十九.SpringCloud源码剖析-Zuul的执行流程

叁歲伎倆 2022-11-19 07:49 224阅读 0赞

## 前言 ##

在之前的章节我们详细分析了Zuul的Filter，这一章节我们来详细跟一下Zuul的执行流程

--------------------

Zuul的执行流程是这样的

*  首先请求进来会先到达ZuulController ，ZuulController把请求交给ZuulServlet去处理
 *  在ZuulServelt会调用 ZuulRunner 依次执行： init初始化，pre前置filter，route路由filter,post后置filter, error 异常filter
 *  ZuulRunner通过 FilterProcessor 去执行各种Filter,FilterProcessor通过 FilterLoader 加载 各种filters
 *  执行完成之后，把结果响应给客户端

在上一章节我们分析了Zuul中的各种filter，那这一章我们来跟踪一下zuul的执行流程。那么入口肯定是我们的 ZuulServlet ，他类似于 DispatcherServlet 在请求的最前面做分发。我们来看一下他的源码

## Zuul执行流程 ##

### 1.`ZuulController` 请求入口 ###

`ZuulController` 是请求的入口，把请求交给`ZuulServlet`去处理,ZuulServlet 类似于 DispatcherServlet 在请求的最前面做分发

public class ZuulController extends ServletWrappingController { 
    
    	public ZuulController() { 	
    		//1.为父类的serveltClass 做初始化，是一个 ZuulServlet
    		setServletClass(ZuulServlet.class);
    		setServletName("zuul");
    		setSupportedMethods((String[]) null); // Allow all
    	}
    
    	@Override
    	public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception { 
    		try { 
    			// We don't care about the other features of the base class, just want to
    			// handle the request
    			//2.请求交个父类
    			return super.handleRequestInternal(request, response);
    		}
    		finally { 
    			// @see com.netflix.zuul.context.ContextLifecycleFilter.doFilter
    			RequestContext.getCurrentContext().unset();
    		}
    	}
    
    }

下面是它父类的源码

public class ServletWrappingController extends AbstractController implements BeanNameAware, InitializingBean, DisposableBean { 
        @Nullable
        private Class<? extends Servlet> servletClass;
        @Nullable
        private String servletName;
        private Properties initParameters = new Properties();
        @Nullable
        private String beanName;
    	//servletInstance 就是 ZuulServelt
        @Nullable
        private Servlet servletInstance;
    
       	...省略...
       	 public void afterPropertiesSet() throws Exception { 
            if (this.servletClass == null) { 
                throw new IllegalArgumentException("'servletClass' is required");
            } else { 
                if (this.servletName == null) { 
                    this.servletName = this.beanName;
                }
    			//1.反射，根据 servletClass 创建实例
                this.servletInstance = (Servlet)ReflectionUtils.accessibleConstructor(this.servletClass, new Class[0]).newInstance();
                this.servletInstance.init(new ServletWrappingController.DelegatingServletConfig());
            }
        }
    
        protected ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response) throws Exception { 
            Assert.state(this.servletInstance != null, "No Servlet instance");
            //2.调用ZuulServelt的service方法
            this.servletInstance.service(request, response);
            return null;
        }

#### 2.`ZuulServlet` 请求的分发 ####

在`ZuulServelt`会调用 `ZuulRunner` 依次执行： init初始化，pre前置filter，route路由filter,post后置filter, error 异常filter，`ZuulServlet` 源码如下

/** 1.核心Zuul servlet，可初始化和协调zuulFilter执行 * Core Zuul servlet which intializes and orchestrates zuulFilter execution * * @author Mikey Cohen * Date: 12/23/11 * Time: 10:44 AM */
    public class ZuulServlet extends HttpServlet { 
    
        private static final long serialVersionUID = -3374242278843351500L;
        private ZuulRunner zuulRunner;
    
    	//初始化 ZuulRunner 
        @Override
        public void init(ServletConfig config) throws ServletException { 
            super.init(config);
    
            String bufferReqsStr = config.getInitParameter("buffer-requests");
            boolean bufferReqs = bufferReqsStr != null && bufferReqsStr.equals("true") ? true : false;
    
            zuulRunner = new ZuulRunner(bufferReqs);
        }
    	//请求执行核心方法
        @Override
        public void service(javax.servlet.ServletRequest servletRequest, javax.servlet.ServletResponse servletResponse) throws ServletException, IOException { 
            try { 
            	//初始化 ， 调用zuulRunner的init方法，
            	//主要是把ServletRequest请求对象设置给RequestContext上下文
                init((HttpServletRequest) servletRequest, (HttpServletResponse) servletResponse);
    
