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Modern server-side Java template engine for both web and standalone environments
/*
* =============================================================================
*
* Copyright (c) 2011-2018, The THYMELEAF team (http://www.thymeleaf.org)
*
* 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 org.thymeleaf.spring5.expression;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.expression.EvaluationContext;
import org.springframework.expression.spel.SpelCompilerMode;
import org.springframework.expression.spel.SpelParserConfiguration;
import org.springframework.expression.spel.standard.SpelExpression;
import org.springframework.expression.spel.standard.SpelExpressionParser;
import org.springframework.expression.spel.support.StandardEvaluationContext;
import org.thymeleaf.IEngineConfiguration;
import org.thymeleaf.TemplateEngine;
import org.thymeleaf.cache.ExpressionCacheKey;
import org.thymeleaf.cache.ICache;
import org.thymeleaf.cache.ICacheManager;
import org.thymeleaf.context.IEngineContext;
import org.thymeleaf.context.IExpressionContext;
import org.thymeleaf.context.ITemplateContext;
import org.thymeleaf.exceptions.TemplateProcessingException;
import org.thymeleaf.expression.IExpressionObjects;
import org.thymeleaf.spring5.context.IThymeleafBindStatus;
import org.thymeleaf.spring5.util.FieldUtils;
import org.thymeleaf.spring5.util.SpringValueFormatter;
import org.thymeleaf.spring5.util.SpringVersionUtils;
import org.thymeleaf.standard.expression.IStandardConversionService;
import org.thymeleaf.standard.expression.IStandardVariableExpression;
import org.thymeleaf.standard.expression.IStandardVariableExpressionEvaluator;
import org.thymeleaf.standard.expression.SelectionVariableExpression;
import org.thymeleaf.standard.expression.StandardExpressionExecutionContext;
import org.thymeleaf.standard.expression.StandardExpressions;
import org.thymeleaf.standard.expression.VariableExpression;
import org.thymeleaf.standard.util.StandardExpressionUtils;
import org.thymeleaf.util.ClassLoaderUtils;
/**
*
* Evaluator for variable expressions ({@code ${...}}) in Thymeleaf Standard Expressions, using the
* SpringEL expression language.
*
*
* Note a class with this name existed since 2.0.9, but it was completely reimplemented
* in Thymeleaf 3.0
*
*
* @author Daniel Fernández
* @author Guven Demir
*
* @since 3.0.3
*
*/
public class SPELVariableExpressionEvaluator
implements IStandardVariableExpressionEvaluator {
public static final SPELVariableExpressionEvaluator INSTANCE = new SPELVariableExpressionEvaluator();
private static final String EXPRESSION_CACHE_TYPE_SPEL = "spel";
private static final Logger logger = LoggerFactory.getLogger(SPELVariableExpressionEvaluator.class);
private static final SpelExpressionParser PARSER_WITHOUT_COMPILED_SPEL = new SpelExpressionParser();
private static final SpelExpressionParser PARSER_WITH_COMPILED_SPEL;
/*
* INITIALIZATION OF THE Spring EL parser.
* Two parsers will be always initialized: one with expression compilation enabled (if the Spring version allows)
* and another one without. Then during template execution we will check which one should be used.
*/
static {
SpelExpressionParser spelCompilerExpressionParser = null;
if (SpringVersionUtils.isSpring41AtLeast()) {
try {
// Enable the SpEL compiler, in MIXED mode (not IMMEDIATE) in order to avoid ClassCastExceptions
// when executing the same compiled expression against targets of different classes.
final SpelParserConfiguration spelParserConfiguration =
new SpelParserConfiguration(
SpelCompilerMode.MIXED,
ClassLoaderUtils.getClassLoader(SPELVariableExpressionEvaluator.class));
spelCompilerExpressionParser = new SpelExpressionParser(spelParserConfiguration);
} catch (final Throwable t) {
if (logger.isDebugEnabled()) {
// We are issuing a WARN even if we checked for DEBUG, but in this case we will log the entire
// exception trace (if DEBUG is not available, we will avoid polluting the log).
logger.warn(
"An error happened during the initialization of the Spring EL expression compiler. " +
"However, initialization was completed anyway. Note that compilation of SpEL expressions " +
"will not be available even if you configure your Spring dialect to use them.", t);
} else {
logger.warn(
"An error happened during the initialization of the Spring EL expression compiler. " +
"However, initialization was completed anyway. Note that compilation of SpEL expressions " +
"will not be available even if you configure your Spring dialect to use them. For more " +
"info, set your log to at least DEBUG level: " + t.getMessage());
}
}
}
PARSER_WITH_COMPILED_SPEL = spelCompilerExpressionParser;
}
protected SPELVariableExpressionEvaluator() {
super();
}
public final Object evaluate(
final IExpressionContext context,
final IStandardVariableExpression expression,
final StandardExpressionExecutionContext expContext) {
if (logger.isTraceEnabled()) {
logger.trace("[THYMELEAF][{}] SpringEL expression: evaluating expression \"{}\" on target", TemplateEngine.threadIndex(), expression.getExpression());
}
try {
final String spelExpression = expression.getExpression();
final boolean useSelectionAsRoot = expression.getUseSelectionAsRoot();
if (spelExpression == null) {
throw new TemplateProcessingException("Expression content is null, which is not allowed");
}
/*
* TRY TO DELEGATE EVALUATION TO SPRING IF EXPRESSION IS ON A BOUND OBJECT
*/
if (expContext.getPerformTypeConversion()) {
// This is a {{...}} expression, so we should use binding info (if available) for formatting.
