/*
* The contents of this file are subject to the terms
* of the Common Development and Distribution License
* (the "License"). You may not use this file except
* in compliance with the License.
*
* You can obtain a copy of the license at
* glassfish/bootstrap/legal/CDDLv1.0.txt or
* https://glassfish.dev.java.net/public/CDDLv1.0.html.
* See the License for the specific language governing
* permissions and limitations under the License.
*
* When distributing Covered Code, include this CDDL
* HEADER in each file and include the License file at
* glassfish/bootstrap/legal/CDDLv1.0.txt. If applicable,
* add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your
* own identifying information: Portions Copyright [yyyy]
* [name of copyright owner]
*
* Copyright 2005 Sun Microsystems, Inc. All rights reserved.
*/
package javax.el;
/**
* Parses a <code>String</code> into a {@link ValueExpression} or
* {@link MethodExpression} instance for later evaluation.
*
* <p>Classes that implement the EL expression language expose their
* functionality via this abstract class.
* The {@link #newInstance} method can be used to obtain an
* instance of the implementation.
* Technologies such as
* JavaServer Pages and JavaServer Faces provide access to an
* implementation via factory methods.</p>
*
* <p>The {@link #createValueExpression} method is used to parse expressions
* that evaluate to values (both l-values and r-values are supported).
* The {@link #createMethodExpression} method is used to parse expressions
* that evaluate to a reference to a method on an object.</p>
*
* <p>Unlike previous incarnations of this API, there is no way to parse
* and evaluate an expression in one single step. The expression needs to first
* be parsed, and then evaluated.</p>
*
* <p>Resolution of model objects is performed at evaluation time, via the
* {@link ELResolver} associated with the {@link ELContext} passed to
* the <code>ValueExpression</code> or <code>MethodExpression</code>.</p>
*
* <p>The ELContext object also provides access to the {@link FunctionMapper}
* and {@link VariableMapper} to be used when parsing the expression.
* EL function and variable mapping is performed at parse-time, and
* the results are
* bound to the expression. Therefore, the {@link ELContext},
* {@link FunctionMapper},
* and {@link VariableMapper}
* are not stored for future use and do not have to be
* <code>Serializable</code>.</p>
*
* <p>The <code>createValueExpression</code> and
* <code>createMethodExpression</code> methods must be thread-safe. That is,
* multiple threads may call these methods on the same
* <code>ExpressionFactory</code> object simultaneously. Implementations
* should synchronize access if they depend on transient state.
* Implementations should not, however, assume that only one object of
* each <code>ExpressionFactory</code> type will be instantiated; global
* caching should therefore be static.</p>
*
* <p>The <code>ExpressionFactory</code> must be able to handle the following
* types of input for the <code>expression</code> parameter:
* <ul>
* <li>Single expressions using the <code>${}</code> delimiter
* (e.g. <code>"${employee.lastName}"</code>).</li>
* <li>Single expressions using the <code>#{}</code> delimiter
* (e.g. <code>"#{employee.lastName}"</code>).</li>
* <li>Literal text containing no <code>${}</code> or <code>#{}</code>
* delimiters (e.g. <code>"John Doe"</code>).</li>
* <li>Multiple expressions using the same delimiter (e.g.
* <code>"${employee.firstName}${employee.lastName}"</code> or
* <code>"#{employee.firstName}#{employee.lastName}"</code>).</li>
* <li>Mixed literal text and expressions using the same delimiter (e.g.
* <code>"Name: ${employee.firstName} ${employee.lastName}"</code>).</li>
* </ul></p>
*
* <p>The following types of input are illegal and must cause an
* {@link ELException} to be thrown:
* <ul>
* <li>Multiple expressions using different delimiters (e.g.
* <code>"${employee.firstName}#{employee.lastName}"</code>).</li>
* <li>Mixed literal text and expressions using different delimiters(e.g.
* <code>"Name: ${employee.firstName} #{employee.lastName}"</code>).</li>
* </ul></p>
*
* @since JSP 2.1
*/
import java.util.Properties;
public abstract class ExpressionFactory {
/**
* Creates a new instance of a <code>ExpressionFactory</code>.
* This method uses the following ordered lookup procedure to determine
* the <code>ExpressionFactory</code> implementation class to load:
* <ul>
* <li>Use the Services API (as detailed in the JAR specification).
* If a resource with the name of
* <code>META-INF/services/javax.el.ExpressionFactory</code> exists,
* then its first line, if present, is used as the UTF-8 encoded name of
* the implementation class. </li>
* <li>Use the properties file "lib/el.properties" in the JRE directory.
* If this file exists and it is readable by the
* <code> java.util.Properties.load(InputStream)</code> method,
* and it contains an entry whose key is "javax.el.ExpressionFactory",
* then the value of that entry is used as the name of the
* implementation class.</li>
* <li>Use the <code>javax.el.ExpressionFactory</code> system property.
* If a system property with this name is defined, then its value is
* used as the name of the implementation class.</li>
* <li>Use a platform default implementation.</li>
* </ul>
*/
public static ExpressionFactory newInstance() {
return ExpressionFactory.newInstance(null);
}
/**
* <p>Create a new instance of a <code>ExpressionFactory</code>, with
* optional properties.
* This method uses the same lookup procedure as the one used in
* <code>newInstance()</code>.
