今天就跟大家聊聊有关SpringCloud中怎么声明式调用Feign，可能很多人都不太了解，为了让大家更加了解，小编给大家总结了以下内容，希望大家根据这篇文章可以有所收获。
使用Ribbon和RestTemplate消费服务的时候，有一个最麻烦的点在于，每次都要拼接URL，组织参数，所以有了Feign声明式调用，Feign的首要目标是将Java HTTP客户端的调用过程非常简单。它采用声明式API接口的风格，将Java Http客户端绑定到它的内部，以此来方便调用。
从前面Ribbon中拿到项目整体，然后再整改成如下目录
帖子地址：https://my.oschina.net/devilsblog/blog/3115061
码云地址：https://gitee.com/devilscode/cloud-practice/tree/ribbon-test
修改项目名称为feign-test
修改原来的子Module ribbon-service为feign-service
<modelVersion>4.0.0</modelVersion> <groupId>com.calvin.feigb</groupId> <artifactId>feign-test</artifactId> <packaging>pom</packaging> <version>1.0-SNAPSHOT</version> <modules> <module>common-service</module> <module>eureka-server</module> <module>feign-service</module> </modules> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>1.5.3.RELEASE</version> </parent> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding> <java.version>1.8</java.version> </properties> <dependencyManagement> <dependencies> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-dependencies</artifactId> <version>Dalston.SR4</version> <type>pom</type> <scope>import</scope> </dependency> </dependencies> </dependencyManagement>
<parent> <groupId>com.calvin.feigb</groupId> <artifactId>feign-test</artifactId> <version>1.0-SNAPSHOT</version> </parent> <modelVersion>4.0.0</modelVersion> <artifactId>common-service</artifactId> <dependencies> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-eureka</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> </dependencies> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> </plugins> </build>
<parent> <groupId>com.calvin.feigb</groupId> <artifactId>feign-test</artifactId> <version>1.0-SNAPSHOT</version> </parent> <modelVersion>4.0.0</modelVersion> <artifactId>eureka-server</artifactId> <properties> <java.version>1.8</java.version> </properties> <dependencies> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-eureka-server</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> </dependency> </dependencies> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> </plugins> </build>
<parent> <groupId>com.calvin.feigb</groupId> <artifactId>feign-test</artifactId> <version>1.0-SNAPSHOT</version> </parent> <modelVersion>4.0.0</modelVersion> <artifactId>feign-service</artifactId> <dependencies> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-eureka</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-feign</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> </dependency> </dependencies> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> </plugins> </build>
这样就可以从eureka注册中心中区别出我们的服务是feign-service
server: port: 8082 spring: application: name: feign-service eureka: client: service-url: defaultZone: http://localhost:8080/eureka/
服务启动的时候，此注解的作用会使得所有使用了注解FeignClient的类，被扫描解析，然后注册到IoC容器中。
/**
* <p>
* 启动类
* </p>
*
* @author Calvin
* @date 2019/10/09
* @since
*/
@EnableEurekaClient
@SpringBootApplication
@EnableFeignClients
public class FeignServerApplication {
public static void main(String[] args) {
SpringApplication.run(FeignServerApplication.class);
}
}/**
* <p> FeignClient的配置类 </p>
*
* @author Calvin
* @date 2019/10/21
* @since
*/
@Configuration
public class FeignConfiguration {
/**
* 覆盖默认的重试
* 重试间隔100ms
* 最大重试时间1s
* 最大重试次数5次
*/
@Bean
public Retryer feignRetryer(){
return new Retryer.Default(100,SECONDS.toMillis(1), 5);
}
}关于FeignClient的相关配置，如果我们不主动去配置，都有默认配置，配置类为FeignClientsConfiguration.class,详细内容后续分析
/**
* <p>
* 远程调用公共服务消费端
* </p>
*
* @author Calvin
* @date 2019/10/21
* @since
*/
