purejavareflectionprovider.java

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/*
 * 	This program is free software; you can redistribute it and/or modify it under the terms of 
 * the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, 
 * or (at your option) any later version. 
 * 
 * 	This program is distributed in the hope that it will be useful, 
 * but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  
 * See the GNU General Public License for more details. 
 * 	You should have received a copy of the GNU General Public License along with this program; 
 * if not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 */
package com.meidusa.amoeba.bean;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectStreamClass;
import java.io.ObjectStreamConstants;
import java.io.Serializable;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

import com.meidusa.amoeba.util.JVM;


/**
 * Pure Java ObjectFactory that instantiates objects using standard Java reflection, however the types of objects
 * that can be constructed are limited.
 * <p/>
 * Can newInstance: classes with public visibility, outer classes, static inner classes, classes with default constructors
 * and any class that implements java.io.Serializable.
 * Cannot newInstance: classes without public visibility, non-static inner classes, classes without default constructors.
 * Note that any code in the constructor of a class will be executed when the ObjectFactory instantiates the object.
 * </p>
 */
@SuppressWarnings("unchecked")
public class PureJavaReflectionProvider implements ReflectionProvider {

    private transient Map serializedDataCache = Collections.synchronizedMap(new HashMap());
    protected transient FieldDictionary fieldDictionary = new FieldDictionary();

    public Object newInstance(Class type) {
        try {
            Constructor[] constructors = type.getDeclaredConstructors();
            for (int i = 0; i < constructors.length; i++) {
                if (constructors[i].getParameterTypes().length == 0) {
                    if (!Modifier.isPublic(constructors[i].getModifiers())) {
                        constructors[i].setAccessible(true);
                    }
                    return constructors[i].newInstance(new Object[0]);
                }
            }
            if (Serializable.class.isAssignableFrom(type)) {
                return instantiateUsingSerialization(type);
            } else {
                throw new ObjectAccessException("Cannot construct " + type.getName()
                        + " as it does not have a no-args constructor");
            }
        } catch (InstantiationException e) {
            throw new ObjectAccessException("Cannot construct " + type.getName(), e);
        } catch (IllegalAccessException e) {
            throw new ObjectAccessException("Cannot construct " + type.getName(), e);
        } catch (InvocationTargetException e) {
            if (e.getTargetException() instanceof RuntimeException) {
                throw (RuntimeException)e.getTargetException();
            } else if (e.getTargetException() instanceof Error) {
                throw (Error)e.getTargetException();
            } else {
                throw new ObjectAccessException("Constructor for " + type.getName() + " threw an exception", e.getTargetException());
            }
        }
    }

    private Object instantiateUsingSerialization(Class type) {
        try {
            byte[] data;
            if (serializedDataCache.containsKey(type)) {
                data = (byte[]) serializedDataCache.get(type);
            } else {
                ByteArrayOutputStream bytes = new ByteArrayOutputStream();
                DataOutputStream stream = new DataOutputStream(bytes);
                stream.writeShort(ObjectStreamConstants.STREAM_MAGIC);
                stream.writeShort(ObjectStreamConstants.STREAM_VERSION);
                stream.writeByte(ObjectStreamConstants.TC_OBJECT);
                stream.writeByte(ObjectStreamConstants.TC_CLASSDESC);
                stream.writeUTF(type.getName());
                stream.writeLong(ObjectStreamClass.lookup(type).getSerialVersionUID());
                stream.writeByte(2);  // classDescFlags (2 = Serializable)
                stream.writeShort(0); // field count
                stream.writeByte(ObjectStreamConstants.TC_ENDBLOCKDATA);
                stream.writeByte(ObjectStreamConstants.TC_NULL);
                data = bytes.toByteArray();
                serializedDataCache.put(type, data);
            }

            ObjectInputStream in = new ObjectInputStream(new ByteArrayInputStream(data));
            return in.readObject();
        } catch (IOException e) {
            throw new ObjectAccessException("Cannot create " + type.getName() + " by JDK serialization", e);
        } catch (ClassNotFoundException e) {
            throw new ObjectAccessException("Cannot find class " + e.getMessage());
        }
    }

    public void visitSerializableFields(Object object, ReflectionProvider.Visitor visitor) {
        for (Iterator iterator = fieldDictionary.serializableFieldsFor(object.getClass()); iterator.hasNext();) {
            Field field = (Field) iterator.next();
            if (!fieldModifiersSupported(field)) {
                continue;
            }
            validateFieldAccess(field);
            try {
                Object value = field.get(object);
                visitor.visit(field.getName(), field.getType(), field.getDeclaringClass(), value);
            } catch (IllegalArgumentException e) {
                throw new ObjectAccessException("Could not get field " + field.getClass() + "." + field.getName(), e);
            } catch (IllegalAccessException e) {
                throw new ObjectAccessException("Could not get field " + field.getClass() + "." + field.getName(), e);
            }
        }
    }

    public void writeField(Object object, String fieldName, Object value, Class definedIn) {
        Field field = fieldDictionary.field(object.getClass(), fieldName, definedIn);
        validateFieldAccess(field);
        try {
            field.set(object, value);
        } catch (IllegalArgumentException e) {
            throw new ObjectAccessException("Could not set field " +field.getName()+"@"+ object.getClass() , e);
        } catch (IllegalAccessException e) {
        	throw new ObjectAccessException("Could not set field " +field.getName()+"@"+ object.getClass() , e);
        }
    }

    public void invokeMethod(Object object, String methodName, Object value, Class definedIn) {
    	try {
    		Method method = object.getClass().getMethod(methodName,new Class[]{value.getClass()});
    		method.invoke(object,new Object[]{value});
        } catch (Exception e) {
            throw new ObjectAccessException("Could not invoke " + object.getClass() + "." + methodName, e);
        }
    }
    
    public Class getFieldType(Object object, String fieldName, Class definedIn) {
        return fieldDictionary.field(object.getClass(), fieldName, definedIn).getType();
    }

    public boolean fieldDefinedInClass(String fieldName, Class type) {
        try {
            Field field = fieldDictionary.field(type, fieldName, null);
            return fieldModifiersSupported(field);
        } catch (ObjectAccessException e) {
            return false;
        }
    }

    protected boolean fieldModifiersSupported(Field field) {
        return !(Modifier.isStatic(field.getModifiers())
                || Modifier.isTransient(field.getModifiers()));
    }

    protected void validateFieldAccess(Field field) {
        if (Modifier.isFinal(field.getModifiers())) {
            if (JVM.is15()) {
                field.setAccessible(true);
            } else {
                throw new ObjectAccessException("Invalid final field "
                        + field.getDeclaringClass().getName() + "." + field.getName());
            }
        }
    }

    public Field getField(Class definedIn, String fieldName) {
        return fieldDictionary.field(definedIn, fieldName, null);
    }

    protected Object readResolve() {
        serializedDataCache = Collections.synchronizedMap(new HashMap());
        fieldDictionary = new FieldDictionary();
        return this;
    }

}