if (useSelectionAsRoot || !isLocalVariableOverriding(context, spelExpression)) {
// The "local variable override" check avoids scenarios where a locally defined variable
// (e.g. the iterated variable in a th:each) has the same name as a bound object (e.g. a
// form-backing bean). If this was not detected, the bound object value would be always used
// instead of the local variable's
final IThymeleafBindStatus bindStatus =
FieldUtils.getBindStatusFromParsedExpression(context, true, useSelectionAsRoot, spelExpression);
if (bindStatus != null) {
// The expression goes against a bound object! Let Spring do its magic for displaying it...
return SpringValueFormatter.getDisplayString(bindStatus.getValue(), bindStatus.getEditor(), false);
}
}
}
final IEngineConfiguration configuration = context.getConfiguration();
/*
* OBTAIN THE EXPRESSION (SpelExpression OBJECT) FROM THE CACHE, OR PARSE IT
*/
final ComputedSpelExpression exp = obtainComputedSpelExpression(configuration, expression, spelExpression);
/*
* COMPUTE EXPRESSION OBJECTS AND ADDITIONAL CONTEXT VARIABLES MAP
* The IExpressionObjects implementation returned by processing contexts that include the Standard
* Dialects will be lazy in the creation of expression objects (i.e. they won't be created until really
* needed).
*/
final IExpressionObjects expressionObjects =
(exp.mightNeedExpressionObjects? context.getExpressionObjects() : null);
/*
* CREATE/OBTAIN THE SPEL EVALUATION CONTEXT OBJECT
*/
EvaluationContext evaluationContext =
(EvaluationContext) context.
getVariable(ThymeleafEvaluationContext.THYMELEAF_EVALUATION_CONTEXT_CONTEXT_VARIABLE_NAME);
if (evaluationContext == null) {
// Using a StandardEvaluationContext one as base: we are losing bean resolution and conversion service!!
//
// The ideal scenario is that this is created before processing the page, e.g. at the ThymeleafView
// class, but it can happen that no ThymeleafView is ever called if we are using the Spring-integrated
// template engine on a standalone (non-web) scenario...
//
// Also, note Spring's EvaluationContexts are NOT THREAD-SAFE (in exchange for SpelExpressions being
// thread-safe). That's why we need to create a new EvaluationContext for each request / template
// execution, even if it is quite expensive to create because of requiring the initialization of
// several ConcurrentHashMaps.
evaluationContext = new ThymeleafEvaluationContextWrapper(new StandardEvaluationContext());
if (context instanceof IEngineContext) {
((IEngineContext)context).setVariable(
ThymeleafEvaluationContext.THYMELEAF_EVALUATION_CONTEXT_CONTEXT_VARIABLE_NAME, evaluationContext);
}
} else if (!(evaluationContext instanceof IThymeleafEvaluationContext)) {
evaluationContext = new ThymeleafEvaluationContextWrapper(evaluationContext);
if (context instanceof IEngineContext) {
((IEngineContext)context).setVariable(
ThymeleafEvaluationContext.THYMELEAF_EVALUATION_CONTEXT_CONTEXT_VARIABLE_NAME, evaluationContext);
}
}
/*
* AT THIS POINT, WE ARE SURE IT IS AN IThymeleafEvaluationContext
*
* This is needed in order to be sure we can modify the 'requestParametersRestricted' flag and also the
* expression objects.
*/
final IThymeleafEvaluationContext thymeleafEvaluationContext = (IThymeleafEvaluationContext) evaluationContext;
/*
* CONFIGURE THE IThymeleafEvaluationContext INSTANCE: expression objects and restrictions
*
* NOTE this is possible even if the evaluation context object is shared for the whole template execution
* because evaluation contexts are not thread-safe and are only used in a single template execution
*/
thymeleafEvaluationContext.setExpressionObjects(expressionObjects);
thymeleafEvaluationContext.setVariableAccessRestricted(expContext.getRestrictVariableAccess());
/*
* RESOLVE THE EVALUATION ROOT
*/
final ITemplateContext templateContext = (context instanceof ITemplateContext ? (ITemplateContext) context : null);
final Object evaluationRoot =
(useSelectionAsRoot && templateContext != null && templateContext.hasSelectionTarget()?
