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CompositeELResolver.java
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CompositeELResolver.java
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/*
* Copyright (c) 1997, 2023 Oracle and/or its affiliates and others.
* 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 jakarta.el;
/**
* Maintains an ordered composite list of child <code>ELResolver</code>s.
*
* <p>
* Though only a single <code>ELResolver</code> is associated with an <code>ELContext</code>, there are usually multiple
* resolvers considered for any given variable or property resolution. <code>ELResolver</code>s are combined together
* using a <code>CompositeELResolver</code>, to define rich semantics for evaluating an expression.
* </p>
*
* <p>
* For the {@link #getValue}, {@link #getType}, {@link #setValue} and {@link #isReadOnly} methods, an
* <code>ELResolver</code> is not responsible for resolving all possible (base, property) pairs. In fact, most resolvers
* will only handle a <code>base</code> of a single type. To indicate that a resolver has successfully resolved a
* particular (base, property) pair, it must set the <code>propertyResolved</code> property of the
* <code>ELContext</code> to <code>true</code>. If it could not handle the given pair, it must leave this property
* alone. The caller must ignore the return value of the method if <code>propertyResolved</code> is <code>false</code>.
* </p>
*
* <p>
* The <code>CompositeELResolver</code> initializes the <code>ELContext.propertyResolved</code> flag to
* <code>false</code>, and uses it as a stop condition for iterating through its component resolvers.
* </p>
*
* <p>
* The <code>ELContext.propertyResolved</code> flag is not used for the design-time method
* {@link #getCommonPropertyType}. Instead, results are collected and combined from
* all child <code>ELResolver</code>s for this method.
* </p>
*
* @see ELContext
* @see ELResolver
* @since Jakarta Server Pages 2.1
*/
public class CompositeELResolver extends ELResolver {
public CompositeELResolver() {
this.size = 0;
this.elResolvers = new ELResolver[16];
}
/**
* Adds the given resolver to the list of component resolvers.
*
* <p>
* Resolvers are consulted in the order in which they are added.
* </p>
*
* @param elResolver The component resolver to add.
* @throws NullPointerException If the provided resolver is <code>null</code>.
*/
public void add(ELResolver elResolver) {
if (elResolver == null) {
throw new NullPointerException();
}
if (size >= elResolvers.length) {
ELResolver[] newResolvers = new ELResolver[size * 2];
System.arraycopy(elResolvers, 0, newResolvers, 0, size);
elResolvers = newResolvers;
}
elResolvers[size++] = elResolver;
}
/**
* Attempts to resolve the given <code>property</code> object on the given <code>base</code> object by querying all
* component resolvers.
*
* <p>
* If this resolver handles the given (base, property) pair, the <code>propertyResolved</code> property of the
* <code>ELContext</code> object must be set to <code>true</code> by the resolver, before returning. If this property is
* not <code>true</code> after this method is called, the caller should ignore the return value.
*
* <p>
* First, <code>propertyResolved</code> is set to <code>false</code> on the provided <code>ELContext</code>.
*
* <p>
* Next, for each component resolver in this composite:
* <ol>
* <li>The <code>getValue()</code> method is called, passing in the provided <code>context</code>, <code>base</code> and
* <code>property</code>.</li>
* <li>If the <code>ELContext</code>'s <code>propertyResolved</code> flag is <code>false</code> then iteration
* continues.</li>
* <li>Otherwise, iteration stops and no more component resolvers are considered. The value returned by
* <code>getValue()</code> is returned by this method.</li>
* </ol>
*
* <p>
* If none of the component resolvers were able to perform this operation, the value <code>null</code> is returned and
* the <code>propertyResolved</code> flag remains set to <code>false</code>.
*
* <p>
* Any exception thrown by component resolvers during the iteration is propagated to the caller of this method.
*
* @param context The context of this evaluation.
* @param base The base object whose property value is to be returned, or <code>null</code> to resolve a top-level
* variable.
