XSLT can't handle entity

I have a XML- String and i'am trying to remove all empty XML-Tags and whitespaces. For that i'am using the following XSL-Sheet:

<xsl:stylesheet version="1.0"
 xmlns:xsl="http://ift.tt/tCZ8VR">
 <xsl:strip-space elements="*"/>

 <xsl:template match="node()|@*">
     <xsl:copy>
       <xsl:apply-templates select="node()|@*"/>
     </xsl:copy>
 </xsl:template>

 <xsl:template match="*[not(*) and not(text()[normalize-space()])]"/>
</xsl:stylesheet>

My input String XML is for example:

String s = "<main>           <test>123öü aksdjf0192301ß09aasdfg   0</test>            <test> </test>  <test>12031</test>"

             + "\n" +

             "<test>" + "</test>" + "</main>";

For the XSL Transformation i'am using the following Java code:

StringReader reader = new StringReader(xmlContent);
  StringWriter writer = new StringWriter();
  TransformerFactory tFactory = TransformerFactory.newInstance();
  Transformer transformer = tFactory.newTransformer(new javax.xml.transform.stream.StreamSource(
     "style.xsl"));
  transformer.transform(new javax.xml.transform.stream.StreamSource(reader),
     new javax.xml.transform.stream.StreamResult(writer));
  String result = writer.toString();

My Output is:

<?xml version="1.0" encoding="UTF-8"?><main><test>123öü aksdjf0192301ß09aasdfg   0</test><test>12031</test></main>

That's exactly my expected result but when i add an entity for example '&' to my Input string the transformation fails.

With the error: The entity name must immediately follow the '&' in the entity reference.

How can i solve that Problem? And is XSL the correct why to implement a functionality like this?

I expect this Output:

 <?xml version="1.0" encoding="UTF-8"?><main><test>123öü aksdjf0192301ß09aasdfg   0</test><test>120>&& | 31</test></main>

With this Input:

 String s = "<main>           <test>123öü aksdjf0192301ß09aasdfg   0 >&& |  </test>            <test> </test>  <test>120>&& | 31</test>"

                 + "\n" +

                 "<test>" + "</test>" + "</main>";