Assuming that your XML won't change of structure over time, you can generate a XSD file from a tool like http://www.freeformatter.com/xsd-generator.html.
Here it gives me:
<xs:schema attributeFormDefault="unqualified" elementFormDefault="qualified"
xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="tag1">
<xs:complexType>
<xs:sequence>
<xs:element name="tag2">
<xs:complexType>
<xs:sequence>
<xs:element name="tag3">
<xs:complexType>
<xs:sequence>
<xs:element type="xs:string" name="tag4"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>
Then you can store this schema on your local file system, and launch the command xjc myFile.xsd which will generate JAXB files for you.
More details about xjc, here