Error when trying to deserialize XML into object

[Marcos Silvestri]

Hi guys,

I've been trying to solve a deserialization problem without success for a few hours now.

I obtain an XML from an API call, and this is what needs to be deserialized into a Java object. For so, I use Jackson:

        <dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-annotations</artifactId> <version>2.16.1</version> </dependency> <dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-core</artifactId> <version>2.16.1</version> </dependency> <dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-databind</artifactId> <version>2.16.1</version> </dependency> <dependency> <groupId>com.fasterxml.jackson.dataformat</groupId> <artifactId>jackson-dataformat-xml</artifactId> <version>2.16.1</version> </dependency>

This is my class Conversion whose constructor takes a String as a parameter, the xml itself that needs to be deserialized:

package com.mpsilvestri.api;

import java.io.IOException;

import com.fasterxml.jackson.dataformat.xml.XmlMapper;
import com.mpsilvestri.model.ApiResponse;


public class Conversion {
	
	private String xml;
	
	public Conversion(String xml) {
		
		this.xml = xml;
				
		try {
			XmlMapper xmlMapper = new XmlMapper();	
			ApiResponse apiResponse = xmlMapper.readValue(xml, ApiResponse.class);
			System.out.println("Convertion successful!!!");
		} catch (IOException ioe) {
			System.out.println("Error while converting from XML to Object: " + ioe.getMessage());
		}

	}
	
}

Here we have the class that needs to be used for deserialization:

package com.mpsilvestri.model;

import java.util.List;

public class ApiResponse {
	
	private List<Messages> data;
	private List<Message> messages;
	private Message message;
	

	public ApiResponse() {

	}


	public ApiResponse(List<Messages> data, List<Message> messages, Message message) {
		this.data = data;
		this.messages = messages;
		this.message = message;
	}


	public List<Messages> getData() {
		return data;
	}


	public void setData(List<Messages> data) {
		this.data = data;
	}


	public List<Message> getMessages() {
		return messages;
	}


	public void setMessages(List<Message> messages) {
		this.messages = messages;
	}


	public Message getMessage() {
		return message;
	}


	public void setMessage(Message message) {
		this.message = message;
	}


	@Override
	public String toString() {
		return "ApiResponse []";
	}
}

class Data {
	
	private List<Messages> messages;

	public Data() {

	}
	
	public Data(List<Messages> messages) {
		this.messages = messages;
	}

	public List<Messages> getMessages() {
		return messages;
	}

	public void setMessages(List<Messages> messages) {
		this.messages = messages;
	}

	@Override
	public String toString() {
		return "Data [messages=" + messages + "]";
	}
}

class Messages {
	
	private List<Message> messages;

	public Messages() {
		
	}
	
	public Messages(List<Message> messages) {
		this.messages = messages;
	}

	public List<Message> getMessages() {
		return messages;
	}

	public void setMessages(List<Message> messages) {
		this.messages = messages;
	}

	@Override
	public String toString() {
		return "Messages [messages=" + messages + "]";
	}
	
}

class Message {
	
	private String subject;
	private String id;
	private String type;
	private String sentDate;
	private String tags;
	private String fromName;
	private String fromEmail;
	
	public Message() {
		
	}

	public Message(String subject, String id, String type, String sentDate, String tags, String fromName,
			String fromEmail) {
		this.subject = subject;
		this.id = id;
		this.type = type;
		this.sentDate = sentDate;
		this.tags = tags;
		this.fromName = fromName;
		this.fromEmail = fromEmail;
	}

	public String getSubject() {
		return subject;
	}

	public void setSubject(String subject) {
		this.subject = subject;
	}

	public String getId() {
		return id;
	}

	public void setId(String id) {
		this.id = id;
	}

	public String getType() {
		return type;
	}

	public void setType(String type) {
		this.type = type;
	}

	public String getSentDate() {
		return sentDate;
	}

	public void setSentDate(String sentDate) {
		this.sentDate = sentDate;
	}

	public String getTags() {
		return tags;
	}

	public void setTags(String tags) {
		this.tags = tags;
	}

	public String getFromName() {
		return fromName;
	}

	public void setFromName(String fromName) {
		this.fromName = fromName;
	}

	public String getFromEmail() {
		return fromEmail;
	}

	public void setFromEmail(String fromEmail) {
		this.fromEmail = fromEmail;
	}

	@Override
	public String toString() {
		return "Message [subject=" + subject + ", id=" + id + ", type=" + type + ", sentDate=" + sentDate + ", tags="
				+ tags + ", fromName=" + fromName + ", fromEmail=" + fromEmail + "]";
	}
	
