Servlet3之NIO线程池隔离

线程隔离主要是针对业务中不同业务场景，按照权重区分使用不同的线程池，以达到某一个业务出现问题，不会将故障扩散到其他的业务线程池，从而达到保证主要业务高可用。

本案例主要讲解基于servlet3的线程隔离术。
首先我们回忆一下在tomcat6，tomcat6只支持BIO，它的处理流程如下：
1）.tomcat负责接收servletRequest请求
2）.将接收的请求分配给servlet处理业务
3）.处理完请求之后，通过servletResponse写会数据
上面这三步都是在一个线程里面完成的，也就是同步进行。
如下图：

tomcat7之后版本引入了servlet3，它基于NIO能处理更大的并发数。
我们可以将整个请求改造成如下步骤：
1）.tomcat单线程进行请求解析
2）.解析完之后将task放入队列（可以根据不同业务类型放入不同的队列）
3）.每个队列指定相应业务线程池对task进行处理
这样改造以后就可以把业务按照重要性发送到不同线程池，两个线程池分开独立配置，互不干扰。当非核心的业务出现问题之后，不会影响核心的业务。另外由于此线程池是有我们创建的，我们可以对该线程池进行监控，处理，灵活了很多。
如下图：

下面是实现代码：

接口层调用

@RestController
@RequestMapping("/app")
public class NIOCtrl {
    @Autowired
    private LocalNewsAsyncContext localNewsAsyncContext;
    @Autowired
    private NewsService newsService;

    @RequestMapping("/news")
    public void getNews(HttpServletRequest request,@RequestParam(value = "type",required = false) String type){
        if("1".equals(type)){
            localNewsAsyncContext.submit(request, () -> newsService.getNews());
            return;
        }
        localNewsAsyncContext.submit(request, () -> newsService.getNewsMap());
    }
}

将请求丢进指定线程池

@Service
public class LocalNewsAsyncContext {
    private final static Long timeOutSeconds= 5L;
    @Autowired
    private CustomAsyncListener asyncListener;
    @Autowired
    private ThreadPoolExecutor executor;

    public void submit(final HttpServletRequest request,final Callable<Object> task){
        final String uri= request.getRequestURI();
        final Map<String,String[]> params= request.getParameterMap();
        //开启异步上下文
        final AsyncContext asyncContext= request.startAsync();
        asyncContext.getRequest().setAttribute(Constant.URI,uri);
        asyncContext.getRequest().setAttribute(Constant.PARAMS, params);
        asyncContext.setTimeout(timeOutSeconds * 1000);
        if(asyncContext!=null){
            asyncContext.addListener(asyncListener);
        }
        executor.submit(new CustomCallable(asyncContext, task));

    }
}

自定义线程处理

public class CustomCallable implements Callable{
    private static final Logger LOG = LoggerFactory.getLogger(CustomCallable.class);

    public AsyncContext asyncContext;
    private Callable<Object> task;
    private String uri;
    private  Map<String,String[]> params;

    public CustomCallable(AsyncContext asyncContext, Callable<Object> task){
        this.asyncContext= asyncContext;
        this.task= task;
        this.uri= (String) asyncContext.getRequest().getAttribute(Constant.URI);
        this.params= (Map<String, String[]>) asyncContext.getRequest().getAttribute(Constant.PARAMS);
    }
    @Override public Object call() throws Exception {
        Object o= task.call();
        if(o==null){
            callback(asyncContext,o);
        }else if(o instanceof String){
            callback(asyncContext, o);
        }else if(o instanceof CompletableFuture){
            CompletableFuture<Object> future= (CompletableFuture<Object>) o;
            future.thenAccept(o1 -> callback(asyncContext, o1))
                    .exceptionally(throwable -> {
                        callback(asyncContext,"");
                        return null;
                    });
        }else {
            callback(asyncContext, o);
        }
        return null;
    }

    private void callback(AsyncContext asyncContext,Object result){
        HttpServletResponse response= (HttpServletResponse) asyncContext.getResponse();
        try{
            if(result instanceof String){
                write(response, (String) result);
            }else {
                write(response, JSON.toJSONString(result));
            }
        }catch (Exception e){
            response.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
            e.printStackTrace();
            try {
                LOG.error("get info error for uri:{}, params:{}",uri,JSON.toJSONString(params),e);
            }catch (Exception e1){}
        }finally {
            asyncContext.complete();
        }
    }

    private void write(HttpServletResponse response,String result) throws IOException {
        response.getOutputStream().write(result.getBytes());
    }
}

