java.net.URI get host with underscores

Question

I got a strange behavior of that method:

import java.net.URI

    URI url = new URI("https://pmi_artifacts_prod.s3.amazonaws.com");
    System.out.println(url.getHost()); /returns NULL
    URI url2 = new URI("https://s3.amazonaws.com");
    System.out.println(url2.getHost());  //returns s3.amazonaws.com

`

i want first url.getHost() to be pmi_artifacts_prod.s3.amazonaws.com, but it gives me NULL. Turned out that problem is with underscores in domain name, its a known bug, but still what can be done as I need to work with this host exactly?

Answer 1

https://en.wikipedia.org/wiki/Hostname#Restrictions_on_valid_hostnames

public static void main(String...a) throws URISyntaxException, NoSuchFieldException, SecurityException, IllegalArgumentException, IllegalAccessException {
    URI url = new URI("https://pmi_artifacts_prod.s3.amazonaws.com");
    System.out.println(url.getHost()); //NULL


    URI uriObj = new URI("https://pmi_artifacts_prod.s3.amazonaws.com");
    if (uriObj.getHost() == null) {
        final Field hostField = URI.class.getDeclaredField("host");
        hostField.setAccessible(true);
        hostField.set(uriObj, "pmi_artifacts_prod.s3.amazonaws.com");
    }
    System.out.println(uriObj.getHost()); //pmi_artifacts_prod.s3.amazonaws.com


    URI url2 = new URI("https://s3.amazonaws.com");
    System.out.println(url2.getHost());  //s3.amazonaws.com
}

Answer 2

Underscore support could be added right into URI by patching:

public static void main(String[] args) throws Exception {
    patchUriField(35184372088832L, "L_DASH");
    patchUriField(2147483648L, "H_DASH");

    URI s = URI.create("http://my_favorite_host:3892");
    // prints "my_favorite_host"
    System.out.println(s.getHost());
}

private static void patchUriField(String methodName, String fieldName)
        throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, NoSuchFieldException {
        Field field = URI.class.getDeclaredField(fieldName);

        Field modifiers = Field.class.getDeclaredField("modifiers");
        modifiers.setAccessible(true);
        modifiers.setInt(field, field.getModifiers() & ~Modifier.FINAL);

        field.setAccessible(true);
        field.setLong(null, maskValue);
}

Answer 3

No, the result is absolutely coming right. Kindly go through the documentation for url.getHost()

Java docs says :

The host component of a URI, if defined, will have one of the following forms: 

    A domain name consisting of one or more labels separated by period characters ('.'), optionally followed by a period character. Each label consists of alphanum characters as well as hyphen characters ('-'), though hyphens never occur as the first or last characters in a label. The rightmost label of a domain name consisting of two or more labels, begins with an alpha character. 

    A dotted-quad IPv4 address of the form digit+.digit+.digit+.digit+, where no digit sequence is longer than three characters and no sequence has a value larger than 255. 

    An IPv6 address enclosed in square brackets ('[' and ']') and consisting of hexadecimal digits, colon characters (':'), and possibly an embedded IPv4 address. The full syntax of IPv6 addresses is specified in RFC 2373: IPv6 Addressing Architecture. 

    The host component of a URI cannot contain escaped octets, hence this method does not perform any decoding.
    Returns:
    The host component of this URI, or null if the host is undefined

To add to this answer, if using eclipse kindly jump to the method definition (press f3) you will get your answer.