feign使用
在實現的效果上來說Feign = RestTemplate+Ribbon+Hystrix
Feign實現RestTemplate+Ribbon效果
Feign實現RestTemplate+Ribbon效果,只需要以下幾步
在springcloud項目調用方的pom文件中加入openFeign的配置
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>
在啓動類中加入@EnableFeignClients
同時使用接口聲明的方式來實現接口調用
@FeignClient(name = "zhao-service-resume")
public interface ResumeFeignClient {
@GetMapping("/resume/openstate/{userId}")
public Integer findDefaultResumeState(@PathVariable Long userId) ;
}
這個接口的聲明與被調用方的實現完全一樣,我們需要在聲明時@FeignClient(name = "zhao-service-resume")聲明被調用的服務,即可按照默認的方式進行調用
使用單元測試測試即可測試到負載均衡的效果,訪問兩次,分別訪問到8081和8082端口的服務
@RunWith(SpringRunner.class)
@SpringBootTest(classes = DeliverApplication8091.class)
public class FeignTest {
@Autowired
ResumeFeignClient feignClient;
@Test
public void feignTest(){
Integer port = feignClient.findDefaultResumeState(2195321L);
System.out.println("測試的結果"+port);
}
}
那麼如何在配置類中配置負載均衡呢?格式如下,同時我們還配置了請求的超時時間,在沒有配置hystrix的情況下,會出現超時的情況,
zhao-service-resume:
ribbon: #請求連接超時時間
ConnectTimeout: 2000
#請求處理超時時間
ReadTimeout: 5000
#對所有操作都進⾏重試
OkToRetryOnAllOperations: true
####根據如上配置,當訪問到故障請求的時候,它會再嘗試訪問⼀次當前實例(次數由MaxAutoRetries配置),
####如果不⾏,就換⼀個實例進⾏訪問,如果還不⾏,再換⼀次實例訪問(更換次數由MaxAutoRetriesNextServer配置),
####如果依然不⾏,返回失敗信息。
MaxAutoRetries: 0 #對當前選中實例重試次數,不包括第⼀次調⽤
MaxAutoRetriesNextServer: 0 #切換實例的重試次數
NFLoadBalancerRuleClassName: com.netflix.loadbalancer.RoundRobinRule #負載策略調整
超時的報錯feign.RetryableException: Read timed out executing GET http://zhao-service-resume/resume/openstate/2195321
即是沒有配置重試的這幾個參數也是同樣的效果
Feign實現Hystrix效果
首先是先開啓熔斷器
feign:
hystrix:
enabled: true
接着增加超時處理邏輯的相關配置
hystrix:
command:
default:
execution:
isolation:
thread:
timeoutInMilliseconds: 15000
但是即使我在被調用方只線程休眠了十秒,程序依然被熔斷了。查閱資料表明,Hystrix將採用feign和hystrix超時時間中較小的那個進行超時判定
增加降級兜底方法
@Component
public class FeignClientFallBack implements ResumeFeignClient {
@Override
public Integer findDefaultResumeState(Long userId) {
return -1;
}
}
在調用方增加降級配置
@FeignClient(name = "zhao-service-resume",fallback = FeignClientFallBack.class)
public interface ResumeFeignClient {
@GetMapping("/resume/openstate/{userId}")
public Integer findDefaultResumeState(@PathVariable Long userId) ;
}
同時可以在@FeignClient中增加path屬性,將方法上的公共路徑提取到類中
Feign使用上的其他特性
Feign請求壓縮和響應壓縮配置
配置屬性如下
feign:
compression:
request:
enabled: true
min-request-size: 2048
mime-types: text/html,application/xml,application/json # 設置壓縮的數據類型
response:
enabled: true
以上配置包含的兩個屬性,min-request-size: 2048表示開啓壓縮的最小值爲2048字節,mime-types爲支持壓縮的數據類型,當前的這幾種類型未默認值
Feign請求日誌配置
首先在yml中設置具體的類的日誌響應級別
logging:
level:
# Feign⽇志只會對⽇志級別爲debug的做出響應
com.lagou.edu.controller.service.ResumeServiceFeignClient:
debug
然後就是針對feign的log的配置
import feign.Logger;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class FeignConfig {
@Bean
Logger.Level feignLevel(){
return Logger.Level.FULL;
}
}
需要注意的是,此處引入的是feign.Logger,此處表示的含義是feign將會打印請求的所有信息如下
Feign源碼簡要分析
還是依據前文,依照啓動類註解和spring.factories中配置的自動配置類來進行分析,首先我們看@EnableFeignClients註解中的FeignClientsRegistrar的具體內容,實現的依然是Spring中的注入beanDefinition的內容
@Override
public void registerBeanDefinitions(AnnotationMetadata metadata,
BeanDefinitionRegistry registry) {
registerDefaultConfiguration(metadata, registry);
registerFeignClients(metadata, registry);
}
registerDefaultConfiguration注入默認配置我們基本可以確定就是加入一些默認配置,而registerFeignClients就是最終實現邏輯的地方。而最終實現邏輯的地方是在該方法下的
private void registerFeignClient(BeanDefinitionRegistry registry,
AnnotationMetadata annotationMetadata, Map<String, Object> attributes) {
String className = annotationMetadata.getClassName();
BeanDefinitionBuilder definition = BeanDefinitionBuilder
.genericBeanDefinition(FeignClientFactoryBean.class);
validate(attributes);
definition.addPropertyValue("url", getUrl(attributes));
definition.addPropertyValue("path", getPath(attributes));
String name = getName(attributes);
definition.addPropertyValue("name", name);
String contextId = getContextId(attributes);
definition.addPropertyValue("contextId", contextId);
definition.addPropertyValue("type", className);
definition.addPropertyValue("decode404", attributes.get("decode404"));
definition.addPropertyValue("fallback", attributes.get("fallback"));
definition.addPropertyValue("fallbackFactory", attributes.get("fallbackFactory"));
definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
String alias = contextId + "FeignClient";
AbstractBeanDefinition beanDefinition = definition.getBeanDefinition();
boolean primary = (Boolean)attributes.get("primary"); // has a default, won't be null
beanDefinition.setPrimary(primary);