                // Marks this request as having passed through the "Zuul engine", as opposed to servlets
                // explicitly bound in web.xml, for which requests will not have the same data attached
                RequestContext context = RequestContext.getCurrentContext();
                //将此请求标记为“ Zuul引擎”，而不是servlet
                context.setZuulEngineRan();
    
                try { 
                	//执行pre的filter
                    preRoute();
                } catch (ZuulException e) { 
                	//如果异常了会走 error的filter,然后再走post的filter
                    error(e);
                    postRoute();
                    return;
                }
                try { 
                	//执行route的filter
                    route();
                } catch (ZuulException e) { 
                   //如果异常了会走 error的filter,然后再走post的filter
                    error(e);
                    postRoute();
                    return;
                }
                try { 
                	//执行post的filter
                    postRoute();
                } catch (ZuulException e) { 
                   //如果异常了会走 error的filter,不会再走post的filter
                    error(e);
                    return;
                }
    
            } catch (Throwable e) { 
                //如果异常了会走 error的filter,默认错误码500
                error(new ZuulException(e, 500, "UNHANDLED_EXCEPTION_" + e.getClass().getName()));
            } finally { 
                RequestContext.getCurrentContext().unset();
            }
        }
    
        /** * executes "post" ZuulFilters * * @throws ZuulException */
         //调用zuulRunner执行 post filter
        void postRoute() throws ZuulException { 
            zuulRunner.postRoute();
        }
    
        /** * executes "route" filters * * @throws ZuulException */
         //调用zuulRunner执行 route filter
        void route() throws ZuulException { 
            zuulRunner.route();
        }
    
        /** * executes "pre" filters * * @throws ZuulException */
         //调用zuulRunner执行 pre filter
        void preRoute() throws ZuulException { 
            zuulRunner.preRoute();
        }
    
        /** * initializes request * * @param servletRequest * @param servletResponse */
         //调用zuulRunner执行 初始化 ，主要是把servletRequest设置给ReqestContext上下文对象
         void init(HttpServletRequest servletRequest, HttpServletResponse servletResponse) { 
            zuulRunner.init(servletRequest, servletResponse);
        }
    
        /** * sets error context info and executes "error" filters * * @param e */
         //通过RequestContext设置异常
         //通过zuulRunner执行 error filter
        void error(ZuulException e) { 
            RequestContext.getCurrentContext().setThrowable(e);
            zuulRunner.error();
        }

#### 3.`ZuulRunner` 执行器 ####

上面涉及到一个非常重要的类`ZuulRunner`所有的请求都是通过它来执行的，此类将Servlet请求和响应初始化到RequestContext中，并将FilterProcessor调用包装为preRoute（），route（），postRoute（）和error（）方法　，我们看一下ZuulRunner的源码

/** * This class initializes servlet requests and responses into the RequestContext and wraps the FilterProcessor calls * to preRoute(), route(), postRoute(), and error() methods * * @author mikey@netflix.com * @version 1.0 */
    public class ZuulRunner { 
    
        private boolean bufferRequests;
    
        /** * Creates a new <code>ZuulRunner</code> instance. */
        public ZuulRunner() { 
            this.bufferRequests = true;
        }
    
        /** * * @param bufferRequests - whether to wrap the ServletRequest in HttpServletRequestWrapper and buffer the body. 在ZuulServlet中创建ZuulRunner的时候传入的配置参数 bufferRequests， 它决定了是否把 ServletRequest包装在HttpServletRequestWrapper中并缓冲主体。 */
        public ZuulRunner(boolean bufferRequests) { 
            this.bufferRequests = bufferRequests;
        }
    
        /** * sets HttpServlet request and HttpResponse 设置 请求对象和响应对象到 RequestContext 中 * @param servletRequest * @param servletResponse */
        public void init(HttpServletRequest servletRequest, HttpServletResponse servletResponse) { 
    
