api/src/main/java/javax/el/ArrayELResolver.java

/*
 * Copyright (c) 1997-2018 Oracle and/or its affiliates. All rights reserved.
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed 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 javax.el;

import java.lang.reflect.Array;
import java.util.List;
import java.util.Iterator;
import java.beans.FeatureDescriptor;

/**
 * Defines property resolution behavior on arrays.
 *
 * <p>This resolver handles base objects that are Java language arrays.
 * It accepts any object as a property and coerces that object into an
 * integer index into the array. The resulting value is the value in the array
 * at that index.</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>
 *
 * @see CompositeELResolver
 * @see ELResolver
 * @since JSP 2.1
 */
public class ArrayELResolver extends ELResolver {

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

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

    /**
     * If the base object is an array, returns the most general acceptable type 
     * for a value in this array.
     *
     * <p>If the base is a <code>array</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>Assuming the base is an <code>array</code>, this method will always
     * return <code>base.getClass().getComponentType()</code>, which is
     * the most general type of component that can be stored at any given
     * index in the array.</p>
     *
     * @param context The context of this evaluation.
     * @param base The array to analyze. Only bases that are Java language
     *     arrays are handled by this resolver.
     * @param property The index of the element in the array to return the 
     *     acceptable type for. Will be coerced into an integer, but 
     *     otherwise ignored by this resolver.
     * @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 PropertyNotFoundException if the given index is out of 
     *     bounds for this array.
     * @throws NullPointerException if context is <code>null</code>
     * @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 && base.getClass().isArray()) {
            context.setPropertyResolved(true);
            int index = toInteger (property);
            if (index < 0 || index >= Array.getLength(base)) {
                throw new PropertyNotFoundException();
            }
            return base.getClass().getComponentType();
        }
        return null;
    }

    /**
     * If the base object is a Java language array, returns the value at the 
     * given index. The index is specified by the <code>property</code> 
     * argument, and coerced into an integer. If the coercion could not be 
     * performed, an <code>IllegalArgumentException</code> is thrown. If the
     * index is out of bounds, <code>null</code> is returned.
     *
     * <p>If the base is a Java language array, 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>
     *
     * @param context The context of this evaluation.
     * @param base The array to analyze. Only bases that are Java language
     *     arrays are handled by this resolver.
     * @param property The index of the value to be returned. Will be coerced
     *     into an integer.
     * @return If the <code>propertyResolved</code> property of 
     *     <code>ELContext</code> was set to <code>true</code>, then
     *     the value at the given index or <code>null</code>
     *     if the index was out of bounds. Otherwise, undefined.
     * @throws IllegalArgumentException if the property could not be coerced
     *     into an integer.
     * @throws NullPointerException if context is <code>null</code>.
     * @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 && base.getClass().isArray()) {
            context.setPropertyResolved(base, property);
            int index = toInteger (property);
            if (index >= 0 && index < Array.getLength(base)) {
                return Array.get(base, index);
            }
        }
        return null;
    }

    /**
     * If the base object is a Java language array, attempts to set the 
     * value at the given index with the given value. The index is specified 
     * by the <code>property</code> argument, and coerced into an integer. 
     * If the coercion could not be performed, an 
     * <code>IllegalArgumentException</code> is thrown. If the index is
     * out of bounds, a <code>PropertyNotFoundException</code> is thrown.
     *
     * <p>If the base is a Java language array, 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>
     *
     * <p>If this resolver was constructed in read-only mode, this method will
     * always throw <code>PropertyNotWritableException</code>.</p>
     *
     * @param context The context of this evaluation.
     * @param base The array to be modified. Only bases that are Java language
     *     arrays are handled by this resolver.
     * @param property The index of the value to be set. Will be coerced
     *     into an integer.
     * @param val The value to be set at the given index.
     * @throws ClassCastException if the class of the specified element 
     *     prevents it from being added to this array.
     * @throws NullPointerException if context is <code>null</code>.
     * @throws IllegalArgumentException if the property could not be coerced
     *     into an integer, or if some aspect of the specified element 
     *     prevents it from being added to this array.
     * @throws PropertyNotWritableException if this resolver was constructed
     *     in read-only mode.
     * @throws PropertyNotFoundException if the given index is out of 
     *     bounds for this array.
     * @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 void setValue(ELContext context,
                         Object base,
                         Object property,
                         Object val) {

