[FIXED] What does the first line means in a Maven pom.xml

Issue

What does first line means in Mavens pom.xml?

<project xmlns="http://maven.apache.org/POM/4.0.0" 
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
         https://maven.apache.org/xsd/maven-4.0.0.xsd">

Solution

What you actually mean is the first element and not the first line. There could be processing instructions or comments before the first element.

The first element after the opening < is the name of the first XML element.

The attribute xmlns specifies the URI of the XML namespace the element belongs to. XML allows you to combine multiple XML namespaces in one document. In the case of Maven, the name of the namespace is http://maven.apache.org/POM/4.0.0. As this is an URI, it is not necessarily a valid URL. It is just a canonical name of a resource.

The next attribute xmlns:xsi uses the possibility to declare another namespace for the same XML document (pom.xml). It declares the namespace xsi, which is identified by the URI http://www.w3.org/2001/XMLSchema-instance.

The last attribute schemaLocation comes from the namespace http://www.w3.org/2001/XMLSchema-instance and provides a mapping from the URI of the namespace Maven uses for its POM to a URL, where the XML parser can find the XML Schema Declaration for the namespace.

By the way, you can choose any identifier as namespace identifier. For example you can replace both occurences of xsi by xyz and the document is still valid. In many cases the identifier choosen for an identifier is more a convention then a hard requirement.

<project xmlns="http://maven.apache.org/POM/4.0.0" 
         xmlns:xyz="http://www.w3.org/2001/XMLSchema-instance"
         xyz:schemaLocation="http://maven.apache.org/POM/4.0.0
         https://maven.apache.org/xsd/maven-4.0.0.xsd">

Answered By - Oliver
Answer Checked By - Marie Seifert (JavaFixing Admin)