            RequestContext ctx = RequestContext.getCurrentContext();
            if (bufferRequests) { 
    			//把 ServletRequest包装在HttpServletRequestWrapper中并缓冲主体。
                ctx.setRequest(new HttpServletRequestWrapper(servletRequest));
            } else { 
                ctx.setRequest(servletRequest);
            }
    
            ctx.setResponse(new HttpServletResponseWrapper(servletResponse));
        }
    
    	//这里通过 FilterProcessor 执行器调用各种 ZuulFilters
        /** * executes "post" filterType ZuulFilters * * @throws ZuulException */
        public void postRoute() throws ZuulException { 
            FilterProcessor.getInstance().postRoute();
        }
    
        /** * executes "route" filterType ZuulFilters * * @throws ZuulException */
        public void route() throws ZuulException { 
            FilterProcessor.getInstance().route();
        }
    
        /** * executes "pre" filterType ZuulFilters * * @throws ZuulException */
        public void preRoute() throws ZuulException { 
            FilterProcessor.getInstance().preRoute();
        }
    
        /** * executes "error" filterType ZuulFilters */
        public void error() { 
            FilterProcessor.getInstance().error();
        }

#### 4.`FilterProcessor` filter执行器 ####

继续跟踪一下 FilterProcessor的源码

public class FilterProcessor { 
      ...省略代码...
      /** * runs "post" filters which are called after "route" filters. ZuulExceptions from ZuulFilters are thrown. * Any other Throwables are caught and a ZuulException is thrown out with a 500 status code * * @throws ZuulException */
        public void postRoute() throws ZuulException { 
            try { 
            	//执行 post 类型的filter
                runFilters("post");
            } catch (ZuulException e) { 
                throw e;
            } catch (Throwable e) { 
                throw new ZuulException(e, 500, "UNCAUGHT_EXCEPTION_IN_POST_FILTER_" + e.getClass().getName());
            }
        }
    
        /** * runs all "error" filters. These are called only if an exception occurs. Exceptions from this are swallowed and logged so as not to bubble up. */
        public void error() { 
            try { 
            	//执行 error 类型的filter
                runFilters("error");
            } catch (Throwable e) { 
                logger.error(e.getMessage(), e);
            }
        }
    
        /** * Runs all "route" filters. These filters route calls to an origin. * * @throws ZuulException if an exception occurs. */
        public void route() throws ZuulException { 
            try { 
            	//执行 post 类型的filter
                runFilters("post");
            } catch (ZuulException e) { 
                throw e;
            } catch (Throwable e) { 
                throw new ZuulException(e, 500, "UNCAUGHT_EXCEPTION_IN_ROUTE_FILTER_" + e.getClass().getName());
            }
        }
    
        /** * runs all "pre" filters. These filters are run before routing to the orgin. * * @throws ZuulException */
        public void preRoute() throws ZuulException { 
            try { 
            	//执行 pre 类型的filter
                runFilters("pre");
            } catch (ZuulException e) { 
                throw e;
            } catch (Throwable e) { 
                throw new ZuulException(e, 500, "UNCAUGHT_EXCEPTION_IN_PRE_FILTER_" + e.getClass().getName());
            }
        }
    
        /** * runs all filters of the filterType sType/ Use this method within filters to run custom filters by type * * @param sType the filterType. * @return * @throws Throwable throws up an arbitrary exception */
         //执行Filter的核心方法，运行所有过滤器/在过滤器中使用此方法可按类型运行自定义过滤器
        public Object runFilters(String sType) throws Throwable { 
            if (RequestContext.getCurrentContext().debugRouting()) { 
                Debug.addRoutingDebug("Invoking {" + sType + "} type filters");
            }
            boolean bResult = false;
            //通过 FilterLoader 加载 filters
            List<ZuulFilter> list = FilterLoader.getInstance().getFiltersByType(sType);
            if (list != null) { 
                for (int i = 0; i < list.size(); i++) { 
                    ZuulFilter zuulFilter = list.get(i);
                    //拿到每个filter，调用 processZuulFilter 去执行
                    Object result = processZuulFilter(zuulFilter);
                    if (result != null && result instanceof Boolean) { 
                        bResult |= ((Boolean) result);
                    }
                }
            }
            //返回结果
            return bResult;
        }
    
        /** * Processes an individual ZuulFilter. This method adds Debug information. Any uncaught Thowables are caught by this method and converted to a ZuulException with a 500 status code. * * @param filter * @return the return value for that filter * @throws ZuulException */
         //filter的执行方法
        public Object processZuulFilter(ZuulFilter filter) throws ZuulException { 
    
