To convert XML File in to JSON include the following dependency
<dependency>
    <groupId>org.json</groupId>
    <artifactId>json</artifactId>
    <version>20140107</version>
</dependency>
and you can Download Jar from Maven Repository here. Then implement as:
String soapmessageString = "<xml>yourStringURLorFILE</xml>";
JSONObject soapDatainJsonObject = XML.toJSONObject(soapmessageString);
System.out.println(soapDatainJsonObject);