}

This is a sample of the XML I receive from the API call:

<ApiResponse xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">  <Data>    <Messages>      <Message>        <Subject>Confetes no ar, é Carnaval no Hotel Jequitimar!</Subject>        <Id>409</Id>        <Type>Newsletter</Type>        <Tags>Sofitel_SP, Messias</Tags>        <FromName>Hotel Jequitimar Guarujá Resort & Spa by Accor.</FromName>        <FromEmail>[e-mail]</FromEmail>      </Message>      <Message>        <Subject>Em fevereiro, garanta seus dias de Sol e mar</Subject>        <Id>414</Id>        <Type>Newsletter</Type>        <Tags>Sofitel_SP, Messias</Tags>        <FromName>Hotel Jequitimar Guarujá Resort & Spa by Accor.</FromName>        <FromEmail>[e-mail]</FromEmail>      </Message>      .      .      .    </Messages>  </Data> </ApiResponse>

Lastly, the error message I've been getting:

Error while converting from XML to Object: Unrecognized field "Data" (class com.mpsilvestri.model.ApiResponse), not marked as ignorable (3 known properties: "data", "messages", "message"])
at [Source: (StringReader); line: 3, column: 15] (through reference chain: com.mpsilvestri.model.ApiResponse["Data"])

For a long time along my tests, only "data" was mentioned as a known property.

Would you have any ideas of what the problem could be so that I could proceed with my deserialization process?

Thank you in advance!

[Carey Brown]

Mostly new stuff to me but I'll take a stab at it.

Messages (plural) is a class to encapsulate a collection of Message objects. So far, so good.

Data should be using the Messages class and not attempting to define it's own "messages" collection.

[Marcos Silvestri]

Carey Brown wrote:Mostly new stuff to me but I'll take a stab at it.

Messages (plural) is a class to encapsulate a collection of Message objects. So far, so good.

Data should be using the Messages class and not attempting to define it's own "messages" collection.

Hi Carey, thanks for joining in!

I did these changes:

public class ApiResponse {
	
	private Messages data;
	private List<Message> messages;
	private Message message;
	
	public ApiResponse() {

	}

	public ApiResponse(Messages data, List<Message> messages, Message message) {
		this.data = data;
		this.messages = messages;
		this.message = message;
	}

	public Messages getData() {
		return data;
	}

	public void setData(Messages data) {
		this.data = data;
	}
.
.
.

I started using the Messages list as you suggested, but the error message remained the same:

Error while converting from XML to Object: Unrecognized field "Data" (class com.mpsilvestri.model.ApiResponse), not marked as ignorable (3 known properties: "data", "messages", "message"])
at [Source: (StringReader); line: 3, column: 15] (through reference chain: com.mpsilvestri.model.ApiResponse["Data"])

Thanks!

[Stephan van Hulst]

By default, Jackson maps XML elements to JavaBean properties with the same name.

A getter called "getData" would be associated with a JavaBean propery called "data". But that's not what your XML element is called. Your XML element is called "Data".

To deserialize XML elements to properties that have a different name, you need to use annotations to override the default mapping.

