https://github.com/spring-projects/spring-framework: Spring Core (Spring IO)
  • Juergen Hoeller 
/*
 * Copyright 2002-2020 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 localhost. 
Within this class, a TCP port refers to a port for a ServerSocket; whereas, a UDP port refers to a port for a DatagramSocket. 
Author:Sam Brannen, Ben Hale, Arjen Poutsma, Gunnar Hillert, Gary Russell
Since:4.0
/**
 * 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.

/**
	 * 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.

/**
	 * 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.nanoTime());


	
Although SocketUtils consists solely of static utility methods, this constructor is intentionally public. 
Rationale


Static methods from this class may be invoked from within XML
configuration files using the Spring Expression Language (SpEL) and the
following syntax.

<bean id="bean1" ... p:port="#{T(org.springframework.util.SocketUtils).findAvailableTcpPort(12000)}" />
 If this constructor were private, you would be required to supply the fully qualified class name to SpEL's T() function for each usage. Thus, the fact that this constructor is public allows you to reduce boilerplate configuration with SpEL as can be seen in the following example. 
<bean id="socketUtils" class="org.springframework.util.SocketUtils" />
<bean id="bean1" ... p:port="#{socketUtils.findAvailableTcpPort(12000)}" />
<bean id="bean2" ... p:port="#{socketUtils.findAvailableTcpPort(30000)}" />


/**
	 * 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>&lt;bean id="bean1" ... p:port="#{T(org.springframework.util.SocketUtils).findAvailableTcpPort(12000)}" /&gt;</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>&lt;bean id="socketUtils" class="org.springframework.util.SocketUtils" /&gt;
	 * &lt;bean id="bean1" ... p:port="#{socketUtils.findAvailableTcpPort(12000)}" /&gt;
	 * &lt;bean id="bean2" ... p:port="#{socketUtils.findAvailableTcpPort(30000)}" /&gt;</code></pre>
	 */
	public SocketUtils() {
	}


	
Find an available TCP port randomly selected from the range [1024, 65535]. 
Throws:
Returns:an available TCP port number
/**
	 * 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 [minPort, 65535]. 
Params:
  • minPort – the minimum port number
Throws:
Returns:an available TCP port number
/**
	 * 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 [minPort, maxPort]. 
Params:
  • minPort – the minimum port number
  • maxPort – the maximum port number
Throws:
Returns:an available TCP port number
/**
	 * 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 [1024, 65535]. 
Params:
  • numRequested – the number of available ports to find
Throws:
Returns:a sorted set of available TCP port numbers
/**
	 * 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 [minPort, maxPort]. 
Params:
  • numRequested – the number of available ports to find
  • minPort – the minimum port number
  • maxPort – the maximum port number
Throws:
Returns:a sorted set of available TCP port numbers
/**
	 * 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 [1024, 65535]. 
Throws:
Returns:an available UDP port number
/**
	 * 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 [minPort, 65535]. 
Params:
  • minPort – the minimum port number
Throws:
Returns:an available UDP port number
/**
	 * 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 [minPort, maxPort]. 
Params:
  • minPort – the minimum port number
  • maxPort – the maximum port number
Throws:
Returns:an available UDP port number
/**
	 * 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 [1024, 65535]. 
Params:
  • numRequested – the number of available ports to find
Throws:
Returns:a sorted set of available UDP port numbers
/**
	 * 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 [minPort, maxPort]. 
Params:
  • numRequested – the number of available ports to find
  • minPort – the minimum port number
  • maxPort – the maximum port number
Throws:
Returns:a sorted set of available UDP port numbers
/**
	 * 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 SocketType is currently available on localhost. 
/**
		 * 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 [minPort, maxPort]. 
Params:
  • minPort – the minimum port number
  • maxPort – the maximum port number
Returns:a random port number within the specified range
/**
		 * 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 SocketType, randomly selected from the range [minPort, maxPort]. 
Params:
  • minPort – the minimum port number
  • maxPort – the maximum port number
Throws:
Returns:an available port number for this socket type
/**
		 * 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 SocketType, each randomly selected from the range [minPort, maxPort]. 
Params:
  • numRequested – the number of available ports to find
  • minPort – the minimum port number
  • maxPort – the maximum port number
Throws:
Returns:a sorted set of available port numbers for this socket type
/**
		 * 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;
		}
	}

}