业务线程）
package test;
import java.util.HashMap;
import java.util.List;
import org.eclipse.jetty.continuation.Continuation;
import org.eclipse.jetty.server.*;
import org.eclipse.jetty.server.nio.SelectChannelConnector;
import org.eclipse.jetty.servlet.ServletContextHandler;
import org.eclipse.jetty.servlet.ServletHolder;
import org.eclipse.jetty.util.thread.QueuedThreadPool;
import org.json.simple.*;
import redis.clients.jedis.Jedis;
public class PJetty{
public static HashMapglobalMap = new HashMap();
// 用一个守护线程阻塞等待结果队列返回数据
public static class DaemonThread extends Thread{
private JSONObject obj = new JSONObject();
private Jedis jedis = new Jedis("127.0.0.1",6379);
private List res;
public void run(){
while(true){
// 阻塞等待响应队列
res = jedis.brpop(0, "response_queue");
// 获取结果信息
String response = res.get(1);
obj=(JSONObject) JSONValue.parse(response);
String request_sid = obj.get("request_sid").toString();
String result = obj.get("results").toString();
if(request_sid == null){
continue;
}
// 通过消息中的连接的sessonid获取到响应的continuation实例，然后设置结果信息再唤醒实例
Continuation con = globalMap.get(request_sid);
if(con == null){continue;}
globalMap.remove(request_sid);
//客户端异常断开这里会抛错
try{
con.setAttribute("results", result);
con.resume();
} catch(Exception e){
continue;
}
}
}
}
public static void main(String[] args) throws Exception {
//开启守护线程去阻塞等待响应结果队列，唤醒请求
DaemonThread dt = new DaemonThread();
dt.start();
//设置connectors
SelectChannelConnector connector1 = new SelectChannelConnector();
connector1.setPort(1987);
connector1.setThreadPool(new QueuedThreadPool(5));
Server server = new Server();
server.setConnectors(new Connector[]{connector1});
//使用servlet处理请求
ServletContextHandler context = new ServletContextHandler(ServletContextHandler.SESSIONS);
context.setContextPath("/");
context.addServlet(new ServletHolder(new NonBlockingServlet()), "/fetch");
server.setHandler(context);
server.start();
server.join();
}
}
A.2，实现自定义的servlets接受前端client连接，将请求信息传入队列request queue
package test;
import java.io.IOException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import org.eclipse.jetty.continuation.Continuation;
import org.eclipse.jetty.continuation.ContinuationSupport;
import org.json.simple.JSONObject;
import redis.clients.jedis.Jedis;
public class NonBlockingServlet extends HttpServlet {
/**
* generated serialize number
*/
private static final long serialVersionUID = 3313258432391586994L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException
{
// 用sleeptime来模拟后台工作量
String sleepTime = request.getParameter("st");
if(sleepTime == null){
sleepTime = "0";
}
// 查看结果队列是否返回此连接的请求结果
Object results = request.getAttribute("results");
if (results==null) // 如果异步处理尚未返回结果
{
Continuation continuation = ContinuationSupport.getContinuation(request);
if(continuation.isInitial()){
// 设置连接超时时间
continuation.setTimeout(10000);
response.setContentType("text/plain");
response.getWriter().flush();
HttpSession session=request.getSession();
String sid = session.getId();
Jedis jedis = new Jedis("127.0.0.1",6379);
//将请求连接sessionid以及请求内容encode后传到处理队列中
JSONObject obj=new JSONObject();
obj.put("request_sid",sid);
