feign 如何压缩数据

Feign默认并没有提供数据压缩的功能，但我们可以通过自定义编解码器的方式来实现数据压缩。

具体实现步骤如下：

1. 创建自定义编解码器

可以使用GZIP进行数据压缩，然后使用Base64进行编码。创建一个实现了`feign.codec.Encoder`和`feign.codec.Decoder`接口的编解码器实现类，具体实现如下：

public class GzipEncoderDecoder implements Encoder, Decoder {
    private final Encoder delegateEncoder;
    private final Decoder delegateDecoder;

    public GzipEncoderDecoder(Encoder delegateEncoder, Decoder delegateDecoder) {
        this.delegateEncoder = delegateEncoder;
        this.delegateDecoder = delegateDecoder;
    }

    @Override
    public Object decode(Response response, Type type) throws IOException, DecodeException, FeignException {
        String encoding = response.headers().getOrDefault("Content-Encoding", "");
        if (encoding.contains("gzip")) {
            GZIPInputStream gzipInputStream = new GZIPInputStream(response.body().asInputStream());
            return delegateDecoder.decode(response.toBuilder().body(gzipInputStream).build(), type);
        }
        return delegateDecoder.decode(response, type);
    }

    @Override
    public void encode(Object object, Type bodyType, RequestTemplate template) throws EncodeException {
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        try (GZIPOutputStream gzipOutputStream = new GZIPOutputStream(outputStream)) {
            delegateEncoder.encode(object, bodyType, new RequestTemplateAdapter(template, gzipOutputStream));
        } catch (IOException e) {
            throw new EncodeException(e.getMessage(), e);
        }
        template.header("Content-Encoding", "gzip");
        template.body(outputStream.toByteArray(), null);
    }

    private static class RequestTemplateAdapter extends RequestTemplate {
        private final RequestTemplate delegate;
        private final OutputStream outputStream;

        private RequestTemplateAdapter(RequestTemplate delegate, OutputStream outputStream) {
            this.delegate = delegate;
            this.outputStream = outputStream;
        }

        @Override
        public void body(byte[] data, Charset charset) {
            try {
                outputStream.write(data);
                outputStream.flush();
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }

        @Override
        public Collection<String> headerNames() {
            return delegate.headerNames();
        }

        @Override
        public Collection<String> headers(String key) {
            return delegate.headers(key);
        }

        @Override
        public void header(String key, String value) {
            delegate.header(key, value);
        }

        @Override
        public String method() {
            return delegate.method();
        }

        @Override
        public void method(String method) {
            delegate.method(method);
        }

        @Override
        public void uri(String uri) {
            delegate.uri(uri);
        }
    }
}

2. 注册自定义编解码器

在Feign客户端配置类中注册自定义编解码器，如下所示：

@Configuration
public class FeignClientConfiguration {
    @Bean
    public Decoder decoder() {
        return new GzipEncoderDecoder(new JacksonDecoder(), new JacksonDecoder());
    }

    @Bean
    public Encoder encoder() {
        return new GzipEncoderDecoder(new JacksonEncoder(), new JacksonDecoder());
    }
}

这样就可以在Feign客户端中使用数据压缩功能了。