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Springcloud中zuul的Zuul Filter是什么，很多新手对此不是很清楚，为了帮助大家解决这个难题，下面小编将为大家详细讲解，有这方面需求的人可以来学习下，希望你能有所收获。
Springcloud的版本是Greenwich.SR2，Springboot版本是2.1.6.release.
最近使用到Springcloud的zuul，分析了下源码，记录下。
如下List-1，我们自己定义的ZuulFilter继承zuul的zuulFilter，之后定义为Bean，交给Spring容器:
List-1
//将过滤器交给Spring管理
@Bean
public AuthFilter authFilter(){
return new AuthFilter();
}
//xss过滤
@Bean
public XssFilter xssFilter(){
return new XssFilter();
}
@Bean
public HelloZuulFilter firewallFilter(){
return new HelloZuulFilter();
}
@Bean
public HelloInfoFilter helloInfoFilter(){
return new HelloInfoFilter();
}之后看下ZuulServerAutoConfiguration，如下List-2，@Autowired private Map<String, ZuulFilter> filters会从Spring容器中获取所有的ZuulFilter，之后实例化ZuulFilterInitializer时，将这个filters传入。
List-2
...
@Configuration
protected static class ZuulFilterConfiguration {
@Autowired
private Map<String, ZuulFilter> filters;
@Bean
public ZuulFilterInitializer zuulFilterInitializer(CounterFactory counterFactory,
TracerFactory tracerFactory) {
FilterLoader filterLoader = FilterLoader.getInstance();
FilterRegistry filterRegistry = FilterRegistry.instance();
return new ZuulFilterInitializer(this.filters, counterFactory, tracerFactory,
filterLoader, filterRegistry);
}
}
...如下List-3，
FilterRegistry是属性类型，contextInitialized方法上加了@PostConstruct，所以Spring创建这个Bean之后就会调用这个方法，遍历filters之后，放入filterRegistry中，filterRegistry中有个ConcurrentHashMap类型的属性，这些filter就是放入这个ConcurrentHashMap中。
方法contextDestroyed上加了@PreDestroy注解，之后遍历filters，将其从filterRegistry中移除。
List-3
public class ZuulFilterInitializer {
private static final Log log = LogFactory.getLog(ZuulFilterInitializer.class);
private final Map<String, ZuulFilter> filters;
private final CounterFactory counterFactory;
private final TracerFactory tracerFactory;
private final FilterLoader filterLoader;
private final FilterRegistry filterRegistry;
public ZuulFilterInitializer(Map<String, ZuulFilter> filters,
CounterFactory counterFactory, TracerFactory tracerFactory,
FilterLoader filterLoader, FilterRegistry filterRegistry) {
this.filters = filters;
this.counterFactory = counterFactory;
this.tracerFactory = tracerFactory;
this.filterLoader = filterLoader;
this.filterRegistry = filterRegistry;
}
@PostConstruct
public void contextInitialized() {
log.info("Starting filter initializer");
TracerFactory.initialize(tracerFactory);
CounterFactory.initialize(counterFactory);
for (Map.Entry<String, ZuulFilter> entry : this.filters.entrySet()) {
filterRegistry.put(entry.getKey(), entry.getValue());
}
}
@PreDestroy
public void contextDestroyed() {
log.info("Stopping filter initializer");
for (Map.Entry<String, ZuulFilter> entry : this.filters.entrySet()) {
filterRegistry.remove(entry.getKey());
}
clearLoaderCache();
TracerFactory.initialize(null);
CounterFactory.initialize(null);
}
...默认会将ZuulServlet或者ZuulServletFilter注入到Spring容器中，如下如果设置zuul.use-filter为true，那么使用的是ZuulServletFilter，默认没有设置zuul.use-filter，所以使用的是ZuulServlet，如下List-4，ZuulServlet继承了HttpServlet，是个Servlet，之后交给ServletRegistrationBean，将这个ZuulServlet放入到web容器中。
List-4
...
