Reading information from XML file using Java

Question

I have the following XML file generated by some tool. I have to convert them into java objects. It looks similar to this

<A>
  <B name = "ming">
     <B name = "giang">
        <B name = "long">
         <text>CCVVV</text>
        </B>
        <B name = "long4">
         <text>CCVVvvvV</text>
        </B>
    </B>
  </B>
</A>

How do I extract those information from that xml using java so I can get the smallest child in that XML file(<B name = "long"> and <B name = "long4">). I am thinking of creating classes like this

class B{
  List<B> objects;
  String text;
}

class A{
  B objectB;
}

Answer 1

1. Generate XSD by your XML (https://www.google.com/search?q=xsd+by+xml)

2. Generate java classes by XSD using xjc tool (jdk\bin\xjc.exe classa.xsd -verbose -catalog C:\tmp\classa)

3. Easily unmarshal objects from xml like this:

    JAXBContext context;
    context = JAXBContext.newInstance(AClass.class);
    Unmarshaller u = context.createUnmarshaller();
    AClass obj = (AClass) u.unmarshal(new File("object.xml"));
   

UPD: src\generated\A.java

//
// This file was generated by the JavaTM Architecture for XML Binding(JAXB) Reference Implementation, v2.2.4 
// See <a href="http://java.sun.com/xml/jaxb">http://java.sun.com/xml/jaxb</a> 
// Any modifications to this file will be lost upon recompilation of the source schema. 
// Generated on: 2020.09.01 at 04:57:38 PM MSK 
//


package generated;

import java.util.ArrayList;
import java.util.List;
import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlType;


/**
 * <p>Java class for anonymous complex type.
 * 
 * <p>The following schema fragment specifies the expected content contained within this class.
 * 
 * <pre>
 * &lt;complexType>
 *   &lt;complexContent>
 *     &lt;restriction base="{http://www.w3.org/2001/XMLSchema}anyType">
 *       &lt;sequence>
 *         &lt;element name="B">
 *           &lt;complexType>
 *             &lt;complexContent>
 *               &lt;restriction base="{http://www.w3.org/2001/XMLSchema}anyType">
 *                 &lt;sequence>
 *                   &lt;element name="B">
 *                     &lt;complexType>
 *                       &lt;complexContent>
 *                         &lt;restriction base="{http://www.w3.org/2001/XMLSchema}anyType">
 *                           &lt;sequence>
 *                             &lt;element name="B" maxOccurs="unbounded">
 *                               &lt;complexType>
 *                                 &lt;complexContent>
 *                                   &lt;restriction base="{http://www.w3.org/2001/XMLSchema}anyType">
 *                                     &lt;sequence>
 *                                       &lt;element name="text" type="{http://www.w3.org/2001/XMLSchema}string"/>
 *                                     &lt;/sequence>
 *                                     &lt;attribute name="name" use="required" type="{http://www.w3.org/2001/XMLSchema}string" />
 *                                   &lt;/restriction>
 *                                 &lt;/complexContent>
 *                               &lt;/complexType>
 *                             &lt;/element>
 *                           &lt;/sequence>
 *                           &lt;attribute name="name" use="required" type="{http://www.w3.org/2001/XMLSchema}string" />
 *                         &lt;/restriction>
 *                       &lt;/complexContent>
 *                     &lt;/complexType>
 *                   &lt;/element>
 *                 &lt;/sequence>
 *                 &lt;attribute name="name" use="required" type="{http://www.w3.org/2001/XMLSchema}string" />
 *               &lt;/restriction>
 *             &lt;/complexContent>
 *           &lt;/complexType>
 *         &lt;/element>
 *       &lt;/sequence>
 *     &lt;/restriction>
 *   &lt;/complexContent>
 * &lt;/complexType>
 * </pre>
 * 
 * 
 */
@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(name = "", propOrder = {
    "b"
})
@XmlRootElement(name = "A")
public class A {

    @XmlElement(name = "B", required = true)
    protected A.B b;

    /**
     * Gets the value of the b property.
     * 
     * @return
     *     possible object is
     *     {@link A.B }
     *     
     */
    public A.B getB() {
        return b;
    }

    /**
     * Sets the value of the b property.
     * 
     * @param value
     *     allowed object is
     *     {@link A.B }
     *     
     */
    public void setB(A.B value) {
        this.b = value;
    }


