Java tutorial
/* * Copyright 2002-2019 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.util; import java.net.DatagramSocket; import java.net.InetAddress; import java.net.ServerSocket; import java.util.Random; import java.util.SortedSet; import java.util.TreeSet; import javax.net.ServerSocketFactory; /** * Simple utility methods for working with network sockets — for example, * for finding available ports on {@code localhost}. * * <p>Within this class, a TCP port refers to a port for a {@link ServerSocket}; * whereas, a UDP port refers to a port for a {@link DatagramSocket}. * * @author Sam Brannen * @author Ben Hale * @author Arjen Poutsma * @author Gunnar Hillert * @author Gary Russell * @since 4.0 */ public class SocketUtils { /** * The default minimum value for port ranges used when finding an available * socket port. */ public static final int PORT_RANGE_MIN = 1024; /** * The default maximum value for port ranges used when finding an available * socket port. */ public static final int PORT_RANGE_MAX = 65535; private static final Random random = new Random(System.currentTimeMillis()); /** * Although {@code SocketUtils} consists solely of static utility methods, * this constructor is intentionally {@code public}. * <h4>Rationale</h4> * <p>Static methods from this class may be invoked from within XML * configuration files using the Spring Expression Language (SpEL) and the * following syntax. * <pre><code><bean id="bean1" ... p:port="#{T(org.springframework.util.SocketUtils).findAvailableTcpPort(12000)}" /></code></pre> * If this constructor were {@code private}, you would be required to supply * the fully qualified class name to SpEL's {@code T()} function for each usage. * Thus, the fact that this constructor is {@code public} allows you to reduce * boilerplate configuration with SpEL as can be seen in the following example. * <pre><code><bean id="socketUtils" class="org.springframework.util.SocketUtils" /> * <bean id="bean1" ... p:port="#{socketUtils.findAvailableTcpPort(12000)}" /> * <bean id="bean2" ... p:port="#{socketUtils.findAvailableTcpPort(30000)}" /></code></pre> */ public SocketUtils() { } /** * Find an available TCP port randomly selected from the range * [{@value #PORT_RANGE_MIN}, {@value #PORT_RANGE_MAX}]. * @return an available TCP port number * @throws IllegalStateException if no available port could be found */ public static int findAvailableTcpPort() { return findAvailableTcpPort(PORT_RANGE_MIN); } /** * Find an available TCP port randomly selected from the range * [{@code minPort}, {@value #PORT_RANGE_MAX}]. * @param minPort the minimum port number * @return an available TCP port number * @throws IllegalStateException if no available port could be found */ public static int findAvailableTcpPort(int minPort) { return findAvailableTcpPort(minPort, PORT_RANGE_MAX); } /** * Find an available TCP port randomly selected from the range * [{@code minPort}, {@code maxPort}]. * @param minPort the minimum port number * @param maxPort the maximum port number * @return an available TCP port number * @throws IllegalStateException if no available port could be found */ public static int findAvailableTcpPort(int minPort, int maxPort) { return SocketType.TCP.findAvailablePort(minPort, maxPort); } /** * Find the requested number of available TCP ports, each randomly selected * from the range [{@value #PORT_RANGE_MIN}, {@value #PORT_RANGE_MAX}]. * @param numRequested the number of available ports to find * @return a sorted set of available TCP port numbers * @throws IllegalStateException if the requested number of available ports could not be found */ public static SortedSet<Integer> findAvailableTcpPorts(int numRequested) { return findAvailableTcpPorts(numRequested, PORT_RANGE_MIN, PORT_RANGE_MAX); } /** * Find the requested number of available TCP ports, each randomly selected * from the range [{@code minPort}, {@code maxPort}]. * @param numRequested the number of available ports to find * @param minPort the minimum port number * @param maxPort the maximum port number * @return a sorted set of available TCP port numbers * @throws IllegalStateException if the requested number of available ports could not be found */ public static SortedSet<Integer> findAvailableTcpPorts(int numRequested, int minPort, int maxPort) { return SocketType.TCP.findAvailablePorts(numRequested, minPort, maxPort); } /** * Find an available UDP port randomly selected from the range * [{@value #PORT_RANGE_MIN}, {@value #PORT_RANGE_MAX}]. * @return an available UDP port number * @throws IllegalStateException if no available port could be found */ public static int findAvailableUdpPort() { return findAvailableUdpPort(PORT_RANGE_MIN); } /** * Find an available UDP port randomly selected from the range * [{@code minPort}, {@value #PORT_RANGE_MAX}]. * @param minPort the minimum port number * @return an available UDP port number * @throws IllegalStateException if no available port could be found */ public static int findAvailableUdpPort(int minPort) { return findAvailableUdpPort(minPort, PORT_RANGE_MAX); } /** * Find an