added RestartServlet, which is able to trigger a complete restart of the context

scm-webapp/src/main/java/sonia/scm/boot/RestartServlet.java

@@ -0,0 +1,97 @@
+package sonia.scm.boot;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import sonia.scm.Priority;
+import sonia.scm.SCMContext;
+import sonia.scm.Stage;
+import sonia.scm.event.ScmEventBus;
+import sonia.scm.filter.WebElement;
+
+import javax.inject.Inject;
+import javax.servlet.http.HttpServlet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+/**
+ * This servlet sends a {@link RestartEvent} to the {@link ScmEventBus} which causes scm-manager to restart the context.
+ * The {@link RestartServlet} can be used for reloading java code or for installing plugins without a complete restart.
+ * At the moment the Servlet accepts only request, if scm-manager was started in the {@link Stage#DEVELOPMENT} stage.
+ *
+ * @since 2.0.0
+ */
+@Priority(0)
+@WebElement("/restart")
+public class RestartServlet extends HttpServlet {
+
+  private static final Logger LOG = LoggerFactory.getLogger(RestartServlet.class);
+
+  private final ObjectMapper objectMapper = new ObjectMapper();
+  private final AtomicBoolean restarting = new AtomicBoolean();
+
+  private final ScmEventBus eventBus;
+  private final Stage stage;
+
+  @Inject
+  public RestartServlet() {
+    this(ScmEventBus.getInstance(), SCMContext.getContext().getStage());
+  }
+
+  RestartServlet(ScmEventBus eventBus, Stage stage) {
+    this.eventBus = eventBus;
+    this.stage = stage;
+  }
+
+  @Override
+  protected void doPost(HttpServletRequest req, HttpServletResponse resp) {
+    LOG.info("received sendRestartEvent request");
+
+    if (isRestartAllowed()) {
+
+      try (InputStream requestInput = req.getInputStream()) {
+        Reason reason = objectMapper.readValue(requestInput, Reason.class);
+        sendRestartEvent(resp, reason);
+      } catch (IOException ex) {
+        LOG.warn("failed to trigger sendRestartEvent event", ex);
+        resp.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
+      }
+
+    } else {
+      LOG.debug("received restart event in non development stage");
+      resp.setStatus(HttpServletResponse.SC_NOT_ACCEPTABLE);
+    }
+  }
+
+  private boolean isRestartAllowed() {
+    return stage == Stage.DEVELOPMENT;
+  }
+
+  private void sendRestartEvent(HttpServletResponse response, Reason reason) {
+    if ( restarting.compareAndSet(false, true) ) {
+      LOG.info("trigger sendRestartEvent, because of {}", reason.getMessage());
+      eventBus.post(new RestartEvent(RestartServlet.class, reason.getMessage()));
+
+      response.setStatus(HttpServletResponse.SC_ACCEPTED);
+    } else {
+      LOG.warn("scm-manager restarts already");
+      response.setStatus(HttpServletResponse.SC_CONFLICT);
+    }
+  }
+
+  public static class Reason {
+
+    private String message;
+
+    public void setMessage(String message) {
+      this.message = message;
+    }
+
+    public String getMessage() {
+      return message;
+    }
+  }
+}