[Stephan van Hulst]

This should work:

package com.mpsilvestri.model;

import java.util.*;

import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlElementWrapper;
import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlProperty;
import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlRootElement;

@JacksonXmlRootElement(localName = "ApiResponse")
public final class ApiResponse {

  private final Data data = new Data();

  @JacksonXmlProperty(localName = "Data")
  public Data getData() {
    return data;
  }
  


  public static final class Data {

    private final List<Message> messages = new ArrayList<>();

    @JacksonXmlElementWrapper(localName = "Messages")
    @JacksonXmlProperty(localName = "Message")
    public List<Message> getMessages() {
      return messages;
    }
  }



  public static final class Message {

    private String subject;

    private String id;

    private String type;

    private String tags;

    private String fromName;

    private String fromEmail;

    @JacksonXmlProperty(localName = "Subject")
    public String getSubject() {
      return subject;
    }

    public void setSubject(String subject) {
      this.subject = subject;
    }

    @JacksonXmlProperty(localName = "Id")
    public String getId() {
      return id;
    }

    public void setId(String id) {
      this.id = id;
    }

    @JacksonXmlProperty(localName = "Type")
    public String getType() {
      return type;
    }

    public void setType(String type) {
      this.type = type;
    }

    @JacksonXmlProperty(localName = "Tags")
    public String getTags() {
      return tags;
    }

    public void setTags(String tags) {
      this.tags = tags;
    }

    @JacksonXmlProperty(localName = "FromName")
    public String getFromName() {
      return fromName;
    }

    public void setFromName(String fromName) {
      this.fromName = fromName;
    }

    @JacksonXmlProperty(localName = "FromEmail")
    public String getFromEmail() {
      return fromEmail;
    }

    public void setFromEmail(String fromEmail) {
      this.fromEmail = fromEmail;
    }
  }
}

I strongly recommend you to use the JAXB API instead though, and just use Jackson as an implementation provider.

[Tim Holloway]

Stephan van Hulst wrote:I strongly recommend you to use the JAXB API instead though, and just use Jackson as an implementation provider.

Another alternative is to use the Apache Digester. It is specifically designed to convert XML into a graph of Java objects and is widely used in products like the Tomcat webapp server, which digests not only the Tomcat server config file into a graph of JavaBeans, but also deals with digesting webapp deployment descriptors (Context.xml, /WEB-INF/web.xml).

[Marcos Silvestri]

Stephan van Hulst wrote:This should work:

package com.mpsilvestri.model;

import java.util.*;

import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlElementWrapper;
import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlProperty;
import com.fasterxml.jackson.dataformat.xml.annotation.JacksonXmlRootElement;

@JacksonXmlRootElement(localName = "ApiResponse")
public final class ApiResponse {

  private final Data data = new Data();

  @JacksonXmlProperty(localName = "Data")
  public Data getData() {
    return data;
  }
  


  public static final class Data {

    private final List<Message> messages = new ArrayList<>();

    @JacksonXmlElementWrapper(localName = "Messages")
    @JacksonXmlProperty(localName = "Message")
    public List<Message> getMessages() {
      return messages;
    }
  }



  public static final class Message {

    private String subject;

    private String id;

    private String type;

    private String tags;

    private String fromName;

    private String fromEmail;

    @JacksonXmlProperty(localName = "Subject")
    public String getSubject() {
      return subject;
    }

    public void setSubject(String subject) {
      this.subject = subject;
    }

    @JacksonXmlProperty(localName = "Id")
    public String getId() {
      return id;
    }

    public void setId(String id) {
      this.id = id;
    }

    @JacksonXmlProperty(localName = "Type")
    public String getType() {
      return type;
    }

    public void setType(String type) {
      this.type = type;
    }

    @JacksonXmlProperty(localName = "Tags")
    public String getTags() {
      return tags;
    }

    public void setTags(String tags) {
      this.tags = tags;
    }

    @JacksonXmlProperty(localName = "FromName")
    public String getFromName() {
      return fromName;
    }

    public void setFromName(String fromName) {
      this.fromName = fromName;
    }

    @JacksonXmlProperty(localName = "FromEmail")
    public String getFromEmail() {
      return fromEmail;
    }

    public void setFromEmail(String fromEmail) {
      this.fromEmail = fromEmail;
    }
  }
}

I strongly recommend you to use the JAXB API instead though, and just use Jackson as an implementation provider.

