在使用feign做服务间调用的时候，如何修改请求的头部或编码信息呢，可以通过实现RequestInterceptor接口的apply方法，feign在发送请求之前都会调用该接口的apply方法，所以我们也可以通过实现该接口来记录请求发出去的时间点。
以下是参考文章的内容
RequestInterceptor
feign-core-10.2.!/feign/
public interface RequestInterceptor {
/**
* Called for every request. Add data using methods on the supplied {@link RequestTemplate}.
*/
void apply(RequestTemplate template);
}
- RequestInterceptor接口定义了apply方法，其参数为RequestTemplate；它有一个抽象类为BaseRequestInterceptor，还有几个实现类分别为BasicAuthRequestInterceptor、FeignAcceptGzipEncodingInterceptor、FeignContentGzipEncodingInterceptor
BasicAuthRequestInterceptor
feign-core-10.2.!/feign/auth/
public class BasicAuthRequestInterceptor implements RequestInterceptor {
private final String headerValue;
/**
* Creates an interceptor that authenticates all requests with the specified username and password
* encoded using ISO-8859-1.
*
* @param username the username to use for authentication
* @param password the password to use for authentication
*/
public BasicAuthRequestInterceptor(String username, String password) {
this(username, password, ISO_8859_1);
}
/**
* Creates an interceptor that authenticates all requests with the specified username and password
* encoded using the specified charset.
*
* @param username the username to use for authentication
* @param password the password to use for authentication
* @param charset the charset to use when encoding the credentials
*/
public BasicAuthRequestInterceptor(String username, String password, Charset charset) {
checkNotNull(username, "username");
checkNotNull(password, "password");
= "Basic " + base64Encode((username + ":" + password).getBytes(charset));
}
/*
* This uses a Sun internal method; if we ever encounter a case where this method is not
* available, the appropriate response would be to pull the necessary portions of Guava's
* BaseEncoding class into Util.
*/
private static String base64Encode(byte[] bytes) {
return (bytes);
}
@Override
public void apply(RequestTemplate template) {
("Authorization", headerValue);
}
}
- BasicAuthRequestInterceptor实现了RequestInterceptor接口，其apply方法往RequestTemplate添加名为Authorization的header
BaseRequestInterceptor
spring-cloud-openfeign-core-2.2.0.!/org/springframework/cloud/openfeign/encoding/
public abstract class BaseRequestInterceptor implements RequestInterceptor {
/**
* The encoding properties.
*/
private final FeignClientEncodingProperties properties;
/**
* Creates new instance of {@link BaseRequestInterceptor}.
* @param properties the encoding properties
*/
protected BaseRequestInterceptor(FeignClientEncodingProperties properties) {
(properties, "Properties can not be null");
= properties;
}
/**
* Adds the header if it wasn't yet specified.
* @param requestTemplate the request
* @param name the header name
* @param values the header values
*/
protected void addHeader(RequestTemplate requestTemplate, String name,
String... values) {
if (!().containsKey(name)) {
(name, values);
}
}
protected FeignClientEncodingProperties getProperties() {
return ;
}
}
- BaseRequestInterceptor定义了addHeader方法，往requestTemplate添加非重名的header
FeignAcceptGzipEncodingInterceptor
spring-cloud-openfeign-core-2.2.0.!/org/springframework/cloud/openfeign/encoding/
public class FeignAcceptGzipEncodingInterceptor extends BaseRequestInterceptor {
/**
* Creates new instance of {@link FeignAcceptGzipEncodingInterceptor}.
* @param properties the encoding properties
*/
protected FeignAcceptGzipEncodingInterceptor(
FeignClientEncodingProperties properties) {
super(properties);
}
/**
* {@inheritDoc}
*/
@Override
public void apply(RequestTemplate template) {
addHeader(template, HttpEncoding.ACCEPT_ENCODING_HEADER,
HttpEncoding.GZIP_ENCODING, HttpEncoding.DEFLATE_ENCODING);
}
}
- FeignAcceptGzipEncodingInterceptor继承了BaseRequestInterceptor，它的apply方法往RequestTemplate添加了名为Accept-Encoding，值为gzip,deflate的header
FeignContentGzipEncodingInterceptor
spring-cloud-openfeign-core-2.2.0.!/org/springframework/cloud/openfeign/encoding/
public class FeignContentGzipEncodingInterceptor extends BaseRequestInterceptor {
/**
* Creates new instance of {@link FeignContentGzipEncodingInterceptor}.