    /**
     * <p>Java class for anonymous complex type.
     * 
     * <p>The following schema fragment specifies the expected content contained within this class.
     * 
     * <pre>
     * &lt;complexType>
     *   &lt;complexContent>
     *     &lt;restriction base="{http://www.w3.org/2001/XMLSchema}anyType">
     *       &lt;sequence>
     *         &lt;element name="B">
     *           &lt;complexType>
     *             &lt;complexContent>
     *               &lt;restriction base="{http://www.w3.org/2001/XMLSchema}anyType">
     *                 &lt;sequence>
     *                   &lt;element name="B" maxOccurs="unbounded">
     *                     &lt;complexType>
     *                       &lt;complexContent>
     *                         &lt;restriction base="{http://www.w3.org/2001/XMLSchema}anyType">
     *                           &lt;sequence>
     *                             &lt;element name="text" type="{http://www.w3.org/2001/XMLSchema}string"/>
     *                           &lt;/sequence>
     *                           &lt;attribute name="name" use="required" type="{http://www.w3.org/2001/XMLSchema}string" />
     *                         &lt;/restriction>
     *                       &lt;/complexContent>
     *                     &lt;/complexType>
     *                   &lt;/element>
     *                 &lt;/sequence>
     *                 &lt;attribute name="name" use="required" type="{http://www.w3.org/2001/XMLSchema}string" />
     *               &lt;/restriction>
     *             &lt;/complexContent>
     *           &lt;/complexType>
     *         &lt;/element>
     *       &lt;/sequence>
     *       &lt;attribute name="name" use="required" type="{http://www.w3.org/2001/XMLSchema}string" />
     *     &lt;/restriction>
     *   &lt;/complexContent>
     * &lt;/complexType>
     * </pre>
     * 
     * 
     */
    @XmlAccessorType(XmlAccessType.FIELD)
    @XmlType(name = "", propOrder = {
        "b"
    })
    public static class B {

        @XmlElement(name = "B", required = true)
        protected A.B.B1 b;
        @XmlAttribute(name = "name", required = true)
        protected String name;

        /**
         * Gets the value of the b property.
         * 
         * @return
         *     possible object is
         *     {@link A.B.B1 }
         *     
         */
        public A.B.B1 getB() {
            return b;
        }

        /**
         * Sets the value of the b property.
         * 
         * @param value
         *     allowed object is
         *     {@link A.B.B1 }
         *     
         */
        public void setB(A.B.B1 value) {
            this.b = value;
        }

        /**
         * Gets the value of the name property.
         * 
         * @return
         *     possible object is
         *     {@link String }
         *     
         */
        public String getName() {
            return name;
        }

        /**
         * Sets the value of the name property.
         * 
         * @param value
         *     allowed object is
         *     {@link String }
         *     
         */
        public void setName(String value) {
            this.name = value;
        }


        /**
         * <p>Java class for anonymous complex type.
         * 
         * <p>The following schema fragment specifies the expected content contained within this class.
         * 
         * <pre>
         * &lt;complexType>
         *   &lt;complexContent>
         *     &lt;restriction base="{http://www.w3.org/2001/XMLSchema}anyType">
         *       &lt;sequence>
         *         &lt;element name="B" maxOccurs="unbounded">
         *           &lt;complexType>
         *             &lt;complexContent>
         *               &lt;restriction base="{http://www.w3.org/2001/XMLSchema}anyType">
         *                 &lt;sequence>
         *                   &lt;element name="text" type="{http://www.w3.org/2001/XMLSchema}string"/>
         *                 &lt;/sequence>
         *                 &lt;attribute name="name" use="required" type="{http://www.w3.org/2001/XMLSchema}string" />
         *               &lt;/restriction>
         *             &lt;/complexContent>
         *           &lt;/complexType>
         *         &lt;/element>
         *       &lt;/sequence>
         *       &lt;attribute name="name" use="required" type="{http://www.w3.org/2001/XMLSchema}string" />
         *     &lt;/restriction>
         *   &lt;/complexContent>
         * &lt;/complexType>
         * </pre>
         * 
         * 
         */
        @XmlAccessorType(XmlAccessType.FIELD)
        @XmlType(name = "", propOrder = {
            "b"
        })
        public static class B1 {

            @XmlElement(name = "B", required = true)
            protected List<A.B.B1.B2> b;
            @XmlAttribute(name = "name", required = true)
            protected String name;

            /**
             * Gets the value of the b property.
             *
             * <p>
             * This accessor method returns a reference to the live list,
             * not a snapshot. Therefore any modification you make to the
             * returned list will be present inside the JAXB object.
             * This is why there is not a <CODE>set</CODE> method for the b property.
             *
             * <p>
             * For example, to add a new item, do as follows:
             * <pre>
             *    getB().add(newItem);
             * </pre>
             *
             *
             * <p>
             * Objects of the following type(s) are allowed in the list
             * {@link A.B.B1.B2 }
             *
             *
             */
            public List<A.B.B1.B2> getB() {
                if (b == null) {
                    b = new ArrayList<A.B.B1.B2>();
                }
                return this.b;
            }

            /**
             * Gets the value of the name property.
             *
             * @return
             *     possible object is
             *     {@link String }
             *
             */
            public String getName() {
                return name;
            }

            /**
             * Sets the value of the name property.
             *
             * @param value
             *     allowed object is
             *     {@link String }
             *
             */
            public void setName(String value) {
                this.name = value;
            }