Hi Stephan,

You definetly helped, I used your idea and managed to walk one step more. However, at the next step, I'm stuck again because I'm running against a visibility problem of the data since the other classes are not public and cannot be in the same Java file.

To demonstrate the issue, look at an attempt to print the data:

XmlMapper xmlMapper = new XmlMapper();
ApiResponse apiResponse = xmlMapper.readValue(xml, ApiResponse.class);
			
System.out.println("Convertion successful!!!");
System.out.println("toString(): " + apiResponse.toString());
System.out.println("getData(): " + apiResponse.getData());
System.out.println("getMessages(): " + apiResponse.getMessages());
System.out.println("getMessage(): " + apiResponse.getMessage());
// NullPointer: System.out.println(apiResponse.getMessages().get(0));
// Type Message not visible: System.out.println(apiResponse.getMessage().getFromEmail());
// Type Messages not visible: System.out.println("getData(): " + apiResponse.getData().getMessage());

This is what I obtain:

Convertion successful!!! toString(): ApiResponse [data=Message [message=[Message [subject=Confetes no ar, é Carnaval no Hotel Jequitimar!, id=409,... getData(): Message [message=[Message [subject=Confetes no ar, é Carnaval no Hotel Jequitimar!, id=409, type=Newsletter,... getMessages(): null getMessage(): null

I tried using inner classes too, like

- ApiResponse
 - Data
   - Messages
     - Message

but that returned the error message:

Error while converting from XML to Object: Cannot construct instance of `com.mpsilvestri.model.ApiResponse$Data$Messages`: non-static inner classes like this can only by instantiated using default, no-argument constructor
at [Source: (StringReader); line: 3, column: 5] (through reference chain: com.mpsilvestri.model.ApiResponse["Data"])


Would you have any suggestions to me so that I can fetch the data already present after the successful deserialization?

Thank you!

[Marcos Silvestri]

Tim Holloway wrote:

Stephan van Hulst wrote:I strongly recommend you to use the JAXB API instead though, and just use Jackson as an implementation provider.

Another alternative is to use the Apache Digester. It is specifically designed to convert XML into a graph of Java objects and is widely used in products like the Tomcat webapp server, which digests not only the Tomcat server config file into a graph of JavaBeans, but also deals with digesting webapp deployment descriptors (Context.xml, /WEB-INF/web.xml).

Hi Tim,

I've never heard of it before, but as per your description, it is worth having a look if my current options are not enough.

Thanks!

[Tim Holloway]

I highly recommend it for anything that needs to construct Java objects from XML, as it makes things much simpler. The basic docs with examples can be found here: https://commons.apache.org/proper/commons-digester/guide/core.html

Just for info, in addition to the basic SAX parser, there's also STaX. SAX basically feeds what it reads to listeners and the listeners have to extract the data they are interested in and build any objects that you want to produce and it's the base reader for both STaX and the Digester. The difference between SAX and STaX is that STaX essentially inverts the parse. Instead of simply listening to the XML stream and pulling out data, you tell STaX what you want retrieved and it only passes on those items.

For completeness, there's also XML Documents, which can invoke SAX to populate themselves, but they have theit own rather complex structure which makes them more suitable for modifications of XML than simply producing objects from XML. Plus the entire Document lives in RAM, so large Documents can be very nenory-hungry.

[Marcos Silvestri]

Hi everyone,

I've managed to resolve my problems with JDOM, with this example (https://www.tutorialspoint.com/java_xml/java_jdom_parse_document.htm)

Actually, I have just solved this, accomplished 5 minutes ago:

package com.mpsilvestri.api;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;

import org.jdom2.Document;
import org.jdom2.Element;
import org.jdom2.JDOMException;
import org.jdom2.input.SAXBuilder;

import com.mpsilvestri.model.Campaign;

public class Deserialize {
	
	private String xml;
	private List<Campaign> campaigns = new ArrayList<>();
	
	public Deserialize(String xml) throws JDOMException, IOException {
		
		this.xml = xml;

		InputStream xml_stream = new ByteArrayInputStream(xml.getBytes("UTF-8")); 
		
