Feign series (03) Feign works

Feign series (03) Feign works

How 1. Feign is designed

First, look at Feignthe basic usage:

// 1. Feign 动态代理
GitHub github = Feign.builder()
    .decoder(new GsonDecoder())
    .target(GitHub.class, "https://api.github.com");
// 2. Feign 执行
List<Contributor> contributors = github.contributors("OpenFeign", "feign");

Summary: Feign into the use of two steps: first, to generate dynamic proxy Feign; second Feign performed.

Figure 1: Feign overall design

to sum up:

1. The first two steps is to generate a dynamic object: Method A Resolution annotations into MethodMetadata, and ultimately generate Feign dynamic proxy object.
2. After calling process steps: The analytical MethodMetadata objects, the method of converting into a Method parameter Request, Client last call transmission request.

2. Feign dynamic proxy

2.1

public Feign build() {
    // client 有三种实现 JdkHttp/ApacheHttp/okHttp，默认是 jdk 的实现
    SynchronousMethodHandler.Factory synchronousMethodHandlerFactory =
        new SynchronousMethodHandler.Factory(client, retryer, requestInterceptors, logger,
                                             logLevel, decode404, closeAfterDecode, propagationPolicy);
    ParseHandlersByName handlersByName =
        new ParseHandlersByName(contract, options, encoder, decoder, queryMapEncoder,
                                errorDecoder, synchronousMethodHandlerFactory);
    return new ReflectiveFeign(handlersByName, invocationHandlerFactory, queryMapEncoder);
}

3. Feign calling process

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