* @param property The property or variable to be resolved.
* @return If the <code>propertyResolved</code> property of <code>ELContext</code> was set to <code>true</code>, then
* the result of the variable or property resolution; otherwise undefined.
* @throws NullPointerException if context is <code>null</code>
* @throws PropertyNotFoundException if the given (base, property) pair is handled by this <code>ELResolver</code> but
* the specified variable or 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.
*/
@Override
public Object getValue(ELContext context, Object base, Object property) {
context.setPropertyResolved(false);
Object value = null;
for (int i = 0; i < size; i++) {
value = elResolvers[i].getValue(context, base, property);
if (context.isPropertyResolved()) {
return value;
}
}
return null;
}
/**
* Attempts to resolve and invoke the given <code>method</code> on the given <code>base</code> object by querying all
* component resolvers.
*
* <p>
* If this resolver handles the given (base, method) pair, the <code>propertyResolved</code> property of the
* <code>ELContext</code> object must be set to <code>true</code> by the 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>
* First, <code>propertyResolved</code> is set to <code>false</code> on the provided <code>ELContext</code>.
* </p>
*
* <p>
* Next, for each component resolver in this composite:
* <ol>
* <li>The <code>invoke()</code> method is called, passing in the provided <code>context</code>, <code>base</code>,
* <code>method</code>, <code>paramTypes</code>, and <code>params</code>.</li>
* <li>If the <code>ELContext</code>'s <code>propertyResolved</code> flag is <code>false</code> then iteration
* continues.</li>
* <li>Otherwise, iteration stops and no more component resolvers are considered. The value returned by
* <code>getValue()</code> is returned by this method.</li>
* </ol>
*
* <p>
* If none of the component resolvers were able to perform this operation, the value <code>null</code> is returned and
* the <code>propertyResolved</code> flag remains set to <code>false</code>
* </p>
* .
*
* <p>
* Any exception thrown by component resolvers during the iteration is propagated to the caller of this method.
* </p>
*
* @param context The context of this evaluation.
* @param base The bean on which to invoke the method
* @param method The simple name of the method to invoke. Will be coerced to a <code>String</code>.
* @param paramTypes An array of Class objects identifying the method's formal parameter types, in declared order. Use
* an empty array if the method has no parameters. Can be <code>null</code>, in which case the method's formal parameter
* types are assumed to be unknown.
* @param params The parameters to pass to the method, or <code>null</code> if no parameters.
*
* @return The result of the method invocation (<code>null</code> if the method has a <code>void</code> return type).
*
* @since Jakarta Expression Language 2.2
*/
@Override
public Object invoke(ELContext context, Object base, Object method, Class<?>[] paramTypes, Object[] params) {
context.setPropertyResolved(false);
Object value;
for (int i = 0; i < size; i++) {
value = elResolvers[i].invoke(context, base, method, paramTypes, params);
if (context.isPropertyResolved()) {
return value;
}
}
return null;
}
/**
* For a given <code>base</code> and <code>property</code>, attempts to identify the most general type that is
* acceptable for an object to be passed as the <code>value</code> parameter in a future call to the {@link #setValue}
* method. The result is obtained by querying all component resolvers.
*
* <p>
* If this resolver handles the given (base, property) pair, the <code>propertyResolved</code> property of the
* <code>ELContext</code> object must be set to <code>true</code> by the 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>
* First, <code>propertyResolved</code> is set to <code>false</code> on the provided <code>ELContext</code>.
* </p>
*
* <p>
* Next, for each component resolver in this composite:
* <ol>
* <li>The <code>getType()</code> method is called, passing in the provided <code>context</code>, <code>base</code> and
* <code>property</code>.</li>
* <li>If the <code>ELContext</code>'s <code>propertyResolved</code> flag is <code>false</code> then iteration
* continues.</li>
* <li>Otherwise, iteration stops and no more component resolvers are considered. The value returned by
* <code>getType()</code> is returned by this method.</li>
* </ol>
*
* <p>
* If none of the component resolvers were able to perform this operation, the value <code>null</code> is returned and
* the <code>propertyResolved</code> flag remains set to <code>false</code>.
