网关——过滤器
从网关组件请求流程分析，可以看出网关的核心类为ZuulServlet，所有的请求都是走到这里来处理的！
public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
try {
this.init((HttpServletRequest)servletRequest, (HttpServletResponse)servletResponse);
RequestContext context = RequestContext.getCurrentContext();
context.setZuulEngineRan();
try {
this.preRoute();
} catch (ZuulException var12) {
this.error(var12);
this.postRoute();
return;
}
try {
this.route();
} catch (ZuulException var13) {
this.error(var13);
this.postRoute();
return;
}
try {
this.postRoute();
} catch (ZuulException var11) {
this.error(var11);
}
} catch (Throwable var14) {
this.error(new ZuulException(var14, 500, "UNHANDLED_EXCEPTION_" + var14.getClass().getName()));
} finally {
RequestContext.getCurrentContext().unset();
}
}
zuulServlet-service
从service方法中可以看出，preRoute()、route()、postRoute()、error（）这4个方法为一套模板方法，定义了整个zuul组件的处理规则：
先执行preRoute()、再执行route()，然后是postRoute()，当任意环节出问题时，走到error()方法。
void postRoute() throws ZuulException {
this.zuulRunner.postRoute();
}
void route() throws ZuulException {
this.zuulRunner.route();
}
void preRoute() throws ZuulException {
this.zuulRunner.preRoute();
}
void error(ZuulException e) {
RequestContext.getCurrentContext().setThrowable(e);
this.zuulRunner.error();
}
从上述代码可以看出，实际执行这套模板方法的时zuulRunner类
这次以preRoute()方法为例进行分析，最终preRoute()
在ZuulRunner中，调用的是FilterProcessor实例的preRoute（）;FilterProcessor类为单例模式，同时看其类名就可以知道该类是过滤器处理类；
public void preRoute() throws ZuulException {
FilterProcessor.getInstance().preRoute();
}
查看在FilterProcessor类中preRoute()的具体实现
public void preRoute() throws ZuulException {
try {
//这里是运行指定类型的过滤器
//只有类型为pre的过滤器才会被调用
this.runFilters("pre");
} catch (ZuulException var2) {
throw var2;
} catch (Throwable var3) {
throw new ZuulException(var3, 500, "UNCAUGHT_EXCEPTION_IN_PRE_FILTER_" + var3.getClass().getName());
}
}
public Object runFilters(String sType) throws Throwable {
if (RequestContext.getCurrentContext().debugRouting()) {
Debug.addRoutingDebug("Invoking {" + sType + "} type filters");
}
//根据类型获取过滤器
boolean bResult = false;
List<ZuulFilter> list = FilterLoader.getInstance().getFiltersByType(sType);
if (list != null) {
for(int i = 0; i < list.size(); ++i) {
//执行过滤器
ZuulFilter zuulFilter = (ZuulFilter)list.get(i);
Object result = this.processZuulFilter(zuulFilter);
if (result != null && result instanceof Boolean) {
bResult |= ((Boolean)result).booleanValue();
}
}
}
return bResult;
}
processZuulFilter(Zuulfilter filter)的具体内容
public Object processZuulFilter(ZuulFilter filter) throws ZuulException {
RequestContext ctx = RequestContext.getCurrentContext();
boolean bDebug = ctx.debugRouting();
String metricPrefix = "zuul.filter-";
long execTime = 0L;
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();
}
// 主要内容
ZuulFilterResult result = filter.runFilter();
ExecutionStatus s = result.getStatus();
execTime = System.currentTimeMillis() - ltime;
switch(s) {
case FAILED:
t = result.getException();
ctx.addFilterExecutionSummary(filterName, ExecutionStatus.FAILED.name(), execTime);
break;
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);
}
}
if (t != null) {
throw t;
} else {
this.usageNotifier.notify(filter, s);
return o;
}
} catch (Throwable var15) {
if (bDebug) {
Debug.addRoutingDebug("Running Filter failed " + filterName + " type:" + filter.filterType() + " order:" + filter.filterOrder() + " " + var15.getMessage());
}
this.usageNotifier.notify(filter, ExecutionStatus.FAILED);
if (var15 instanceof ZuulException) {
throw (ZuulException)var15;
} else {
ZuulException ex = new ZuulException(var15, "Filter threw Exception", 500, filter.filterType() + ":" + filterName);
ctx.addFilterExecutionSummary(filterName, ExecutionStatus.FAILED.name(), execTime);
throw ex;
}
}
runFilter()中的内容
public ZuulFilterResult runFilter() {
ZuulFilterResult zr = new ZuulFilterResult();
if (!this.isFilterDisabled()) {
//判断是否执行filter
if (this.shouldFilter()) {
Tracer t = TracerFactory.instance().startMicroTracer("ZUUL::" + this.getClass().getSimpleName());
try {
//执行filter中的run方法
Object res = this.run();
zr = new ZuulFilterResult(res, ExecutionStatus.SUCCESS);
} catch (Throwable var7) {
t.setName("ZUUL::" + this.getClass().getSimpleName() + " failed");
zr = new ZuulFilterResult(ExecutionStatus.FAILED);
zr.setException(var7);
} finally {
t.stopAndLog();
}
} else {
zr = new ZuulFilterResult(ExecutionStatus.SKIPPED);
}
}
return zr;
}
从上面代码可以看出，preRoute()方法为运行类型为”pre“的过滤器;从runFilter()方法可以看出，只有过滤器需要执行时才会执行过滤器中的run（）方法；即过滤器中的run方法中包含了所有的过滤器要做的所有业务。
其他route(),postRoute(),error()中的代码也遵循这一规则，只有过滤器类型不同这一点
总结：
网关组件Zuul中的过滤器：
在ZuulServlet中的service方法中定义过滤器的执行顺序，按preRoute()、route()、postRoute()顺序执行，error()时在出现异常时的处理规则。
追踪preRoute()方法的执行可以得知，preRoute()经过了这3个类：ZuulServlet——>ZuulRunner——>FilterProcessor；
最终preRoute的具体实现规则是在FilterProcessor中定义的
在runFilters中定义了过滤器的类型:pre、route、post、error
在ZuulFilter抽象类中的runFilter定义了过滤器是否被执行以及执行的方法体为run()方法
综上，要想添加一个能在网关中使用的自定义的过滤器；必须继承ZuulFilter抽象类，同时在filterType方法中定义好过滤器类型：pre、route、post、error；shouldFilter方法必须返回true才能执行，过滤器的具体实现逻辑要定义在run()方法中。
原文地址：https://www.cnblogs.com/AWSL/p/10624709.html