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There is a newer version: 3.9.0
/*
 * tksCommons / mugwort
 *
 * Author : Thomas Kuhlmann (ThK-Systems, http://oss.thk-systems.de) License : LGPL (https://www.gnu.org/licenses/lgpl.html)
 */
package de.thksystems.persistence.xstream.converters;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.math.BigDecimal;
import java.util.HashMap;
import java.util.Map;

import com.thoughtworks.xstream.XStreamException;
import com.thoughtworks.xstream.annotations.XStreamConverter;
import com.thoughtworks.xstream.converters.Converter;
import com.thoughtworks.xstream.converters.MarshallingContext;
import com.thoughtworks.xstream.converters.UnmarshallingContext;
import com.thoughtworks.xstream.io.HierarchicalStreamReader;
import com.thoughtworks.xstream.io.HierarchicalStreamWriter;

/**
 * Converts a map to a list of xml-attributes. The key of the {@link Map} becomes the name of the xml-attribute, and the value of the {@link Map} becomes the value of the xml-attribute.
 * 
 * For example
 * 

 * The following {@link Map} named 'myMap':
 * 

 * firstname -> homer
 * lastname -> simpson
 * spouse- > marge
 * 
 * will be converted to the following XML:
 * 
 * 
 * {@code
 * 
 * }
 * 
 * 
 * Usage
 * 

 * Use the converter by adding a {@link XStreamConverter} annotation, like:
 * 

 * @XStreamConverter(MapToAttributesConverter.class)
 * 

 * 

 * 

 * Allowed Parameter Types
 * 

 * The default use of the converter is for {@link Map} of {@link String},{@link String}. The type of the key must be {@link String}.
 * 

 * As the value type another type may be choosen. This type must be 'convertable' to {@link String}, so it must have a usable {@link #toString()} method and a constructor which takes a single {@link String} as its only argument. (Example types: {@link Integer}, {@link Long}, {@link BigDecimal}.) You need to specify the value type to the {@link XStreamConverter} annotation like this:
 * 
 * @XStreamConverter(value = MapToAttributesConverter.class, useImplicitType = false, types = { Integer.class }).
 */
public class MapToAttributesConverter implements Converter {

    protected static final Class TARGET_CLASS = Map.class;
    private Class valueClass = String.class;
    private Constructor valueClassConstructor;

    public MapToAttributesConverter() {
        this(String.class);
    }

    public MapToAttributesConverter(Class valueClass) {
        if (!TARGET_CLASS.isAssignableFrom(valueClass)) {
            this.valueClass = valueClass;
            checkValueClass();
        }
    }

    private void checkValueClass() {
        if (!String.class.isAssignableFrom(valueClass)) {
            Class[] parameterTypes = new Class[]{String.class};
            try {
                valueClassConstructor = valueClass.getConstructor(parameterTypes);
            } catch (NoSuchMethodException e) {
                throw new IllegalArgumentException("Value class cannot be converted to string: " + valueClass);
            } catch (SecurityException e) {
                throw new IllegalArgumentException("Cannot check value class: " + e.getMessage(), e);
            }
        }
    }

    @SuppressWarnings("rawtypes")
    @Override
    public boolean canConvert(Class type) {
        return TARGET_CLASS.isAssignableFrom(type);
    }

    @Override
    @SuppressWarnings({"unchecked"})
    public void marshal(Object source, HierarchicalStreamWriter writer, MarshallingContext context) {
        Map map = (Map) source;
        for (Map.Entry entry : map.entrySet()) {
            writer.addAttribute(entry.getKey(), entry.getValue().toString());
        }
    }

    @Override
    public Object unmarshal(HierarchicalStreamReader reader, UnmarshallingContext context) {
        Map map = new HashMap<>();
        for (int i = 0; i < reader.getAttributeCount(); i++) {
            String key = reader.getAttributeName(i);
            String valueString = reader.getAttribute(key);
            Object valueObject;
            if (valueClassConstructor != null) {
                try {
                    valueObject = valueClassConstructor.newInstance(valueString);
                } catch (InstantiationException | IllegalAccessException | IllegalArgumentException | InvocationTargetException e) {
                    throw new XStreamException(String.format("Cannot convert string value '%s' to class '%s': %s", valueString, valueClass, e.getMessage()), e);
                }
            } else {
                valueObject = valueString;
            }
            map.put(key, valueObject);
        }
        return map;
    }
}