* </p>
*
*
* <p>
* Any exception thrown by component resolvers during the iteration is propagated to the caller of this method.
* </p>
*
* @param context The context of this evaluation.
* @param base The base object whose property value is to be analyzed, or <code>null</code> to analyze a top-level
* variable.
* @param property The property or variable to return the acceptable type for.
* @return If the <code>propertyResolved</code> property of <code>ELContext</code> was set to <code>true</code>, then
* the most general acceptable type which must be {@code null} if the either the property or the resolver is
* read-only; otherwise undefined
* @throws NullPointerException if context is <code>null</code>
* @throws PropertyNotFoundException if the given (base, property) pair is handled by this <code>ELResolver</code> but
* the specified variable or 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.
*/
@Override
public Class<?> getType(ELContext context, Object base, Object property) {
context.setPropertyResolved(false);
Class<?> type;
for (int i = 0; i < size; i++) {
type = elResolvers[i].getType(context, base, property);
if (context.isPropertyResolved()) {
return type;
}
}
return null;
}
/**
* Attempts to set the value of the given <code>property</code> object on the given <code>base</code> object. All
* component resolvers are asked to attempt to set the value.
*
* <p>
* If this resolver handles the given (base, property) pair, the <code>propertyResolved</code> property of the
* <code>ELContext</code> object must be set to <code>true</code> by the resolver, before returning. If this property is
* not <code>true</code> after this method is called, the caller can safely assume no value has been set.
*
* <p>
* First, <code>propertyResolved</code> is set to <code>false</code> on the provided <code>ELContext</code>.
*
* <p>
* Next, for each component resolver in this composite:
* <ol>
* <li>The <code>setValue()</code> method is called, passing in the provided <code>context</code>, <code>base</code>,
* <code>property</code> and <code>value</code>.</li>
* <li>If the <code>ELContext</code>'s <code>propertyResolved</code> flag is <code>false</code> then iteration
* continues.</li>
* <li>Otherwise, iteration stops and no more component resolvers are considered.</li>
* </ol>
*
* <p>
* If none of the component resolvers were able to perform this operation, the <code>propertyResolved</code> flag
* remains set to <code>false</code>.
*
* <p>
* Any exception thrown by component resolvers during the iteration is propagated to the caller of this method.
*
* @param context The context of this evaluation.
* @param base The base object whose property value is to be set, or <code>null</code> to set a top-level variable.
* @param property The property or variable to be set.
* @param val The value to set the property or variable to.
* @throws NullPointerException if context is <code>null</code>
* @throws PropertyNotFoundException if the given (base, property) pair is handled by this <code>ELResolver</code> but
* the specified variable or property does not exist.
* @throws PropertyNotWritableException if the given (base, property) pair is handled by this <code>ELResolver</code>
* but the specified variable or property is not writable.
* @throws ELException if an exception was thrown while attempting to set the property or variable. The thrown exception
* must be included as the cause property of this exception, if available.
*/
@Override
public void setValue(ELContext context, Object base, Object property, Object val) {
context.setPropertyResolved(false);
for (int i = 0; i < size; i++) {
elResolvers[i].setValue(context, base, property, val);
if (context.isPropertyResolved()) {
return;
}
}
}
/**
* For a given <code>base</code> and <code>property</code>, attempts to determine whether a call to {@link #setValue}
* will always fail. The result is obtained by querying all component resolvers.
*
* <p>
* If this resolver handles the given (base, property) pair, the <code>propertyResolved</code> property of the
* <code>ELContext</code> object must be set to <code>true</code> by the 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>
* First, <code>propertyResolved</code> is set to <code>false</code> on the provided <code>ELContext</code>.
