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/*
* 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.commons.jexl3;
import java.io.Reader;
import java.io.StringReader;
import java.io.Writer;
import java.util.List;
import java.util.Map;
import java.util.Set;
/**
* A simple "JeXL Template" engine.
*
* At the base is an evaluator similar to the Unified EL evaluator used in JSP/JSF based on JEXL.
* At the top is a template engine inspired by Velocity that uses JEXL (instead of OGNL/VTL) as the scripting
* language.
*
* The evaluator is intended to be used in configuration modules, XML based frameworks or JSP taglibs
* and facilitate the implementation of expression evaluation.
*
* The template engine is intended to output any form of text; html, XML, CSV...
*
* @since 3.0
*/
public abstract class JxltEngine {
/**
* The sole type of (runtime) exception the JxltEngine can throw.
*/
public static class Exception extends JexlException {
/** Serial version UID. */
private static final long serialVersionUID = 201112030113L;
/**
* Creates an Exception.
*
* @param info the contextual information
* @param msg the exception message
* @param cause the exception cause
*/
public Exception(JexlInfo info, String msg, Throwable cause) {
super(info, msg, cause);
}
}
/**
* A unified expression that can mix immediate, deferred and nested sub-expressions as well as string constants;
*
* - The "immediate" syntax is of the form
"...${jexl-expr}..."
* - The "deferred" syntax is of the form
"...#{jexl-expr}..."
* - The "nested" syntax is of the form
"...#{...${jexl-expr0}...}..."
* - The "composite" syntax is of the form
"...${jexl-expr0}... #{jexl-expr1}..."
*
*
* Deferred and immediate expression carry different intentions:
*
*
* - An immediate expression indicate that evaluation is intended to be performed close to
* the definition/parsing point.
* - A deferred expression indicate that evaluation is intended to occur at a later stage.
*
*
* For instance: "Hello ${name}, now is #{time}" is a composite "deferred" expression since one
* of its subexpressions is deferred. Furthermore, this (composite) expression intent is
* to perform two evaluations; one close to its definition and another one in a later
* phase.
*
* The API reflects this feature in 2 methods, prepare and evaluate. The prepare method
* will evaluate the immediate subexpression and return an expression that contains only
* the deferred subexpressions (and constants), a prepared expression. Such a prepared expression
* is suitable for a later phase evaluation that may occur with a different JexlContext.
* Note that it is valid to call evaluate without prepare in which case the same JexlContext
* is used for the 2 evaluation phases.
*
* In the most common use-case where deferred expressions are to be kept around as properties of objects,
* one should createExpression and prepare an expression before storing it and evaluate it each time
* the property storing it is accessed.
*
* Note that nested expression use the JEXL syntax as in:
*
* "#{${bar}+'.charAt(2)'}"
*
* The most common mistake leading to an invalid expression being the following:
*
* "#{${bar}charAt(2)}"
*
* Also note that methods that createExpression evaluate expressions may throw unchecked exceptions;
* The {@link JxltEngine.Exception} are thrown when the engine instance is in "non-silent" mode
* but since these are RuntimeException, user-code should catch them where appropriate.
*
* @since 2.0
*/
public interface Expression {
/**
* Generates this expression's string representation.
*
* @return the string representation
*/
String asString();
/**
* Adds this expression's string representation to a StringBuilder.
*
* @param strb the builder to fill
* @return the builder argument
*/
StringBuilder asString(StringBuilder strb);
/**
* Evaluates this expression.
*
* If the underlying JEXL engine is silent, errors will be logged through its logger as warning.
*
* @param context the variable context
* @return the result of this expression evaluation or null if an error occurs and the {@link JexlEngine} is
* running in silent mode
* @throws Exception if an error occurs and the {@link JexlEngine}
* is not silent
*/
Object evaluate(JexlContext context);
/**
* Retrieves this expression's source expression.
*
* If this expression was prepared, this allows to retrieve the
* original expression that lead to it.
* Other expressions return themselves.
*
* @return the source expression
*/
Expression getSource();
/**
* Gets the list of variables accessed by this expression.
* This method will visit all nodes of the sub-expressions and extract all variables whether they
* are written in 'dot' or 'bracketed' notation. (a.b is equivalent to a['b']).
*
* @return the set of variables, each as a list of strings (ant-ish variables use more than 1 string)
* or the empty set if no variables are used
*/
Set> getVariables();
/**
* Checks whether this expression is deferred.
*
* @return true if deferred, false otherwise
*/
boolean isDeferred();
/**
* Checks whether this expression is immediate.
*
* @return true if immediate, false otherwise
*/
boolean isImmediate();
/**
* Evaluates the immediate sub-expressions.
*
* When the expression is dependant upon immediate and deferred sub-expressions,
* evaluates the immediate sub-expressions with the context passed as parameter
* and returns this expression deferred form.
*
* In effect, this binds the result of the immediate sub-expressions evaluation in the
* context, allowing to differ evaluation of the remaining (deferred) expression within another context.
* This only has an effect to nested and composite expressions that contain differed and
* immediate sub-expressions.
*
* If the underlying JEXL engine is silent, errors will be logged through its logger as warning.*
*
* @param context the context to use for immediate expression evaluations
* @return an {@link Expression} or null if an error occurs and the {@link JexlEngine} is running
* in silent mode
* @throws Exception if an error occurs and the {@link JexlEngine} is not in silent mode
*/
Expression prepare(JexlContext context);
/**
* Formats this expression, adding its source string representation in
* comments if available: 'expression /*= source *\/'' .
