如何从 Java 中的 XML 读取特殊字符的映射？

Question

I'm not sure if this is possible, but I am writing a program that converts data from a database into XML. The issue is that some of the values in the database have special characters. We have the typical XML special characters hardcoded in a map, but we would like to have a configurable XML mapping file that we will read at run time.

    <mapping source="ÿ" target="&#255;"/>
    <mapping source="þ" target="&#254;"/>
    <mapping source="ý" target="&#253;"/>
    <mapping source="ü" target="&#252;"/>
    <mapping source="û" target="&#251;"/>
    <mapping source="ú" target="&#250;"/>

We are using xstream to read the XML.

public class CharMapping {

    private static final String CHAR_MAPPING_FILE = "char_mapping.xml";
    private static final String XML_ROOT_ELEMENT = "mappings";

    private static String readXmlFile(String filename) {
        StringBuffer xmlContent = new StringBuffer();
        try (BufferedReader br = new BufferedReader(
                new InputStreamReader(new FileInputStream(filename),"ISO-8859-1"))) {

            String currentLine;

            while ((currentLine = br.readLine()) != null) {
                xmlContent.append(currentLine);
            }

        } catch (IOException e) {
            e.printStackTrace();
        }
        return xmlContent.toString();
    }

    @SuppressWarnings("unchecked")
    public static Map<String, String> getCharMapping() {
        XStream xstream = new XStream();
        xstream.alias(XML_ROOT_ELEMENT, java.util.Map.class);
        xstream.registerConverter(new XMLConfigConverter("source", "target", null, null));

        String xml = readXmlFile(CHAR_MAPPING_FILE);
        Map<String, String> relationsMapping = (Map<String, String>) xstream.fromXML(xml);
        return relationsMapping;
    }
}

public class XMLConfigConverter implements Converter {

    private String keyAttribute;
    private String valueAttribute;
    private String filterAttribute;
    private String filterValue;

    public XMLConfigConverter(String keyAttribute, String valueAttribute, String filterAttribute,
            String filterValue) {
        this.keyAttribute = keyAttribute;
        this.valueAttribute = valueAttribute;
        this.filterAttribute = filterAttribute;
        this.filterValue = filterValue;
    }

    @SuppressWarnings("rawtypes")
    public boolean canConvert(Class clazz) {
        return AbstractMap.class.isAssignableFrom(clazz);
    }

    @Override
    public void marshal(Object arg0, HierarchicalStreamWriter writer, MarshallingContext context) {
    }

    @Override
    public Object unmarshal(HierarchicalStreamReader reader, UnmarshallingContext context) {
        Map<String, String> map = new HashMap<String, String>();

        while (reader.hasMoreChildren()) {
            reader.moveDown();
            if (reader.getNodeName().equals("mapping")) {
                if (filterAttribute != null && filterValue != null) {
                    if (reader.getAttribute(filterAttribute).equals(filterValue)) {
                        putValueInMap(reader, map);
                    }
                } else {
                    putValueInMap(reader, map);
                }
            }
            reader.moveUp();
        }
        for(String charKey : map.keySet()) {
            System.out.println("mapping: " + charKey + " - " + map.get(charKey));       }
        return map;
    }

    private void putValueInMap(HierarchicalStreamReader reader, Map<String, String> map) {
        String key = reader.getAttribute(keyAttribute);
        String value = reader.getAttribute(valueAttribute);
        System.out.println("Key: " + key + " - Value: " + value);
        map.put(key, value);
    }

}

The output is:

Key: ?¿ - Value: ÿ
Key: ?? - Value: ?
Key: ?½ - Value: ?
Key: ?¼ - Value: ü
Key: ?» - Value: û
Key: ?º - Value: ú

I know this seems a bit weird to pull mappings for an XML FROM an XML. Idf this isn't possible is there any advice on a better solution? Would a CSV mapping be better?

Thanks!

Answer 1

Your bug is probably in the line

 new InputStreamReader(new FileInputStream(filename),"ISO-8859-1")))

where you are decoding the file using Java, rather than letting the XML parser do the decoding. From the evidence of your output, it appears the file is not encoded in iso-8859-1, but in utf-8, and if you had left the XML parser to do the decoding it would probably have got it right.

I don't actually know XStream, but the Javadoc says there is a version of the fromXML() method that accepts a File as input. I suggest you use that version of the method, which is likely to get the decoding right, and get rid of your readXmlFile() method, which appears to be getting it wrong.

It is possible, of course, that you will still have problems: perhaps the file is encoded in UTF-8 but declares its encoding as ISO-8859-1. But I think there's a good chance this change will fix it.