How to bind ServletRequest params to domain objects?

I want to bind parameters of a ServletRequest to arbitrary domain objects. Params are available as a map of type

Map<String, String[]> // String = key, String[] = values

They should be converte开发者_JS百科d and bound to the fields of the target object. Id like to have a method like this:

// definition: 
public void bind(Map<String, String[]>, T target)

// usage:
bind(request.getParameterMap(), domainObject);

What is the best way to bind request parameters to a domain object in a Java Servlet? What libs are available for this purpose or how would you write one?

Have you looked into the Spring MVC (http://springsource.org) framework at all? It provides binding functionality which you can use outside of Spring. Also, if you are not currently using another MVC framework, it's a good one to consider.

I'd say it depends on what kind of object the actual domainObject is. If it's a bean, you could use an reflection based automated bean populator such as my BeanPropertyController (it's free so give it a try! License is ASF2.0) to do the following:

/* Assumed parameter input:
 * a=hello
 * c=123
 * e=f,g,h
 * 
 * Matching bean:  
 */
public class ParamBean {
    private String a;
    private int c;
    private String[] e;
    /* + all the normal getters and setters you'd see in a bean */
}

/* somewhere in your servlet: */

BeanPropertyController bpc = BeanPropertyController.of(ParamBean.class);

for (Entry<String, String[]> entry : request.getParameterMap().entrySet()) {
    bpc.mutate(entry.getKey(),
               getNiceValue(entry.getValue(), bpc.typeOf(entry.getKey()));
}

ParamBean bean = bpc.getObject(ParamBean.class);

/* somewhere else in the class */

public Object getNiceValue(String[] objs, Class<?> desiredClass) {
    if (objs.length == 1) {
        Object o = objs[0];
        return convertString(o);
    } else {
        Object[] newObjs = Object[objs.length];

        for (int i=0;i<objs.length;i++) {
            newObjs[i] = convertString(objs[i]);
        }

        return (Object) newObjs;
    }
}

private Object convertString(String value, Class<> desiredClass) {
    if (Number.class.isAssignableFrom(desiredClass)) {
        Double d = null;
        try {
            d = Double.parseDouble(value)
        } catch (NumberFormatException e) {
            // Not of the desired type, do whatever you want
        }
        if (Double.class.isAssignableFrom(desiredClass)) {
            return d;
        } else if (Long.class.isAssignableFrom(desiredClass)) {
            return d.longValue();
        } else if (Integer.class.isAssignableFrom(desiredClass)) {
            return d.intValue();
        } // and so on...
    } else if (Boolean.class.isAssignableFrom(desiredClass)) {
        try {
            return Boolean.valueOf(value);
        } catch (NullPointerException e) {
            // Not of the desired type, do whatever you want
        }
    } else {
        return value; // or whatever your default type is
    }
}