CODEWITHSUNDEEP
javarestjersey
Joeblackdev
Joeblackdev

Reputation: 7327

Jersey - The @Context annotation for injection. How does it work?

I was looking at a good REST tutorial using Jersey. Down the page, there is a web resource that is built which is entitled TodoResource which itself contains two instance variables

public class TodoResource {
    @Context
    UriInfo uriInfo;

    @Context
    Request request;

    String id;

    public TodoResource(UriInfo uriInfo, Request request, String id) {
        this.uriInfo = uriInfo;
        this.request = request;
        this.id = id;
    }
}

I was wondering exactly how the UriInfo and Request instance variables are initialized? I know that using the @Context annotation allows for information to be injected, but at what point does this happen? Will this be handled automatically by Jersey?

Upvotes: 37

Views: 69056

Answers (3)

Mike Summers
Mike Summers

Reputation: 2239

I've run into some interesting results with the Rules of Injection, here's what I've found:

public class TodoResource{
  @Context
  UriInfo uriInfo; // Set second
  public TodoResource(@Context UriInfo value){
    uriInfo = value; // Set first (makes sense)
  }
  @Context
  public void setUriInfo(UriInfo value){
    uriInfo = value; // Set third
  }
}

I hope this helps.

Upvotes: 27

Kinjeiro
Kinjeiro

Reputation: 917

Use @PostConstruct method annotation:

import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;

@Path("foo")
public class AuthResource {
    @Context
    HttpServletRequest request;

    public AuthResource() {
        //request is null
    }

    @PostConstruct
    public void postConstruct() {
        //request is NOT null
    }

    @PreDestroy
    public void preDestroy() {
       //after rest method executing
    }
}

Upvotes: 16

java.is.for.desktop.indeed
java.is.for.desktop.indeed

Reputation: 1426

Jersey doesn't modify the class, but it creates it on every request from the client.

After the class constructor was invoked, the context fields are injected.
(Should you try to access those fields inside the constructor, they will be null)

In your case, the class wouldn't need a specific constructor, so just:

public TodoResource () {
    // in most cases the ctor stays empty.
    // don't do much work here, remember: the ctor is invoked at every client request
}

But inside methods (which represent web-resources) annotated with @POST, @GET, ... you would have access to context fields.

Upvotes: 23

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