How to “remove the gobal prefix('/api') then goto the lb:// ” when migrate to spring cloud gateway from zuul

问题

I want to Migrating from zuul to spring cloud gateway, I don't want to change my config of previous app. I want to know how to handle with the url with "/api/ + 'serviceId'", route to lb://serviceId

the previous zuul config

zuul: 
  prefix: /api

there are lots of service regist to eureka ,i don't want to config a route for each one.

eg. the auto generated route by org.springframework.cloud.gateway.discovery.DiscoveryClientRouteDefinitionLocator

{
"route_id": "CompositeDiscoveryClient_APIGATEWAY",
"route_definition": {
  "id": "CompositeDiscoveryClient_APIGATEWAY",
  "predicates": [
    {
      "name": "Path",
      "args": {
        "pattern": "/apigateway/**"
      }
    }
  ],
  "filters": [
    {
      "name": "RewritePath",
      "args": {
        "regexp": "/apigateway/(?<remaining>.*)",
        "replacement": "/${remaining}"
      }
    }
  ],
  "uri": "lb://APIGATEWAY",
  "order": 0
}

what i wanted is

 {
"route_id": "CompositeDiscoveryClient_APIGATEWAY",
"route_definition": {
  "id": "CompositeDiscoveryClient_APIGATEWAY",
  "predicates": [
    {
      "name": "Path",
      "args": {
        "pattern": "/api/apigateway/**"
      }
    }
  ],
  "filters": [
    {
      "name": "RewritePath",
      "args": {
        "regexp": "/api/apigateway/(?<remaining>.*)",
        "replacement": "/${remaining}"
      }
    }
  ],
  "uri": "lb://APIGATEWAY",
  "order": 0
}

how can i config my route to get what i want

And I also found the source code

    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;
}

the "'/'+serviceId+'/**'" is there without a prefix

[2019-01-10] UPDATE I think @spencergibb's suggestion is a good solution, but I had new trouble with the (SpEL) I tried many ways:

args:
  regexp: "'/api/' + serviceId.toLowerCase() + '/(?<remaining>.*)'"
  replacement: '/${remaining}'
args:
  regexp: "'/api/' + serviceId.toLowerCase() + '/(?<remaining>.*)'"
  replacement: "'/${remaining}'"

start failed

Origin: class path resource [application.properties]:23:70
Reason: Could not resolve placeholder 'remaining' in value "'${remaining}'"

when i use an escape "\" like

args:
  regexp: "'/api/' + serviceId.toLowerCase() + '/(?<remaining>.*)'"
  replacement: '/$\{remaining}'

it start success but i got an exception when running

org.springframework.expression.spel.SpelParseException: Expression [/$\{remaining}] @2: EL1065E: unexpected escape character.
at org.springframework.expression.spel.standard.Tokenizer.raiseParseException(Tokenizer.java:590) ~[spring-expression-5.0.5.RELEASE.jar:5.0.5.RELEASE]
at org.springframework.expression.spel.standard.Tokenizer.process(Tokenizer.java:265) ~[spring-expression-5.0.5.RELEASE.jar:5.0.5.RELEASE]

UPDATE 2

I found in the org.springframework.cloud.gateway.filter.factory.RewritePathGatewayFilterFactory, there's a replacement to deal with "\"

...    
@Override
        public GatewayFilter apply(Config config) {
            String replacement = config.replacement.replace("$\\", "$");
            return (exchange, chain) -> {
...

when it comes to SpelParseException there's none

回答1:

You can customize the automatic filters and predicates used via properties.

spring:
  cloud:
    gateway:
      discovery:
        locator:
          enabled: true
          predicates:
            - name: Path
              args:
                pattern: "'/api/'+serviceId.toLowerCase()+'/**'"
          filters:
            - name: RewritePath
              args:
                regexp: "'/api/' + serviceId.toLowerCase() + '/(?<remaining>.*)'"
                replacement: "'/${remaining}'"

Note the values (ie args.pattern or args.regexp) are all Spring Expression Language (SpEL) expressions, hence the single quotes and + etc...

If different routes need to have different prefixes, you'd need to define each route in properties.

来源：https://stackoverflow.com/questions/54104281/how-to-remove-the-gobal-prefix-api-then-goto-the-lb-when-migrate-to-sp