title: JAXB - flag 'required' from XmlAttribute being ignored on primitive types
body: <p>I have some problem while trying to use the schemagen tool from JAXB library to generate a Schema for my project. The problem is that the annotation <code>@XmlAttribute</code> is not being parsed properlly.</p>
  
  <pre><code>- src
   - teste
    - entity
  </code></pre>
  
  <p>So, the problem is that for some classes, the flag <code>required</code> in <code>XmlAttribute</code> is being ignored completly by the schemagen task.</p>
  
  <p>I'll paste here some examples of classes and the generated schema so you can understand what is going on</p>
  
  <pre><code>package teste.entity;
  
  import javax.xml.bind.annotation.XmlAttribute;
  
  public abstract class Class2 {
  
      @XmlAttribute(required=false)
      public String stringNotRequired;
  
      @XmlAttribute(required=true)
      public String stringRequired;
  
      @XmlAttribute(required=false)
      public int anotherIntNotRequired;
  
      @XmlAttribute(required=true)
      public int anotherIntRequired;
  
  }
  
  package teste.entity;
  
  import javax.xml.bind.annotation.XmlAttribute;
  
  public class Class1 extends Class2 {
  
      @XmlAttribute(required=true)
      public Integer integerRequired;
  
      @XmlAttribute(required=false)
      public Integer integerNotRequired;
  
      @XmlAttribute(required=false)
      public int intNotRequired;
  
      @XmlAttribute(required=true)
      public int intRequired;
  
      public Class1() {
      }
  }
  </code></pre>
  
  <p>My package-info.java</p>
  
  <pre><code>@XmlSchema(xmlns = @XmlNs(prefix = "t", namespaceURI = "http://test.com"),
  namespace = "http://test.com",
  elementFormDefault = XmlNsForm.UNQUALIFIED,
  attributeFormDefault = XmlNsForm.UNQUALIFIED)
  package teste.entity;
  
  import javax.xml.bind.annotation.XmlNs;
  import javax.xml.bind.annotation.XmlNsForm;
  import javax.xml.bind.annotation.XmlSchema;
  </code></pre>
  
  <p>When I run the <code>schemagen</code> task, I got this output:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8" standalone="yes"?&gt;
  &lt;xs:schema attributeFormDefault="unqualified" elementFormDefault="unqualified" version="1.0" targetNamespace="http://test.com" xmlns:t="http://test.com" xmlns:tns="http://test.com" xmlns:xs="http://www.w3.org/2001/XMLSchema"&gt;
  
    &lt;xs:complexType name="class1"&gt;
      &lt;xs:complexContent&gt;
        &lt;xs:extension base="tns:class2"&gt;
          &lt;xs:sequence/&gt;
          &lt;xs:attribute name="integerRequired" type="xs:int" use="required"/&gt;
          &lt;xs:attribute name="integerNotRequired" type="xs:int"/&gt;
          &lt;xs:attribute name="intNotRequired" type="xs:int" use="required"/&gt;
          &lt;xs:attribute name="intRequired" type="xs:int" use="required"/&gt;
        &lt;/xs:extension&gt;
      &lt;/xs:complexContent&gt;
    &lt;/xs:complexType&gt;
  
    &lt;xs:complexType name="class2" abstract="true"&gt;
      &lt;xs:sequence/&gt;
      &lt;xs:attribute name="stringNotRequired" type="xs:string"/&gt;
      &lt;xs:attribute name="stringRequired" type="xs:string" use="required"/&gt;
      &lt;xs:attribute name="anotherIntNotRequired" type="xs:int" use="required"/&gt;
      &lt;xs:attribute name="anotherIntRequired" type="xs:int" use="required"/&gt;
    &lt;/xs:complexType&gt;
  &lt;/xs:schema&gt;
  </code></pre>
  
  <p>Here is my Ant Task</p>
  
  <pre><code>&lt;target name="generate-schema" &gt;
      &lt;path id="mycp"&gt;
          &lt;fileset dir="lib/jaxb/lib\"&gt;
              &lt;include name="*.jar"/&gt;
          &lt;/fileset&gt;
          &lt;fileset dir="lib" &gt;
              &lt;include name="*.jar"/&gt;
          &lt;/fileset&gt;
          &lt;fileset dir="dist" &gt;
              &lt;include name="*.jar"/&gt;
          &lt;/fileset&gt;
      &lt;/path&gt;
  
      &lt;taskdef name="schemagen" classname="com.sun.tools.jxc.SchemaGenTask"&gt;
          &lt;classpath refid="mycp"/&gt;
      &lt;/taskdef&gt;
  
      &lt;mkdir dir="schema"/&gt;
  
      &lt;schemagen srcdir="src/teste/entity" destdir="schema" &gt;
          &lt;classpath refid="mycp"/&gt;
          &lt;schema namespace="http://test.com" file="full.xsd" /&gt;            
      &lt;/schemagen&gt;
  &lt;/target&gt;
  </code></pre>