Add property to limit maximum connections for Jetty

Closes gh-35899

Author: mhalbritter

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/ServerProperties.java

@@ -1123,6 +1123,12 @@ public static class Jetty {
 		 */
 		private DataSize maxHttpResponseHeaderSize = DataSize.ofKilobytes(8);
 
+		/**
+		 * Maximum number of connections that the server accepts and processes at any
+		 * given time.
+		 */
+		private int maxConnections = -1;
+
 		public Accesslog getAccesslog() {
 			return this.accesslog;
 		}
@@ -1155,6 +1161,14 @@ public void setMaxHttpResponseHeaderSize(DataSize maxHttpResponseHeaderSize) {
 			this.maxHttpResponseHeaderSize = maxHttpResponseHeaderSize;
 		}
 
+		public int getMaxConnections() {
+			return this.maxConnections;
+		}
+
+		public void setMaxConnections(int maxConnections) {
+			this.maxConnections = maxConnections;
+		}
+
 		/**
 		 * Jetty access log properties.
 		 */

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/embedded/JettyWebServerFactoryCustomizer.java

@@ -81,6 +81,7 @@ public void customize(ConfigurableJettyWebServerFactory factory) {
 		ServerProperties.Jetty.Threads threadProperties = properties.getThreads();
 		factory.setThreadPool(determineThreadPool(properties.getThreads()));
 		PropertyMapper map = PropertyMapper.get().alwaysApplyingWhenNonNull();
+		map.from(properties::getMaxConnections).to(factory::setMaxConnections);
 		map.from(threadProperties::getAcceptors).to(factory::setAcceptors);
 		map.from(threadProperties::getSelectors).to(factory::setSelectors);
 		map.from(this.serverProperties::getMaxHttpRequestHeaderSize)

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/jetty/ConfigurableJettyWebServerFactory.java

@@ -25,6 +25,7 @@
  * {@link ConfigurableWebServerFactory} for Jetty-specific features.
  *
  * @author Brian Clozel
+ * @author Moritz Halbritter
  * @since 2.0.0
  * @see JettyServletWebServerFactory
  * @see JettyReactiveWebServerFactory
@@ -63,4 +64,11 @@ public interface ConfigurableJettyWebServerFactory extends ConfigurableWebServer
 	 */
 	void addServerCustomizers(JettyServerCustomizer... customizers);
 
+	/**
+	 * Sets the maximum number of concurrent connections.
+	 * @param maxConnections the maximum number of concurrent connections
+	 * @since 3.2.0
+	 */
+	void setMaxConnections(int maxConnections);
+
 }

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/jetty/JettyReactiveWebServerFactory.java

@@ -29,6 +29,7 @@
 import org.eclipse.jetty.http2.server.HTTP2CServerConnectionFactory;
 import org.eclipse.jetty.server.AbstractConnector;
 import org.eclipse.jetty.server.ConnectionFactory;
+import org.eclipse.jetty.server.ConnectionLimit;
 import org.eclipse.jetty.server.Handler;
 import org.eclipse.jetty.server.HttpConfiguration;
 import org.eclipse.jetty.server.HttpConnectionFactory;
@@ -55,6 +56,7 @@
  * {@link ReactiveWebServerFactory} that can be used to create {@link JettyWebServer}s.
  *
  * @author Brian Clozel
+ * @author Moritz Halbritter
  * @since 2.0.0
  */
 public class JettyReactiveWebServerFactory extends AbstractReactiveWebServerFactory
@@ -80,6 +82,8 @@ public class JettyReactiveWebServerFactory extends AbstractReactiveWebServerFact
 
 	private ThreadPool threadPool;
 
+	private int maxConnections = -1;
+
 	/**
 	 * Create a new {@link JettyServletWebServerFactory} instance.
 	 */
@@ -118,6 +122,11 @@ public void addServerCustomizers(JettyServerCustomizer... customizers) {
 		this.jettyServerCustomizers.addAll(Arrays.asList(customizers));
 	}
 
+	@Override
+	public void setMaxConnections(int maxConnections) {
+		this.maxConnections = maxConnections;
+	}
+
 	/**
 	 * Sets {@link JettyServerCustomizer}s that will be applied to the {@link Server}
 	 * before it is started. Calling this method will replace any existing customizers.
@@ -180,6 +189,9 @@ protected Server createJettyServer(JettyHttpHandlerAdapter servlet) {
 		contextHandler.addServlet(servletHolder, "/");
 		server.setHandler(addHandlerWrappers(contextHandler));
 		JettyReactiveWebServerFactory.logger.info("Server initialized with port: " + port);
+		if (this.maxConnections > -1) {
+			server.addBean(new ConnectionLimit(this.maxConnections, server));
+		}
 		if (Ssl.isEnabled(getSsl())) {
 			customizeSsl(server, address);
 		}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/jetty/JettyServletWebServerFactory.java