		SAXBuilder saxBuilder = new SAXBuilder();
		Document document = saxBuilder.build(xml_stream);
		System.out.println("Root element: " + document.getRootElement().getName());
		Element classElement = document.getRootElement();
		
		List<Element> data = classElement.getChildren();
		System.out.println(data.get(0).getName());
		List<Element> messages = data.get(0).getChildren();
		System.out.println(messages.get(0).getName());
		List<Element> message = messages.get(0).getChildren();
		System.out.println(message.get(0).getName());
		List<Element> subject = message.get(0).getChildren();
		System.out.println(subject.get(0).getName());
		System.out.println(subject.get(0).getText());
		
		for (int i = 0; i < message.size(); i++) {

			Campaign campaign_obj = new Campaign();
			Element campaign = message.get(i);
			
			System.out.println("\nCurrent Element :" + campaign.getName());
			if(campaign.getChild("Subject") != null) {
				System.out.println("Subject: " + campaign.getChild("Subject").getText());
				campaign_obj.setSubject(campaign.getChild("Subject").getText());
			}
			if(campaign.getChild("Id") != null) {
				System.out.println("Id: " + campaign.getChild("Id").getText());
				campaign_obj.setId(campaign.getChild("Id").getText());
			}
			if(campaign.getChild("Type") != null) {
				System.out.println("Type: " + campaign.getChild("Type").getText());
				campaign_obj.setType(campaign.getChild("Type").getText());
			}
			if(campaign.getChild("SentDate") != null) {
				System.out.println("SentDate: " + campaign.getChild("SentDate").getText());
				campaign_obj.setSentDate(campaign.getChild("SentDate").getText());
			}
			if(campaign.getChild("Tags") != null) {
				System.out.println("Tags: " + campaign.getChild("Tags").getText());
				campaign_obj.setTags(campaign.getChild("Tags").getText());
			}
			if(campaign.getChild("FromName") != null) {
				System.out.println("FromName: " + campaign.getChild("FromName").getText());
				campaign_obj.setFromName(campaign.getChild("FromName").getText());
			}
			if(campaign.getChild("FromEmail") != null) {
				System.out.println("FromEmail: " + campaign.getChild("FromEmail").getText());
				campaign_obj.setFromEmail(campaign.getChild("FromEmail").getText());
			}
			
			campaigns.add(campaign_obj);
		}
		
	}	

}

Now I have an ArrayList full of objects, each representing a message from my XML, everything ready to become database entities as soon as I can.

Thank you all for the help!

[Stephan van Hulst]

Marcos Silvestri wrote:I've managed to resolve my problems with JDOM

I'm glad you got it to work. It's just a pity that you ditched a high level, strongly typed API for a low level, weakly typed API. Your old approach was more elegant and robust.

Marcos Silvestri wrote:Would you have any suggestions to me so that I can fetch the data already present after the successful deserialization?

Literally just replace all the contents of your ApiResponse class with the code I posted. After deserializing it using XmlMapper you can just do this:

for (var message: response.getData().getMessages()) {
  System.out.printf("Subject: %s%n", message.getSubject());
}

[Marcos Silvestri]

Stephan van Hulst wrote:

Marcos Silvestri wrote:I've managed to resolve my problems with JDOM

I'm glad you got it to work. It's just a pity that you ditched a high level, strongly typed API for a low level, weakly typed API. Your old approach was more elegant and robust.

Marcos Silvestri wrote:Would you have any suggestions to me so that I can fetch the data already present after the successful deserialization?

Literally just replace all the contents of your ApiResponse class with the code I posted. After deserializing it using XmlMapper you can just do this:

for (var message: response.getData().getMessages()) {
  System.out.printf("Subject: %s%n", message.getSubject());
}

Hi Stephan,

If you knew how much I'm running out of time, I think you could comprehend it... if your answer had come before, I'd certainly go for it.

If what I'm attempting to do works down the line, I'll be coding lots of similar tasks in the near future, with a variety of XML responses from API calls, so I'll still have the change to try what you suggested, I didn't delete the class, neither will this post be erased

Thank you very much! Regards from Brazil!