Subresources and Runtime Resource Resolution
Java Platform, Enterprise Edition (Java EE) 8
The Java EE Tutorial

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Subresources and Runtime Resource Resolution

You can use a resource class to process only a part of the URI request. A root resource can then implement subresources that can process the remainder of the URI path.

A resource class method that is annotated with @Path is either a subresource method or a subresource locator.

  • A subresource method is used to handle requests on a subresource of the corresponding resource.

  • A subresource locator is used to locate subresources of the corresponding resource.

The following topics are addressed here:

Subresource Methods

A subresource method handles an HTTP request directly. The method must be annotated with a request method designator, such as @GET or @POST, in addition to @Path. The method is invoked for request URIs that match a URI template created by concatenating the URI template of the resource class with the URI template of the method.

The following code snippet shows how a subresource method can be used to extract the last name of an employee when the employee’s email address is provided:

@Path("/employeeinfo")
public class EmployeeInfo {

    public employeeinfo() {}

    @GET
    @Path("/employees/{firstname}.{lastname}@{domain}.com")
    @Produces("text/xml")
    public String getEmployeeLastName(@PathParam("lastname") String lastName) {
       ...
    }
}

The getEmployeeLastName method returns doe for the following GET request:

GET /employeeinfo/employees/john.doe@example.com

Subresource Locators

A subresource locator returns an object that will handle an HTTP request. The method must not be annotated with a request method designator. You must declare a subresource locator within a subresource class, and only subresource locators are used for runtime resource resolution.

The following code snippet shows a subresource locator:

// Root resource class
@Path("/employeeinfo")
public class EmployeeInfo {

    // Subresource locator: obtains the subresource Employee
    // from the path /employeeinfo/employees/{empid}
    @Path("/employees/{empid}")
    public Employee getEmployee(@PathParam("empid") String id) {
        // Find the Employee based on the id path parameter
        Employee emp = ...;
        ...
        return emp;
    }
}

// Subresource class
public class Employee {

    // Subresource method: returns the employee's last name
    @GET
    @Path("/lastname")
    public String getEmployeeLastName() {
        ...
        return lastName;
    }
}

In this code snippet, the getEmployee method is the subresource locator that provides the Employee object, which services requests for lastname.

If your HTTP request is GET /employeeinfo/employees/as209/, the getEmployee method returns an Employee object whose id is as209. At runtime, JAX-RS sends a GET /employeeinfo/employees/as209/lastname request to the getEmployeeLastName method. The getEmployeeLastName method retrieves and returns the last name of the employee whose id is as209.


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