聊聊spring cloud的DiscoveryClientRouteDefinitionLocator

@Configuration
@ConditionalOnProperty(name = "spring.cloud.gateway.enabled", matchIfMissing = true)
@EnableConfigurationProperties
@AutoConfigureBefore(HttpHandlerAutoConfiguration.class)
@AutoConfigureAfter({GatewayLoadBalancerClientAutoConfiguration.class, GatewayClassPathWarningAutoConfiguration.class})
@ConditionalOnClass(DispatcherHandler.class)
public class GatewayAutoConfiguration {
    //......
    @Bean
    @ConditionalOnMissingBean
    public PropertiesRouteDefinitionLocator propertiesRouteDefinitionLocator(GatewayProperties properties) {
        return new PropertiesRouteDefinitionLocator(properties);
    }

    @Bean
    @ConditionalOnMissingBean(RouteDefinitionRepository.class)
    public InMemoryRouteDefinitionRepository inMemoryRouteDefinitionRepository() {
        return new InMemoryRouteDefinitionRepository();
    }
    @Bean
    @Primary
    public RouteDefinitionLocator routeDefinitionLocator(List<RouteDefinitionLocator> routeDefinitionLocators) {
        return new CompositeRouteDefinitionLocator(Flux.fromIterable(routeDefinitionLocators));
    }
    //......
}

@Configuration
@ConditionalOnProperty(name = "spring.cloud.gateway.enabled", matchIfMissing = true)
@AutoConfigureBefore(GatewayAutoConfiguration.class)
@ConditionalOnClass({DispatcherHandler.class, DiscoveryClient.class})
@EnableConfigurationProperties
public class GatewayDiscoveryClientAutoConfiguration {

    @Bean
    @ConditionalOnBean(DiscoveryClient.class)
    @ConditionalOnProperty(name = "spring.cloud.gateway.discovery.locator.enabled")
    public DiscoveryClientRouteDefinitionLocator discoveryClientRouteDefinitionLocator(
            DiscoveryClient discoveryClient, DiscoveryLocatorProperties properties) {
        return new DiscoveryClientRouteDefinitionLocator(discoveryClient, properties);
    }

    @Bean
    public DiscoveryLocatorProperties discoveryLocatorProperties() {
        DiscoveryLocatorProperties properties = new DiscoveryLocatorProperties();
        properties.setPredicates(initPredicates());
        properties.setFilters(initFilters());
        return properties;
    }

    public static List<PredicateDefinition> initPredicates() {
        ArrayList<PredicateDefinition> definitions = new ArrayList<>();
        // TODO: add a predicate that matches the url at /serviceId?

        // add a predicate that matches the url at /serviceId/**
        PredicateDefinition predicate = new PredicateDefinition();
        predicate.setName(normalizeRoutePredicateName(PathRoutePredicateFactory.class));
        predicate.addArg(PATTERN_KEY, "'/'+serviceId+'/**'");
        definitions.add(predicate);
        return definitions;
    }

    public static List<FilterDefinition> initFilters() {
        ArrayList<FilterDefinition> definitions = new ArrayList<>();

        // add a filter that removes /serviceId by default
        FilterDefinition filter = new FilterDefinition();
        filter.setName(normalizeFilterFactoryName(RewritePathGatewayFilterFactory.class));
        String regex = "'/' + serviceId + '/(?<remaining>.*)'";
        String replacement = "'/${remaining}'";
        filter.addArg(REGEXP_KEY, regex);
        filter.addArg(REPLACEMENT_KEY, replacement);
        definitions.add(filter);

        return definitions;
    }

}

@ConfigurationProperties("spring.cloud.gateway.discovery.locator")
public class DiscoveryLocatorProperties {

    /** Flag that enables DiscoveryClient gateway integration */
    private boolean enabled = false;

    /**
     * The prefix for the routeId, defaults to discoveryClient.getClass().getSimpleName() + "_".
     * Service Id will be appended to create the routeId.
     */
    private String routeIdPrefix;

    /**
     * SpEL expression that will evaluate whether to include a service in gateway integration or not,
     * defaults to: true
     */
    private String includeExpression = "true";

    /** SpEL expression that create the uri for each route, defaults to: 'lb://'+serviceId */
    private String urlExpression = "'lb://'+serviceId";

    /**
     * Option to lower case serviceId in predicates and filters, defaults to false.
     * Useful with eureka when it automatically uppercases serviceId.
     * so MYSERIVCE, would match /myservice/**
     */
    private boolean lowerCaseServiceId = false;

    private List<PredicateDefinition> predicates = new ArrayList<>();

    private List<FilterDefinition> filters = new ArrayList<>();

    //......