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

        if (base != null && base.getClass().isArray()) {
            context.setPropertyResolved(base, property);
            if (isReadOnly) {
                throw new PropertyNotWritableException();
            }
            Class<?> type = base.getClass().getComponentType();
            if (val != null && ! type.isAssignableFrom(val.getClass())) {
                throw new ClassCastException();
            }
            int index = toInteger (property);
            if (index < 0 || index >= Array.getLength(base)) {
                throw new PropertyNotFoundException();
            }
            Array.set(base, index, val);
        }
    }

    /**
     * If the base object is a Java language array, returns whether a call to 
     * {@link #setValue} will always fail.
     *
     * <p>If the base is a Java language array, 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>If this resolver was constructed in read-only mode, this method will
     * always return <code>true</code>. Otherwise, it returns 
     * <code>false</code>.</p>
     *
     * @param context The context of this evaluation.
     * @param base The array to analyze. Only bases that are a Java language
     *     array are handled by this resolver.
     * @param property The index of the element in the array to return the 
     *     acceptable type for. Will be coerced into an integer, but 
     *     otherwise ignored by this resolver.
     * @return If the <code>propertyResolved</code> property of 
     *     <code>ELContext</code> was set to <code>true</code>, then
     *     <code>true</code> if calling the <code>setValue</code> method
     *     will always fail or <code>false</code> if it is possible that
     *     such a call may succeed; otherwise undefined.
     * @throws PropertyNotFoundException if the given index is out of 
     *     bounds for this array.
     * @throws NullPointerException if context is <code>null</code>
     * @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 boolean isReadOnly(ELContext context,
                              Object base,
                              Object property) {

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

        if (base != null && base.getClass().isArray()) {
            context.setPropertyResolved(true);
            int index = toInteger (property);
            if (index < 0 || index >= Array.getLength(base)) {
                throw new PropertyNotFoundException();
            }
        }
        return isReadOnly;
    }

    /**
     * Always returns <code>null</code>, since there is no reason to 
     * iterate through set set of all integers.
     *
     * <p>The {@link #getCommonPropertyType} method returns sufficient
     * information about what properties this resolver accepts.</p>
     *
     * @param context The context of this evaluation.
     * @param base The array to analyze. Only bases that are a Java language
     *     array are handled by this resolver.
     * @return <code>null</code>.
     */
    public Iterator<FeatureDescriptor> getFeatureDescriptors(
                                          ELContext context,
                                          Object base) {
        return null;
    }

    /**
     * If the base object is a Java language array, returns the most general 
     * type that this resolver accepts for the <code>property</code> argument.
     * Otherwise, returns <code>null</code>.
     *
     * <p>Assuming the base is an array, this method will always return 
     * <code>Integer.class</code>. This is because arrays accept integers
     * for their index.</p>
     *
     * @param context The context of this evaluation.
     * @param base The array to analyze. Only bases that are a Java language
     *     array are handled by this resolver.
     * @return <code>null</code> if base is not a Java language array;
     *     otherwise <code>Integer.class</code>.
     */
    public Class<?> getCommonPropertyType(ELContext context,
                                               Object base) {

        if (base != null && base.getClass().isArray()) {
            return Integer.class;
        }
        return null;
    }

    private int toInteger(Object p) {

        if (p instanceof Integer) {
            return ((Integer) p).intValue();
        }
        if (p instanceof Character) {
            return ((Character) p).charValue();
        }
        if (p instanceof Boolean) {
            return ((Boolean) p).booleanValue()? 1: 0;
        }
        if (p instanceof Number) {
            return ((Number) p).intValue();
        }
        if (p instanceof String) {
            return Integer.parseInt((String) p);
        }
        throw new IllegalArgumentException();
    }

    private boolean isReadOnly;
}