@@ -43,6 +43,7 @@
 import org.eclipse.jetty.http2.server.HTTP2CServerConnectionFactory;
 import org.eclipse.jetty.server.AbstractConnector;
 import org.eclipse.jetty.server.ConnectionFactory;
+import org.eclipse.jetty.server.ConnectionLimit;
 import org.eclipse.jetty.server.Connector;
 import org.eclipse.jetty.server.Handler;
 import org.eclipse.jetty.server.HttpConfiguration;
@@ -101,6 +102,7 @@
  * @author Eddú Meléndez
  * @author Venil Noronha
  * @author Henri Kerola
+ * @author Moritz Halbritter
  * @since 2.0.0
  * @see #setPort(int)
  * @see #setConfigurations(Collection)
@@ -129,6 +131,8 @@ public class JettyServletWebServerFactory extends AbstractServletWebServerFactor
 
 	private ThreadPool threadPool;
 
+	private int maxConnections = -1;
+
 	/**
 	 * Create a new {@link JettyServletWebServerFactory} instance.
 	 */
@@ -163,6 +167,9 @@ public WebServer getWebServer(ServletContextInitializer... initializers) {
 		configureWebAppContext(context, initializers);
 		server.setHandler(addHandlerWrappers(context));
 		this.logger.info("Server initialized with port: " + port);
+		if (this.maxConnections > -1) {
+			server.addBean(new ConnectionLimit(this.maxConnections, server));
+		}
 		if (Ssl.isEnabled(getSsl())) {
 			customizeSsl(server, address);
 		}
@@ -458,6 +465,11 @@ public void setSelectors(int selectors) {
 		this.selectors = selectors;
 	}
 
+	@Override
+	public void setMaxConnections(int maxConnections) {
+		this.maxConnections = maxConnections;
+	}
+
 	/**
 	 * Sets {@link JettyServerCustomizer}s that will be applied to the {@link Server}
 	 * before it is started. Calling this method will replace any existing customizers.

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/web/embedded/jetty/JettyReactiveWebServerFactoryTests.java

@@ -22,6 +22,7 @@
 import java.util.Arrays;
 
 import org.awaitility.Awaitility;
+import org.eclipse.jetty.server.ConnectionLimit;
 import org.eclipse.jetty.server.Connector;
 import org.eclipse.jetty.server.Server;
 import org.eclipse.jetty.server.ServerConnector;
@@ -47,6 +48,7 @@
  *
  * @author Brian Clozel
  * @author Madhura Bhave
+ * @author Moritz Halbritter
  */
 @Servlet5ClassPathOverrides
 class JettyReactiveWebServerFactoryTests extends AbstractReactiveWebServerFactoryTests {
@@ -148,4 +150,15 @@ void whenServerIsShuttingDownGracefullyThenNewConnectionsCannotBeMade() {
 		this.webServer.stop();
 	}
 
+	@Test
+	void shouldApplyMaxConnections() {
+		JettyReactiveWebServerFactory factory = getFactory();
+		factory.setMaxConnections(1);
+		this.webServer = factory.getWebServer(new EchoHandler());
+		Server server = ((JettyWebServer) this.webServer).getServer();
+		ConnectionLimit connectionLimit = server.getBean(ConnectionLimit.class);
+		assertThat(connectionLimit).isNotNull();
+		assertThat(connectionLimit.getMaxConnections()).isOne();
+	}
+
 }

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/web/embedded/jetty/JettyServletWebServerFactoryTests.java

@@ -40,6 +40,7 @@
 import org.apache.hc.core5.http.HttpResponse;
 import org.apache.jasper.servlet.JspServlet;
 import org.awaitility.Awaitility;
+import org.eclipse.jetty.server.ConnectionLimit;
 import org.eclipse.jetty.server.Connector;
 import org.eclipse.jetty.server.Handler;
 import org.eclipse.jetty.server.Server;
@@ -86,6 +87,7 @@
  * @author Dave Syer
  * @author Andy Wilkinson
  * @author Henri Kerola
+ * @author Moritz Halbritter
  */
 @Servlet5ClassPathOverrides
 class JettyServletWebServerFactoryTests extends AbstractServletWebServerFactoryTests {
@@ -518,6 +520,17 @@ public void configure(WebAppContext context) throws Exception {
 		assertThat(context.getErrorHandler()).isInstanceOf(CustomErrorHandler.class);
 	}
 
+	@Test
+	void shouldApplyMaxConnections() {
+		JettyServletWebServerFactory factory = getFactory();
+		factory.setMaxConnections(1);
+		this.webServer = factory.getWebServer();
+		Server server = ((JettyWebServer) this.webServer).getServer();
+		ConnectionLimit connectionLimit = server.getBean(ConnectionLimit.class);
+		assertThat(connectionLimit).isNotNull();
+		assertThat(connectionLimit.getMaxConnections()).isOne();
+	}
+
 	private WebAppContext findWebAppContext(JettyWebServer webServer) {
 		return findWebAppContext(webServer.getServer().getHandler());
 	}