*
* @return the formatted expression string
*/
@Override
String toString();
}
/**
* Creates a a {@link Expression} from an expression string.
* Uses and fills up the expression cache if any.
*
* If the underlying JEXL engine is silent, errors will be logged through its logger as warnings.
*
* @param expression the {@link Template} string expression
* @return the {@link Expression}, null if silent and an error occurred
* @throws Exception if an error occurs and the {@link JexlEngine} is not silent
*/
public Expression createExpression(String expression) {
return createExpression(null, expression);
}
/**
* Creates a a {@link Expression} from an expression string.
* Uses and fills up the expression cache if any.
*
* If the underlying JEXL engine is silent, errors will be logged through its logger as warnings.
*
* @param info the {@link JexlInfo} source information
* @param expression the {@link Template} string expression
* @return the {@link Expression}, null if silent and an error occured
* @throws Exception if an error occurs and the {@link JexlEngine} is not silent
*/
public abstract Expression createExpression(JexlInfo info, String expression);
/**
* A template is a JEXL script that evaluates by writing its content through a Writer.
*
* The source text is parsed considering each line beginning with '$$' (as default pattern) as JEXL script code
* and all others as Unified JEXL expressions; those expressions will be invoked from the script during
* evaluation and their output gathered through a writer.
* It is thus possible to use looping or conditional construct "around" expressions generating output.
*
* For instance:
*
* $$ for(var x : [1, 3, 5, 42, 169]) {
* $$ if (x == 42) {
* Life, the universe, and everything
* $$ } else if (x > 42) {
* The value $(x} is over fourty-two
* $$ } else {
* The value ${x} is under fourty-two
* $$ }
* $$ }
*
*
* Will evaluate as:
*
*
* The value 1 is under fourty-two
* The value 3 is under fourty-two
* The value 5 is under fourty-two
* Life, the universe, and everything
* The value 169 is over fourty-two
*
*
* During evaluation, the template context exposes its writer as '$jexl' which is safe to use in this case.
* This allows writing directly through the writer without adding new-lines as in:
*
*
* $$ for(var cell : cells) { $jexl.print(cell); $jexl.print(';') }
*
*
* A template is expanded as one JEXL script and a list of template expressions; each template expression is
* being replaced in the script by a call to jexl:print(expr) (the expr is in fact the expr number in the template).
* This integration uses a specialized JexlContext (TemplateContext) that serves as a namespace (for jexl:)
* and stores the template expression array and the writer (java.io.Writer) that the 'jexl:print(...)'
* delegates the output generation to.
*
* @since 3.0
*/
public interface Template {
/**
* Recreate the template source from its inner components.
*
* @return the template source rewritten
*/
String asString();
/**
* Evaluates this template.
*
* @param context the context to use during evaluation
* @param writer the writer to use for output
*/
void evaluate(JexlContext context, Writer writer);
/**
* Evaluates this template.
*
* @param context the context to use during evaluation
* @param writer the writer to use for output
* @param args the arguments
*/
void evaluate(JexlContext context, Writer writer, Object... args);
/**
* Prepares this template by expanding any contained deferred TemplateExpression.
*
* @param context the context to prepare against
* @return the prepared version of the template
*/
Template prepare(JexlContext context);
/**
* Gets the list of variables accessed by this template.
* This method will visit all nodes of the sub-expressions and extract all variables whether they
* are written in 'dot' or 'bracketed' notation. (a.b is equivalent to a['b']).
*
* @return the set of variables, each as a list of strings (ant-ish variables use more than 1 string)
* or the empty set if no variables are used
*/
Set> getVariables();
/**
* Gets the list of parameters expected by this template.
*
* @return the parameter names array
*/
String[] getParameters();
/**
* Gets this script pragmas.
*
* @return the (non null, may be empty) pragmas map
* @since 3.1
*/
Map getPragmas();
}
/**
* Creates a new template.
*
* @param info the jexl info (file, line, column)
* @param prefix the directive prefix
* @param source the source
* @param parms the parameter names
* @return the template
*/
public abstract Template createTemplate(JexlInfo info, String prefix, Reader source, String... parms);
/**
* Creates a new template.
*
* @param info the source info
* @param parms the parameter names
* @param source the source
* @return the template
*/
public Template createTemplate(JexlInfo info, String source, String... parms) {
return createTemplate(info, "$$", new StringReader(source), parms);
}
/**
* Creates a new template.
*
* @param info the source info
* @param source the source
* @return the template
*/
public Template createTemplate(JexlInfo info, String source) {
return createTemplate(info, "$$", new StringReader(source), (String[]) null);
}
/**
* Creates a new template.
*
* @param prefix the directive prefix
* @param source the source
* @param parms the parameter names
* @return the template
*/
public Template createTemplate(String prefix, Reader source, String... parms) {
return createTemplate(null, prefix, source, parms);
}
/**
* Creates a new template.
*
* @param source the source
* @param parms the parameter names
* @return the template
*/
public Template createTemplate(String source, String... parms) {
return createTemplate(null, source, parms);
}
/**
* Creates a new template.
*
* @param source the source
* @return the template
*/
public Template createTemplate(String source) {
return createTemplate(null, source);
}
/**
* Gets the {@link JexlEngine} underlying this template engine.
*
* @return the JexlEngine
*/
public abstract JexlEngine getEngine();
/**
* Clears the cache.
*/
public abstract void clearCache();
}