How can I read all child elements of a XML file using Java?

The goal: read through the entire XML file and return only specific values, in this case, a "username" and "password", so I validate a user login.

The problem: when the program reads the "users.xml" file, it returns all attributes and values from the "user id=0001", but other child elements like "user id=0002" it won't return. Like there's nothing else in the file but the first element.

What I tried: printing all info from the file using a for loop to read line by line and it works just fine, but when it comes to getting one particular value, it can only see the first one.

I'd like to know how can I make it so that "getUser()" returns any "username" and "password" in the file?

Here's what I have so far:

users.xml

<!--I made some modifications in the password field-->
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE Users>
<Users>
<User id = "0001">
<firstname>sinead</firstname>
<lastname>o'connor</lastname>
<email>sinead@oconnor.ie</email>
<username>sinead</username>
<password>oconnor</password>
</User>
<User id= "0002">
<firstname>John</firstname>
<lastname>Don</lastname>
<email>john@don.ie</email>
<username>john</username>
<password>pass</password>
</User>
</Users>

readFile() method

    void readFile(){
String pathXML = "src/user_system/my_library/xml/users.xml";
File usersXML = new File(pathXML);
try {
DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder documentBuilder = builderFactory.newDocumentBuilder();
Document document = documentBuilder.parse(usersXML);
document.getDocumentElement().normalize();
} catch (ParserConfigurationException | SAXException | IOException e) {
e.printStackTrace();
}
}

getUser() method

    //I just split between readFile() and getUser() for better readability.
//Just changed "Users" to "User".
void getUser(){
NodeList nodeList = document.getElementsByTagName("User");
for (int i =  0; i < nodeList.getLength(); i++) {
Node node = nodeList.item(i);
//I also modified this bit.
Element xmlElement = (Element)nodeList.item(i);
String usernameElement = xmlElement.getElementsByTagName("username").item(0)
.getTextContent();
String passwordElement = xmlElement.getElementsByTagName("password").item(0)
.getTextContent();
if (!usernameElement.equals(users.getUsername())){
System.out.println("\nUsername "+ "\""+ users.getUsername()+ "\"" + 
" was not found in our registry." + "\nPlease try again");
//users.login() is just a simple username/password form in another class.
users.login();
}
else if(!passwordElement.equals(users.getPassword())){
System.out.println("\nWrong password. Please try again.");
users.login();
}else {
System.out.println("Welcome " + WordUtils.capitalize(xmlElement.getElementsByTagName("firstname").item(0)
.getTextContent())+ " " +WordUtils.capitalize(xmlElement.getElementsByTagName("lastname").item(0).getTextContent()));
}
}
}

I updated the code, but I still can't get other users, only the first one.
I get the following output:

Please, choose one of the options below:
1) Press 1 to Log In.
2) Press 2 to Create an Account.
3) Press 3 to Log Off.
>  1
Log In.
Please, enter your username: 
>  john
Please, enter your password: 
>  pass
Username "john" was not found in our registry.

Any help is appreciated.

You can pick up all the nodes based on their tag name, here you have used Users as your base node but you can also query User tag by calling,

NodeList nodeList = document.getElementsByTagName("User");

Using code above from root of the xml document you have only User nodes, once you have all the User nodes you can iterate it one by one and query nodes which are inside of User node as shown below.

NodeList nodeList = document.getElementsByTagName("User");
for(int i=0;i<nodeList.getLength();i++) {
Element xmlElement = (Element)nodeList.item(i);
System.out.println(xmlElement.getElementsByTagName("username").item(0).getTextContent());
System.out.println(xmlElement.getElementsByTagName("password").item(0).getTextContent());
}

Note that in your sample xml username and password tag has same values which you might want to change to validate the output.

Some outputs would be helpful.
My guess is that when you create nodelist, you're creating a list of length 1, since "User" will grab the single element with the tag "Users".

NodeList nodeList = document.getElementsByTagName("Users");

You probably want to populate the nodelist with

NodeList nodeList = document.getElementsByTagName("User");