* </p>
* <p>
* If the argument <code>properties</code> is not null, and if the
* implementation contains a constructor with a single parameter of
* type <code>java.util.Properties</code>, then the constructor is used
* to create the instance.
* </p>
* <p>
* Properties are optional and can be ignored by an implementation.
* </p>
* <p>The name of a property should start with "javax.el."</p>
* <p>
* The following are some suggested names for properties.
* <ul>
* <li>javax.el.cacheSize</li>
* </ul></p>
*
* @param properties Properties passed to the implementation.
* If null, then no properties.
*/
public static ExpressionFactory newInstance(Properties properties) {
return (ExpressionFactory) FactoryFinder.find(
"javax.el.ExpressionFactory",
"com.sun.el.ExpressionFactoryImpl",
properties);
}
/**
* Parses an expression into a {@link ValueExpression} for later
* evaluation. Use this method for expressions that refer to values.
*
* <p>This method should perform syntactic validation of the expression.
* If in doing so it detects errors, it should raise an
* <code>ELException</code>.</p>
*
* @param context The EL context used to parse the expression.
* The <code>FunctionMapper</code> and <code>VariableMapper</code>
* stored in the ELContext
* are used to resolve functions and variables found in
* the expression. They can be <code>null</code>, in which case
* functions or variables are not supported for this expression.
* The object
* returned must invoke the same functions and access the same
* variable mappings
* regardless of whether
* the mappings in the provided <code>FunctionMapper</code>
* and <code>VariableMapper</code> instances
* change between calling
* <code>ExpressionFactory.createValueExpression()</code> and any
* method on <code>ValueExpression</code>.
* <p>
* Note that within the EL, the ${} and #{} syntaxes are treated identically.
* This includes the use of VariableMapper and FunctionMapper at expression creation
* time. Each is invoked if not null, independent
* of whether the #{} or ${} syntax is used for the expression.</p>
* @param expression The expression to parse
* @param expectedType The type the result of the expression
* will be coerced to after evaluation.
* @return The parsed expression
* @throws NullPointerException Thrown if expectedType is null.
* @throws ELException Thrown if there are syntactical errors in the
* provided expression.
*/
public abstract ValueExpression createValueExpression(
ELContext context,
String expression,
Class<?> expectedType);
/**
* Creates a ValueExpression that wraps an object instance. This
* method can be used to pass any object as a ValueExpression. The
* wrapper ValueExpression is read only, and returns the wrapped
* object via its <code>getValue()</code> method, optionally coerced.
*
* @param instance The object instance to be wrapped.
* @param expectedType The type the result of the expression
* will be coerced to after evaluation. There will be no
* coercion if it is Object.class,
* @throws NullPointerException Thrown if expectedType is null.
*/
public abstract ValueExpression createValueExpression(
Object instance,
Class<?> expectedType);
/**
* Parses an expression into a {@link MethodExpression} for later
* evaluation. Use this method for expressions that refer to methods.
*
* <p>
* If the expression is a String literal, a <code>MethodExpression
* </code> is created, which when invoked, returns the String literal,
* coerced to expectedReturnType. An ELException is thrown if
* expectedReturnType is void or if the coercion of the String literal
* to the expectedReturnType yields an error (see Section "1.16 Type
* Conversion").
* </p>
* <p>This method should perform syntactic validation of the expression.
* If in doing so it detects errors, it should raise an
* <code>ELException</code>.</p>
*
* @param context The EL context used to parse the expression.
* The <code>FunctionMapper</code> and <code>VariableMapper</code>
* stored in the ELContext
* are used to resolve functions and variables found in
* the expression. They can be <code>null</code>, in which
* case functions or variables are not supported for this expression.
* The object
* returned must invoke the same functions and access the same variable
* mappings
* regardless of whether
* the mappings in the provided <code>FunctionMapper</code>
* and <code>VariableMapper</code> instances
* change between calling
* <code>ExpressionFactory.createMethodExpression()</code> and any
* method on <code>MethodExpression</code>.
* <p>
* Note that within the EL, the ${} and #{} syntaxes are treated identically.
* This includes the use of VariableMapper and FunctionMapper at expression creation
* time. Each is invoked if not null, independent
* of whether the #{} or ${} syntax is used for the expression.</p>
*
* @param expression The expression to parse
* @param expectedReturnType The expected return type for the method
* to be found. After evaluating the expression, the
* <code>MethodExpression</code> must check that the return type of
* the actual method matches this type. Passing in a value of
* <code>null</code> indicates the caller does not care what the
* return type is, and the check is disabled.
* @param expectedParamTypes The expected parameter types for the method to
* be found. Must be an array with no elements if there are
* no parameters expected. It is illegal to pass <code>null</code>.
* @return The parsed expression
* @throws ELException Thrown if there are syntactical errors in the
* provided expression.
* @throws NullPointerException if paramTypes is <code>null</code>.
*/
public abstract MethodExpression createMethodExpression(
ELContext context,
String expression,
Class<?> expectedReturnType,
Class<?>[] expectedParamTypes);
/**
* Coerces an object to a specific type according to the
* EL type conversion rules.
*
* <p>An <code>ELException</code> is thrown if an error results from
* applying the conversion rules.
* </p>
*
* @param obj The object to coerce.
* @param targetType The target type for the coercion.
* @throws ELException thrown if an error results from applying the
* conversion rules.
*/
public abstract Object coerceToType(
Object obj,
Class<?> targetType);
}
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