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RESTEasy
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modified by <a href="https://community.jboss.org/people/Daffy">Nuwan Bandara</a> in <i>JBoss Web Services Development</i> - <a href="https://community.jboss.org/docs/DOC-48310">View the full document</a>
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<div class="jive-rendered-content"><h2>Purpose</h2><p>Purpose of the article is to show how to handle exception in RESTEasy. </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><h2>Solution</h2><p>RESTEasy provides such a exception handling mechanism which simplifies the exception handling process. RESTEasy ExceptionMappers are custom, application provided, components that can catch thrown application exceptions and write specific HTTP responses. The are classes annotated with @Provider and that implement this interface. </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>When an application exception is thrown it will be caught by the JAX-RS runtime. JAX-RS will then scan registered ExceptionMappers to see which one support marshalling the exception type thrown.</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><h2>How to Do?</h2><h4>High-Level Steps</h4><ul><li>Implements <span style="font-family: 'Lucida Grande', Arial, Helvetica, sans-serif; background-color: #ffffff;">ExceptionMapper</span></li><li><span style="font-family: 'Lucida Grande', Arial, Helvetica, sans-serif; background-color: #ffffff;">Register <span style="font-family: 'Lucida Grande', Arial, Helvetica, sans-serif; background-color: #ffffff;">ExceptionMapper</span> in the web.xml<br/></span></li><li><span style="font-family: 'Lucida Grande', Arial, Helvetica, sans-serif; background-color: #ffffff;">Create JAXB model class for the response (Optional)<br/></span></li><li><span style="font-family: 'Lucida Grande', Arial, Helvetica, sans-serif; background-color: #ffffff;">Create RESTEasy method<br/></span></li><li><span style="font-family: 'Lucida Grande', Arial, Helvetica, sans-serif; background-color: #ffffff;">WebService Output<br/></span></li></ul><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><h3><span style="color: #333333;">Implementation</span></h3><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>Create a exception handler/mapper to marshal the exception.</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><pre class="jive-pre"><code class="jive-code">package com.nuwan.poc.wsmodule.exception;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;
import javax.ws.rs.ext.ExceptionMapper;
import javax.ws.rs.ext.Provider;
/**
* User: Nuwan.N.Bandara
*/
@Provider
public class DefaultExceptionHandler implements ExceptionMapper<Exception> {
    @Override
    public Response toResponse(Exception e) {       
        // For simplicity I am preparing error xml by hand.
        // Ideally we should create an ErrorResponse class to hold the error info.
        StringBuilder response = new StringBuilder("<response>");
        response.append("<status>ERROR</status>");
        response.append("<message>" + e.getMessage() + "</message>");
        response.append("</response>");
        return Response.serverError().entity(response.toString()).type(MediaType.APPLICATION_XML).build();
    }
}
</code></pre><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>Register the <span style="font-family: 'Lucida Grande', Arial, Helvetica, sans-serif; background-color: #ffffff;">DefaultExceptionHandler </span>in your web.xml</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><pre class="jive-pre"><code class="jive-code"><context-param>
        <param-name>resteasy.providers</param-name>
        <param-value>com.nuwan.poc.wsmodule.exception.DefaultExceptionHandler</param-value>
</context-param></code></pre><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>Create JAXB model class for marshalling POJO to XML to produce the response. (This is optional)</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><pre class="jive-pre"><code class="jive-code">package com.nuwan.poc.wsmodule.model;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlElement;
import java.util.Date;
/**
* User: Nuwan.N.Bandara
*/
@XmlRootElement
public class Response {
    private long id;
    private String status;
    private String message;
    public long getId() {
        return (new Date()).getTime();
    }
    @XmlAttribute
    public void setId(long id) {
        this.id = id;
    }
    public String getStatus() {
        return status;
    }
    @XmlElement
    public void setStatus(String status) {
        this.status = status;
    }
    public String getMessage() {
        return message;
    }
    @XmlElement
    public void setMessage(String message) {
        this.message = message;
    }
}
</code></pre><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>Here's the RESTEasy web service method implementation. When method receives value 0, code hit the catch block and throws an <span style="font-family: 'Lucida Grande', Arial, Helvetica, sans-serif; background-color: #ffffff;">ArithmeticException</span>. Which is a type of an Exception that we have already handled in <span style="font-family: 'Lucida Grande', Arial, Helvetica, sans-serif; background-color: #ffffff;">DefaultExceptionHandler class.</span></p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><pre class="jive-pre"><code class="jive-code">
    @GET
    @Path("testWebService")
    @Produces({MediaType.APPLICATION_XML})
    public Response testWebService(int value) throws Exception {
        Response response = new Response();
        try {
            if((100 / value) > 0) {
                response.setStatus("OK");
                response.setMessage("Greater Than Zero");
            }
            else {
                response.setStatus("OK");
                response.setMessage("Less Than Zero");
            }
        }
        catch (ArithmeticException e) {
            throw new ArithmeticException("Division by zero!");
        }
        return response;
    }
</code></pre><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>Output of the web service would look like this;</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p style="padding-left: 30px;">Successful response output. <span style="font-family: 'Lucida Grande', Arial, Helvetica, sans-serif; background-color: #ffffff;">Response</span> class generates this XML.</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><pre class="jive-pre"><code class="jive-code"><response>
  <status>SUCCESSFUL</status>
  <message>Greater Than Zero</message>
</response></code></pre><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p style="padding-left: 30px;">Error response output. <span style="font-family: 'Lucida Grande', Arial, Helvetica, sans-serif; background-color: #ffffff;">DefaultExceptionHandler </span>toResponse() generates this XML.</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><pre class="jive-pre"><code class="jive-code"><response>
  <status>ERROR</status>
  <message>Division by zero!</message>
</response></code></pre><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><h2>Reference</h2><ul><li><a class="jive-link-external-small" href="http://docs.jboss.org/resteasy/docs/1.1.GA/userguide/html/ExceptionHandling.html#builtinException" rel="nofollow">Chapter 25. Exception Handling</a></li></ul></div>
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<p style="margin: 0;">Comment by <a href="https://community.jboss.org/docs/DOC-48310">going to Community</a></p>
<p style="margin: 0;">Create a new document in JBoss Web Services Development at <a href="https://community.jboss.org/choose-container!input.jspa?contentType=102&containerType=14&container=2047">Community</a></p>
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