jdk.net.hosts.file Java System Property

Default Value

Empty - By default, if the jdk.net.hosts.file system property is not defined Java will use the default address resolution.

Overview of jdk.net.hosts.file

The jdk.net.hosts.file system property specifies a file system path to a file that provides DNS name resolution to the InetAddress methods getByAddress or getByName. The format of this file is the same as a /etc/hosts file, here's an example:

# comment
127.0.0.1   localhost
10.11.12.13 api.example.com

If the jdk.net.hosts.file system property points to a file path that does not exist, all DNS resolutions will fail with an UnknownHostException.

Other Networking System Properties

Here are some other networking Java system properties:

• http.agent
• http.keepAlive
• http.maxConnections
• https.protocols
• java.net.preferIPv4Stack
• java.net.preferIPv6Addresses
• java.net.useSystemProxies
• javax.net.debug
• javax.net.ssl.trustStore
• jdk.tls.client.protocols
• jdk.tls.disabledAlgorithms
• networkaddress.cache.negative.ttl
• networkaddress.cache.ttl
• sun.net.client.defaultConnectTimeout
• sun.net.client.defaultReadTimeout
• sun.net.inetaddr.ttl

Supported Since

Java has supported the jdk.net.hosts.file system property since Java 9.

Setting jdk.net.hosts.file on Startup

You can set the jdk.net.hosts.file java system property during startup of the java runtime using the -D command line argument:

java -Djdk.net.hosts.file=/path/to/hosts MyAppMain

You may also be able to specify jdk.net.hosts.file via the JAVA_TOOL_OPTIONS environment variable:

JAVA_TOOL_OPTIONS=-Djdk.net.hosts.file=/path/to/hosts

Setting / Reading jdk.net.hosts.file at Runtime

You can set jdk.net.hosts.file at runtime with the following Java code:

System.setProperty("jdk.net.hosts.file", "/path/to/hosts");

WARNING: Depending on the property and JVM version using setProperty may or may not work if the JDK Java class that uses this variable has already been loaded. The value of the jdk.net.hosts.file system property may be cached within an internal private static variable of the implementing class.

To read the value of jdk.net.hosts.file at runtime, you can use this Java code:

String propertyValue = System.getProperty("jdk.net.hosts.file");
if (propertyValue != null) {
    System.out.println("jdk.net.hosts.file = " + propertyValue);
} else {
    System.out.println("jdk.net.hosts.file was null");
}