@FeignClient(value = "common-service", configuration = FeignConfiguration.class)
public interface CommonFeignClient {
/**
* 调用 common-service/hello接口
* @return
*/
@GetMapping(value = "/hello")
String sayHi();
}/**
* <p>
* 测试接口
* </p>
*
* @author Calvin
* @date 2019/10/09
* @since
*/
@RestController
public class SayHiController {
// @Autowired
// private RemoteCommonService remoteCommonService;
@Autowired
private CommonFeignClient commonFeignClient;
@GetMapping("/hi")
public String sayHi(){
return commonFeignClient.sayHi() + "， this is feign service";
}
}删除RemoteCommonService.java即可
step1. EurekaSeverApplicaton
step2. CommonServiceApplication
step3. CommonServiceApplication2
step4. FeignServerApplication
Eureka管理界面 http://localhost:8080/
调用 http://localhost:8082/hi
刷新页面
/**
* @author Dave Syer
* @author Venil Noronha
*/
@Configuration
public class FeignClientsConfiguration {
/**
* 配置消息转换器
*/
@Autowired
private ObjectFactory<HttpMessageConverters> messageConverters;
/**
* 注入参数解析，用于解析@RequestParam
*/
@Autowired(required = false)
private List<AnnotatedParameterProcessor> parameterProcessors = new ArrayList<>();
/**
*
*/
@Autowired(required = false)
private List<FeignFormatterRegistrar> feignFormatterRegistrars = new ArrayList<>();
@Autowired(required = false)
private Logger logger;
/**
* 返回值解析
*/
@Bean
@ConditionalOnMissingBean
public Decoder feignDecoder() {
return new ResponseEntityDecoder(new SpringDecoder(this.messageConverters));
}
/**
* url编码
*/
@Bean
@ConditionalOnMissingBean
public Encoder feignEncoder() {
return new SpringEncoder(this.messageConverters);
}
@Bean
@ConditionalOnMissingBean
public Contract feignContract(ConversionService feignConversionService) {
return new SpringMvcContract(this.parameterProcessors, feignConversionService);
}
@Bean
public FormattingConversionService feignConversionService() {
FormattingConversionService conversionService = new DefaultFormattingConversionService();
for (FeignFormatterRegistrar feignFormatterRegistrar : feignFormatterRegistrars) {
feignFormatterRegistrar.registerFormatters(conversionService);
}
return conversionService;
}
@Configuration
@ConditionalOnClass({ HystrixCommand.class, HystrixFeign.class })
protected static class HystrixFeignConfiguration {
@Bean
@Scope("prototype")
@ConditionalOnMissingBean
@ConditionalOnProperty(name = "feign.hystrix.enabled", matchIfMissing = false)
public Feign.Builder feignHystrixBuilder() {
return HystrixFeign.builder();
}
}
/**
* 配置重试，NEVER_RETRY代表从不重试
*/
@Bean
@ConditionalOnMissingBean
public Retryer feignRetryer() {
return Retryer.NEVER_RETRY;
}
/**
* 给Feign绑定重试器
*/
@Bean
@Scope("prototype")
@ConditionalOnMissingBean
public Feign.Builder feignBuilder(Retryer retryer) {
return Feign.builder().retryer(retryer);
}
/**
* 日志工厂
*/
@Bean
@ConditionalOnMissingBean(FeignLoggerFactory.class)
public FeignLoggerFactory feignLoggerFactory() {
return new DefaultFeignLoggerFactory(logger);
}
}通过@EnableFeignClients开启注解扫描
扫描@FeignClient注解修饰的元注解信息，使用BeanDefinitionBuilder解析成BeanDefinition，交给IoC容器中
通过JDK代理，当发现FeignClient被调用的时候，拦截该方法
拦截到该方法后，在SynchronousMethodHandler类中，使用生成的RequestTemplate，重新生成Request对象
使用HttpClient调用请求，获取Response
class FeignClientsRegistrar implements ImportBeanDefinitionRegistrar,
ResourceLoaderAware, BeanClassLoaderAware, EnvironmentAware {
/**
* <p>
* 检查EnableFeignClients注解是否开启，如果开启，则开始注册默认配置
* </p>
*/
private void registerDefaultConfiguration(AnnotationMetadata metadata,
BeanDefinitionRegistry registry) {
Map<String, Object> defaultAttrs = metadata
.getAnnotationAttributes(EnableFeignClients.class.getName(), true);