            RequestContext ctx = RequestContext.getCurrentContext();
            //获取时候开启：debug
            boolean bDebug = ctx.debugRouting();
            final String metricPrefix = "zuul.filter-";
            long execTime = 0;
            String filterName = "";
            try { 
                long ltime = System.currentTimeMillis();
                //filter的类名
                
                filterName = filter.getClass().getSimpleName();
                
                RequestContext copy = null;
                Object o = null;
                Throwable t = null;
    
                if (bDebug) { 
                    Debug.addRoutingDebug("Filter " + filter.filterType() + " " + filter.filterOrder() + " " + filterName);
                    copy = ctx.copy();
                }
                //【重要】调用 ZuulFilter.runFilter方法真正执行Filter
                ZuulFilterResult result = filter.runFilter();
                //拿到响应状态
                ExecutionStatus s = result.getStatus();
                execTime = System.currentTimeMillis() - ltime;
    
                switch (s) { 
                	//执行失败
                    case FAILED:
                        t = result.getException();
                        //将过滤器名称和状态附加到当前请求的过滤器执行历史记录中
                        ctx.addFilterExecutionSummary(filterName, ExecutionStatus.FAILED.name(), execTime);
                        break;
                	//执行成功
                    case SUCCESS:
                        o = result.getResult();
                        ctx.addFilterExecutionSummary(filterName, ExecutionStatus.SUCCESS.name(), execTime);
                        if (bDebug) { 
                            Debug.addRoutingDebug("Filter {" + filterName + " TYPE:" + filter.filterType() + " ORDER:" + filter.filterOrder() + "} Execution time = " + execTime + "ms");
                            Debug.compareContextState(filterName, copy);
                        }
                        break;
                    default:
                        break;
                }
                
                if (t != null) throw t;
    
                usageNotifier.notify(filter, s);
                return o;
    
            } catch (Throwable e) { 
                if (bDebug) { 
                    Debug.addRoutingDebug("Running Filter failed " + filterName + " type:" + filter.filterType() + " order:" + filter.filterOrder() + " " + e.getMessage());
                }
                usageNotifier.notify(filter, ExecutionStatus.FAILED);
                if (e instanceof ZuulException) { 
                    throw (ZuulException) e;
                } else { 
                    ZuulException ex = new ZuulException(e, "Filter threw Exception", 500, filter.filterType() + ":" + filterName);
                    ctx.addFilterExecutionSummary(filterName, ExecutionStatus.FAILED.name(), execTime);
                    throw ex;
                }
            }
        }
    ...省略代码...

不管是前置，后置，路由，异常的Filter ，`FilterProcessor` 都通过 `runFilters("类型");` 方法去执行filter,方法中通过 `FilterLoader`加载指定类型的Filter列表，然后交给 `processZuulFilter`方法去执行 ，该方法最终调用`ZuulFilter.runFilter();`方法去执行具体的Filter 。它会以下面的顺序去执行内置的Filter:

<table> 
 <thead> 
  <tr> 
   <th>类型</th> 
   <th>过滤器</th> 
   <th>描述</th> 
   <th>顺序</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>pre</td> 
   <td>ServletDetectionFilter</td> 
   <td>在pre过滤器中，ServletDetectionFilter是第一个执行的过滤器，检测请求是用 DispatcherServlet还是 ZuulServlet，将结果设置到RequestContext中</td> 
   <td>-3</td> 
  </tr> 
  <tr> 
   <td>pre</td> 
   <td>Servlet30WrapperFilter</td> 
   <td>主要是将原始请求进行包装，将原始的HttpServletRequest请求包装成Servlet30RequestWrapper类型</td> 
   <td>-2</td> 
  </tr> 
  <tr> 
   <td>pre</td> 
   <td>FormBodyWrapperFilter</td> 
   <td>同Servlet30RequestWrapper一样，也是对请求的一个包装，只不过他只包装表单数据，即：content-type中必须带有“application/x-www-form-urlencoded”或“multipart/form-data”</td> 
   <td>-1</td> 
  </tr> 
  <tr> 
   <td>error</td> 
   <td>SendErrorFilter</td> 
   <td>这个是用来发送错误的Filter</td> 
   <td>0</td> 
  </tr> 
  <tr> 
   <td>pre</td> 
   <td>DebugFilter</td> 
   <td>设置请求过程是否开启debug,将当前请求上下文中的<code>debugRouting</code>和<code>debugRequest</code>参数设置为true</td> 
   <td>1</td> 
  </tr> 
  <tr> 
   <td>pre</td> 
   <td>PreDecorationFilter</td> 
   <td>基本的路由转发配置,根据uri调用哪一个route过滤器</td> 
   <td>5</td> 
  </tr> 
  <tr> 
   <td>route</td> 
   <td>RibbonRoutingFilter</td> 
   <td>服务路由的过滤器，使用用Ribbon 做负载均衡，hystrix做熔断</td> 
   <td>10</td> 
  </tr> 
  <tr> 
   <td>route</td> 
   <td>SimpleHostRoutingFilter</td> 
   <td>简单主机路由过滤器，如果使用url路由，则用这个过滤器</td> 
   <td>100</td> 
  </tr> 
  <tr> 
   <td>route</td> 
   <td>SendForwardFilter</td> 
   <td>它使用RequestDispatcher转发请求</td> 
   <td>500</td> 
  </tr> 
  <tr> 
   <td>post</td> 
   <td>SendResponseFilter</td> 
   <td>SendResponseFilter是Zuul的最后一个Filter，负责最终响应结果的输出。</td> 
   <td>1000</td> 
  </tr> 
 </tbody> 
</table>

