beanelresolver.java

java属性邦定的（JSR-295）的一个实现

/*
 * Copyright (C) 2007 Sun Microsystems, Inc. All rights reserved. Use is
 * subject to license terms.
 */

package org.jdesktop.el;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.beans.FeatureDescriptor;
import java.beans.BeanInfo;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.beans.IntrospectionException;
import java.util.Iterator;
import java.util.ArrayList;
import java.util.Map;
import java.util.HashMap;
import java.util.concurrent.ConcurrentHashMap;

/**
 * Defines property resolution behavior on objects using the JavaBeans
 * component architecture.
 *
 * <p>This resolver handles base objects of any type, as long as the
 * base is not <code>null</code>. It accepts any object as a property, and
 * coerces it to a string. That string is then used to find a JavaBeans
 * compliant property on the base object. The value is accessed using
 * JavaBeans getters and setters.</p>
 * 
 * <p>This resolver can be constructed in read-only mode, which means that
 * {@link #isReadOnly} will always return <code>true</code> and 
 * {@link #setValue} will always throw
 * <code>PropertyNotWritableException</code>.</p>
 *
 * <p><code>ELResolver</code>s are combined together using 
 * {@link CompositeELResolver}s, to define rich semantics for evaluating 
 * an expression. See the javadocs for {@link ELResolver} for details.</p>
 *
 * <p>Because this resolver handles base objects of any type, it should
 * be placed near the end of a composite resolver. Otherwise, it will
 * claim to have resolved a property before any resolvers that come after
 * it get a chance to test if they can do so as well.</p>
 *
 * @see CompositeELResolver
 * @see ELResolver
 * @since JSP 2.1
 */
public class BeanELResolver extends ELResolver {

    private boolean isReadOnly;

    // Set a limit for the number of beans in the cache.
    private final static int SIZE = 2000;
    // Two maps are used here, to facilitate discarding the older cache
    // when cache size reaches the limit.
    private static final Map<Class, BeanProperties> properties =
        new ConcurrentHashMap<Class, BeanProperties>(SIZE);
    private static final Map<Class, BeanProperties> properties2 =
        new ConcurrentHashMap<Class, BeanProperties>(SIZE);
                                                                                
    /*
     * Defines a property for a bean.
     */
    protected final static class BeanProperty {

        private Method readMethod;
        private Method writeMethod;
        private Class baseClass;
        private PropertyDescriptor descriptor;
                                                                                
        public BeanProperty(Class<?> baseClass,
                            PropertyDescriptor descriptor) {
            this.baseClass = baseClass;
            this.descriptor = descriptor;
        }
                                                                                
        public Class getPropertyType() {
            return descriptor.getPropertyType();
        }
                                                                                
        public boolean isReadOnly() {
            return getWriteMethod() == null;
        }
                                                                                
        public Method getReadMethod() {
            if (readMethod == null) {
                readMethod = getMethod(baseClass, descriptor.getReadMethod());
            }
            return readMethod;
        }
                                                                                
        public Method getWriteMethod() {
            if (writeMethod == null) {
                writeMethod = getMethod(baseClass, descriptor.getWriteMethod());
            }
            return writeMethod;
        }
    }
                                                                                
    /*
     * Defines the properties for a bean.
     */
    protected final static class BeanProperties {

        private final Class baseClass;
        private final Map<String, BeanProperty> propertyMap =
            new HashMap<String, BeanProperty>();
                                                                                
        public BeanProperties(Class<?> baseClass) {
            this.baseClass = baseClass;
            PropertyDescriptor[] descriptors;
            try {
                BeanInfo info = Introspector.getBeanInfo(baseClass);
                descriptors = info.getPropertyDescriptors();
            } catch (IntrospectionException ie) {
                throw new ELException(ie);
            }
            for (PropertyDescriptor pd: descriptors) {
                propertyMap.put(pd.getName(),
                                new BeanProperty(baseClass, pd));
            }
        }
                                                                                
        public BeanProperty getBeanProperty(String property) {
            return propertyMap.get(property);
        }
    }

    /**
     * Creates a new read/write <code>BeanELResolver</code>.
     */
    public BeanELResolver() {
        this.isReadOnly = false;
    }

    /**
     * Creates a new <code>BeanELResolver</code> whose read-only status is
     * determined by the given parameter.
     *
     * @param isReadOnly <code>true</code> if this resolver cannot modify
     *     beans; <code>false</code> otherwise.
     */
    public BeanELResolver(boolean isReadOnly) {
        this.isReadOnly = isReadOnly;
    }

