ValueExpressionImpl.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.el;
import java.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;
import jakarta.el.ELContext;
import jakarta.el.ELException;
import jakarta.el.FunctionMapper;
import jakarta.el.PropertyNotFoundException;
import jakarta.el.PropertyNotWritableException;
import jakarta.el.ValueExpression;
import jakarta.el.ValueReference;
import jakarta.el.VariableMapper;
import org.apache.el.lang.EvaluationContext;
import org.apache.el.lang.ExpressionBuilder;
import org.apache.el.parser.AstLiteralExpression;
import org.apache.el.parser.Node;
import org.apache.el.util.ReflectionUtil;
/**
* An <code>Expression</code> that can get or set a value.
* <p>
* In previous incarnations of this API, expressions could only be read. <code>ValueExpression</code> objects can now be
* used both to retrieve a value and to set a value. Expressions that can have a value set on them are referred to as
* l-value expressions. Those that cannot are referred to as r-value expressions. Not all r-value expressions can be
* used as l-value expressions (e.g. <code>"${1+1}"</code> or <code>"${firstName} ${lastName}"</code>). See the EL
* Specification for details. Expressions that cannot be used as l-values must always return <code>true</code> from
* <code>isReadOnly()</code>.
* </p>
* <p>
* The {@link jakarta.el.ExpressionFactory#createValueExpression} method can be used to parse an expression string and
* return a concrete instance of <code>ValueExpression</code> that encapsulates the parsed expression. The
* {@link FunctionMapper} is used at parse time, not evaluation time, so one is not needed to evaluate an expression
* using this class. However, the {@link ELContext} is needed at evaluation time.
* </p>
* <p>
* The {@link #getValue}, {@link #setValue}, {@link #isReadOnly} and {@link #getType} methods will evaluate the
* expression each time they are called. The {@link jakarta.el.ELResolver} in the <code>ELContext</code> is used to
* resolve the top-level variables and to determine the behavior of the <code>.</code> and <code>[]</code> operators.
* For any of the four methods, the {@link jakarta.el.ELResolver#getValue} method is used to resolve all properties up
* to but excluding the last one. This provides the <code>base</code> object. At the last resolution, the
* <code>ValueExpression</code> will call the corresponding {@link jakarta.el.ELResolver#getValue},
* {@link jakarta.el.ELResolver#setValue}, {@link jakarta.el.ELResolver#isReadOnly} or
* {@link jakarta.el.ELResolver#getType} method, depending on which was called on the <code>ValueExpression</code>.
* </p>
* <p>
* See the notes about comparison, serialization and immutability in the {@link jakarta.el.Expression} javadocs.
*
* @see jakarta.el.ELResolver
* @see jakarta.el.Expression
* @see jakarta.el.ExpressionFactory
* @see jakarta.el.ValueExpression
*
* @author Jacob Hookom [jacob@hookom.net]
*/
public final class ValueExpressionImpl extends ValueExpression implements Externalizable {
private Class<?> expectedType;
private String expr;
private FunctionMapper fnMapper;
private VariableMapper varMapper;
private transient Node node;
public ValueExpressionImpl() {
super();
}
public ValueExpressionImpl(String expr, Node node, FunctionMapper fnMapper, VariableMapper varMapper,
Class<?> expectedType) {
this.expr = expr;
this.node = node;
this.fnMapper = fnMapper;
this.varMapper = varMapper;
this.expectedType = expectedType;
}
@Override
public boolean equals(Object obj) {
if (!(obj instanceof ValueExpressionImpl)) {
return false;
}
if (obj.hashCode() != this.hashCode()) {
return false;
}
return this.getNode().equals(((ValueExpressionImpl) obj).getNode());
}
@Override
public Class<?> getExpectedType() {
return this.expectedType;
}
/**
* Returns the type the result of the expression will be coerced to after evaluation.
*
* @return the <code>expectedType</code> passed to the <code>ExpressionFactory.createValueExpression</code> method
* that created this <code>ValueExpression</code>.
*
* @see jakarta.el.Expression#getExpressionString()
*/
@Override
public String getExpressionString() {
return this.expr;
}
private Node getNode() throws ELException {
if (this.node == null) {
this.node = ExpressionBuilder.createNode(this.expr);
}
return this.node;
}
@Override
public Class<?> getType(ELContext context) throws PropertyNotFoundException, ELException {
EvaluationContext ctx = new EvaluationContext(context, this.fnMapper, this.varMapper);
context.notifyBeforeEvaluation(getExpressionString());
Class<?> result = this.getNode().getType(ctx);
context.notifyAfterEvaluation(getExpressionString());
return result;
}
@SuppressWarnings("unchecked")
@Override
public <T> T getValue(ELContext context) throws PropertyNotFoundException, ELException {
EvaluationContext ctx = new EvaluationContext(context, this.fnMapper, this.varMapper);
context.notifyBeforeEvaluation(getExpressionString());
Object value = this.getNode().getValue(ctx);
if (this.expectedType != null) {
value = context.convertToType(value, this.expectedType);
}
context.notifyAfterEvaluation(getExpressionString());
return (T) value;
}
@Override
public int hashCode() {
return this.getNode().hashCode();
}
@Override
public boolean isLiteralText() {
try {
return this.getNode() instanceof AstLiteralExpression;
} catch (ELException ele) {
return false;
}
}
@Override
public boolean isReadOnly(ELContext context) throws PropertyNotFoundException, ELException {
EvaluationContext ctx = new EvaluationContext(context, this.fnMapper, this.varMapper);
context.notifyBeforeEvaluation(getExpressionString());
boolean result = this.getNode().isReadOnly(ctx);
context.notifyAfterEvaluation(getExpressionString());
return result;
}
@Override
public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
this.expr = in.readUTF();
String type = in.readUTF();
if (!type.isEmpty()) {
this.expectedType = ReflectionUtil.forName(type);
}
this.fnMapper = (FunctionMapper) in.readObject();
this.varMapper = (VariableMapper) in.readObject();
}
@Override
public void setValue(ELContext context, Object value)
throws PropertyNotFoundException, PropertyNotWritableException, ELException {
EvaluationContext ctx = new EvaluationContext(context, this.fnMapper, this.varMapper);
context.notifyBeforeEvaluation(getExpressionString());
this.getNode().setValue(ctx, value);
context.notifyAfterEvaluation(getExpressionString());
}
@Override
public void writeExternal(ObjectOutput out) throws IOException {
out.writeUTF(this.expr);
out.writeUTF((this.expectedType != null) ? this.expectedType.getName() : "");
out.writeObject(this.fnMapper);
out.writeObject(this.varMapper);
}
@Override
public String toString() {
return "ValueExpression[" + this.expr + "]";
}
@Override
public ValueReference getValueReference(ELContext context) {
EvaluationContext ctx = new EvaluationContext(context, this.fnMapper, this.varMapper);
context.notifyBeforeEvaluation(getExpressionString());
ValueReference result = this.getNode().getValueReference(ctx);
context.notifyAfterEvaluation(getExpressionString());
return result;
}
}