available UDP port randomly selected from the range * [{@code minPort}, {@code maxPort}]. * @param minPort the minimum port number * @param maxPort the maximum port number * @return an available UDP port number * @throws IllegalStateException if no available port could be found */ public static int findAvailableUdpPort(int minPort, int maxPort) { return SocketType.UDP.findAvailablePort(minPort, maxPort); } /** * Find the requested number of available UDP ports, each randomly selected * from the range [{@value #PORT_RANGE_MIN}, {@value #PORT_RANGE_MAX}]. * @param numRequested the number of available ports to find * @return a sorted set of available UDP port numbers * @throws IllegalStateException if the requested number of available ports could not be found */ public static SortedSet<Integer> findAvailableUdpPorts(int numRequested) { return findAvailableUdpPorts(numRequested, PORT_RANGE_MIN, PORT_RANGE_MAX); } /** * Find the requested number of available UDP ports, each randomly selected * from the range [{@code minPort}, {@code maxPort}]. * @param numRequested the number of available ports to find * @param minPort the minimum port number * @param maxPort the maximum port number * @return a sorted set of available UDP port numbers * @throws IllegalStateException if the requested number of available ports could not be found */ public static SortedSet<Integer> findAvailableUdpPorts(int numRequested, int minPort, int maxPort) { return SocketType.UDP.findAvailablePorts(numRequested, minPort, maxPort); } private enum SocketType { TCP { @Override protected boolean isPortAvailable(int port) { try { ServerSocket serverSocket = ServerSocketFactory.getDefault().createServerSocket(port, 1, InetAddress.getByName("localhost")); serverSocket.close(); return true; } catch (Exception ex) { return false; } } }, UDP { @Override protected boolean isPortAvailable(int port) { try { DatagramSocket socket = new DatagramSocket(port, InetAddress.getByName("localhost")); socket.close(); return true; } catch (Exception ex) { return false; } } }; /** * Determine if the specified port for this {@code SocketType} is * currently available on {@code localhost}. */ protected abstract boolean isPortAvailable(int port); /** * Find a pseudo-random port number within the range * [{@code minPort}, {@code maxPort}]. * @param minPort the minimum port number * @param maxPort the maximum port number * @return a random port number within the specified range */ private int findRandomPort(int minPort, int maxPort) { int portRange = maxPort - minPort; return minPort + random.nextInt(portRange + 1); } /** * Find an available port for this {@code SocketType}, randomly selected * from the range [{@code minPort}, {@code maxPort}]. * @param minPort the minimum port number * @param maxPort the maximum port number * @return an available port number for this socket type * @throws IllegalStateException if no available port could be found */ int findAvailablePort(int minPort, int maxPort) { Assert.isTrue(minPort > 0, "'minPort' must be greater than 0"); Assert.isTrue(maxPort >= minPort, "'maxPort' must be greater than or equal to 'minPort'"); Assert.isTrue(maxPort <= PORT_RANGE_MAX, "'maxPort' must be less than or equal to " + PORT_RANGE_MAX); int portRange = maxPort - minPort; int candidatePort; int searchCounter = 0; do { if (searchCounter > portRange) { throw new IllegalStateException(String.format( "Could not find an available %s port in the range [%d, %d] after %d attempts", name(), minPort, maxPort, searchCounter)); } candidatePort = findRandomPort(minPort, maxPort); searchCounter++; } while (!isPortAvailable(candidatePort)); return candidatePort; } /** * Find the requested number of available ports for this {@code SocketType}, * each randomly selected from the range [{@code minPort}, {@code maxPort}]. * @param numRequested the number of available ports to find * @param minPort the minimum port number * @param maxPort the maximum port number * @return a sorted set of available port numbers for this socket type * @throws IllegalStateException if the requested number of available ports could not be found */ SortedSet<Integer> findAvailablePorts(int numRequested, int minPort, int maxPort) { Assert.isTrue(minPort > 0, "'minPort' must be greater than 0"); Assert.isTrue(maxPort > minPort, "'maxPort' must be greater than 'minPort'"); Assert.isTrue(maxPort <= PORT_RANGE_MAX, "'maxPort' must be less than or equal to " + PORT_RANGE_MAX); Assert.isTrue(numRequested > 0, "'numRequested' must be greater than 0"); Assert.isTrue((maxPort - minPort) >= numRequested, "'numRequested' must not be greater than 'maxPort' - 'minPort'"); SortedSet<Integer> availablePorts = new TreeSet<>(); int attemptCount = 0; while ((++attemptCount <= numRequested + 100) && availablePorts.size() < numRequested) { availablePorts.add(findAvailablePort(minPort, maxPort)); } if (availablePorts.size() != numRequested) { throw new IllegalStateException( String.format("Could not find %d available %s ports in the range [%d, %d]", numRequested, name(), minPort, maxPort)); } return availablePorts; } } }