            /**
             * <p>Java class for anonymous complex type.
             *
             * <p>The following schema fragment specifies the expected content contained within this class.
             *
             * <pre>
             * &lt;complexType>
             *   &lt;complexContent>
             *     &lt;restriction base="{http://www.w3.org/2001/XMLSchema}anyType">
             *       &lt;sequence>
             *         &lt;element name="text" type="{http://www.w3.org/2001/XMLSchema}string"/>
             *       &lt;/sequence>
             *       &lt;attribute name="name" use="required" type="{http://www.w3.org/2001/XMLSchema}string" />
             *     &lt;/restriction>
             *   &lt;/complexContent>
             * &lt;/complexType>
             * </pre>
             *
             *
             */
            @XmlAccessorType(XmlAccessType.FIELD)
            @XmlType(name = "", propOrder = {
                "text"
            })
            public static class B2 {

                @XmlElement(required = true)
                protected String text;
                @XmlAttribute(name = "name", required = true)
                protected String name;

                /**
                 * Gets the value of the text property.
                 *
                 * @return
                 *     possible object is
                 *     {@link String }
                 *
                 */
                public String getText() {
                    return text;
                }

                /**
                 * Sets the value of the text property.
                 *
                 * @param value
                 *     allowed object is
                 *     {@link String }
                 *
                 */
                public void setText(String value) {
                    this.text = value;
                }

                /**
                 * Gets the value of the name property.
                 *
                 * @return
                 *     possible object is
                 *     {@link String }
                 *
                 */
                public String getName() {
                    return name;
                }

                /**
                 * Sets the value of the name property.
                 *
                 * @param value
                 *     allowed object is
                 *     {@link String }
                 *
                 */
                public void setName(String value) {
                    this.name = value;
                }

            }

        }

    }

}

src\generated\ObjectFactory.java:

//
// This file was generated by the JavaTM Architecture for XML Binding(JAXB) Reference Implementation, v2.2.4 
// See <a href="http://java.sun.com/xml/jaxb">http://java.sun.com/xml/jaxb</a> 
// Any modifications to this file will be lost upon recompilation of the source schema. 
// Generated on: 2020.09.01 at 04:57:38 PM MSK 
//


package generated;

import javax.xml.bind.annotation.XmlRegistry;


/**
 * This object contains factory methods for each 
 * Java content interface and Java element interface 
 * generated in the generated package. 
 * <p>An ObjectFactory allows you to programatically 
 * construct new instances of the Java representation 
 * for XML content. The Java representation of XML 
 * content can consist of schema derived interfaces 
 * and classes representing the binding of schema 
 * type definitions, element declarations and model 
 * groups.  Factory methods for each of these are 
 * provided in this class.
 * 
 */
@XmlRegistry
public class ObjectFactory {


    /**
     * Create a new ObjectFactory that can be used to create new instances of schema derived classes for package: generated
     * 
     */
    public ObjectFactory() {
    }

    /**
     * Create an instance of {@link A }
     * 
     */
    public A createA() {
        return new A();
    }

    /**
     * Create an instance of {@link A.B }
     * 
     */
    public A.B createAB() {
        return new A.B();
    }

    /**
     * Create an instance of {@link A.B.B1 }
     * 
     */
    public A.B.B1 createABB() {
        return new A.B.B1();
    }

    /**
     * Create an instance of {@link A.B.B1.B2 }
     * 
     */
    public A.B.B1.B2 createABBB() {
        return new A.B.B1.B2();
    }

}

src\XMLTest.java:

import generated.A;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.Unmarshaller;
import java.io.File;

public class XMLTest {
    public static void main(String[] args) throws Exception {
        JAXBContext context;
        context = JAXBContext.newInstance(A.class);
        Unmarshaller u = context.createUnmarshaller();
        A obj = (A) u.unmarshal(new File("object.xml"));
        ...
    }
}

Answer 2

You can use the Java DOM API. Here is an example how you can create and read a XML file.

    String string = "text";
    Document document = DocumentBuilderFactory.newInstance().newDocumentBuilder().newDocument();
    Element element = document.createElement("element");
    element.appendChild(document.createTextNode(string));
    document.appendChild(element);
    TransformerFactory.newInstance().newTransformer().transform(new DOMSource(document), new StreamResult(new File("test.xml")));
    // creates <?xml version="1.0" encoding="UTF-8" standalone="no"?><element>text</element>
    document = DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(new File("test.xml"));
    System.out.println(document.getDocumentElement().getTextContent()));
    // prints text

Now you can recursively iterate through the child elements and nodes and build your Java object structure. I have done something similar in a more general project here for example: https://github.com/stonar96/Configuration/blob/master/src/main/java/com/vanillage/utils/configuration/xml/XmlConfigurationParser.java#L63