微服务网关Zuul源码分析
网关介绍
请参考我上一篇文章：
微服务关键系统网关及实现技术Zuul和Spring Cloud Gateway的区别
Zuul 是 Netflix 公司的开源项目，Spring Cloud 在 Netflix 项目中也已经集成了 Zuul，依赖名叫：spring-cloud-starter-netflix-zuul。
Zuul是基于 Servlet 框架构建，采用的是阻塞和多线程方式，即一个线程处理一次连接请求，
Zuul源码分析
本文来分析Zuul作为网关的核心源码。
对于Servlet，我们分析源码一般从HttpServlet的实现类开始分析。
对于Zuul，我们从ZuulServlet开始分析，它是HttpServlet的实现类。
/**
* zuul的核心servlet，进行初始化并协调zul过滤器的执行
*/
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);
// 将此请求标记为已通过“Zuul引擎”，而不是显式绑定到servlet中的web.xml文件，请求将不会附加相同的数据
RequestContext context = RequestContext.getCurrentContext();
context.setZuulEngineRan();
try {
preRoute();
} catch (ZuulException e) {
error(e);
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();
}
}
主要的几步：
// 过滤前执行
preRoute()
// 执行过滤
route()
// 过滤后执行
postRoute()
还有一个error()方法
这三步的方法类似，我们选择route源码来看
public void route() throws ZuulException {
try {
runFilters("route"); //preRoute方法输入"pre"，postRoute方法输入"post"，error方法输入"error"
} catch (ZuulException e) {
// 执行过滤不通过会抛出ZuulException异常，则过滤失败
throw e;
} catch (Throwable e) {
// 抛出其他异常也是失败，
throw new ZuulException(e, 500, "UNCAUGHT_EXCEPTION_IN_ROUTE_FILTER_" + e.getClass().getName());
}
}
这三步包括error都会调用到runFilters核心方法，源码如下：
/**
* 运行filterType类型的所有筛选器
* 在筛选器中使用此方法可按类型运行自定义筛选器
*/
public Object runFilters(String sType) throws Throwable {
if (RequestContext.getCurrentContext().debugRouting()) {
Debug.addRoutingDebug("Invoking {" + sType + "} type filters");
}
boolean bResult = false;
List<ZuulFilter> list = FilterLoader.getInstance().getFiltersByType(sType);
if (list != null) {
for (int i = 0; i < list.size(); i++) {
ZuulFilter zuulFilter = list.get(i);
Object result = processZuulFilter(zuulFilter);
if (result != null && result instanceof Boolean) {
bResult |= ((Boolean) result);
}
}
}
return bResult;
}
再来看看processZuulFilter源码
/**
* 处理一个单独的ZuulFilter。
* 此方法添加调试信息。
* 任何未捕获的thowable都会被这个方法捕获，并转换为带有500个状态代码的ZuulException。
*/
public Object processZuulFilter(ZuulFilter filter) throws ZuulException {
RequestContext ctx = RequestContext.getCurrentContext();
boolean bDebug = ctx.debugRouting();
final String metricPrefix = "zuul.filter-";
long execTime = 0;
String filterName = "";
try {
long ltime = System.currentTimeMillis();
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();
}
ZuulFilterResult result = filter.runFilter();
ExecutionStatus s = result.getStatus();
execTime = System.currentTimeMillis() - ltime;
switch (s) {
case FAILED:
t = result.getException(); // 过滤失败抛出异常
ctx.addFilterExecutionSummary(filterName, ExecutionStatus.FAILED.name(), execTime);
break;
case SUCCESS:
o = result.getResult(); //过滤成功
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); //通知成功消息
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);//通知失败消息
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;
}
}
}