OpenFeign源码1-环境搭建及核心类说明

比眉伴天荒 2023-10-03 21:38 32阅读 0赞

## 0. 环境 ##

*  nacos版本：1.4.1
 *  Spring Cloud : Hoxton.SR9（`没用2020.0.2版本后面说明`）
 *  Spring Boot ：2.4.4
 *  Spring Cloud alibaba: 2.2.5.RELEASE
 *  Spring Cloud openFeign 2.2.2.RELEASE

测试代码：[github.com/hsfxuebao/s…][github.com_hsfxuebao_s]

> `2020.0.X版本`开始的OpenFeign底层不再使用Ribbon了

## 1. 下载 ##

github地址：[github.com/spring-clou…][github.com_spring-clou]

![format_png][]

由于是maven工程，直接导入IDEA中就可以了

## 2. 核心类介绍 ##

### 2.1 @EnableFeignClients ###

// @EnableFeignClients注解用来启动FeignClient，以支持Feign。
    // 该注解可以通过配置，扫描指定位置的@FeignClient注解声明的Feign客户端接口
    @Retention(RetentionPolicy.RUNTIME)
    @Target(ElementType.TYPE)
    @Documented
    @Import(FeignClientsRegistrar.class)
    public @interface EnableFeignClients {
    
       // value和basePackage具有相同的功能，其中value是basePackage的别名
       // value和basePackage只能同时使用一个
       /**
        * Alias for the {@link #basePackages()} attribute. Allows for more concise annotation
        * declarations e.g.: {@code @ComponentScan("org.my.pkg")} instead of
        * {@code @ComponentScan(basePackages="org.my.pkg")}.
        * @return the array of 'basePackages'.
        */
       // 为basePackages属性的别名，允许使用更简洁的书写方式。例如：@EnableFeignClients({"com.cd", "com.ad"})
       String[] value() default {};
    
       /**
        * Base packages to scan for annotated components.
        * <p>
        * {@link #value()} is an alias for (and mutually exclusive with) this attribute.
        * <p>
        * Use {@link #basePackageClasses()} for a type-safe alternative to String-based
        * package names.
        * @return the array of 'basePackages'.
        */
       // 设置自动扫描带有@FeignClient注解的基础包路径。例如 @EnableFeignClients(basePackages = {"com.cd", "com.ad"})
       String[] basePackages() default {};
    
       /**
        * Type-safe alternative to {@link #basePackages()} for specifying the packages to
        * scan for annotated components. The package of each class specified will be scanned.
        * <p>
        * Consider creating a special no-op marker class or interface in each package that
        * serves no purpose other than being referenced by this attribute.
        * @return the array of 'basePackageClasses'.
        */
       // 该属性是basePackages属性的安全替代属性。该属性将扫描指定的每个类所在的包下面的所有被@FeignClient修饰的类；
       // 这需要考虑在每个包中创建一个特殊的标记类或接口，该类或接口除了被该属性引用外，没有其他用途
       Class<?>[] basePackageClasses() default {};
    
       /**
        * A custom <code>@Configuration</code> for all feign clients. Can contain override
        * <code>@Bean</code> definition for the pieces that make up the client, for instance
        * {@link feign.codec.Decoder}, {@link feign.codec.Encoder}, {@link feign.Contract}.
        *
        * @see FeignClientsConfiguration for the defaults
        * @return list of default configurations
        */
       // 该属性用来自定义所有Feign客户端的配置，使用@Configuration进行配置。
       // 当然也可以为某一个Feign客户端进行配置。具体配置方法见@FeignClient的configuration属性。
       Class<?>[] defaultConfiguration() default {};
    
       /**
        * List of classes annotated with @FeignClient. If not empty, disables classpath
        * scanning.
        * @return list of FeignClient classes
        */
       // 设置由@FeignClient注解修饰的类列表。如果clients不是空数组，则不通过类路径自动扫描功能来加载FeignClient
       // 例如 @EnableFeignClients(clients = {SchedualService.class})
       // 上面代码中引入FeignClient客户端SchedualService，且也只引入该FeignClient客户端。
       Class<?>[] clients() default {};
    
    }
    复制代码

### 2.2 @FeignClient ###

@Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface FeignClient {
    
       // name 和 value 两个属性等价，至少要配置一个
       /**
        * The name of the service with optional protocol prefix. Synonym for {@link #name()
        * name}. A name must be specified for all clients, whether or not a url is provided.
        * Can be specified as property key, eg: ${propertyKey}.
        * @return the name of the service with optional protocol prefix
        */
       @AliasFor("name")
       String value() default "";
    
       /**
        * The service id with optional protocol prefix. Synonym for {@link #value() value}.
        * @deprecated use {@link #name() name} instead
        * @return the service id with optional protocol prefix
        */
       @Deprecated
       String serviceId() default "";
    
       /**
        * This will be used as the bean name instead of name if present, but will not be used
        * as a service id.
        * @return bean name instead of name if present
        */
       // 别名，假设一个User服务有两个FeignClient,都需要调用Product服务, 因为name属性值一样,所以需要通过配置contextId来区分,否则启动项目时会报错
       String contextId() default "";
    
