spring-cloud - 使用 RestTemplate 时 Spring Cloud Ribbon 引发错误

Question

尝试使用 Ribbon 将信息从微服务 B 检索到我的微服务 A 时，我遇到了问题。

我正在使用 spring cloud Brixton.M4，这是我的 build.gradle 文件：

buildscript {
    ext {
        grailsVersion = project.grailsVersion
        springBootVersion = '1.3.1.RELEASE'
    }
    repositories {
        mavenLocal()
        maven { url "https://repo.grails.org/grails/core" }
    }
    dependencies {
        classpath "org.grails:grails-gradle-plugin:$grailsVersion"
        classpath "org.grails.plugins:hibernate:4.3.10.5"
    }
}

plugins {
    id "io.spring.dependency-management" version "0.5.4.RELEASE"
}

version "0.1"
group "vz.attachments.mcrsrv"

apply plugin: "spring-boot"
apply plugin: "war"
apply plugin: 'eclipse'
apply plugin: 'idea'
apply plugin: "org.grails.grails-web"

ext {
    grailsVersion = project.grailsVersion
    gradleWrapperVersion = project.gradleWrapperVersion
}

repositories {
    mavenCentral()
    mavenLocal()
    maven { url "https://repo.grails.org/grails/core" }
    maven { url "https://repo.spring.io/snapshot" }
    maven { url "https://repo.spring.io/milestone" }

}

dependencyManagement {
    imports {
        mavenBom "org.grails:grails-bom:$grailsVersion"
        mavenBom 'org.springframework.cloud:spring-cloud-starter-parent:Brixton.M4'
    }
    applyMavenExclusions false
}

dependencies {

    compile ("org.springframework.boot:spring-boot-starter-web") {
        exclude module: "spring-boot-starter-tomcat"
    }
    compile "org.springframework.boot:spring-boot-starter-undertow"
    compile "org.springframework.cloud:spring-cloud-starter-eureka"
    compile "org.springframework.cloud:spring-cloud-starter-hystrix"
    compile "org.springframework.cloud:spring-cloud-starter-ribbon"

    compile "org.springframework.boot:spring-boot-starter-logging"
    compile "org.springframework.boot:spring-boot-starter-actuator"
    compile "org.springframework.boot:spring-boot-autoconfigure"
    compile "org.springframework.boot:spring-boot-starter-tomcat"
    compile "org.grails:grails-plugin-url-mappings"
    compile "org.grails:grails-plugin-rest"
    compile "org.grails:grails-plugin-interceptors"
    compile "org.grails:grails-plugin-services"
    compile "org.grails:grails-plugin-datasource"
    compile "org.grails:grails-plugin-databinding"
    compile "org.grails:grails-plugin-async"
    compile "org.grails:grails-web-boot"
    compile "org.grails:grails-logging"

    compile "org.grails.plugins:hibernate"
    compile "org.grails.plugins:cache"
    compile "org.hibernate:hibernate-ehcache"

    runtime "com.h2database:h2"

    testCompile "org.grails:grails-plugin-testing"
    testCompile "org.grails.plugins:geb"

    console "org.grails:grails-console"
}

task wrapper(type: Wrapper) {
    gradleVersion = gradleWrapperVersion
}

我正在使用 Grails 3.0 作为 Web 框架，当我使用功能区执行对我的其他微服务的调用时，这是 groovy 文件，但这是检索正确的值（例如本例中的 2）：

public String getGiveMeTheNumber() { 
        ServiceInstance instance = ribbonLoadBalancer.choose("VzAttachmentsMcrSrv")
        URI uri = instance.getUri()
        String service_url = uri.toString().concat("/index/giveMeTheNumber")
        String number_result = null;

