Jersey(1.19.1) - Rules of Injection

Previous sections have presented examples of annotated types, mostly annotated method parameters but also annotated fields of a class, for the injection of values onto those types.

This section presents the rules of injection of values on annotated types. Injection can be performed on fields, constructor parameters, resource/sub-resource/sub-resource locator method parameters and bean setter methods. The following presents an example of all such injection cases:

@Path("id: \d+")
public class InjectedResource {
    // Injection onto field
    @DefaultValue("q") @QueryParam("p")
    private String p;

    // Injection onto constructor parameter
    public InjectedResource(@PathParam("id") int id) { ... }
    
    // Injection onto resource method parameter
    @GET
    public String get(@Context UriInfo ui) { ... }
    
    // Injection onto sub-resource resource method parameter
    @Path("sub-id")
    @GET
    public String get(@PathParam("sub-id") String id) { ... }
    
    // Injection onto sub-resource locator method parameter
    @Path("sub-id")
    public SubResource getSubResource(@PathParam("sub-id") String id) { ... }
    
    // Injection using bean setter method
    @HeaderParam("X-header")
    public void setHeader(String header) { ... }
}

There are some restrictions when injecting on to resource classes with a life-cycle other than per-request. In such cases it is not possible to injected onto fields for the annotations associated with extraction of request parameters. However, it is possible to use the @Context annotation on fields, in such cases a thread local proxy will be injected.

The @FormParam annotation is special and may only be utilized on resource and sub-resource methods. This is because it extracts information from a request entity.