在阅读这篇博客以前,但愿你对SpringCloud套件熟悉和理解,更但愿关注下微服务开发平台java
在使用springcloud ribbon客户端负载均衡的时候，能够给RestTemplate bean 加一个@LoadBalanced注解，就能让这个RestTemplate在请求时拥有客户端负载均衡的能力,先前有细嚼过可是没有作过笔记,恰好处理此类问题记录下git
/**
* 注释将RestTemplate bean标记为配置为使用LoadBalancerClient。
*/
@Target({ ElementType.FIELD, ElementType.PARAMETER, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Qualifier
public @interface LoadBalanced {
}
经过源码能够发现这是一个LoadBalanced标记注解而且标记了@Qualifier(基于Spring Boot的自动配置机制),咱们能够溯源到LoadBalancerAutoConfigurationspring
/**
* 功能区的自动配置（客户端负载平衡）
*/
@Configuration
@ConditionalOnClass(RestTemplate.class)
@ConditionalOnBean(LoadBalancerClient.class)
@EnableConfigurationProperties(LoadBalancerRetryProperties.class)
public class LoadBalancerAutoConfiguration {
@LoadBalanced
@Autowired(required = false)
private List<RestTemplate> restTemplates = Collections.emptyList(); //这里持有@LoadBalanced标记的RestTemplate实例
@Autowired(required = false)
private List<LoadBalancerRequestTransformer> transformers = Collections.emptyList();
@Bean
public SmartInitializingSingleton loadBalancedRestTemplateInitializerDeprecated(
final ObjectProvider<List<RestTemplateCustomizer>> restTemplateCustomizers) {
return () -> restTemplateCustomizers.ifAvailable(customizers -> {
for (RestTemplate restTemplate : LoadBalancerAutoConfiguration.this.restTemplates) {
for (RestTemplateCustomizer customizer : customizers) {
//为restTemplate添加定制
customizer.customize(restTemplate);
}
}
});
}
// ...
/**
* 如下针对classpath存在RetryTemplate.class的状况配置，先忽略
*/
@Configuration
@ConditionalOnClass(RetryTemplate.class)
public static class RetryAutoConfiguration {
@Bean
@ConditionalOnMissingBean
public LoadBalancedRetryFactory loadBalancedRetryFactory() {
return new LoadBalancedRetryFactory() {
};
}
}
// ...
}
@LoadBalanced和@Autowried结合使用,意思就是这里注入的RestTempate Bean是全部加有@LoadBalanced注解标记的(持有@LoadBalanced标记的RestTemplate实例)api
这段自动装配的代码的含义不难理解，就是利用了RestTempllate的拦截器，使用RestTemplateCustomizer对全部标注了@LoadBalanced的RestTemplate Bean添加了一个LoadBalancerInterceptor拦截器，而这个拦截器的做用就是对请求的URI进行转换获取到具体应该请求哪一个服务实例ServiceInstance。app
关键问下本身：为何？负载均衡
继续扒看源码>
上面能够看出，会LoadBalancerAutoConfiguration类对咱们加上@LoadBalanced注解的bean 添加loadBalancerInterceptor拦截器ide
/**
* 功能区的自动配置（客户端负载平衡）。
*/
public class LoadBalancerInterceptor implements ClientHttpRequestInterceptor {
private LoadBalancerClient loadBalancer;
private LoadBalancerRequestFactory requestFactory;
public LoadBalancerInterceptor(LoadBalancerClient loadBalancer,
LoadBalancerRequestFactory requestFactory) {
this.loadBalancer = loadBalancer;
this.requestFactory = requestFactory;
}
public LoadBalancerInterceptor(LoadBalancerClient loadBalancer) {
// for backwards compatibility
this(loadBalancer, new LoadBalancerRequestFactory(loadBalancer));
}
@Override
public ClientHttpResponse intercept(final HttpRequest request, final byte[] body,
final ClientHttpRequestExecution execution) throws IOException {
final URI originalUri = request.getURI();
String serviceName = originalUri.getHost();
Assert.state(serviceName != null,
"Request URI does not contain a valid hostname: " + originalUri);
return this.loadBalancer.execute(serviceName,
this.requestFactory.createRequest(request, body, execution));
}
}
重点看intercept方法 当咱们restTemplate执行请求操做时，就会被拦截器拦截进入intercept方法,而loadBalancer是LoadBalancerClient的具体实现微服务
public <T> T execute(String serviceId, LoadBalancerRequest<T> request, Object hint)
throws IOException {
ILoadBalancer loadBalancer = getLoadBalancer(serviceId);
Server server = getServer(loadBalancer, hint);
if (server == null) {
throw new IllegalStateException("No instances available for " + serviceId);
}
RibbonServer ribbonServer = new RibbonServer(serviceId, server,
isSecure(server, serviceId),
serverIntrospector(serviceId).getMetadata(server));
return execute(serviceId, ribbonServer, request);
}
看到这里相信都遇到过相似的错误，恍然大悟ui
No instances available for xxxxx
这里this
注意: @LoadBalanced 标记注解获取到最后经过负载均衡规则获取具体的具体的server来发起请求
/**
* 服务注册中心配置
*
* @author <a href="mailto:shangzhi.ibyte@gmail.com">iByte</a>
* @since 1.0.1
*/
@Configuration
@EnableConfigurationProperties(ModuleMappingHelper.class)
public class DiscoveryConfig {
@Autowired
Environment environment;
/**
* DiscoveryHeaderHelper默认bean
* @return
*/
@Bean
public DiscoveryHeaderHelper discoveryHeaderHelper() {
DiscoveryHeaderHelper discoveryHeaderHelper = new DiscoveryHeaderHelper(environment);
DiscoveryHeaderHelper.INSTANCE = discoveryHeaderHelper;
return discoveryHeaderHelper;
}
/**
* resttemplate构建
*/
@Resource
private RestTemplateBuilder restTemplateBuilder;
/**
* resttemplate请求bean,更改系统自己的builder
* @return
*/
@Bean
@LoadBalanced
public RestTemplate restTemplate() {
RestTemplate restTemplate = restTemplateBuilder.configure(new RestTemplate());
//RestTemplate interceptors 远程调用请求增长头部信息处理
restTemplate.getInterceptors().add(new RestApiHeaderInterceptor());
//RestTemplate Set the error handler 错误处理
restTemplate.setErrorHandler(new RestResponseErrorHandler());
return restTemplate;
}
@Bean
public DiscoveryClient.DiscoveryClientOptionalArgs discoveryClientOptionalArgs() {
DiscoveryClient.DiscoveryClientOptionalArgs discoveryClientOptionalArgs = new DiscoveryClient.DiscoveryClientOptionalArgs();
discoveryClientOptionalArgs.setAdditionalFilters(Collections.singletonList(new DiscoveryHeaderClientFilter()));
discoveryClientOptionalArgs.setEventListeners(Collections.singleton(new EurekaClientEventListener()));
return discoveryClientOptionalArgs;
}
}
源码地址 > DiscoveryConfig