String qualifier = getQualifier(attributes);
if (StringUtils.hasText(qualifier)) {
alias = qualifier;
}
BeanDefinitionHolder holder = new BeanDefinitionHolder(beanDefinition, className,
new String[] { alias });
BeanDefinitionReaderUtils.registerBeanDefinition(holder, registry);
}
而這個類都依賴於 BeanDefinitionBuilder definition = BeanDefinitionBuilder.genericBeanDefinition(FeignClientFactoryBean.class);幾乎可以確定注入的時候就是FeignClientFactoryBean這個工廠Bean在起作用,那麼我們在進入裏面看一看,工廠Bean最重要的就是getObject返回的類型情況
@Override
public Object getObject() throws Exception {
return getTarget();
}
/**
* @param <T> the target type of the Feign client
* @return a {@link Feign} client created with the specified data and the context information
*/
<T> T getTarget() {
FeignContext context = applicationContext.getBean(FeignContext.class);
Feign.Builder builder = feign(context);
if (!StringUtils.hasText(this.url)) {
if (!this.name.startsWith("http")) {
url = "http://" + this.name;
}
else {
url = this.name;
}
url += cleanPath();
return (T) loadBalance(builder, context, new HardCodedTarget<>(this.type,
this.name, url));
}
if (StringUtils.hasText(this.url) && !this.url.startsWith("http")) {
this.url = "http://" + this.url;
}
String url = this.url + cleanPath();
Client client = getOptional(context, Client.class);
if (client != null) {
if (client instanceof LoadBalancerFeignClient) {
// not load balancing because we have a url,
// but ribbon is on the classpath, so unwrap
client = ((LoadBalancerFeignClient)client).getDelegate();
}
builder.client(client);
}
Targeter targeter = get(context, Targeter.class);
return (T) targeter.target(this, builder, context, new HardCodedTarget<>(
this.type, this.name, url));
}
在上述代碼中,基本上就是構造客戶端並調用的過程,那麼最關鍵的就是實現了Ribbon功能的負載均衡的loadBalance操作中內容
protected <T> T loadBalance(Feign.Builder builder, FeignContext context,
HardCodedTarget<T> target) {
Client client = getOptional(context, Client.class);
if (client != null) {
builder.client(client);
Targeter targeter = get(context, Targeter.class);
return targeter.target(this, builder, context, target);
}
throw new IllegalStateException(
"No Feign Client for loadBalancing defined. Did you forget to include spring-cloud-starter-netflix-ribbon?");
}
而 targeter.target這段最後都會執行到feign類中的這個方法中
public <T> T target(Target<T> target) {
return build().newInstance(target);
}
關注到newInstance方法發現最終實現時在ReflectiveFeign類中
@Override
public <T> T newInstance(Target<T> target) {
Map<String, MethodHandler> nameToHandler = targetToHandlersByName.apply(target);
Map<Method, MethodHandler> methodToHandler = new LinkedHashMap<Method, MethodHandler>();
List<DefaultMethodHandler> defaultMethodHandlers = new LinkedList<DefaultMethodHandler>();
for (Method method : target.type().getMethods()) {
if (method.getDeclaringClass() == Object.class) {
continue;
} else if (Util.isDefault(method)) {
DefaultMethodHandler handler = new DefaultMethodHandler(method);
defaultMethodHandlers.add(handler);
methodToHandler.put(method, handler);
} else {
methodToHandler.put(method, nameToHandler.get(Feign.configKey(target.type(), method)));
}
}
InvocationHandler handler = factory.create(target, methodToHandler);
T proxy = (T) Proxy.newProxyInstance(target.type().getClassLoader(),
new Class<?>[] {target.type()}, handler);
for (DefaultMethodHandler defaultMethodHandler : defaultMethodHandlers) {
defaultMethodHandler.bindTo(proxy);
}
return proxy;
}
上述可見,最終生成的類實際上一個代理類完成了最終的調用,而在代理對象就完成了最後的負載均衡等處理,生成代理對象使用的死FeignInvocationHandler的invoke方法
static final class Default implements InvocationHandlerFactory {
@Override
public InvocationHandler create(Target target, Map<Method, MethodHandler> dispatch) {
return new ReflectiveFeign.FeignInvocationHandler(target, dispatch);
}
}
最後執行了相關的編解碼操作
@Override
public Object invoke(Object[] argv) throws Throwable {
RequestTemplate template = buildTemplateFromArgs.create(argv);
Retryer retryer = this.retryer.clone();
while (true) {
try {
return executeAndDecode(template);
} catch (RetryableException e) {
try {
retryer.continueOrPropagate(e);
} catch (RetryableException th) {
Throwable cause = th.getCause();
if (propagationPolicy == UNWRAP && cause != null) {
throw cause;
} else {
throw th;
}
}
if (logLevel != Logger.Level.NONE) {
logger.logRetry(metadata.configKey(), logLevel);
}
continue;
}
}
}
而執行並解碼的操作executeAndDecode中最重要的就是client.execute方法,點進去之後發現,居然最終調用的就是LoadBalancerFeignClient.execute方法
最終在該方法中實現了遠程調用和負載均衡
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