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| |
| <h1>MicroProfile Fault Tolerance - Fallback</h1> |
| </div> |
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| |
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| <div id="preamble"> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>This is an example of how to use Microprofile @Fallback in TomEE.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_fallback_feature">Fallback Feature</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>Fault Tolerance Fallback provides an alternative execution in case of failure. This alternative will be called when |
| <code>Retry</code> or <code>CircuitBreaker</code> has failed.</p> |
| </div> |
| <div class="paragraph"> |
| <p>To use this feature you need to annotate the method with <code>@Fallback</code>.</p> |
| </div> |
| <div class="paragraph"> |
| <p>The Fallback policy allows to configure :</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p><strong>value</strong>: A class which implements <code>FallbackHandler</code></p> |
| </li> |
| <li> |
| <p><strong>fallbackMethod</strong>: a method which will be executed.</p> |
| </li> |
| </ul> |
| </div> |
| <div class="paragraph"> |
| <p>The parameters <code>value</code> and <code>fallbackMethod</code> cannot be specified at the same time.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Check the <a href="http://download.eclipse.org/microprofile/microprofile-fault-tolerance-1.1/microprofile-fault-tolerance-spec.html">specification</a> for more details.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_examples">Examples</h2> |
| <div class="sectionbody"> |
| <div class="sect2"> |
| <h3 id="_run_the_application">Run the application</h3> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre>mvn clean install tomee:run</pre> |
| </div> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="_example_1">Example 1</h3> |
| <div class="paragraph"> |
| <p>The method <code>statusOfDay</code> will always fail throwing a <code>WeatherException</code> and as the |
| <code>@CircuitBreaker</code> annotation is configured to <code>failOn</code> in case of that exception, the fallback, |
| <code>WeatherDayStatusFallbackHandler#handle</code> will be invoked.</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="highlight"><code class="language-java" data-lang="java">@RequestScoped |
| public class WeatherService { |
| ... |
| @GET |
| @Path("/day/status") |
| @CircuitBreaker(failOn = WeatherException.class) |
| @Fallback(WeatherDayStatusFallbackHandler.class) |
| public String dayStatus() { |
| throw new WeatherException(); |
| } |
| ... |
| } |
| |
| public class WeatherDayStatusFallbackHandler implements FallbackHandler<String> { |
| |
| @Override |
| public String handle(ExecutionContext executionContext) { |
| return "Hi, today is a sunny day!"; |
| } |
| }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Day status call</p> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre>GET http://localhost:8080/mp-faulttolerance-fallback/weather/day/status</pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Server log</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="highlight"><code>SEVERE [http-nio-8080-exec-2] org.superbiz.rest.WeatherDayStatusFallbackHandler.handle WeatherDayStatusFallbackHandler was triggered due a fail</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Response</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="highlight"><code>Hi, today is a sunny day!</code></pre> |
| </div> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="_example_2">Example 2</h3> |
| <div class="paragraph"> |
| <p>The method <code>statusOfDay</code> will always fail throwing a <code>WeatherException</code> and as the |
| <code>@Retry</code> annotation is configured to <code>maxRetries = 1</code> in case of fail, the fallback method, |
| <code>fallbackForWeekStatus</code> will be invoked after retrying once.</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="highlight"><code class="language-java" data-lang="java">@RequestScoped |
| public class WeatherService { |
| ... |
| @GET |
| @Path("/week/status") |
| @Retry(maxRetries = 1) |
| @Fallback(fallbackMethod = "fallbackForWeekStatus") |
| public String weekStatus() { |
| throw new WeatherException(); |
| } |
| |
| public String fallbackForWeekStatus() { |
| return "Hi, week will be mostly sunny!"; |
| } |
| ... |
| }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Week status call</p> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre>GET http://localhost:8080/mp-faulttolerance-fallback/weather/week/status</pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Server log</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="highlight"><code>SEVERE [http-nio-8080-exec-2] org.superbiz.rest.WeatherService.fallbackForWeekStatus Fallback was triggered due a fail</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Response</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="highlight"><code>Hi, week will be mostly sunny!</code></pre> |
| </div> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="_run_the_tests">Run the tests</h3> |
| <div class="paragraph"> |
| <p>You can also try it out using the <a href="src/test/java/org/superbiz/rest/WeatherServiceTest.java">WeatherServiceTest.java</a> available in the project.</p> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre>mvn clean test</pre> |
| </div> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="highlight"><code>[INFO] Results: |
| [INFO] |
| [INFO] Tests run: 2, Failures: 0, Errors: 0, Skipped: 0</code></pre> |
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