obj.put("params",sleepTime);
jedis.lpush("request_queue", obj.toJSONString());
//将连接和continuation实例做个映射关系存到全局hashmap中，不确定这里是否应该加锁
PJetty.globalMap.put(sid, continuation);
}
// 判断是否超时
if (continuation.isExpired())
{
// 返回超时Response
response.getWriter().println("timeout");
response.getWriter().flush();
return;
}
// 挂起HTTP连接
continuation.suspend();
return; // or continuation.undispatch();
}
// 连接恢复后返回结果
response.getWriter().println("Got Result:\t" + results);
response.getWriter().flush();
}
}
业务服务器：
B，实现后端worker.php（可以自定义worker进程数，我这里设置为5个php进程，进程数多能获取更好的并发）（用到predis库）
#!/root/bin/php
运行结果如下：
这只是一个简单的demo，为了防止redis，workers进程挂掉或者客户端异常断开，还需要做些异常处理，比如设置请求超时，捕获一些空指针等，超时需要将continuation从globalMap中剔除，防止内存得不到释放。
root # for((i=10;i>=1;i--)) ; do lynx -dump http://127.0.0.1:1987/fetch?st=$i & done
14112
14113
14114
14115
14116
14117
14118
14119
14120
14121
root # Got Result: 3
Got Result: 4
Got Result: 2
Got Result: 7
Got Result: 1
Got Result: 9
Got Result: 6
timeout
timeout
timeout
Done lynx -dump http://127.0.0.1:1987/fetch?st=$i
Done lynx -dump http://127.0.0.1:1987/fetch?st=$i
Done lynx -dump http://127.0.0.1:1987/fetch?st=$i
Done lynx -dump http://127.0.0.1:1987/fetch?st=$i
Done lynx -dump http://127.0.0.1:1987/fetch?st=$i
Done lynx -dump http://127.0.0.1:1987/fetch?st=$i
Done lynx -dump http://127.0.0.1:1987/fetch?st=$i
Done lynx -dump http://127.0.0.1:1987/fetch?st=$i
-Done lynx -dump http://127.0.0.1:1987/fetch?st=$i
+Done lynx -dump http://127.0.0.1:1987/fetch?st=$i
redis数据库中存储的内容如下，可以看出虽然经后台处理后顺序变化了，但是对应关系正确，接入服务器能够根据request_sid把结果返回给相应的用户：
redis 127.0.0.1:6379> lrange request_queue 0 15
1) "{\"request_sid\":\"igiwkwnb715aphw8uvtfa6rj\",\"params\":\"3\"}"
2) "{\"request_sid\":\"wsrglxa3h6ef19ik5i0nbiiys\",\"params\":\"2\"}"
3) "{\"request_sid\":\"tyiqoj6awj5t16ddpqusftwc8\",\"params\":\"6\"}"
4) "{\"request_sid\":\"1052tgkiyy7c31bmxjtbom7ca\",\"params\":\"5\"}"
5) "{\"request_sid\":\"17jo1xwnnkd3h1mhcqcfplrl5k\",\"params\":\"8\"}"
6) "{\"request_sid\":\"1xk521sq6vmmf6enxauwzduj9\",\"params\":\"4\"}"
7) "{\"request_sid\":\"1cxnir1slgjiq1o2n3xwznh0kk\",\"params\":\"9\"}"
8) "{\"request_sid\":\"961vf8hao3stsv4vt1qif3ws\",\"params\":\"7\"}"
9) "{\"request_sid\":\"35pfn5au6p8qdbri17p636si\",\"params\":\"10\"}"
10) "{\"request_sid\":\"1ca4wy8qsfr7av0hwk8xtlqhp\",\"params\":\"1\"}"
redis 127.0.0.1:6379> lrange response_queue 0 15
1) "{\"request_sid\":\"tyiqoj6awj5t16ddpqusftwc8\",\"results\":\"6\"}"
2) "{\"request_sid\":\"igiwkwnb715aphw8uvtfa6rj\",\"results\":\"3\"}"
3) "{\"request_sid\":\"wsrglxa3h6ef19ik5i0nbiiys\",\"results\":\"2\"}"
4) "{\"request_sid\":\"35pfn5au6p8qdbri17p636si\",\"results\":\"10\"}"
5) "{\"request_sid\":\"1052tgkiyy7c31bmxjtbom7ca\",\"results\":\"5\"}"
6) "{\"request_sid\":\"1cxnir1slgjiq1o2n3xwznh0kk\",\"results\":\"9\"}"
7) "{\"request_sid\":\"17jo1xwnnkd3h1mhcqcfplrl5k\",\"results\":\"8\"}"
8) "{\"request_sid\":\"961vf8hao3stsv4vt1qif3ws\",\"results\":\"7\"}"
9) "{\"request_sid\":\"1xk521sq6vmmf6enxauwzduj9\",\"results\":\"4\"}"
10) "{\"request_sid\":\"1ca4wy8qsfr7av0hwk8xtlqhp\",\"results\":\"1\"}"
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