templateContext.getSelectionTarget() : new SPELContextMapWrapper(context, thymeleafEvaluationContext));
/*
* If no conversion is to be made, JUST RETURN
*/
if (!expContext.getPerformTypeConversion()) {
return exp.expression.getValue(thymeleafEvaluationContext, evaluationRoot);
}
/*
* If a conversion is to be made, OBTAIN THE CONVERSION SERVICE AND EXECUTE IT
*/
final IStandardConversionService conversionService =
StandardExpressions.getConversionService(configuration);
if (conversionService instanceof SpringStandardConversionService) {
// The conversion service is a mere bridge with the Spring ConversionService, therefore
// this makes use of the complete Spring type conversion infrastructure, without needing
// to manually execute the conversion.
return exp.expression.getValue(thymeleafEvaluationContext, evaluationRoot, String.class);
}
// We need type conversion, but conversion service is not a mere bridge to the Spring one,
// so we need manual execution.
final Object result = exp.expression.getValue(thymeleafEvaluationContext, evaluationRoot);
return conversionService.convert(context, result, String.class);
} catch (final TemplateProcessingException e) {
throw e;
} catch(final Exception e) {
throw new TemplateProcessingException(
"Exception evaluating SpringEL expression: \"" + expression.getExpression() + "\"", e);
}
}
private static ComputedSpelExpression obtainComputedSpelExpression(
final IEngineConfiguration configuration, final IStandardVariableExpression expression, final String spelExpression) {
if (expression instanceof VariableExpression) {
final VariableExpression vexpression = (VariableExpression) expression;
Object cachedExpression = vexpression.getCachedExpression();
if (cachedExpression != null && cachedExpression instanceof ComputedSpelExpression) {
return (ComputedSpelExpression) cachedExpression;
}
cachedExpression = getExpression(configuration, spelExpression);
if (cachedExpression != null) {
vexpression.setCachedExpression(cachedExpression);
}
return (ComputedSpelExpression) cachedExpression;
}
if (expression instanceof SelectionVariableExpression) {
final SelectionVariableExpression vexpression = (SelectionVariableExpression) expression;
Object cachedExpression = vexpression.getCachedExpression();
if (cachedExpression != null && cachedExpression instanceof ComputedSpelExpression) {
return (ComputedSpelExpression) cachedExpression;
}
cachedExpression = getExpression(configuration, spelExpression);
if (cachedExpression != null) {
vexpression.setCachedExpression(cachedExpression);
}
return (ComputedSpelExpression) cachedExpression;
}
return getExpression(configuration, spelExpression);
}
private static ComputedSpelExpression getExpression(final IEngineConfiguration configuration, final String spelExpression) {
ComputedSpelExpression exp = null;
ICache cache = null;
final ICacheManager cacheManager = configuration.getCacheManager();
if (cacheManager != null) {
cache = cacheManager.getExpressionCache();
if (cache != null) {
exp = (ComputedSpelExpression) cache.get(new ExpressionCacheKey(EXPRESSION_CACHE_TYPE_SPEL,spelExpression));
}
}
if (exp == null) {
// SELECT THE ADEQUATE SpEL EXPRESSION PARSER depending on whether SpEL compilation is enabled
final SpelExpressionParser spelExpressionParser =
PARSER_WITH_COMPILED_SPEL != null && SpringStandardExpressions.isSpringELCompilerEnabled(configuration)?
PARSER_WITH_COMPILED_SPEL : PARSER_WITHOUT_COMPILED_SPEL;
final SpelExpression spelExpressionObject = (SpelExpression) spelExpressionParser.parseExpression(spelExpression);
final boolean mightNeedExpressionObjects = StandardExpressionUtils.mightNeedExpressionObjects(spelExpression);
exp = new ComputedSpelExpression(spelExpressionObject, mightNeedExpressionObjects);
if (cache != null && null != exp) {
cache.put(new ExpressionCacheKey(EXPRESSION_CACHE_TYPE_SPEL,spelExpression), exp);
}
}
return exp;
}
private static boolean isLocalVariableOverriding(final IExpressionContext context, final String expression) {
if (!(context instanceof IEngineContext)) {
// We don't even have support for local variables!
return false;
}
// NOTE this IEngineContext interface is internal and should not be used in users' code
final IEngineContext engineContext = (IEngineContext) context;
final int dotPos = expression.indexOf('.');
if (dotPos == -1) {
return false;
}
// Once we extract the first part of the expression, we check whether it is a local variable...
final String expressionFirstComponent = expression.substring(0, dotPos);
return engineContext.isVariableLocal(expressionFirstComponent);
}
@Override
public String toString() {
return "SpringEL";
}
private static final class ComputedSpelExpression {
final SpelExpression expression;
final boolean mightNeedExpressionObjects;
ComputedSpelExpression(final SpelExpression expression, final boolean mightNeedExpressionObjects) {
super();
this.expression = expression;
this.mightNeedExpressionObjects = mightNeedExpressionObjects;
}
}
}
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