17. Developer Guide
These are basic guides to writing some custom components of the gateway.
17.1. Writing Custom Route Predicate Factories
In order to write a Route Predicate you will need to implement RoutePredicateFactory. There is an abstract class called AbstractRoutePredicateFactory which you can extend.
public class MyRoutePredicateFactory extends AbstractRoutePredicateFactory<HeaderRoutePredicateFactory.Config> {
public MyRoutePredicateFactory() {
super(Config.class);
}
@Override
public Predicate<ServerWebExchange> apply(Config config) {
// grab configuration from Config object
return exchange -> {
//grab the request
ServerHttpRequest request = exchange.getRequest();
//take information from the request to see if it
//matches configuration.
return matches(config, request);
};
}
public static class Config {
//Put the configuration properties for your filter here
}
}17.2. Writing Custom GatewayFilter Factories
To write a GatewayFilter, you must implement GatewayFilterFactory.
You can extend an abstract class called AbstractGatewayFilterFactory.
The following examples show how to do so:
public class PreGatewayFilterFactory extends AbstractGatewayFilterFactory<PreGatewayFilterFactory.Config> {
public PreGatewayFilterFactory() {
super(Config.class);
}
@Override
public GatewayFilter apply(Config config) {
// grab configuration from Config object
return (exchange, chain) -> {
//If you want to build a "pre" filter you need to manipulate the
//request before calling chain.filter
ServerHttpRequest.Builder builder = exchange.getRequest().mutate();
//use builder to manipulate the request
return chain.filter(exchange.mutate().request(builder.build()).build());
};
}
public static class Config {
//Put the configuration properties for your filter here
}
}public class PostGatewayFilterFactory extends AbstractGatewayFilterFactory<PostGatewayFilterFactory.Config> {
public PostGatewayFilterFactory() {
super(Config.class);
}
@Override
public GatewayFilter apply(Config config) {
// grab configuration from Config object
return (exchange, chain) -> {
return chain.filter(exchange).then(Mono.fromRunnable(() -> {
ServerHttpResponse response = exchange.getResponse();
//Manipulate the response in some way
}));
};
}
public static class Config {
//Put the configuration properties for your filter here
}
}17.2.1. Naming Custom Filters And References In Configuration
Custom filters class names should end in GatewayFilterFactory.
For example, to reference a filter named Something in configuration files, the filter
must be in a class named SomethingGatewayFilterFactory.
It is possible to create a gateway filter named without the
GatewayFilterFactory suffix, such as class AnotherThing. This filter could be
referenced as AnotherThing in configuration files. This is not a supported naming
convention and this syntax may be removed in future releases. Please update the filter
name to be compliant.
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17.3. Writing Custom Global Filters
To write a custom global filter, you must implement GlobalFilter interface.
This applies the filter to all requests.
The following examples show how to set up global pre and post filters, respectively:
@Bean
public GlobalFilter customGlobalFilter() {
return (exchange, chain) -> exchange.getPrincipal()
.map(Principal::getName)
.defaultIfEmpty("Default User")
.map(userName -> {
//adds header to proxied request
exchange.getRequest().mutate().header("CUSTOM-REQUEST-HEADER", userName).build();
return exchange;
})
.flatMap(chain::filter);
}
@Bean
public GlobalFilter customGlobalPostFilter() {
return (exchange, chain) -> chain.filter(exchange)
.then(Mono.just(exchange))
.map(serverWebExchange -> {
//adds header to response
serverWebExchange.getResponse().getHeaders().set("CUSTOM-RESPONSE-HEADER",
HttpStatus.OK.equals(serverWebExchange.getResponse().getStatusCode()) ? "It worked": "It did not work");
return serverWebExchange;
})
.then();
}