       /**
        * @return The service id with optional protocol prefix. Synonym for {@link #value()
        * value}.
        */
       @AliasFor("value")
       String name() default "";
    
       /**
        * @return the <code>@Qualifier</code> value for the feign client.
        */
       // 返回默认值=contextId+“FeignClient”。
       String qualifier() default "";
    
       /**
        * @return an absolute URL or resolvable hostname (the protocol is optional).
        */
       // 请求地址, 没配置的话, 会把name/value的属性值当成服务名进行调用, 配置的话则使用url的值
       String url() default "";
    
       /**
        * @return whether 404s should be decoded instead of throwing FeignExceptions
        */
       // 当发生http 404错误时，如果该字段位true，会调用decoder进行解码，否则抛出FeignException
       boolean decode404() default false;
    
       /**
        * A custom configuration class for the feign client. Can contain override
        * <code>@Bean</code> definition for the pieces that make up the client, for instance
        * {@link feign.codec.Decoder}, {@link feign.codec.Encoder}, {@link feign.Contract}.
        *
        * @see FeignClientsConfiguration for the defaults
        * @return list of configurations for feign client
        */
       // Feign配置类，可以自定义Feign的Encoder、Decoder、LogLevel、Contract
       Class<?>[] configuration() default {};
    
       /**
        * Fallback class for the specified Feign client interface. The fallback class must
        * implement the interface annotated by this annotation and be a valid spring bean.
        * @return fallback class for the specified Feign client interface
        */
       // 定义容错的处理类，当调用远程接口失败或超时时，会调用对应接口的容错逻辑，fallback指定的类必须实现@FeignClient标记的接口
       Class<?> fallback() default void.class;
    
       /**
        * Define a fallback factory for the specified Feign client interface. The fallback
        * factory must produce instances of fallback classes that implement the interface
        * annotated by {@link FeignClient}. The fallback factory must be a valid spring bean.
        *
        * @see feign.hystrix.FallbackFactory for details.
        * @return fallback factory for the specified Feign client interface
        */
       // 工厂类，用于生成fallback类示例，通过这个属性我们可以实现每个接口通用的容错逻辑，减少重复的代码
       Class<?> fallbackFactory() default void.class;
    
       /**
        * @return path prefix to be used by all method-level mappings. Can be used with or
        * without <code>@RibbonClient</code>.
        */
       // 所有方法级映射使用的路径前缀
       String path() default "";
    
       /**
        * @return whether to mark the feign proxy as a primary bean. Defaults to true.
        */
       // 是否将外部代理标记为主bean。默认为true。
       boolean primary() default true;
    
    }
    复制代码

### 2.3 FeignClientSpecification ###

`FeignClientSpecification`是 Feign Client 生成规范:

![format_png 1][]

### 2.4 FeignContext ###

`FeignContext` 是一个为 `Feign Client` 创建所准备的上下文对象

// FeignContext 是一个为 Feign Client 创建所准备的上下文对象
    public class FeignContext extends NamedContextFactory<FeignClientSpecification> {
    
       public FeignContext() {
          super(FeignClientsConfiguration.class, "feign", "feign.client.name");
       }
    
    }
    复制代码

其父类为：

public abstract class NamedContextFactory<C extends NamedContextFactory.Specification>
          implements DisposableBean, ApplicationContextAware {
    
       private final String propertySourceName;
    
       private final String propertyName;
    
       // todo 该 map 的 key 为 FeignClient 的名称（其所要调用的微服务名称）， value 是组装这个
       // FeignClient 所必须的组件所在的 Spring 子容器
       private Map<String, AnnotationConfigApplicationContext> contexts = new ConcurrentHashMap<>();
    
        // 这个map中存放的是@EnableFeignClients与@FeignClient两个注解中的configuration属性值。
        // 这个属性值只有两类：
        // 第一类只有一个，其 key 为字符串 default + 当前启动类的全限定性类名 ，例如：
    // default.com.abc.ConsumerFeign8080， value 为@EnableFeignClients 的 defaultConfiguration属性值
        // 第二类有多个，其 key 为当前@FeignClient 的名称， value 为这个注解的 configuration 属性值
       private Map<String, C> configurations = new ConcurrentHashMap<>();
    
       private ApplicationContext parent;
    
       private Class<?> defaultConfigType;
    
       public NamedContextFactory(Class<?> defaultConfigType, String propertySourceName,
             String propertyName) {
          this.defaultConfigType = defaultConfigType;
          this.propertySourceName = propertySourceName;
          this.propertyName = propertyName;
       }

[github.com_hsfxuebao_s]: https://link.juejin.cn?target=https%3A%2F%2Fgithub.com%2Fhsfxuebao%2Fspringcloud-source-study
[github.com_spring-clou]: https://link.juejin.cn?target=https%3A%2F%2Fgithub.com%2Fspring-cloud%2Fspring-cloud-openfeign%2Ftree%2Fv2.2.2.RELEASE
[format_png]: https://img-blog.csdnimg.cn/img_convert/86efb0510796c861a4a3ec4b9cc93414.webp?x-oss-process=image/format,png
[format_png 1]: https://img-blog.csdnimg.cn/img_convert/bc42d698e43ea3c50332ebd61004e1e4.webp?x-oss-process=image/format,png