ExceptionMapperFactory.java

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package com.sun.jersey.server.impl.application;

import com.sun.jersey.core.reflection.ReflectionHelper;
import com.sun.jersey.core.spi.component.ProviderServices;
import com.sun.jersey.spi.container.ExceptionMapperContext;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.util.HashSet;
import java.util.Set;
import javax.ws.rs.ext.ExceptionMapper;

/**
 *
 * @author Paul.Sandoz@Sun.Com
 */
public class ExceptionMapperFactory implements ExceptionMapperContext {
    
    private static class ExceptionMapperType {
        ExceptionMapper em;
        Class<? extends Throwable> c;
        
        public ExceptionMapperType(ExceptionMapper em, Class<? extends Throwable> c) {
            this.em = em;
            this.c = c;
        }
    } 

    private Set<ExceptionMapperType> emts = new HashSet<ExceptionMapperType>();
    
    public ExceptionMapperFactory() {
    }

    public void init(ProviderServices providerServices) {
        for (ExceptionMapper em : providerServices.getProviders(ExceptionMapper.class)) {
            Class<? extends Throwable> c = getExceptionType(em.getClass());
            if (c != null) {
                emts.add(new ExceptionMapperType(em, c));
            }
        }
    }

    // ExceptionMapperContext
    
    public ExceptionMapper find(Class<? extends Throwable> c) {
        int distance = Integer.MAX_VALUE;
        ExceptionMapper selectedEm = null;
        for (ExceptionMapperType emt : emts) {
            int d = distance(c, emt.c);
            if (d < distance) { 
                distance = d;
                selectedEm = emt.em;
                if (distance == 0) break;
            }
        }
        
        return selectedEm;
    }
    
    private int distance(Class<?> c, Class<?> emtc) {
        int distance = 0;
        if (!emtc.isAssignableFrom(c))
            return Integer.MAX_VALUE;
        
        while (c != emtc) {
            c = c.getSuperclass();
            distance++;
        }
        
        return distance;
    }
    
    @SuppressWarnings("unchecked")
    private Class<? extends Throwable> getExceptionType(Class<? extends ExceptionMapper> c) {
        Class<?> t = getType(c);
        if (Throwable.class.isAssignableFrom(t))
            return (Class<? extends Throwable>)t;
        
        // TODO log warning
        return null;
    }
    
    private Class getType(Class<? extends ExceptionMapper> c) {
        Class _c = c;
        while (_c != Object.class) {
            Type[] ts = _c.getGenericInterfaces();
            for (Type t : ts) {
                if (t instanceof ParameterizedType) {
                    ParameterizedType pt = (ParameterizedType)t;
                    if (pt.getRawType() == ExceptionMapper.class) {
                        return getResolvedType(pt.getActualTypeArguments()[0], c, _c);
                    }
                }
            }
            
            _c = _c.getSuperclass();
        }
        
        // This statement will never be reached
        return null;        
    }
    
    private Class getResolvedType(Type t, Class c, Class dc) {
        if (t instanceof Class)
            return (Class)t;
        else if (t instanceof TypeVariable) {
            ReflectionHelper.ClassTypePair ct = ReflectionHelper.
                    resolveTypeVariable(c, dc, (TypeVariable)t);
            if (ct != null)
                return ct.c;
            else 
                return null;
        } else if (t instanceof ParameterizedType) {
            ParameterizedType pt = (ParameterizedType)t;
            return (Class)pt.getRawType();
        } else {
            // TODO log 
            return null;
        }
    }
}