@Bean
@ConditionalOnMissingBean(name = "zuulServlet")
@ConditionalOnProperty(name = "zuul.use-filter", havingValue = "false", matchIfMissing = true)
public ServletRegistrationBean zuulServlet() {
ServletRegistrationBean<ZuulServlet> servlet = new ServletRegistrationBean<>(
new ZuulServlet(), this.zuulProperties.getServletPattern());
// The whole point of exposing this servlet is to provide a route that doesn't
// buffer requests.
servlet.addInitParameter("buffer-requests", "false");
return servlet;
}
@Bean
@ConditionalOnMissingBean(name = "zuulServletFilter")
@ConditionalOnProperty(name = "zuul.use-filter", havingValue = "true", matchIfMissing = false)
public FilterRegistrationBean zuulServletFilter() {
final FilterRegistrationBean<ZuulServletFilter> filterRegistration = new FilterRegistrationBean<>();
filterRegistration.setUrlPatterns(
Collections.singleton(this.zuulProperties.getServletPattern()));
filterRegistration.setFilter(new ZuulServletFilter());
filterRegistration.setOrder(Ordered.LOWEST_PRECEDENCE);
// The whole point of exposing this servlet is to provide a route that doesn't
// buffer requests.
filterRegistration.addInitParameter("buffer-requests", "false");
return filterRegistration;
}
...ZuulServlet的service方法如下，首先会调用preRoute()方法，之后调用route()，最后是postRoute()，preRoute方法调用了zuulRunner.preRoute()，ZuulRunner的preRoute()方法里面调用了FilterProcessor.getInstance().preRoute()，再深入FilterProcessor的preRoute方法，
List-5
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 var13) {
this.error(var13);
this.postRoute();
return;
}
try {
this.route();
} catch (ZuulException var12) {
this.error(var12);
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();
}
}
void postRoute() throws ZuulException {
this.zuulRunner.postRoute();
}
void route() throws ZuulException {
this.zuulRunner.route();
}
void preRoute() throws ZuulException {
this.zuulRunner.preRoute();
}FilterProcessor的preRoute()里面的代码如下List-6，调用runFilters方法，从FilterRegistry取出所有filterType是pre的所有ZuulFilter，之后进行排序，之后逐个调用ZuulFilter的runFilter方法——在方法processZuulFilter里面。ZuulFilter是个抽象类，runFilter方法里面调用了run方法，run方法是抽象方法，由我们自定义实现，如下List-7所示，
List-6
...
public void preRoute() throws ZuulException {
try {
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");
}
boolean bResult = false;
List<ZuulFilter> list = FilterLoader.getInstance().getFiltersByType(sType);
if (list != null) {
for(int i = 0; i < list.size(); ++i) {
ZuulFilter zuulFilter = (ZuulFilter)list.get(i);
Object result = this.processZuulFilter(zuulFilter);
if (result != null && result instanceof Boolean) {
bResult |= (Boolean)result;
}
}
}
return bResult;
}
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();
}
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;
}
}
}
...如下List-7所示，用try catch方式来调用run方法，如果run方法抛出异常，则视为失败，将ZuulFilterResult的ExecutionStatus设置为FAILED，所以我们实现的run方法返回什么值并不重要，重要的是不抛出异常，如果抛出异常则视为处理失败。
List-7
public ZuulFilterResult runFilter() {
ZuulFilterResult zr = new ZuulFilterResult();
if (!this.isFilterDisabled()) {
if (this.shouldFilter()) {
Tracer t = TracerFactory.instance().startMicroTracer("ZUUL::" + this.getClass().getSimpleName());
try {
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;
}要注意的是，上面中涉及到的FilterRegistry引用的都是同一个静态变量，所以各个调用关系见不显示的传递，依然能确保线程安全。
private static final FilterRegistry INSTANCE = new FilterRegistry();
需要注意的是，ZuulServlet和ZuulServletFilter处理的是url为/zuul/*的请求，可以看List-4的this.zuulProperties.getServletPattern()，它的值就是/zuul，之后用ServletRegistration.Dynamic的addMapping方法加上处理的url为/zuul/*的。
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