The HTTP header fields provide the necessary information about the request and response contents in HTTP. For example, the header field, Content-Length: 348, for an HTTP request says that the size of the request body content is 348 octets (8-bit bytes). The @javax.ws.rs.HeaderParam annotation injects the header values present in the request into a class field, a resource class bean property (the getter method for accessing the attribute), or a method parameter.
The following example extracts the referrer header parameter and logs it for audit purposes. The referrer header field in HTTP contains the address of the previous web page from which a request to the currently processed page originated:
@POST
public void createDepartment(@HeaderParam("Referer")
String referer, Department entity) {
logSource(referer);
createDepartmentInDB(department);
}
Remember that HTTP provides a very wide selection of headers that cover most of the header parameters that you are looking for. Although you can use custom HTTP headers to pass some application-specific data to the server, try using standard headers whenever possible. Furthermore, avoid using a custom header for holding properties specific to a resource, the state of the resource, or parameters directly affecting the resource. For such scenarios, you can consider the other approaches discussed in this section, namely PathParam, QueryParam, or MatrixParam.