Jersey 2 filter uses Container Request Context in Client Request Filter

Question

I have a Jersey 2 Web Service that upon receiving a request, makes another request to another web service in order to form the response for the original request. So, when client "A" makes a request to my web service "B", "B" makes a request to "C" as part of forming the response to "A".

A->B->C

I want to implement a filter for a Jersey 2 web service that essentially does this:

• Client "A" will send a request that has a header like "My-Header:first"

• When my web service "B" then makes a client request "C", it should append to that header, so it sends a request with this header "My-Header:first,second".

I want to implement this as a filter so all of my resources don't have to duplicate the logic of appending to the request header.

However, in Jersey 2, you get these 4 filters:

• ContainerRequestFilter - Filter/modify inbound requests
• ContainerResponseFilter - Filter/modify outbound responses
• ClientRequestFilter - Filter/modify outbound requests
• ClientResponseFilter - Filter/modify inbound responses

I need to use the header from an inbound request, modify it, then use it an outbound request, so essentially I need something that is both a ContainerRequestFilter and a ClientRequestFilter. I don't think implementing both in the same filter will work, as you don't know which Client Request maps to which Container Request, or do you?

Answer 1

I found a nice way to do this that doesn't use ThreadLocal to communicate between the ContainerRequestFilter and the ClientRequestFilter, as you can't assume that client requests made in response to a container request will be on the same thread.

The way I achieved this is by setting a property in the ContainerRequestConext object in the ContainerRequestFilter. I can then pass the ContainerRequestContext object (either explicity or through dependency injection) into my ClientRequestFilter. If you use dependency injection (if you're using Jersey 2 then you are probably using HK2), then all of this can be achieved without modifying any of your resource level logic.

Have a ContainerRequestFilter like this:

public class RequestIdContainerFilter implements ContainerRequestFilter {

@Override
public void filter(ContainerRequestContext containerRequestContext) throws IOException {
    containerRequestContext.setProperty("property-name", "any-object-you-like");
}

And a ClientRequestFilter that takes a ContainerRequestContext in its constructor:

public class RequestIdClientRequestFilter implements ClientRequestFilter {

    private ContainerRequestContext containerRequestContext;

    public RequestIdClientRequestFilter(ContainerRequestContext containerRequestContext) {
        this.containerRequestContext = containerRequestContext;
    }

    @Override
    public void filter(ClientRequestContext clientRequestContext) throws IOException {
        String value = containerRequestContext.getProperty("property-name");
        clientRequestContext.getHeaders().putSingle("MyHeader", value);
    }
}

Then it's just a case of tying this all together. You will need a factory to create any Client or WebTarget that you need:

public class MyWebTargetFactory implements Factory<WebTarget> {

    @Context
    private ContainerRequestContext containerRequestContext;

    @Inject
    public MyWebTargetFactory(ContainerRequestContext containerRequestContext) {
        this.containerRequestContext = containerRequestContext;
    }

    @Override
    public WebTarget provide() {
        Client client = ClientBuilder.newClient();
        client.register(new RequestIdClientRequestFilter(containerRequestContext));
        return client.target("path/to/api");
    }

    @Override
    public void dispose(WebTarget target) {

    }
}

Then register the filter and bind your factory on your main application ResourceConfig:

public class MyApplication extends ResourceConfig {

    public MyApplication() {
        register(RequestIdContainerFilter.class);
        register(new AbstractBinder() {
            @Override
            protected void configure() {
                bindFactory(MyWebTargetFactory.class).to(WebTarget.class);
            }
        }
    }
}