    @Override
    public String toString() {
        return new ToStringCreator(this)
                .append("enabled", enabled)
                .append("routeIdPrefix", routeIdPrefix)
                .append("includeExpression", includeExpression)
                .append("urlExpression", urlExpression)
                .append("lowerCaseServiceId", lowerCaseServiceId)
                .append("predicates", predicates)
                .append("filters", filters)
                .toString();
    }
}

public class DiscoveryClientRouteDefinitionLocator implements RouteDefinitionLocator {

    private final DiscoveryClient discoveryClient;
    private final DiscoveryLocatorProperties properties;
    private final String routeIdPrefix;

    public DiscoveryClientRouteDefinitionLocator(DiscoveryClient discoveryClient, DiscoveryLocatorProperties properties) {
        this.discoveryClient = discoveryClient;
        this.properties = properties;
        if (StringUtils.hasText(properties.getRouteIdPrefix())) {
            this.routeIdPrefix = properties.getRouteIdPrefix();
        } else {
            this.routeIdPrefix = this.discoveryClient.getClass().getSimpleName() + "_";
        }
    }

    @Override
    public Flux<RouteDefinition> getRouteDefinitions() {
        SimpleEvaluationContext evalCtxt = SimpleEvaluationContext
                .forReadOnlyDataBinding()
                .withInstanceMethods()
                .build();

        SpelExpressionParser parser = new SpelExpressionParser();
        Expression includeExpr = parser.parseExpression(properties.getIncludeExpression());
        Expression urlExpr = parser.parseExpression(properties.getUrlExpression());

        return Flux.fromIterable(discoveryClient.getServices())
                .map(discoveryClient::getInstances)
                .filter(instances -> !instances.isEmpty())
                .map(instances -> instances.get(0))
                .filter(instance -> {
                    Boolean include = includeExpr.getValue(evalCtxt, instance, Boolean.class);
                    if (include == null) {
                        return false;
                    }
                    return include;
                })
                .map(instance -> {
                    String serviceId = instance.getServiceId();

                    RouteDefinition routeDefinition = new RouteDefinition();
                    routeDefinition.setId(this.routeIdPrefix + serviceId);
                    String uri = urlExpr.getValue(evalCtxt, instance, String.class);
                    routeDefinition.setUri(URI.create(uri));

                    final ServiceInstance instanceForEval = new DelegatingServiceInstance(instance, properties);

                    for (PredicateDefinition original : this.properties.getPredicates()) {
                        PredicateDefinition predicate = new PredicateDefinition();
                        predicate.setName(original.getName());
                        for (Map.Entry<String, String> entry : original.getArgs().entrySet()) {
                            String value = getValueFromExpr(evalCtxt, parser, instanceForEval, entry);
                            predicate.addArg(entry.getKey(), value);
                        }
                        routeDefinition.getPredicates().add(predicate);
                    }

                    for (FilterDefinition original : this.properties.getFilters()) {
                        FilterDefinition filter = new FilterDefinition();
                        filter.setName(original.getName());
                        for (Map.Entry<String, String> entry : original.getArgs().entrySet()) {
                            String value = getValueFromExpr(evalCtxt, parser, instanceForEval, entry);
                            filter.addArg(entry.getKey(), value);
                        }
                        routeDefinition.getFilters().add(filter);
                    }

                    return routeDefinition;
                });
    }

    String getValueFromExpr(SimpleEvaluationContext evalCtxt, SpelExpressionParser parser, ServiceInstance instance, Map.Entry<String, String> entry) {
        Expression valueExpr = parser.parseExpression(entry.getValue());
        return valueExpr.getValue(evalCtxt, instance, String.class);
    }
    //......
}