        // Raise ERROR HERE restTemplate.getForObject, but number_result receive the right value I.e a number.
        number_result = restTemplate.getForObject(service_url, String.class)

        return number_result 
    }

在执行此语句后restTemplate.getForObject，它会引发：

2016-01-04 10:02:27.540 ERROR 7684 --- [  XNIO-2 task-5] o.s.web.servlet.HandlerExecutionChain    : HandlerInterceptor.afterCompletion threw exception

java.lang.NullPointerException: null
    at org.springframework.cloud.netflix.metrics.DefaultMetricsTagProvider.httpRequestTags(DefaultMetricsTagProvider.java:64) ~[spring-cloud-netflix-core-1.1.0.M4.jar:1.1.0.M4]
    at org.springframework.cloud.netflix.metrics.MetricsHandlerInterceptor.recordMetric(MetricsHandlerInterceptor.java:85) ~[spring-cloud-netflix-core-1.1.0.M4.jar:1.1.0.M4]
    at org.springframework.cloud.netflix.metrics.MetricsHandlerInterceptor.afterCompletion(MetricsHandlerInterceptor.java:72) ~[spring-cloud-netflix-core-1.1.0.M4.jar:1.1.0.M4]
    at org.springframework.web.servlet.HandlerExecutionChain.triggerAfterCompletion(HandlerExecutionChain.java:170) ~[spring-webmvc-4.2.4.RELEASE.jar:4.2.4.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1045) [spring-webmvc-4.2.4.RELEASE.jar:4.2.4.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:971) [spring-webmvc-4.2.4.RELEASE.jar:4.2.4.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893) [spring-webmvc-4.2.4.RELEASE.jar:4.2.4.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:969) [spring-webmvc-4.2.4.RELEASE.jar:4.2.4.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:860) [spring-webmvc-4.2.4.RELEASE.jar:4.2.4.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:687) [javax.servlet-api-3.1.0.jar:3.1.0]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:845) [spring-webmvc-4.2.4.RELEASE.jar:4.2.4.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:790) [javax.servlet-api-3.1.0.jar:3.1.0]
    at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:85) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:129) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at org.springframework.boot.actuate.autoconfigure.EndpointWebMvcAutoConfiguration$ApplicationContextHeaderFilter.doFilterInternal(EndpointWebMvcAutoConfiguration.java:243) [spring-boot-actuator-1.3.1.RELEASE.jar:1.3.1.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.2.4.RELEASE.jar:4.2.4.RELEASE]
    at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:60) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at org.springframework.boot.actuate.trace.WebRequestTraceFilter.doFilterInternal(WebRequestTraceFilter.java:111) [spring-boot-actuator-1.3.1.RELEASE.jar:1.3.1.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.2.4.RELEASE.jar:4.2.4.RELEASE]
    at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:60) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at org.grails.web.servlet.mvc.GrailsWebRequestFilter.doFilterInternal(GrailsWebRequestFilter.java:73) [grails-web-mvc-3.0.11.jar:3.0.11]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.2.4.RELEASE.jar:4.2.4.RELEASE]
    at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:60) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at org.grails.web.filters.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:67) [grails-web-mvc-3.0.11.jar:3.0.11]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.2.4.RELEASE.jar:4.2.4.RELEASE]
    at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:60) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:121) [spring-web-4.2.4.RELEASE.jar:4.2.4.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.2.4.RELEASE.jar:4.2.4.RELEASE]
    at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:60) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at org.springframework.boot.actuate.autoconfigure.MetricsFilter.doFilterInternal(MetricsFilter.java:103) [spring-boot-actuator-1.3.1.RELEASE.jar:1.3.1.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.2.4.RELEASE.jar:4.2.4.RELEASE]
    at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:60) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.servlet.handlers.FilterHandler.handleRequest(FilterHandler.java:84) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:131) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) [undertow-core-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46) [undertow-core-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:60) [undertow-core-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:77) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.security.handlers.AbstractSecurityContextAssociationHandler.handleRequest(AbstractSecurityContextAssociationHandler.java:43) [undertow-core-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) [undertow-core-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) [undertow-core-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:284) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:263) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:81) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:174) [undertow-servlet-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.server.Connectors.executeRootHandler(Connectors.java:202) [undertow-core-1.3.10.Final.jar:1.3.10.Final]
    at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:793) [undertow-core-1.3.10.Final.jar:1.3.10.Final]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) [na:1.8.0_60]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) [na:1.8.0_60]
    at java.lang.Thread.run(Unknown Source) [na:1.8.0_60]

拜托，你能帮我解决这个问题吗，因为我使用 Hystrix for Circuit Breaker 它总是调用回退函数。