    /**
     * If the base object is not <code>null</code>, returns the most 
     * general acceptable type that can be set on this bean property.
     *
     * <p>If the base is not <code>null</code>, the 
     * <code>propertyResolved</code> property of the <code>ELContext</code>
     * object must be set to <code>true</code> by this resolver, before
     * returning. If this property is not <code>true</code> after this 
     * method is called, the caller should ignore the return value.</p>
     *
     * <p>The provided property will first be coerced to a <code>String</code>.
     * If there is a <code>BeanInfoProperty</code> for this property and
     * there were no errors retrieving it, the <code>propertyType</code> of
     * the <code>propertyDescriptor</code> is returned. Otherwise, a
     * <code>PropertyNotFoundException</code> is thrown.</p>
     *
     * @param context The context of this evaluation.
     * @param base The bean to analyze.
     * @param property The name of the property to analyze. Will be coerced to
     *     a <code>String</code>.
     * @return If the <code>propertyResolved</code> property of 
     *     <code>ELContext</code> was set to <code>true</code>, then
     *     the most general acceptable type; otherwise undefined.
     * @throws NullPointerException if context is <code>null</code>
     * @throws PropertyNotFoundException if <code>base</code> is not
     *     <code>null</code> and the specified property does not exist
     *     or is not readable.
     * @throws ELException if an exception was thrown while performing
     *     the property or variable resolution. The thrown exception
     *     must be included as the cause property of this exception, if
     *     available.
     */
    public Class<?> getType(ELContext context,
                         Object base,
                         Object property) {

        if (context == null) {
            throw new NullPointerException();
        }

        if (base == null || property == null){
            return null;
        }

        BeanProperty bp = getBeanProperty(context, base, property);
        context.setPropertyResolved(true);
        return bp.getPropertyType();
    }

    /**
     * If the base object is not <code>null</code>, returns the current
     * value of the given property on this bean.
     *
     * <p>If the base is not <code>null</code>, the 
     * <code>propertyResolved</code> property of the <code>ELContext</code>
     * object must be set to <code>true</code> by this resolver, before
     * returning. If this property is not <code>true</code> after this 
     * method is called, the caller should ignore the return value.</p>
     *
     * <p>The provided property name will first be coerced to a
     * <code>String</code>. If the property is a readable property of the 
     * base object, as per the JavaBeans specification, then return the 
     * result of the getter call. If the getter throws an exception, 
     * it is propagated to the caller. If the property is not found or is 
     * not readable, a <code>PropertyNotFoundException</code> is thrown.</p>
     *
     * @param context The context of this evaluation.
     * @param base The bean on which to get the property.
     * @param property The name of the property to get. Will be coerced to
     *     a <code>String</code>.
     * @return If the <code>propertyResolved</code> property of 
     *     <code>ELContext</code> was set to <code>true</code>, then
     *     the value of the given property. Otherwise, undefined.
     * @throws NullPointerException if context is <code>null</code>.
     * @throws PropertyNotFoundException if <code>base</code> is not
     *     <code>null</code> and the specified property does not exist
     *     or is not readable.
     * @throws ELException if an exception was thrown while performing
     *     the property or variable resolution. The thrown exception
     *     must be included as the cause property of this exception, if
     *     available.
     */
    public Object getValue(ELContext context,
                           Object base,
                           Object property) {

        if (context == null) {
            throw new NullPointerException();
        }

        if (base == null || property == null) {
            return null;
        }

        Method method;
        BeanProperty bp = getBeanProperty(context, base, property);
        if (bp == null || (method = bp.getReadMethod()) == null) {
            return null;
        }

        Object value;
        try {
            value = method.invoke(base, new Object[0]);
            context.setPropertyResolved(true);
        } catch (ELException ex) {
            throw ex;
        } catch (InvocationTargetException ite) {
            throw new ELException(ite.getCause());
        } catch (Exception ex) {
            throw new ELException(ex);
        }
        return value;
    }

    /**
     * If the base object is not <code>null</code>, attempts to set the
     * value of the given property on this bean.
     *
     * <p>If the base is not <code>null</code>, the 
     * <code>propertyResolved</code> property of the <code>ELContext</code>
     * object must be set to <code>true</code> by this resolver, before
     * returning. If this property is not <code>true</code> after this 
     * method is called, the caller can safely assume no value was set.</p>
     *