我们在项目中使用Spring cloud zuul的时候，当我们的zuul进行路由分发时，如果后端服务没有启动，或者调用超时，这时候我们希望Zuul提供一种处理机制功能，而不是将异常暴露出来。
使用fallback非常简单只需要实现FallbackProvider类即可，定义MyFallbackProvider类并实现FallbackProvider，具体内容如下：
@Component public class MyFallbackProvider implements FallbackProvider { @Override public String getRoute() { // 表明是为哪个微服务提供回退，*表示为所有微服务提供回退 return "*"; } @Override public ClientHttpResponse fallbackResponse(String route, Throwable cause) { return this.response(HttpStatus.INTERNAL_SERVER_ERROR); } private ClientHttpResponse response(final HttpStatus status) { return new ClientHttpResponse() { @Override public HttpStatus getStatusCode() throws IOException { return status; } @Override public int getRawStatusCode() throws IOException { return status.value(); } @Override public String getStatusText() throws IOException { return status.getReasonPhrase(); } @Override public void close() { } @Override public InputStream getBody() throws IOException { return new ByteArrayInputStream("服务不可用，请稍后再试。".getBytes()); } @Override public HttpHeaders getHeaders() { // headers设定 HttpHeaders headers = new HttpHeaders(); MediaType mt = new MediaType("application", "json", Charset.forName("UTF-8")); headers.setContentType(mt); return headers; } }; } }application.yml 内容：
server: port: 5000 spring: application: name: api-geteway zuul: routes: api-a: path: /user/** service-id: microservice-provider-user api-b: path: /file/** service-id: microservice-file-upload host: connect-timeout-millis: 15000 #HTTP连接超时要比Hystrix的大 socket-timeout-millis: 60000 #socket超时 eureka: client: serviceUrl: defaultZone: http://user:password123@localhost:8761/eureka ribbon: ReadTimeout: 10000 ConnectTimeout: 10000pom.xml内容：
<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <parent> <groupId>com.itmuch.cloud</groupId> <artifactId>microservice-spring-cloud</artifactId> <version>0.0.1-SNAPSHOT</version> </parent> <artifactId>microservice-zuul</artifactId> <packaging>jar</packaging> <properties> <java.version>1.8</java.version> </properties> <dependencies> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-netflix-zuul</artifactId> </dependency> </dependencies> </project>只启动eureka和zuul后，在浏览器中输入请求地址，由于user微服务没有启动，zuul启用fallback显示服务不可用，请稍后再试。