error类型的filter在出异常的时候才会执行

#### 5.ZuulFilter ####

`ZuulFilter` 是所有Filter的抽象类，它的接口是`IZuulFilter` ，它里面有四个很重要的方法

//这个是
    public interface IZuulFilter { 
    	//是否要执行Run方法
        boolean shouldFilter();
    	//filter的核心业务方法
        Object run() throws ZuulException;
    }
    
    public abstract class ZuulFilter implements IZuulFilter, Comparable<ZuulFilter> { 
    
        private final AtomicReference<DynamicBooleanProperty> filterDisabledRef = new AtomicReference<>();
    
        /** * to classify a filter by type. Standard types in Zuul are "pre" for pre-routing filtering, * "route" for routing to an origin, "post" for post-routing filters, "error" for error handling. * We also support a "static" type for static responses see StaticResponseFilter. * Any filterType made be created or added and run by calling FilterProcessor.runFilters(type) * * @return A String representing that type */
         //这个是filter的类型 ，有 pre ,route,post error
        abstract public String filterType();
    
        /** * filterOrder() must also be defined for a filter. Filters may have the same filterOrder if precedence is not * important for a filter. filterOrders do not need to be sequential. * * @return the int order of a filter */
         //这个是filter的执行顺序，越小越先执行
        abstract public int filterOrder();
        ...省略...
    }

详细看一下`ZuulFilter` 的源码

public abstract class ZuulFilter implements IZuulFilter, Comparable<ZuulFilter> { 
    ...省略...
     public ZuulFilterResult runFilter() { 
            ZuulFilterResult zr = new ZuulFilterResult();
            if (!isFilterDisabled()) { 
            	//调用shouldFilter方法，这是个抽象方法，子类需要复写该方法返回 bool值决定要不要执行run方法
                if (shouldFilter()) { 
                    Tracer t = TracerFactory.instance().startMicroTracer("ZUUL::" + this.getClass().getSimpleName());
                    try { 
                 		 //调用 filter的run方法去执行，也是个抽象方法，需要子类去实现自己的业务逻辑
                        Object res = run();
                        //执行成功，包装一个成功状态的ZuulFilterResult对象返回
                        zr = new ZuulFilterResult(res, ExecutionStatus.SUCCESS);
                    } catch (Throwable e) { 
                        t.setName("ZUUL::" + this.getClass().getSimpleName() + " failed");
                        //执行失败，包装一个失败状态的ZuulFilterResult对象返回
                        zr = new ZuulFilterResult(ExecutionStatus.FAILED);
                        zr.setException(e);
                    } finally { 
                        t.stopAndLog();
                    }
                } else { 
                    zr = new ZuulFilterResult(ExecutionStatus.SKIPPED);
                }
            }
            return zr;
        }

`ZuulFilter` 是个抽象类，需要具体的子类类去复写其中的四个方法，然后 ZuulFilter 做的事情就依次调用 `shouldFilter` 方法，如果返回true就调用 `run`方法执行子类的业务逻辑，然后把结果封装成`ZuulFilterResult`返回。

到这里Zuul的执行流程的跟踪就算结束了，剩下的就是具体的Filter本身的业务代码的理解了，Zuul通过依次调用这个写Filter来完成整个生命周期的执行。最后总结一下流程

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