Zuul【工作原理】，工作原理

Zuul【工作原理】，工作原理

zuul的核心逻辑都是由一系列filter过滤器链实现的，但是filter的类型不同，执行的时机也不同，效果自然也不一样，主要特点如下：

zuul内部有一套完整的机制，可以动态读取编译运行filter机制，filter与filter之间不直接通信，在请求线程中会通过RequestContext来共享状态，它内部是用ThreadLocal实现的，例如HttpServletRequest、HttpServletResponse、异常信息等。部分源码如下：

public class RequestContext extends ConcurrentHashMap<String, Object> {

    private static final Logger LOG = LoggerFactory.getLogger(RequestContext.class);

    protected static Class<? extends RequestContext> contextClass = RequestContext.class;

    private static RequestContext testContext = null;

    protected static final ThreadLocal<? extends RequestContext> threadLocal = new ThreadLocal<RequestContext>() {
        @Override
        protected RequestContext initialValue() {
            try {
                return contextClass.newInstance();
            } catch (Throwable e) {
                throw new RuntimeException(e);
            }
        }
    };

　　//.......
}

zuul中不同类型的filter执行逻辑的核心在ZuulServlet类中，主要代码如下：

public class ZuulServlet extends HttpServlet {

    private static final long serialVersionUID = -3374242278843351500L;
    private ZuulRunner 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);
    }

    @Override
    public void service(javax.servlet.ServletRequest servletRequest, javax.servlet.ServletResponse servletResponse) throws ServletException, IOException {
        try {
            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();
            context.setZuulEngineRan();

            try {
                preRoute(); //如果preRoute方法在执行的时候出现异常，直接就抛出500异常，不会走catch中的error方法，见下图FilterProcessor类中的preRoute方法。
            } catch (ZuulException e) {
                error(e); //如果preRoute在执行过程中，抛出Zuul异常，这里被捕捉到以后，会执行error方法，打印堆栈信息，见下图FilterProcessor类中的error方法。
                postRoute();
                return;
            }
            try {
                route();
            } catch (ZuulException e) {
                error(e);
                postRoute();
                return;
            }
            try {
                postRoute();
            } catch (ZuulException e) {
                error(e);
                return;
            }

        } catch (Throwable e) {
            error(new ZuulException(e, 500, "UNHANDLED_EXCEPTION_" + e.getClass().getName()));
        } finally {
            RequestContext.getCurrentContext().unset();
        }
    }

　　//.......
}

 

 

 

 

 

zuul一共有4种不同的生命周期：