The cause of the fallback is now logged by default to FINE level. You can programmatically inspect
the cause by making your own `FallbackFactory`. In many cases, the cause will be a `FeignException`,
which includes the http status.
Here's an example of using `FallbackFactory`:
```java
// This instance will be invoked if there are errors of any kind.
FallbackFactory<GitHub> fallbackFactory = cause -> (owner, repo) -> {
if (cause instanceof FeignException && ((FeignException) cause).status() == 403) {
return Collections.emptyList();
} else {
return Arrays.asList("yogi");
}
};
GitHub github = HystrixFeign.builder()
...
.target(GitHub.class, "https://api.github.com", fallbackFactory);
```
This exposes means to customize group and command keys, for example to
use non-default conventions from configuration or custom annotation
processing.
Ex.
```java
SetterFactory commandKeyIsRequestLine = (target, method) -> {
String groupKey = target.name();
String commandKey = method.getAnnotation(RequestLine.class).value();
return HystrixCommand.Setter
.withGroupKey(HystrixCommandGroupKey.Factory.asKey(groupKey))
.andCommandKey(HystrixCommandKey.Factory.asKey(commandKey));
};
api = HystrixFeign.builder()
.setterFactory(commandKeyIsRequestLine)
...
```
This also makes the default's more unique to avoid clashing in Hystrix's
cache.
Fallbacks are known values, which you return when there's an error invoking an http method.
For example, you can return a cached result as opposed to raising an error to the caller. To use
this feature, pass a safe implementation of your target interface as the last parameter to `HystrixFeign.Builder.target`.
Here's an example:
```java
// When dealing with fallbacks, it is less tedious to keep interfaces small.
interface GitHub {
@RequestLine("GET /repos/{owner}/{repo}/contributors")
List<String> contributors(@Param("owner") String owner, @Param("repo") String repo);
}
// This instance will be invoked if there are errors of any kind.
GitHub fallback = (owner, repo) -> {
if (owner.equals("Netflix") && repo.equals("feign")) {
return Arrays.asList("stuarthendren"); // inspired this approach!
} else {
return Collections.emptyList();
}
};
GitHub github = HystrixFeign.builder()
...
.target(GitHub.class, "https://api.github.com", fallback);
```
Credit to the idea goes to @stuarthendren!
Adrian Cole
Spencer Gibb
Adrian Cole
Christopher Lakey