Convert complex XML to Java object

Question

i have a xml and i want to save into a string the sub xml formed by the child of a specific tag. this is a xml example:

    <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<SampleDTO>
    <id>1</id>
    <someList>
        <someObject>
            <amount>32</amount>
            <id>1</id>
            <someDescription>I am a description</someDescription>
        </someObject>
        <someObject>
            <amount>66</amount>
            <id>2</id>
            <someDescription>I am another description</someDescription>
        </someObject>
        <someObject>
            <amount>78</amount>
            <id>13</id>
            <someDescription>Guess what? I am a description</someDescription>
        </someObject>
    </someList>
    <otherList>
        <otherObject>
            <flag>true</flag>
            <id>1</id>
            <otherDescription>Oh nice, a description</otherDescription>
        </otherObject>
    </otherList>
</SampleDTO>

i want , passing for example "someList" , to save into a String the sub-xml element and value, because next i deserialize it into a java object

Answer 1

use the JAXB unmarshaller for converting xml document into java objects. firstly add JAXB dependency into your project's classpath. for more info

SampleDTO.java

@XmlRootElement
public class SampleDTO {
    private String id;
    private List<SomeList> someList;
    private List<OtherList> otherList;

    @XmlElement
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    @XmlElement
    public List<SomeList> getSomeList() {
        return someList;
    }
    public void setSomeList(List<SomeList> someList) {
        this.someList = someList;
    }
    @XmlElement
    public List<OtherList> getOtherList() {
        return otherList;
    }
    public void setOtherList(List<OtherList> otherList) {
        this.otherList = otherList;
    }
}

SomeList.java

@XmlRootElement
public class SomeList {
    private List<SomeObject> someObject;

    @XmlElement
    public List<SomeObject> getSomeObject() {
        return someObject;
    }
    public void setSomeObject(List<SomeObject> someObject) {
        this.someObject = someObject;
    }
}

OtherList.java

@XmlRootElement
public class OtherList {
    private List<OtherObject> otherObject;

    @XmlElement
    public List<OtherObject> getOtherObject() {
        return otherObject;
    }
    public void setOtherObject(List<OtherObject> otherObject) {
        this.otherObject = otherObject;
    }
}

SomeObject.java

@XmlRootElement
public class SomeObject {
    private String amount;
    private String id;
    private String someDescription;

    @XmlElement
    public String getAmount() {
        return amount;
    }
    public void setAmount(String amount) {
        this.amount = amount;
    }
    @XmlElement
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    @XmlElement
    public String getSomeDescription() {
        return someDescription;
    }
    public void setSomeDescription(String someDescription) {
        this.someDescription = someDescription;
    }
}

OtherObject.java

@XmlRootElement
public class OtherObject {
    private String flag;
    private String id;
    private String otherDescription;

    @XmlElement
    public String getFlag() {
        return flag;
    }
    public void setFlag(String flag) {
        this.flag = flag;
    }
    @XmlElement
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    @XmlElement
    public String getOtherDescription() {
        return otherDescription;
    }
    public void setOtherDescription(String otherDescription) {
        this.otherDescription = otherDescription;
    }
}

Unmarshalling with JAXB

public class Main {
    public static void main(String[] args) {  
     try {
        File file = new File("file.xml");  
        JAXBContext jaxbContext = JAXBContext.newInstance(SampleDTO.class);  
        Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller();  
        SampleDTO sampleDTO= (SampleDTO) jaxbUnmarshaller.unmarshal(file);  
      } catch (JAXBException e) {  
        e.printStackTrace();  
      }  
    }  
}

Answer 2

Your java class/object should have at least these 3 instance vars :

private int amount
private int id
private String description

Then use some xml parsing library (eg jdom2 ), and for each <someObject> tag you iterate through, initialize a new object of your class and assign to it the values parsed from the xml (amount / id / description) , and add each newly created object in a List or array etc..

Answer 3

There are many open-source XML processing packages available. I like Jackson. Here is a link to a Baeldung Article about Jackson XML

The summary is this:

1. Add a Jackson dependency to your POM.
2. Create an object structure that represents your xml structure.
3. Create an XmlMapper.
4. Use the XmlMapper.