* </p>
*
* <p>
* Next, for each component resolver in this composite:
* <ol>
* <li>The <code>isReadOnly()</code> method is called, passing in the provided <code>context</code>, <code>base</code>
* and <code>property</code>.</li>
* <li>If the <code>ELContext</code>'s <code>propertyResolved</code> flag is <code>false</code> then iteration
* continues.</li>
* <li>Otherwise, iteration stops and no more component resolvers are considered. The value returned by
* <code>isReadOnly()</code> is returned by this method.</li>
* </ol>
*
* <p>
* If none of the component resolvers were able to perform this operation, the value <code>false</code> is returned and
* the <code>propertyResolved</code> flag remains set to <code>false</code>
* </p>
* .
*
* <p>
* Any exception thrown by component resolvers during the iteration is propagated to the caller of this method.
* </p>
*
* @param context The context of this evaluation.
* @param base The base object whose property value is to be analyzed, or <code>null</code> to analyze a top-level
* variable.
* @param property The property or variable to return the read-only status for.
* @return If the <code>propertyResolved</code> property of <code>ELContext</code> was set to <code>true</code>, then
* <code>true</code> if the property is read-only or <code>false</code> if not; otherwise undefined.
* @throws NullPointerException if context is <code>null</code>
* @throws PropertyNotFoundException if the given (base, property) pair is handled by this <code>ELResolver</code> but
* the specified variable or property does not exist.
* @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.
*/
@Override
public boolean isReadOnly(ELContext context, Object base, Object property) {
context.setPropertyResolved(false);
boolean readOnly;
for (int i = 0; i < size; i++) {
readOnly = elResolvers[i].isReadOnly(context, base, property);
if (context.isPropertyResolved()) {
return readOnly;
}
}
return false; // Does not matter
}
/**
* Returns the most general type that this resolver accepts for the <code>property</code> argument, given a
* <code>base</code> object. One use for this method is to assist tools in auto-completion. The result is obtained by
* querying all component resolvers.
*
* <p>
* The <code>Class</code> returned is the most specific class that is a common superclass of all the classes returned by
* each component resolver's <code>getCommonPropertyType</code> method. If <code>null</code> is returned by a resolver,
* it is skipped.
*
* @param context The context of this evaluation.
* @param base The base object to return the most general property type for, or <code>null</code> to enumerate the set
* of top-level variables that this resolver can evaluate.
*
* @return <code>null</code> if this <code>ELResolver</code> does not know how to handle the given <code>base</code>
* object; otherwise <code>Object.class</code> if any type of <code>property</code> is accepted; otherwise the most
* general <code>property</code> type accepted for the given <code>base</code>.
*/
@Override
public Class<?> getCommonPropertyType(ELContext context, Object base) {
Class<?> commonPropertyType = null;
for (int i = 0; i < size; i++) {
Class<?> type = elResolvers[i].getCommonPropertyType(context, base);
if (type == null) {
// skip this Jakarta Expression Language Resolver
continue;
} else if (commonPropertyType == null) {
commonPropertyType = type;
} else if (commonPropertyType.isAssignableFrom(type)) {
continue;
} else if (type.isAssignableFrom(commonPropertyType)) {
commonPropertyType = type;
} else {
// Don't have a commonPropertyType
return null;
}
}
return commonPropertyType;
}
/**
* Converts an object to a specific type.
*
* <p>
* An <code>ELException</code> is thrown if an error occurs during the conversion.
* </p>
*
* @param context The context of this evaluation.
* @param obj The object to convert.
* @param targetType The target type for the convertion.
*
* @throws ELException thrown if errors occur.
*
* @since Jakarta Expression Language 3.0
*/
@Override
public <T> T convertToType(ELContext context, Object obj, Class<T> targetType) {
context.setPropertyResolved(false);
T value = null;
for (int i = 0; i < size; i++) {
value = elResolvers[i].convertToType(context, obj, targetType);
if (context.isPropertyResolved()) {
return value;
}
}
return null;
}
private ELResolver[] elResolvers;
private int size;
}