定义业务线程池

@Configuration
public class LocalNewsPoolConfig {
    private final static Logger LOG= LoggerFactory.getLogger(LocalNewsPoolConfig.class);

    @Bean
    public ThreadPoolExecutor init(){
        int corePoolSize= 10;
        int maximumPoolSize= 100;
        int queueCapacity= 200;
        LinkedBlockingDeque<Runnable> queue= new LinkedBlockingDeque<>(queueCapacity);
        ThreadPoolExecutor executor= new ThreadPoolExecutor(corePoolSize,maximumPoolSize,60L, TimeUnit.SECONDS,queue);
        executor.allowCoreThreadTimeOut(true);
        executor.setRejectedExecutionHandler((r, executor1) -> {
            if(r instanceof CustomCallable){
                CustomCallable call= (CustomCallable) r;
                AsyncContext asyncContext= call.asyncContext;
                if(asyncContext!=null){
                    handler(asyncContext);
                }
            }
        });
        return executor;
    }

    private static void handler(AsyncContext asyncContext){
        try{
            ServletRequest req= asyncContext.getRequest();
            String uri= (String) req.getAttribute(Constant.URI);
            Map params= (Map) req.getAttribute(Constant.PARAMS);
            LOG.error("async req rejected. uri :{},params:{}",uri, JSON.toJSONString(params));
        }catch (Exception e){
            e.printStackTrace();
            try{
                HttpServletResponse response= (HttpServletResponse) asyncContext.getResponse();
                response.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
            }catch (Exception e1){}
        }finally {
            asyncContext.complete();
        }
    }
    
}

定义异步请求监听

@Component
public class CustomAsyncListener implements AsyncListener {
    private Logger LOG= LoggerFactory.getLogger(CustomAsyncListener.class);
    @Override public void onComplete(AsyncEvent asyncEvent) throws IOException {

    }

    @Override public void onTimeout(AsyncEvent asyncEvent) throws IOException {
        AsyncContext asyncContext= asyncEvent.getAsyncContext();
        try{
            ServletRequest req= asyncContext.getRequest();
            String uri= (String) req.getAttribute(Constant.URI);
            Map params= (Map) req.getAttribute(Constant.PARAMS);
            LOG.error("async req timeOut. uri :{},params:{}",uri, JSON.toJSONString(params));
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            try{
                HttpServletResponse response= (HttpServletResponse) asyncContext.getResponse();
                response.setStatus(HttpServletResponse.SC_REQUEST_TIMEOUT);
            }catch (Exception e1){}
            asyncContext.complete();
        }
    }

    @Override public void onError(AsyncEvent asyncEvent) throws IOException {
        AsyncContext asyncContext= asyncEvent.getAsyncContext();
        try{
            ServletRequest req= asyncContext.getRequest();
            String uri= (String) req.getAttribute(Constant.URI);
            Map params= (Map) req.getAttribute(Constant.PARAMS);
            LOG.error("async req error. uri :{},params:{}",uri, JSON.toJSONString(params));
        }catch (Exception e){
            e.printStackTrace();
            try{
                HttpServletResponse response= (HttpServletResponse) asyncContext.getResponse();
                response.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
            }catch (Exception e1){}
        }finally {
            asyncContext.complete();
        }
    }

    @Override public void onStartAsync(AsyncEvent asyncEvent) throws IOException {

    }
}

业务处理和常量类

@Service
public class NewsService {
    public String getNews(){
        return "servlet3 nio test.";
    }
    public StringBuilder getNewsMap(){
        return new StringBuilder("I do and i understand.");
    }
}
public class Constant {
    public static final String URI= "uri";
    public static final String PARAMS= "params";
}