if (defaultAttrs != null && defaultAttrs.containsKey("defaultConfiguration")) {
String name;
if (metadata.hasEnclosingClass()) {
name = "default." + metadata.getEnclosingClassName();
}
else {
name = "default." + metadata.getClassName();
}
registerClientConfiguration(registry, name,
defaultAttrs.get("defaultConfiguration"));
}
}
}public void registerFeignClients(AnnotationMetadata metadata,
BeanDefinitionRegistry registry) {
ClassPathScanningCandidateComponentProvider scanner = getScanner();
scanner.setResourceLoader(this.resourceLoader);
Set<String> basePackages;
Map<String, Object> attrs = metadata
.getAnnotationAttributes(EnableFeignClients.class.getName());
AnnotationTypeFilter annotationTypeFilter = new AnnotationTypeFilter(
FeignClient.class);
final Class<?>[] clients = attrs == null ? null
: (Class<?>[]) attrs.get("clients");
if (clients == null || clients.length == 0) {
scanner.addIncludeFilter(annotationTypeFilter);
basePackages = getBasePackages(metadata);
}
else {
final Set<String> clientClasses = new HashSet<>();
basePackages = new HashSet<>();
for (Class<?> clazz : clients) {
basePackages.add(ClassUtils.getPackageName(clazz));
clientClasses.add(clazz.getCanonicalName());
}
AbstractClassTestingTypeFilter filter = new AbstractClassTestingTypeFilter() {
@Override
protected boolean match(ClassMetadata metadata) {
String cleaned = metadata.getClassName().replaceAll("\\$", ".");
return clientClasses.contains(cleaned);
}
};
scanner.addIncludeFilter(
new AllTypeFilter(Arrays.asList(filter, annotationTypeFilter)));
}
for (String basePackage : basePackages) {
Set<BeanDefinition> candidateComponents = scanner
.findCandidateComponents(basePackage);
for (BeanDefinition candidateComponent : candidateComponents) {
if (candidateComponent instanceof AnnotatedBeanDefinition) {
// verify annotated class is an interface
AnnotatedBeanDefinition beanDefinition = (AnnotatedBeanDefinition) candidateComponent;
AnnotationMetadata annotationMetadata = beanDefinition.getMetadata();
Assert.isTrue(annotationMetadata.isInterface(),
"@FeignClient can only be specified on an interface");
Map<String, Object> attributes = annotationMetadata
.getAnnotationAttributes(
FeignClient.class.getCanonicalName());
String name = getClientName(attributes);
registerClientConfiguration(registry, name,
attributes.get("configuration"));
registerFeignClient(registry, annotationMetadata, attributes);
}
}
}
}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);
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 = name + "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);
}public class ReflectiveFeign extends Feign {
@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;
}
}拦截进行处理，先解析RequestTemplate，然后使用HttpClient调用网络请求
final class SynchronousMethodHandler implements MethodHandler {
/**
* 将传递过来的参数解析成RequestTemplate
*/
@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) {
retryer.continueOrPropagate(e);
if (logLevel != Logger.Level.NONE) {
logger.logRetry(metadata.configKey(), logLevel);
}
continue;
}
}
}
/**
* 将RequestTemplate转换成一个Request，然后使用HttpClient调用请求，拿到返回结果
*/
Object executeAndDecode(RequestTemplate template) throws Throwable {
Request request = targetRequest(template);
Response response;
long start = System.nanoTime();
try {
response = client.execute(request, options);
response.toBuilder().request(request).build();
} catch (IOException e) {
// 处理异常
}
//省略返回的代码
}看完上述内容，你们对SpringCloud中怎么声明式调用Feign有进一步的了解吗？如果还想了解更多知识或者相关内容，请关注亿速云行业资讯频道，感谢大家的支持。
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