This is a limited form of {@code SocketUtils} which is deprecated in Spring + * Framework 5.3 and removed in Spring Framework 6.0. + * + *
{@code SocketUtils} was introduced in Spring Framework 4.0, primarily to + * assist in writing integration tests which start an external server on an + * available random port. However, these utilities make no guarantee about the + * subsequent availability of a given port and are therefore unreliable (the reason + * for deprecation and removal). + * + *
Instead of using {@code TestSocketUtils} to find an available local port for a server,
+ * it is recommended that you rely on a server's ability to start on a random port
+ * that it selects or is assigned by the operating system. To interact with that
+ * server, you should query the server for the port it is currently using.
+ *
+ * @author Sam Brannen
+ * @author Ben Hale
+ * @author Arjen Poutsma
+ * @author Gunnar Hillert
+ * @author Gary Russell
+ * @author Chris Bono
+ * @since 5.3
+ */
+public final class TestSocketUtils {
+
+ /**
+ * The minimum value for port ranges used when finding an available TCP port.
+ */
+ private static final int PORT_RANGE_MIN = 1024;
+
+ /**
+ * The maximum value for port ranges used when finding an available TCP port.
+ */
+ private static final int PORT_RANGE_MAX = 65535;
+
+ private static final int PORT_RANGE = PORT_RANGE_MAX - PORT_RANGE_MIN;
+
+ private static final int MAX_ATTEMPTS = 1_000;
+
+ private static final Random random = new Random(System.nanoTime());
+
+ private TestSocketUtils() {
+ }
+
+ /**
+ * Find an available TCP port randomly selected from the range [1024, 65535].
+ * @return an available TCP port number
+ * @throws IllegalStateException if no available port could be found within max attempts
+ */
+ public static int findAvailableTcpPort() {
+ int candidatePort;
+ int searchCounter = 0;
+ do {
+ if (searchCounter > MAX_ATTEMPTS) {
+ throw new IllegalStateException(String.format(
+ "Could not find an available TCP port in the range [%d, %d] after %d attempts",
+ PORT_RANGE_MIN, PORT_RANGE_MAX, MAX_ATTEMPTS));
+ }
+ candidatePort = PORT_RANGE_MIN + random.nextInt(PORT_RANGE + 1);
+ searchCounter++;
+ }
+ while (!isPortAvailable(candidatePort));
+
+ return candidatePort;
+ }
+
+ /**
+ * Determine if the specified TCP port is currently available on {@code localhost}.
+ */
+ private static boolean isPortAvailable(int port) {
+ try {
+ ServerSocket serverSocket = ServerSocketFactory.getDefault().createServerSocket(
+ port, 1, InetAddress.getByName("localhost"));
+ serverSocket.close();
+ return true;
+ }
+ catch (Exception ex) {
+ return false;
+ }
+ }
+
+}
diff --git a/spring-test/src/test/java/org/springframework/test/util/TestSocketUtilsTests.java b/spring-test/src/test/java/org/springframework/test/util/TestSocketUtilsTests.java
new file mode 100644
index 000000000000..b4879a18cfec
--- /dev/null
+++ b/spring-test/src/test/java/org/springframework/test/util/TestSocketUtilsTests.java
@@ -0,0 +1,55 @@
+/*
+ * Copyright 2002-2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.test.util;
+
+import javax.net.ServerSocketFactory;
+
+import org.junit.jupiter.api.Test;
+import org.mockito.MockedStatic;
+import org.mockito.Mockito;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
+
+/**
+ * Unit tests for {@link TestSocketUtils}.
+ *
+ * @author Sam Brannen
+ * @author Gary Russell
+ * @author Chris Bono
+ */
+class TestSocketUtilsTests {
+
+ @Test
+ void findAvailableTcpPort() {
+ int port = TestSocketUtils.findAvailableTcpPort();
+ assertThat(port >= 1024).as("port [" + port + "] >= " + 1024).isTrue();
+ assertThat(port <= 65535).as("port [" + port + "] <= " + 65535).isTrue();
+ }
+
+ @Test
+ void findAvailableTcpPortWhenNoAvailablePortFoundInMaxAttempts() {
+ try (MockedStatic