Generate Map from POJO

Question

I have a POJO, and a (currently not-yet-built) class that will return Lists of it. I\'d like to automatically generate the code necessary for the POJO to be accessed as a Map. I

Answer 1

Here's my own implementation without any dependencies. Rather than make a copy of the object's state, it implements a live Map over the pojo. Android doesn't support java.beans, but you can use openbeans instead.

import java.beans.*;  // Or, import com.googlecode.openbeans.*
import java.util.*;

public class BeanMap extends AbstractMap {
    private static final Object[] NO_ARGS = new Object[] {};
    private HashMap properties;
    private Object bean;

    public BeanMap(Object bean) throws IntrospectionException {
        this.bean = bean;
        properties = new HashMap();
        BeanInfo info = Introspector.getBeanInfo(bean.getClass());
        for(PropertyDescriptor property : info.getPropertyDescriptors()) {
            properties.put(property.getName(), property);
        }
    }

    @Override public Object get(Object key) {
        PropertyDescriptor property = properties.get(key);
        if(property == null)
            return null;
        try {
            return property.getReadMethod().invoke(bean, NO_ARGS);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    @Override public Object put(String key, Object value) {
        PropertyDescriptor property = properties.get(key);
        try {
            return property.getWriteMethod().invoke(bean, new Object[] {value});
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    @Override public Set> entrySet() {
        HashSet> result = new HashSet>(properties.size() * 2);
        for(PropertyDescriptor property : properties.values()) {
            String key = property.getName();
            Object value;
            try {
                value = property.getReadMethod().invoke(bean, NO_ARGS);
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
            result.add(new PropertyEntry(key, value));
        }
        return Collections.unmodifiableSet(result);
    }

    @Override public int size() { return properties.size(); }

    @Override public boolean containsKey(Object key) { 
        return properties.containsKey(key);
    }

    class PropertyEntry extends AbstractMap.SimpleEntry {
        PropertyEntry(String key, Object value) {
            super(key, value);
        }

        @Override public Object setValue(Object value) {
            super.setValue(value);
            return BeanMap.this.put(getKey(), value);
        }
    }
}