Can't remove element and child element from an XML document by Java code

This is my xml document:

<definitions>       
<task name="TASK1"
     class="CLASS"
     group="GROUP">
  <trigger count="3" interval="400"/>
  <property xmlns:task="URI"
            name="PROPERTY2"
            value="VALUE1"/>
  <property xmlns:task="URI"
            name="PROPERTY2"
            value="VALUE2"/>
</task>
<task name="TASK1"
     class="CLASS"
     group="GROUP">
  <trigger count="1" interval="600"/>
  <property xmlns:task="URI"
            name="PROPERTY2"
            value="VALUE1"/>
  <property xmlns:task="URI"
            name="PROPERTY2"
            value="VALUE2"/>
</task>
<another_tag name="a_name"/>
<another_tag2 name="a_name2"/>
<another_tag3>  something in the middle </another_tag3>

</definitions>

I have to delete all <task> tags and what inside them. I used this java code:

Document esb = new Document();

    SAXBuilder saxBuilder = new SAXBuilder();


    try {
       esb = saxBuilder.build(new File("C:\\...path\\file.xml")); 
    }
    catch (JDOMException ex) {
       System.err.println(ex);
    }
    catch (IOException ex) {
       System.err.println(ex);
    }
    Element root = esb.getRootElement();
    boolean b = root.removeChild("task");
    System.out.println(b);

I can't understand how to obtain an xml file without <task> tag and containing only <another_tag> tag. I've looked for other solutions but nothing useful. I also used removeContent() method, but nothing. I imported jdom2 libraries, I need to use recent libraries, because there are bad interactions among jdom and jdom2, so I would prefer to use recent libraries only. Any suggest about how to remove some element from this xml CODE?

Solution

I solved this problem by managing namespace. There is the code:`

Document doc = new Document();

SAXBuilder saxBuilder = new SAXBuilder();
try {
       doc = saxBuilder.build(new File("....path\MyXMLfile.xml")); 
    }
    catch (JDOMException ex) {
       System.err.println(ex);
    }
    catch (IOException ex) {
       System.err.println(ex);
    }


    Element root = esb.getRootElement();
    System.out.println(root.getName());  // it prints "definitions"

    Namespace namespace = Namespace.getNamespace("task","http://....myDefinitionsNamespace....");

    boolean b = root.removeChildren("task", namespace);

    System.out.println(b);

    XMLOutputter xmlOutputter = new XMLOutputter();
    xmlOutputter.setFormat(Format.getPrettyFormat());
    System.out.println(xmlOutputter.outputString(doc)); //so we can see new XML FILE

In order to understand this code, we need starting xml too:

<?xml version="1.0" encoding="UTF-8"?>
<definitions xmlns="http://....myDefinitionsNamespace....">
<task name="MyTask"
     class="....myClass...."
     group="....myGroup...."> 
<taskChild/>
</task>
<anotherTag1/>
<anotherTag2>
<task/>
.
.
.
</definitions>

The result is an XML file without every task tag, it will contain anotherTags only. Then you need to define the output (for example into a file with a FileOutputStream instance). Thanks to @OkieOth and @rolfl.