ORVE WS (Dynamic) (4) Jackson XML mapper

September 18, 2018

0. Introduction

I love Jackson parser as it is easy to use and can be used to with some data formats such as CSV, JSON, YAML and XML. Just define a wrapper and a class for marshalling/unmarshalling.

Although JAXB is a standard, in the Java ecosystem exists many solutions. And my decision is to use Jackson.

1. Defining MAVEN dependencies

To use Jackson XML it is required this dependency in Maven. Note that ${jackson.version} represents a variable that contains preferably the latest Jackson version.

    <dependency>
      <groupId>com.fasterxml.jackson.dataformat</groupId>
      <artifactId>jackson-dataformat-xml</artifactId>
      <version>${jackson.version}</version>
    </dependency>

But if you want to use CSV, JSON or YAML in the project, it is as easy as including these dependencies

<!-- Jackson for CSV --> 
<dependency>
  <groupId>com.fasterxml.jackson.dataformat</groupId>
  <artifactId>jackson-dataformat-csv</artifactId>
  <version>${jackson.version}</version>
</dependency>

<!-- Jackson for JSON --> 
<groupId>com.fasterxml.jackson.core</groupId>
  <artifactId>jackson-databind</artifactId>
  <version>${jackson.version}</version>
</dependency>

<!-- Jackson for YAML --> 
<groupId>com.fasterxml.jackson.dataformat</groupId>
  <artifactId>jackson-dataformat-yaml</artifactId>
  <version>${jackson.version}</version>
</dependency>

2. Marshalling/unmarshalling instances

The imports in the Java class are

1 2	import com.fasterxml.jackson.dataformat.xml.XmlMapper; import com.fasterxml.jackson.module.jaxb.JaxbAnnotationModule;

And now the mapper can be defined

  XmlMapper mapper = new XmlMapper();
  mapper.setDefaultUseWrapper(false); // No wrapper for List<> !!!!!!!
  mapper.registerModule(new JaxbAnnotationModule()); // Accept JAXB Annotations !!!!

In line 2, this sentence tells the wrapper NOT TO USE A FIELD WRAPPER. I have wasted nearly 2 days trying to unmarshal a class that some of its attributes where collections.

3. Wrapped and unwrapped XML formats

Here is a simple class showing the different XML formats for wrapped and unwrapped. The wrapped format has a tag that surrounds the collection.

package ximodante.orve.dynamicp;

import java.util.ArrayList;
import java.util.List;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.dataformat.xml.XmlMapper;

/**
 * Show the difference betweeen wrapped and unwrapped collections in XML
 * @author Ximo Dante
 *
 */
public class MyClass {
 public List<Integer> myIntList= new ArrayList<Integer>();
 
 public static void main(String[] args) { 
  MyClass c= new MyClass();
  c.myIntList.add(1);
  c.myIntList.add(2);
  c.myIntList.add(3);
  

  XmlMapper wrapMapper = new XmlMapper();
  wrapMapper.setDefaultUseWrapper(true);
  
  XmlMapper noWrapMapper = new XmlMapper();
  noWrapMapper.setDefaultUseWrapper(false); // No wrapper for List<> !!!!!!!
  
  try {
   System.out.println("wrapped collection......");
   System.out.println(wrapMapper.writeValueAsString(c));
   
   System.out.println("\nunwrapped collection......");
   System.out.println(noWrapMapper.writeValueAsString(c));
   
  } catch (JsonProcessingException e) {
   e.printStackTrace();
  }
 }
}

And the generated output is

wrapped collection......
<MyClass>
  <myIntList>
    <myIntList>1</myIntList>
    <myIntList>2</myIntList>
    <myIntList>3</myIntList>
  </myIntList>
</MyClass>

unwrapped collection......
<MyClass>
  <myIntList>1</myIntList>
  <myIntList>2</myIntList>
  <myIntList>3</myIntList>
</MyClass>

4. Accept JAXB annotations

This sentence tells the Jackson XML mapper to accept the annotations.

mapper.registerModule(new JaxbAnnotationModule()); // Accept JAXB Annotations !!!!

Now we can marshall and unmarshal most of the classes.

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