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49.2. Using WebApplicationException exceptions to report errors
Overview
The JAX-RS API introduced the
WebApplicationException runtime exception to provide an easy way for resource methods to create exceptions that are appropriate for RESTful clients to consume. WebApplicationException exceptions can include a Response object that defines the entity body to return to the originator of the request. It also provides a mechanism for specifying the HTTP status code to be returned to the client if no entity body is provided.
Creating a simple exception
The easiest means of creating a
WebApplicationException exception is to use either the no argument constructor or the constructor that wraps the original exception in a WebApplicationException exception. Both constructors create a WebApplicationException with an empty response.
When an exception created by either of these constructors is thrown, the runtime returns a response with an empty entity body and a status code of
500 Server Error.
Setting the status code returned to the client
When you want to return an error code other than
500, you can use one of the four WebApplicationException constructors that allow you to specify the status. Two of these constructors, shown in Example 49.1, “Creating a WebApplicationException with a status code”, take the return status as an integer.
Example 49.1. Creating a WebApplicationException with a status code
WebApplicationException(int status);WebApplicationException(java.lang.Throwable cause,
int status);
The other two, shown in Example 49.2, “Creating a
WebApplicationException with a status code” take the response status as an instance of Response.Status.
Example 49.2. Creating a WebApplicationException with a status code
WebApplicationException(javax.ws.rs.core.Response.Status status);WebApplicationException(java.lang.Throwable cause,
javax.ws.rs.core.Response.Status status);
When an exception created by either of these constructors is thrown, the runtime returns a response with an empty entity body and the specified status code.
Providing an entity body
If you want a message to be sent along with the exception, you can use one of the
WebApplicationException constructors that takes a Response object. The runtime uses the Response object to create the response sent to the client. The entity stored in the response is mapped to the entity body of the message and the status field of the response is mapped to the HTTP status of the message.
Example 49.3, “Sending a message with an exception” shows code for returning a text message to a client containing the reason for the exception and sets the HTTP message status to
409 Conflict.
Example 49.3. Sending a message with an exception
import javax.ws.rs.core.Response;
import javax.ws.rs.WebApplicationException;
import org.apache.cxf.jaxrs.impl.ResponseBuilderImpl;
...
ResponseBuilderImpl builder = new ResponseBuilderImpl();
builder.status(Response.Status.CONFLICT);
builder.entity("The requested resource is conflicted.");
Response response = builder.build();
throw WebApplicationException(response);Extending the generic exception
It is possible to extend the
WebApplicationException exception. This would allow you to create custom exceptions and eliminate some boiler plate code.
Example 49.4, “Extending
WebApplicationException” shows a new exception that creates a similar response to the code in Example 49.3, “Sending a message with an exception”.
Example 49.4. Extending WebApplicationException
public class ConflicteddException extends WebApplicationException
{
public ConflictedException(String message)
{
ResponseBuilderImpl builder = new ResponseBuilderImpl();
builder.status(Response.Status.CONFLICT);
builder.entity(message);
super(builder.build());
}
}
...
throw ConflictedException("The requested resource is conflicted.");