core/src/main/java/org/apache/ki/config/ReflectionBuilder.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.ki.config;

import java.beans.PropertyDescriptor;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Map;

import org.apache.commons.beanutils.BeanUtils;
import org.apache.commons.beanutils.PropertyUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.apache.ki.util.ClassUtils;
import org.apache.ki.util.Nameable;


/**
 * Object builder that uses reflection and Apache Commons BeanUtils to build objects given a
 * map of "property values".  Typically these come from the Ki INI configuration and are used
 * to construct or modify the SecurityManager, its dependencies, and web-based security filters.
 *
 * @author Les Hazlewood
 * @author Jeremy Haile
 * @since 0.9
 */
@SuppressWarnings("unchecked")
public class ReflectionBuilder {

    //TODO - complete JavaDoc

    private static final Logger log = LoggerFactory.getLogger(ReflectionBuilder.class);

    private static final String OBJECT_REFERENCE_BEGIN_TOKEN = "$";
    private static final String ESCAPED_OBJECT_REFERENCE_BEGIN_TOKEN = "\\$";
    private static final String GLOBAL_PROPERTY_PREFIX = "ki";


    protected Map objects;

    public ReflectionBuilder() {
        setObjects(new LinkedHashMap<String, Object>());
    }

    public ReflectionBuilder(Map defaults) {
        setObjects(defaults);
    }

    public Map getObjects() {
        return objects;
    }

    public void setObjects(Map objects) {
        this.objects = objects;
    }

    public Map buildObjects(Map<String, String> kvPairs) {
        if (kvPairs != null && !kvPairs.isEmpty()) {

            // Separate key value pairs into object declarations and property assignment
            // so that all objects can be created up front
            Map<String, String> instanceMap = new HashMap<String, String>();
            Map<String, String> propertyMap = new HashMap<String, String>();
            for (Map.Entry<String, String> entry : kvPairs.entrySet()) {
                if (entry.getKey().indexOf('.') < 0 || entry.getKey().endsWith(".class")) {
                    instanceMap.put(entry.getKey(), entry.getValue());
                } else {
                    propertyMap.put(entry.getKey(), entry.getValue());
                }
            }

            // Create all instances
            for (Map.Entry<String, String> entry : instanceMap.entrySet()) {
                createNewInstance(objects, entry.getKey(), entry.getValue());
            }

            // Set all properties
            for (Map.Entry<String, String> entry : propertyMap.entrySet()) {
                applyProperty(entry.getKey(), entry.getValue(), objects);
            }
        }

        return objects;
    }

    protected void createNewInstance(Map objects, String name, String value) {

        Object currentInstance = objects.get(name);
        if (currentInstance != null) {
            log.info("An instance with name [" + name + "] already exists.  " +
                    "Redefining this object as a new instance of type [" + value + "].");
        }

        Object instance;//name with no property, assume right hand side of equals sign is the class name:
        try {
            instance = ClassUtils.newInstance(value);
            if (instance instanceof Nameable) {
                ((Nameable) instance).setName(name);
            }
        } catch (Exception e) {
            String msg = "Unable to instantiate class [" + value + "] for object named '" + name + "'.  " +
                    "Please ensure you've specified the fully qualified class name correctly.";
            throw new ConfigurationException(msg, e);
        }
        objects.put(name, instance);
    }

    protected void applyProperty(String key, String value, Map objects) {

        int index = key.indexOf('.');

        if (index >= 0) {
            String name = key.substring(0, index);
            String property = key.substring(index + 1, key.length());

            if (GLOBAL_PROPERTY_PREFIX.equalsIgnoreCase(name)) {
                applyGlobalProperty(objects, property, value);
            } else {
                applySingleProperty(objects, name, property, value);
            }


        } else {
            throw new IllegalArgumentException("All property keys must contain a '.' character. " +
                    "(e.g. myBean.property = value)  These should already be separated out by buildObjects().");
        }
    }

    protected void applyGlobalProperty(Map objects, String property, String value) {
        for (Object instance : objects.values()) {
            try {
                PropertyDescriptor pd = PropertyUtils.getPropertyDescriptor(instance, property);
                if (pd != null) {
                    applyProperty(instance, property, value);
                }
            } catch (Exception e) {
                String msg = "Error retrieving property descriptor for instance " +
                        "of type [" + instance.getClass().getName() + "] " +
                        "while setting property [" + property + "]";
                throw new ConfigurationException(msg, e);
            }
        }
    }

    protected void applySingleProperty(Map objects, String name, String property, String value) {
        Object instance = objects.get(name);
        if (property.equals("class")) {
            throw new IllegalArgumentException("Property keys should not contain 'class' properties since these " +
                    "should already be separated out by buildObjects().");

        } else if (instance == null) {
            String msg = "Configuration error.  Specified object [" + name + "] with property [" +
                    property + "] without first defining that object's class.  Please first " +
                    "specify the class property first, e.g. myObject.class = fully_qualified_class_name " +
                    "and then define additional properties.";
            throw new IllegalArgumentException(msg);

        } else {
            applyProperty(instance, property, value);
        }
    }

    protected boolean isReference(String value) {
        return value != null && value.startsWith(OBJECT_REFERENCE_BEGIN_TOKEN);
    }

    protected String getId(String referenceToken) {
        return referenceToken.substring(OBJECT_REFERENCE_BEGIN_TOKEN.length());
    }

    protected Object getReferencedObject(String id) {
        Object o = objects != null && !objects.isEmpty() ? objects.get(id) : null;
        if (o == null) {
            String msg = "The object with id [" + id + "] has not yet been defined and therefore cannot be " +
                    "referenced.  Please ensure objects are defined in the order in which they should be " +
                    "created and made avaialable for future reference.";
            throw new UnresolveableReferenceException(msg);
        }
        return o;
    }

    protected String unescapeIfNecessary(String value) {
        if (value != null && value.startsWith(ESCAPED_OBJECT_REFERENCE_BEGIN_TOKEN)) {
            return value.substring(ESCAPED_OBJECT_REFERENCE_BEGIN_TOKEN.length() - 1);
        }
        return value;
    }

    protected void applyProperty(Object object, String propertyName, String stringValue) {

        Object value;

        if (isReference(stringValue)) {
            String id = getId(stringValue);
            if (log.isDebugEnabled()) {
                log.debug("Encountered object reference [" + stringValue + "].  Looking up object " +
                        "with id [" + id + "]");
            }
            value = getReferencedObject(id);
        } else {
            value = unescapeIfNecessary(stringValue);
        }

        try {
            if (log.isTraceEnabled()) {
                log.trace("Applying property [" + propertyName + "] value [" + value + "] on object of type [" + object.getClass().getName() + "]");
            }
            BeanUtils.setProperty(object, propertyName, value);
        } catch (Exception e) {
            String msg = "Unable to set property [" + propertyName + "] with value [" + stringValue + "].  If " +
                    "'" + stringValue + "' is a reference to another (previously defined) object, please prefix it with " +
                    "'" + OBJECT_REFERENCE_BEGIN_TOKEN + "' to indicate that the referenced " +
                    "object should be used as the actual value.  " +
                    "For example, " + OBJECT_REFERENCE_BEGIN_TOKEN + stringValue;
            throw new ConfigurationException(msg, e);
        }
    }

}