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# Network Operations
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Network utilities for IP address handling, port management, and network validation. These utilities provide comprehensive networking support for microservices, including local address detection, hostname resolution, and URL formatting for both IPv4 and IPv6 environments.
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## Capabilities
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### Network Utilities
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Comprehensive network operations for IP address handling, validation, and network discovery.
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```java { .api }
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/**
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 * Network utilities for IP address handling and validation
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 */
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public class NetUtils {
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    public static final String LOCALHOST = "127.0.0.1";
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    public static final String ANYHOST = "0.0.0.0";
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    // Host validation
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    public static boolean isInvalidLocalHost(String host);
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    public static boolean isValidLocalHost(String host);
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    public static boolean isValidAddress(String address);
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    public static boolean isValidAddress(InetAddress address);
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    // Local address discovery
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    public static InetAddress getLocalAddress();
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    public static InetAddress getLocalAddress(Map<String, Integer> destHostPorts);
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    public static String getLocalAddressByDatagram();
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    // Network operations
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    public static String getHostName(SocketAddress socketAddress);
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    public static int getAvailablePort();
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    // URL formatting
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    public static String hostAndPortToUrlString(String host, int port);
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    public static String ipAddressAndPortToUrlString(InetAddress address, int port);
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    public static String ipAddressToUrlString(InetAddress address);
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    // DNS resolution
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    public static String resolveHost2Address(String fqdn);
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    public static URI resolveUriHost2Address(URI uri);
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}
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```
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**Usage Examples:**
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```java
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import com.networknt.utility.NetUtils;
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import java.net.InetAddress;
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import java.net.URI;
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// Local address discovery
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InetAddress localAddr = NetUtils.getLocalAddress();
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String localIP = NetUtils.getLocalAddressByDatagram();
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// Host validation
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boolean isValid = NetUtils.isValidLocalHost("192.168.1.100"); // true
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boolean isInvalid = NetUtils.isInvalidLocalHost("0.0.0.0"); // true
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// Port management
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int availablePort = NetUtils.getAvailablePort(); // e.g., 8080
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// URL formatting
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String url = NetUtils.hostAndPortToUrlString("localhost", 8080); // "localhost:8080"
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String ipUrl = NetUtils.ipAddressToUrlString(InetAddress.getByName("192.168.1.1")); // "192.168.1.1"
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// IPv6 handling
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InetAddress ipv6 = InetAddress.getByName("2001:db8::1");
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String ipv6Url = NetUtils.ipAddressToUrlString(ipv6); // "[2001:db8::1]"
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// DNS resolution
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String resolved = NetUtils.resolveHost2Address("example.com"); // "93.184.216.34"
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URI resolvedUri = NetUtils.resolveUriHost2Address(URI.create("http://example.com/path"));
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// Advanced local address detection with destination mapping
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Map<String, Integer> destinations = Map.of(
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    "api.service.com", 443,
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    "db.service.com", 5432
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);
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InetAddress bestLocal = NetUtils.getLocalAddress(destinations);
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```
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### Use Cases
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**Microservice Discovery:**
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```java
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// Find best local interface for service registration
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InetAddress serviceAddr = NetUtils.getLocalAddress();
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int servicePort = NetUtils.getAvailablePort();
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String serviceUrl = NetUtils.ipAddressAndPortToUrlString(serviceAddr, servicePort);
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```
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**Load Balancer Health Checks:**
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```java
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// Validate health check source addresses
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boolean isValidSource = NetUtils.isValidAddress("10.0.1.50");
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String sourceName = NetUtils.getHostName(socketAddress);
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```
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**Service Configuration:**
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```java
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// Resolve configuration hostnames to IP addresses
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String dbHost = "database.internal.com";
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String dbIp = NetUtils.resolveHost2Address(dbHost);
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String connectionUrl = "jdbc:postgresql://" + dbIp + ":5432/mydb";
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```
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**IPv6 Support:**
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```java
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// Handle both IPv4 and IPv6 addresses in URL construction
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InetAddress address = InetAddress.getByName(hostString);
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String urlSafeAddress = NetUtils.ipAddressToUrlString(address);
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// IPv4: "192.168.1.1" -> "192.168.1.1"
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// IPv6: "2001:db8::1" -> "[2001:db8::1]"
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```