* @param properties the encoding properties
*/
protected FeignContentGzipEncodingInterceptor(
FeignClientEncodingProperties properties) {
super(properties);
}
/**
* {@inheritDoc}
*/
@Override
public void apply(RequestTemplate template) {
if (requiresCompression(template)) {
addHeader(template, HttpEncoding.CONTENT_ENCODING_HEADER,
HttpEncoding.GZIP_ENCODING, HttpEncoding.DEFLATE_ENCODING);
}
}
/**
* Returns whether the request requires GZIP compression.
* @param template the request template
* @return true if request requires compression, false otherwise
*/
private boolean requiresCompression(RequestTemplate template) {
final Map<String, Collection<String>> headers = ();
return matchesMimeType((HttpEncoding.CONTENT_TYPE))
&& contentLengthExceedThreshold((HttpEncoding.CONTENT_LENGTH));
}
/**
* Returns whether the request content length exceed configured minimum size.
* @param contentLength the content length header value
* @return true if length is grater than minimum size, false otherwise
*/
private boolean contentLengthExceedThreshold(Collection<String> contentLength) {
try {
if (contentLength == null || () != 1) {
return false;
}
final String strLen = ().next();
final long length = (strLen);
return length > getProperties().getMinRequestSize();
}
catch (NumberFormatException ex) {
return false;
}
}
/**
* Returns whether the content mime types matches the configures mime types.
* @param contentTypes the content types
* @return true if any specified content type matches the request content types
*/
private boolean matchesMimeType(Collection<String> contentTypes) {
if (contentTypes == null || () == 0) {
return false;
}
if (getProperties().getMimeTypes() == null
|| getProperties().getMimeTypes().length == 0) {
// no specific mime types has been set - matching everything
return true;
}
for (String mimeType : getProperties().getMimeTypes()) {
if ((mimeType)) {
return true;
}
}
return false;
}
}
- FeignContentGzipEncodingInterceptor继承了BaseRequestInterceptor，其apply方法先判断是否需要compression，即mimeType是否符合要求以及content大小是否超出阈值，需要compress的话则添加名为Content-Encoding，值为gzip,deflate的header
小结
- RequestInterceptor接口定义了apply方法，其参数为RequestTemplate；它有一个抽象类为BaseRequestInterceptor，还有几个实现类分别为BasicAuthRequestInterceptor、FeignAcceptGzipEncodingInterceptor、FeignContentGzipEncodingInterceptor
- BasicAuthRequestInterceptor实现了RequestInterceptor接口，其apply方法往RequestTemplate添加名为Authorization的header
- BaseRequestInterceptor定义了addHeader方法，往requestTemplate添加非重名的header；FeignAcceptGzipEncodingInterceptor继承了BaseRequestInterceptor，它的apply方法往RequestTemplate添加了名为Accept-Encoding，值为gzip,deflate的header；FeignContentGzipEncodingInterceptor继承了BaseRequestInterceptor，其apply方法先判断是否需要compression，即mimeType是否符合要求以及content大小是否超出阈值，需要compress的话则添加名为Content-Encoding，值为gzip,deflate的header
值得注意的是：该拦截器所在的线程不是controller层接收到请求的线程，因为feign是利用多个线程池来发送请求的，所以，主线程中的ThreadLocal对象在这里失效了，解决方案如下（参考资料：/blogs/106521）：
/questions/34719809/unreachable-security-context-using-feign-requestinterceptor 里面提到了使用 HystrixRequestVariableDefault，通过该类的注释可以知道，这个是Hystrix 为自身执行的线程提供的一个类似于ThreadLocal 的类，但是它与ThreadLocal 的不同之处在于，该Locals 的作用范围提升到了这个User Request Scope 级别，通过其注解可知，它是通过父类线程与子类线程共享的方式来共用该Locals 中的信息；所以，达到了User Request 线程与Hystrix 线程共用 attributes 的目的；由此，可以猜测，Hystrix 的线程是由当前Request 线程所创建的子线程；不过，使用的过程中，需要注意的是，HystrixRequestVariable 必须在每一个请求开始的时候进行初始化；也就是说，我们可以将 Request Context 中的有用信息存储到HystrixRequestVariableDefault中达到与Hystrix Context 共享信息；也就实现了Request Context 中的属性与Hystrix Context 之间共享的目的。
总的来说就是用HystrixRequestVariableDefault代替ThreadLocal来作为同一个请求不同环节传递变量，ThreadLocal作用于同一个线程，HystrixRequestVariableDefault作用于同一个请求。
关于HystrixRequestVariableDefault的更多说明，可以直接看该类源码注释。
具体做法看：/blogs/106521