How to convert a subdomain to a path with Embedded Tomcat 8 and Spring boot

Question

How to rewrite subdomains to paths?

Example:

• foo.bar .example.com --> example.com /foo/bar

Or better would be (reverse folders):

• foo.bar .example.com --> example.com /bar/foo

Requesting foo.bar .example.com should ship a file in /src/main/resources/static/ bar/foo /index.html.

With Apache2 it is done by mod_rewrite. I found documentation about rewriting with Tomcat 8 but the question is where to put this files using spring boot?

---

Update

I tried using the UrlRewriteFilter, but it seems not possible to define rules in the domain path using regexes substitution.

This is my configuration:

Maven Dependency:

<dependency>
    <groupId>org.tuckey</groupId>
    <artifactId>urlrewritefilter</artifactId>
    <version>4.0.3</version>
</dependency>

Spring Java Config to register the Servlet Filter:

@Configuration
@ComponentScan
@EnableAutoConfiguration
public class Application
{
    public static void main(String[] args)
    {
        SpringApplication.run(Application.class, args);
    }

    @Bean
    public FilterRegistrationBean filterRegistrationBean()
    {
        FilterRegistrationBean registrationBean = new FilterRegistrationBean();

        registrationBean.setFilter(new UrlRewriteFilter());
        registrationBean.addUrlPatterns("*");
        registrationBean.addInitParameter("confReloadCheckInterval", "5");
        registrationBean.addInitParameter("logLevel", "DEBUG");

        return registrationBean;
    }
}

urlrewrite.xml in /src/main/webapp/WEB-INF

<?xml version="1.0" encoding="utf-8"?>

<!DOCTYPE urlrewrite
    PUBLIC "-//tuckey.org//DTD UrlRewrite 4.0//EN"
    "http://www.tuckey.org/res/dtds/urlrewrite4.0.dtd">

<urlrewrite>
    <rule>
        <name>Translate</name>
        <condition name="host" operator="equal">foo.bar.example.com</condition>
        <from>^(.*)</from>
        <to type="redirect">example.com/bar/foo</to>
    </rule>
</urlrewrite>

With this hardcoded domain it works, but it should work for every subdomain like this.

Answer 1

Create you own Filter.

This Filter should:

• check if you have to rewrite your request
• If yes, rewrite URL and URI
• forward request
• it comes again through same filter, but first check will deliver false
• don't forget and be carefull to call chain.doFilter

Forwarding will not change any URLs in browser. Just ship content of file.

Follow code could be implementation of such filter. This is not any kind of clean code. Just quick and dirty working code:

@Component
public class SubdomainToReversePathFilter implements Filter {
    @Override
    public void doFilter(final ServletRequest request, final ServletResponse response, final FilterChain chain) throws IOException, ServletException {
        final HttpServletRequest req = (HttpServletRequest) request;
        final String requestURI = req.getRequestURI();

        if (!requestURI.endsWith("/")) {
            chain.doFilter(request, response);
        } else {
            final String servername = req.getServerName();
            final Domain domain = getDomain(servername);

            if (domain.hasSubdomain()) {
                final HttpServletRequestWrapper wrapped = wrapServerName(req, domain);
                wrapped.getRequestDispatcher(requestURI + domain.getSubdomainAsPath()).forward(wrapped, response);
            } else {
                chain.doFilter(request, response);
            }
        }
    }

    private Domain getDomain(final String domain) {
        final String[] domainParts = domain.split("\\.");
        String mainDomain;
        String subDomain = null;

        final int dpLength = domainParts.length;
        if (dpLength > 2) {
            mainDomain = domainParts[dpLength - 2] + "." + domainParts[dpLength - 1];

            subDomain = reverseDomain(domainParts);
        } else {
            mainDomain = domain;
        }

        return new Domain(mainDomain, subDomain);
    }
    private HttpServletRequestWrapper wrapServerName(final HttpServletRequest req, final Domain domain) {
        return new HttpServletRequestWrapper(req) {
            @Override
            public String getServerName() {
                return domain.getMaindomain();
            }
            // more changes? getRequesetURL()? ...?
        };
    }

    private String reverseDomain(final String[] domainParts) {
        final List<String> subdomainList = Arrays.stream(domainParts, 0, domainParts.length - 2)//
                .collect(Collectors.toList());

        Collections.reverse(subdomainList);

        return subdomainList.stream().collect(Collectors.joining("."));
    }

    @Override
    public void init(final FilterConfig filterConfig) throws ServletException {
    }

    @Override
    public void destroy() {
    }
}

Here is Domain class:

public static class Domain {
    private final String maindomain;
    private final String subdomain;

    public Domain(final String maindomain, final String subdomain) {
        this.maindomain = maindomain;
        this.subdomain = subdomain;
    }

    public String getMaindomain() {
        return maindomain;
    }

    public String getSubdomain() {
        return subdomain;
    }

    public boolean hasSubdomain() {
        return subdomain != null;
    }

    public String getSubdomainAsPath() {
        return "/" + subdomain.replaceAll("\\.", "/") + "/";
    }
}

And you need a Controller that catches everything

@RestController
public class CatchAllController {

    @RequestMapping("**")
    public FileSystemResource deliver(final HttpServletRequest request) {
        final String file = ((String) request.getAttribute(HandlerMapping.PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE));

        return new FileSystemResource(getStaticFile(file));
    }

    private File getStaticFile(final String path) {
        try {
            // TODO handle correct
            return new File(CatchAllController.class.getResource("/static/" + path + "/index.html").toURI());
        } catch (final Exception e) {
            throw new RuntimeException("not found");
        }
    }
}

I'm not sure if this is necessary to override other methods in HttpServletRequestWrapper. That's reason for comment.

Also you have to handle cases for file delivery (not existent, ...).

Answer 2

You can use Backreferences to use grouped parts that matched in your <condition>. Something like this -

<condition name="host" operator="equal">(*).(*).example.com</condition>
<from>^(.*)</from>
<to type="redirect">example.com/%1/%2</to>

Of course, you'll have to tweak the condition rule above to stop eager matching.

More here - http://urlrewritefilter.googlecode.com/svn/trunk/src/doc/manual/4.0/index.html#condition